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#2 Ease of Use of Squeeze Containers for Users with ArthritisA study of ease of use issues and potential design solutions for designers and consumers.

W. Bradley Fain, Ph.D.Liz Weldon, M.S.

July 2010

PrefaceThis monograph documents the methods and results of research conducted in the Accessibility Evaluation Facility (AEF) of the Georgia Tech Research Institute. The AEF has performed a series of ease of use evaluations for the Arthritis Foundation, the Arthritis Society of Canada, and industry customers. Although information about the outcome of specific evaluations has been withheld, the data and recommendations presented in this monograph are based upon general outcomes and lessons learned from research and product evaluations conducted at the Georgia Tech Research Institute.

For additional information about this monograph, please contact:

Dr. Brad FainGeorgia Tech Research Institute

ELSYS / HSID / HSEB Mail Code 0837Atlanta, GA 30332-0837

Voice: (404) 407-7261Fax: (404) 407-9261

[email protected]

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mailto:[email protected]

Table of ContentsPreface..................................................................................................................................iTable of Contents...............................................................................................................iiiList of Tables.......................................................................................................................vList of Figures.....................................................................................................................viIntroduction..........................................................................................................................1

Impact of Container Design on People with Arthritis.....................................................2Tasks Associated with Squeeze Container Usage...........................................................2Squeeze Container Components and Variations..............................................................4

Container Body............................................................................................................5Closure.........................................................................................................................5Outer Packaging...........................................................................................................6Inner Safety Seal..........................................................................................................7Instructions and Labels................................................................................................7

User Characteristics.............................................................................................................9Types of Arthritis...........................................................................................................10

Osteoarthritis..............................................................................................................10Rheumatoid Arthritis.................................................................................................11

Evaluation Methodologies.................................................................................................13Ease of Use Issues and Potential Solutions.......................................................................16

What are the issues associated with grasping and lifting a squeeze container?............17The squeeze container is too large to be gripped comfortably with adequate force..17The squeeze container is too small to be gripped comfortably with adequate force.20The squeeze container may slip in the user’s hand....................................................21

What are the issues associated with instructions and labeling?.....................................23The text and graphics are difficult to see...................................................................23The text is difficult to find.........................................................................................24The expiration date is difficult to find, read, or interpret..........................................26

What are the issues associated with removing the outer packaging?............................28Removal of the outer safety seal requires the use of a tool.......................................28The box in which the product is packaged does not have a flap or tab to aid in opening......................................................................................................................31

What are the issues associated with using a continuous thread closure?......................33Removing a factory sealed closure may require too much force...............................33Removing a closure may be difficult after it has been tightened by a user...............35The closure may slip in the user’s hand as he or she attempts to twist it..................36The diameter and height of the closure prevents a strong grasp................................38The amount of angular rotation required to remove the closure may be too great....39

What are the issues associated with removing the inner safety seal?............................40The user cannot peel the seal from the squeeze container.........................................40The user cannot puncture the seal with either a finger or the piercing device provided.....................................................................................................................42The user cannot break the seal off.............................................................................44

What are the issues associated with using a hinged top lid?.........................................46The amount of force required to lift the lid open is too great....................................46

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The lift tab is too sharp..............................................................................................47The lid does not stay open.........................................................................................48

What are the issues associated with using a disk top lid?..............................................49The amount of force required to push the disk down is too great.............................49

What are the issues associated with dispensing the contents?.......................................51The contents of the squeeze container are not near the orifice..................................51Squeezing the container to dispense the contents requires too much force...............52Controlling the amount and rate at which contents are dispensed is difficult...........53

Design Guidelines..............................................................................................................54References..........................................................................................................................59Appendix A: GTRI Squeeze Container Closure Evaluation.............................................62

Closure A...................................................................................................................63Closure B...................................................................................................................64Closure C...................................................................................................................65Closure D...................................................................................................................66Closure E...................................................................................................................67

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List of TablesTable 1: Tasks associated with squeeze container usage.....................................................2Table 2: Hand anthropometry of non-disabled individuals (Sources: [11, 15, 25])............9Table 3: Maximum grip diameters of individuals with and without dexterity disabilities (Source: [11]).....................................................................................................................10Table 4: Maximum grip diameters of individuals with and without dexterity disabilities (Source: [11]).....................................................................................................................18Table 5: Relationships between maximum grip diameter and cylinder diameter for maximum grip force..........................................................................................................18Table 6: Ease of use guidelines for squeeze container design...........................................54

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List of FiguresFigure 1: An assortment of squeeze containers...................................................................1Figure 2: Squeeze container components............................................................................5Figure 3: Diagram of a hinged top lid.................................................................................6Figure 4: Diagram of a disk top lid......................................................................................6Figure 5: Inner safety seals include (a) foil with a puncturing device, (b) a cut-off tip, (c) a tear-off tip, or (d) a twist-off seal......................................................................................7Figure 6: Joints of the hand commonly affected by arthritis.............................................11Figure 7: Rheumatoid arthritis can cause deformation of the joints resulting in stiffness and restricted range of motion...........................................................................................12Figure 8: A user’s grip strength (left) and pinch strength (right) are measured................14Figure 9: The Wong-Baker FACES Pain Rating Scale.....................................................15Figure 10: To attract the user’s attention, signal words are a larger text size and bolded, and warnings are presented in an outline format...............................................................24Figure 11: The expiration date is difficult to read due to the lack of contrast...................26Figure 12: The expiration date is clearly labeled and easy to read....................................26Figure 13: The perforated strip (in the red box) is not helpful to users who cannot see it............................................................................................................................................29Figure 15: Steep threading causes the closure to rise more rapidly as it is unscrewed.....35Figure 16: Elliptical closures provide leverage points that aid the user in removing the closure................................................................................................................................36Figure 14: A tool for removing the inner safety seal is provided as a molded integral feature on this squeeze tube closure..................................................................................42Figure 17: The sharp lift tab may cause pain for some users............................................47Figure 18: Components of a disk top lid...........................................................................49Figure 19: An inverted squeeze container design makes it easier to dispense contents....51Figure 20: Distribution of arthritis symptoms...................................................................62Figure 21: Closure A – GTRI Squeeze Tube Closure Evaluation.....................................63Figure 22: Torque Pain Threshold Results – Closure A....................................................63Figure 23: Closure B – GTRI Squeeze Tube Closure Evaluation.....................................64Figure 24: Torque Pain Threshold Results – Closure B....................................................64Figure 25: Closure C – GTRI Squeeze Tube Closure Evaluation.....................................65Figure 26: Torque Pain Threshold Results – Closure C....................................................65Figure 27: Closure D – GTRI Squeeze Tube Closure Evaluation.....................................66Figure 28: Torque Pain Threshold Results – Closure D....................................................66Figure 29: Closure E – GTRI Squeeze Tube Closure Evaluation.....................................67Figure 30: Torque Pain Threshold Results – Closure E....................................................67

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IntroductionAccording to the CDC’s Morbidity and Mortality Weekly Report, over 46 million American adults have been diagnosed with arthritis by a doctor [6]. Of these, 19 million Americans report that arthritis limits their daily activities in some way [7], and nearly 9 million Americans are disabled as a result of arthritis making it the most common cause of disability in the United States [5]. By 2030, it is expected that arthritis will affect an estimated 67 million American adults [6].

Many individuals with arthritis experience significant difficulty completing a variety of everyday tasks such as using squeeze tubes. The products under consideration in this monograph include squeeze tubes and squeeze bottles, which are collectively referred to as “squeeze containers” (see Figure 1). These products vary in size, weight, shape, texture, safety seal design, and operating force requirements. Each of these design components affects the user’s experience with the product, especially users experiencing symptoms of arthritis. As a result, users with arthritis may be unable to use certain products or may experience considerable pain and difficulty during use. This monograph discusses aspects of squeeze container design that affect ease of use for individuals with arthritis.

Figure 1: An assortment of squeeze containers.

There are two primary reasons why a company may choose to design products that are considered arthritis-friendly. First, a considerable portion of the market share is composed of individuals with arthritis, which is the most common cause of functional physical limitations in the United States. For users with arthritis, ease of use can become

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a key market discriminator in a group of similar, competing products. Second, products that are easy to use for individuals with arthritis will also be easy to use to most of the rest of the population.

Impact of Container Design on People with ArthritisUsers with arthritis may frequently experience difficulty and pain when attempting to perform routine tasks such as opening and dispensing products from squeeze containers. Beyond the difficulty and pain, users may also feel a sense of helplessness and a loss of independence. These negative feelings are likely to be directly associated with the product, and might reduce the chance that the product will be purchased again. Instead, the user may seek a competing product that appears to be easier to use. Furthermore, a tarnished product image might be extended to all products of the same brand, and a user might assume that all products of a given brand are equally difficult to use.

Whereas those products that are difficult to use may generate avoidance, products that are easy to use may generate loyalty to the product and brand. Such products may stand out in the user’s mind as notable exceptions to the daily frustrations of living with arthritis, and may help to restore a sense of independence.

Tasks Associated with Squeeze Container UsageTo assess ease of use, the interaction between the user and the product should not be thought of as a single operation. Instead, the interaction should be decomposed into distinct operations. In this manner, the ease or difficulty of each operation can be assessed individually, and specific recommendations for improvement can be provided. Tasks are identified in a structured analysis of all the users’ actions associated with product usage. This may be accomplished by observing individuals as they use the product in a naturalistic setting. It is often beneficial to observe more than one user, because some users might skip operations or perform them differently than other users. For example, some users might neglect a container’s instructions for opening. The results of the task analysis for squeeze container usage are shown in Table 1.

Table 1: Tasks associated with squeeze container usage.

1. Grasp and lift the squeeze container2. Review product labeling and instructions3. Remove the outer packaging and outer safety seal4. Remove the closure5. Remove the inner seal6. Replace the closure7. Open the lid8. Dispense the contents9. Close the lid

Each of the tasks in Table 1 may present difficulty for users with arthritis. In order to make a product that is truly easy to use, it is not sufficient to make most tasks easy, while

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neglecting one or more tasks. A single difficult task can represent a significant barrier to overall ease of use. Hence, designers should carefully consider the ease of all tasks, rather than focusing on a single task that may seem more salient than others. Below is a description of each task, and a brief introduction of the associated container characteristics that impact task performance.

Grasp and lift the squeeze container. For usage and transportation, a squeeze container must be grasped and lifted. In most cases this is a single handed operation, and the other hand is free to open the container or execute other related tasks. Grasping and lifting a squeeze container may be difficult if the container is heavy, large, or does not provide a good gripping surface. Individuals with arthritis may experience difficulty due to limited strength, dexterity, and range of motion. They may also experience pain as they attempt to extend inflamed joints beyond comfortable positions. As a result, some individuals with arthritis may be unable to use the product as intended by the manufacturer, or they may risk dropping the container.

Review product labeling and instructions. In order to safely and effectively use many products, users must be able to read safety information, expiration dates, and dosage instructions. This critical information must be noticeable and readable for all users. Older adults, many of whom have age-related arthritis symptoms, typically have decreased visual acuity. Therefore, older adults may have difficulty reading product labeling and instructions that are printed in small font or with poor contrast. Although this difficulty is not directly related to arthritis, it is an important consideration for a product’s overall ease of use. Failure to read instructions and labels might have notable consequences. For example, a user might misread an expiration date that is printed in small font, and then proceed to consume a product that is no longer safe, efficacious, or fresh. This could obviously lead to a tarnished brand image, or worse. Additionally, users may fail to read the instructions for opening and using the product and, as a result, experience unnecessary pain and difficulty.

Remove the outer packaging and outer safety seal. Outer packaging typically consists of a box that encloses the squeeze container or a tamper-evident plastic wrapping on the closure of the container. Users can open a box by tearing it, peeling it open at a flap, or tearing off a perforated strip. These actions may be difficult for individuals with arthritis if excessive force is required and if the gripping surface is not adequate. The outer plastic wrapping on a container can sometimes be removed by tearing or by twisting the closure to break the seal. Again, the forces required for these actions influence ease of use. If the outer seal consists of a non-perforated plastic sheet, most individuals with arthritis can be expected to experience difficulty. Although these tasks are only performed once for each product, they can represent significant barriers to overall ease of use. They also might establish a poor first impression of the product. A user might be unlikely to purchase the product in the future if the experience is difficult or painful, or if he or she must resort to using a tool (e.g., scissors).

Remove and replace the closure. Traditional closure design requires the user to tightly grasp the lid while twisting it. Individuals with arthritis often have difficulty performing

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simultaneous actions like grasping and twisting. This is particularly true if either one of the actions requires substantial strength. Factory sealed closures may require more torque than some individuals with arthritis can exert. A poor gripping surface on the closure or squeeze container can compound the problem by forcing the user to exert excessive gripping force. Certain containers may simply be impossible to open for some individuals with arthritis. After using a product, the consumer must screw the closure back onto the squeeze container. The act of screwing a closure onto a container sometimes requires a bit of dexterity in order to align the closure threading with the container threading. Due to dexterity limitations, this action might be difficult for some individuals with arthritis if the closure is short and has a small diameter.

Remove the inner seal. Some squeeze containers, such as those containing a topical medication, feature an inner safety seal beneath the closure on the orifice. The user must remove this seal in order to access the container’s contents. This is done by either peeling the seal away from the orifice or puncturing it with a tool, sometimes a molded integral feature of the closure. The act of peeling may be difficult for individuals with arthritis if the seal does not feature a sufficient gripping surface, or if the seal is bound too tightly to the orifice. The act of puncturing a seal may be difficult if the required force exceeds that which the user can exert or if the design of the puncture tip requires too much dexterity to correctly align it with the inner seal.

Flip the lid open and closed. Some squeeze containers have a hinged lid that is flipped open to expose the orifice. Flipping the lid open may be difficult for individuals with arthritis if excessive force is required or the lift tab and/or thumb recess is not sufficiently large. A lift tab with sharp edges may also cause pain to the user. After dispensing the product, the consumer must flip the lid closed again. Depending on how tight the seal between the spud and the orifice is, the force required to securely close the lid may be excessive and cause difficulty for individuals with arthritis.

Dispense the contents. To dispense the contents of a squeeze container, the user must apply pressure to the container by squeezing it with enough force to push the contents through the orifice. Dispensing the contents of a squeeze container will likely be difficult for individuals with arthritis if the squeeze container has thick, rigid walls and the closure has a small dispensing orifice. If the closure has a hinged lid, the hinge should be designed to allow the lid to remain fully open while the contents of the squeeze container are dispensed. If the force requirements for dispensing the contents of the squeeze container are high, individuals with arthritis are more likely to squeeze the container using two hands rather than one. However, if the hinge does not allow the lid to remain fully open, those users will not be able to use the product without experiencing significant pain or difficulty.

Squeeze Container Components and VariationsMost squeeze containers consist of five principal components: the container body, closure, labeling, outer packaging, and inner safety seal (see Figure 2). Each of these may impede easy usage by individuals with arthritis. The following sections describe the components and their common design variations.

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Figure 2: Squeeze container components.

Container BodySqueeze containers differ from each other by virtue of their material composition, shape, surface texture, size, and weight. The material composition of squeeze tubes may be of plastic, aluminum, or laminate. Plastic and laminate tubes tend to be able to retain their shape better than aluminum tubes and are more resistant to cracking or breaking. With aluminum tubes, however, it is easier to control dispensing, and there is not a “suck-back effect” often seen with plastic tubes. Tubes are generally cylindrical with an orifice on one end for dispensing and with the other end sealed. Typically, tubes do not have plastic or paper labels; instead, the labeling is printed directly onto the tube. Squeeze tubes are typically composed of plastic, which can vary in thickness and degree of flexibility.

ClosureClosures vary in size, shape, surface texture, material, operating force requirements, and opening mechanism. Closures for squeeze containers are almost always composed of plastic. The body of the closure may be continuous thread (i.e., twist-off) or snap-on. The closure may also have a hinged or disk top lid. Continuous thread closures are simply unscrewed from the tube; these vary with respect to the amount of rotation that is needed to remove the closure from the container. Snap-on closures are friction fit closures that can be pulled off without a twisting motion. A hinged top lid is attached to the top of a closure. When opened, the hinged top lid exposes a dispensing orifice (see Figure 3). A disk top lid features a “disk” top with an actuator that, when pressed, opens the opposite side of the closure to expose an orifice (see Figure 4).

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Figure 3: Diagram of a hinged top lid.

Figure 4: Diagram of a disk top lid.

Surface texture is one important factor affecting the ease with which users can grasp a closure. The closure for most squeeze containers is either serrated or smooth. Serrated surfaces generally provide a better grip than smooth surfaces. However, sharp serrations can cause pain to the skin, especially for users with arthritis, who may have inflamed finger joints. The closure may also be cylindrical, elliptical, or square in shape.

Outer PackagingBroadly defined, the outer packaging may be a box in which the tube is packaged or a tamper-evident seal around the closure. A common type of tamper-evident seal consists of a shrink wrapped strip of plastic that encircles the closure and a portion of the tube. Some plastic seals have a perforated strip that when pulled allows for easy removal of the

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seal. Others must be cut or torn, possibly requiring the use of a tool such as scissors or a knife.

Inner Safety SealSome tubes feature an inner safety seal that protects product safety and freshness. This type of seal usually features a tab that a user can grasp and pull, either from the edge of the seal or from a tab that flips up from the center of the seal. Tab sizes and the amount of force required to remove them vary among products. Other seals do not provide a tab and must be punctured. For products with this type of seal, a tool is usually provided as a molded integral feature of the closure (see Figure 5a). Most commonly, the closure has a spike recessed into the top which is used to puncture the seal. A third type of inner safety seal requires users to create the orifice by removing the top portion of the orifice or nozzle (see Figure 5b and Figure 5c). Users may have to snap the tip off or cut it off with scissors. A less common version of this type of inner safety seal requires the user to align the inner safety seal with a hole on the top of the closure and then twist the seal off (see Figure 5d). The amount of force required to remove the seal varies among products and the different removal methods.

Figure 5: Inner safety seals include (a) foil with a puncturing device, (b) a cut-off tip, (c) a tear-off tip, or (d) a twist-off seal.

Instructions and LabelsInstructions and labels may be required for safe and proper usage of a product. Instructions include opening instructions, dosage information, and instructions for usage, both text and graphics. Labels include warnings, such as drug interaction precautions and expiration dates. Common to all instructions and labels, the issues of font size and contrast are important. Small font and poor contrast can make it difficult for users to find and read information.

Dosage information and instructions for use are particularly important for safe and proper usage of a product. Recommended doses can be displayed in either paragraph or table format. Typically, this information is made more salient by using a prominent title and by separating it from other text on the squeeze container. Warning labels alert users of

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the dangers associated with a product. Similar to dosage information, warnings can be set apart using spacing and prominent titles so as to make the information easier to find.

Expiration dates are also important for safe and proper usage of a product. A user who fails to notice an expiration date on an expired product may proceed to use a product that no longer meets the manufacturer’s standards, or that may even be unsafe for consumption. Expiration dates are often placed in obscure locations where users are unlikely to see them, even if actively searching. The date may be printed directly on a squeeze container or imprinted on the crimped end of a squeeze tube. The text is often small, with poor contrast to the background. The format of the date is also important for identification and comprehension. The date may be preceded by the words “use by,” “best before,” or “expiration.”

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User CharacteristicsThe design of products that are intended for use by individuals with arthritis should be guided by anthropometric data and by an understanding of the functional limitations associated with arthritis. Arthritis is a term used to describe painful inflammation of the joint or joints. The disability has many causes, and there are over 100 types of arthritis. Inflammation causes a reduction in tactile sensation and range of movement with a corresponding loss of dexterity and mobility. Arthritis is the greatest contributor to mobility and dexterity limitations, the largest category of functional limitations. As noted by TIA access (1996) [29], “Individuals have difficulty reaching things and doing complex or compound manipulations such as pushing while turning or pressing several buttons simultaneously. Twisting motions may be especially difficult. For individuals with arthritis, controls that require pinching or rotating are difficult to operate. In addition, individuals who are functionally limited are unable to exert as much force on controls as individuals without functional limitations. Individuals with poor muscle control may find it difficult to make fine motor movements with their fingers and may be restricted to gross movements with their hand(s).”

Anthropometric data might provide useful guidance for the design of containers for users with arthritis. There exists only a limited amount of anthropometric data on individuals with arthritis. However, hand dimensions may not differ significantly between individuals with and without arthritis [16], except for instances in which arthritis causes deformation of the bones and joints (e.g., rheumatoid arthritis). These deformities may prevent a user’s hand from fully encircling a closure or bottle. Table 2 shows anthropometric data for individuals without arthritis. The data were compiled from several sources [11, 15, 25]. These include measurements from British adults aged 19-65 years [15], and from British adults of unspecified age [11, 25].

Table 2: Hand anthropometry of non-disabled individuals (Sources: [11, 15, 25]).Dimension Gender 5th percentile (mm) 50th percentile (mm) 95th percentile (mm)

Hand lengthMale 173-175 178-189 205-209

Female 159-160 167-174 189-191

Palm lengthMale 98 107 116

Female 89 97 105

Thumb lengthMale 44 51 58

Female 40 47 53

Thumb breadthMale 11-12 23 26-27

Female 10-14 20-21 24

Index finger lengthMale 64 72 79

Female 60 67 74

Hand breadthMale 78 87 95

Female 69 76 83-85

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Table 3 shows maximum grip diameters for individuals with and without dexterity disabilities [11]. Maximum grip diameter is defined as the maximum diameter of a cylinder that a person can grasp with contact between the thumb and middle finger.

Table 3: Maximum grip diameters of individuals with and without dexterity disabilities (Source: [11]).

Gender 5th percentile (mm) 50th percentile (mm) 95th percentile (mm)

Non-disabled Male 45 52 59

Female 43 48 53

Dexterity-disabled Male 34 40 47

Female 34 40 48

Maximum grip diameter is of particular importance for usage of containers. Users with arthritis may experience considerable pain when forcibly grasping an object with a wide grip, in great excess of their maximum grip diameter. Hand breadth should also be taken into consideration when designing the height of a container. If the container spans the entire breadth of the hand (or more), then the user can distribute gripping force across the whole palm and all four fingers.

Types of ArthritisThe term “arthritis” is used to refer to over 100 different diseases that affect the joints of the body and the areas surrounding the joints. The most common types of arthritis are osteoarthritis and rheumatoid arthritis. Osteoarthritis is typically associated with the wear and tear of affected joints and is most prevalent in older adults. Rheumatoid arthritis can affect younger adults and even children, and is associated with inflammation of the lining of the joints. Other types of arthritis include fibromyalgia, gout, ankylosing spondylitis, and scleroderma.

OsteoarthritisOsteoarthritis (OA) is characterized by the deterioration of cartilage in the joints. Healthy cartilage cushions adjacent bones and allows for easy joint movement. Thus, the deterioration of cartilage causes bones to rub against each other, leading to stiffness, swelling, pain, and restricted range of motion. In the final stages of OA, bits of bone may float freely within the joint, and the lining of the joint (synovium) becomes inflamed [1].

Symptoms of osteoarthritis are more common in some joints than others. The base of the thumb and the distal finger joints are most commonly affected [1]. These joints are used in many interactions with squeeze containers. Distal finger joints are heavily involved in certain pinch grips, such as that used to pinch a tab on a squeeze container’s safety seal. They may also be used when puncturing an inner seal with the tip of the finger, grasping a large container or closure, or squeezing a container. The thumb is involved with all grip types, and nearly all manual interactions with squeeze containers. When gripping and squeezing large squeeze containers or closures, users may experience pain in the base of the thumb as they adopt a wide grip. However, pain may also be experienced with smaller grips, such as those used to pinch a safety seal or to twist a small closure.

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Figure 6: Joints of the hand commonly affected by arthritis.

Symptoms are less common in the proximal interphalangeal joints (middle joint; approximately 35% of individuals with OA), and even less common in the metacarpophalangeal joints (base of the fingers; approximately 15% of individuals with OA) [1]. These joints are involved in pinching tabs and gripping containers and closures.

Wrists, which are affected in 20% of men with OA and only 5% of women [1], are involved in lifting and twisting actions. Symptoms are typically symmetric, meaning that symptoms in one hand are often accompanied by symptoms in the other hand [9]. Thus, many users may not be able to avoid pain by simply switching hands. A particularly problematic action for individuals with arthritis in the wrists is the act of twisting open a tightly secured closure. This can be painful for some users, and simply impossible for others.

Rheumatoid ArthritisRheumatoid arthritis (RA) is characterized by inflammation and swelling of the joints accompanied by pain and restricted range of motion [2]. More advanced RA causes deformation of the joints, which can prevent natural movements such as straightening the fingers (see Figure 7). Stiffness and restricted range of motion may cause individuals to adopt different strategies when using a product. For example, restricted wrist movement may force one to use several small movements to twist open a closure rather than one or two large movements. Also, deformation of the finger joints may force users to adopt different grips (e.g., a lateral “key” pinch rather than a finger tip pinch).

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Figure 7: Rheumatoid arthritis can cause deformation of the joints resulting in stiffness and restricted range of motion.

Symptoms of rheumatoid arthritis commonly appear first in the smaller joints of the body [2]. RA often affects the wrist joints and the finger joints closest to the hand (the metacarpophalangeal joints). Pain and swelling in these joints interferes with one’s ability to grip and twist objects, especially those that are large. Like OA, symptoms of RA are often symmetric, affecting the same joints on both sides of the body [2, 21]. Thus, many users may not be able to simply switch hands to avoid pain.

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Evaluation MethodologiesThere are two basic methods of acquiring information about human performance: direct measurement and derived assessment. If the goal is to evaluate the ability of a specific individual to use a product, then he or she is given a series of tasks to complete, and an evaluator observes performance. The tasks that are given to the user should be representative of the tasks associated with use of the product, as intended by the manufacturer, and it should be comprehensive. A list of tasks may be generated by a task analysis, which may involve observing several users as they interact with the product. By observing several users, rather than just one, the observer is more likely to capture all tasks associated with the product.

Direct Measurement. The direct measurement approach allows the collection of detailed data about the ability of a single individual to interact with a given product, although the findings may not generalize to a larger population. More robust direct measurement studies adopt effective population sampling strategies. By testing a diverse and representative group of users, the evaluator can generalize findings to a larger population segment with much better accuracy. Effective sampling for ease of use evaluations for people with arthritis can be very challenging. One must consider the variety of functional abilities and limitations within the population of individuals with arthritis. For example, some users may have limited strength, but normal dexterity. Others may have normal strength, but may experience considerable pain when exerting force. Still others may have limited reaching and grasping capabilities. A user’s level of experience may also have a significant impact on the outcome of the evaluation. For example, experience with difficult inner safety seals may lead one to puncture the seal with a fingernail, rather than attempt to grasp the edge of the seal and peel it off. Therefore, it is necessary to obtain a reasonably large and diverse sample of the population to which the evaluator wishes to generalize.

Derived Assessment. Derived assessment methods, such as functional assessments, checklist evaluations, or expert inspections, do not seek to measure human performance directly. Instead, such techniques are used to determine the extent to which a product meets formal or informal guidelines that have been associated with desired usability objectives. A checklist evaluation, also known as a heuristic evaluation, is employed where a considerable body of knowledge exists about a specific domain of human performance relative to the product of interest [22]. For example, a significant amount of data has been collected on the grip and torque strengths of individuals with arthritis. These data can be used to determine whether a product’s force requirements are likely to exceed the capabilities of the population of interest. However, given the number of factors that affect the usability of a squeeze container (e.g., size and texture) and the wide variations of each factor, it may not be feasible to assess a product solely by its adherence to guidelines. Therefore, it is advisable to combine direct measurements with derived assessments.

Given the challenges of sampling from a diverse population and our somewhat limited knowledge of designing for people with arthritis, it is necessary to combine data from

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both direct measurement and derived assessment evaluation techniques to obtain the desired degree of confidence in the evaluation results. Gaps in our knowledge in designing for people with arthritis can be addressed by performing user testing. Similarly, the sampling issues associated with human performance testing for accessibility can be addressed by using the derived assessment results to eliminate the need to test some populations and focus the assessment on others.

A variety of evaluation techniques and methodologies are available to the evaluator interested in measuring ease of use for individuals with arthritis. For best results, a combination of objective and subjective measures should be used.

The first stage of the evaluation may be accomplished without user participation. The evaluator first performs a task analysis in order to identify the actions that are involved in using the product. Next, the evaluator measures the force required for each of the physical actions identified in the task analysis. For example, one may measure the torque required to break the factory-tightened closure, and the linear force required to puncture a safety seal. Finally, the evaluator determines whether the product meets a pre-specified set of guidelines that are based on prior research.

The second stage of the evaluation involves user participation. The evaluator should obtain measurements of the relevant functional capabilities of each user, such as grip and pinch strengths (see Figure 8).

Figure 8: A user’s grip strength (left) and pinch strength (right) are measured.

Next, the evaluator may objectively measure the forces that each user is able to generate upon the container. This requires instrumentation of the container by, for example, affixing a torque meter to the base of the container and a connecting rod to the closure. Objective force measurements for each user may be compared against the forces that are required to use the product, as measured during the first stage of the evaluation. If a number of participants are unable to generate the required forces upon the instrumented container, then a significant portion of the population with arthritis may experience difficulty with the product.

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Next, the user is given an unopened, unmodified product, and is asked to perform the set of tasks identified in the task analysis. During each task, the evaluator observes performance and records any difficulty or problems that arise. After each task, the user may provide subjective feedback about the experience in a free response format, and in the form of an ease-of-use rating scale. Additionally, users are asked to report any pain experienced and rate the severity of their pain using the Wong-Baker FACES Pain Rating Scale (see Figure 9).

Figure 9: The Wong-Baker FACES Pain Rating Scale.

The evaluator should record all such data, allowing the users to focus their attention on the product. After all tasks are completed, users may be asked to rate their agreement with a series of statements about the product (e.g., “I can use this product without overexerting myself.”). Finally, the results of the evaluation should be documented in order to affirm or deny the product’s ease of use, and to provide recommendations to the manufacturer.

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Ease of Use Issues and Potential SolutionsSqueeze tubes have a number of ease of use issues related to the following tasks:

Grasping and lifting the tube Reviewing the product labeling and instructions Removing the outer packaging Removing and replacing the closure Removing the inner safety seal Opening and closing the lid Squeezing the tube to dispense the contents

The following sections contain detailed information about common ease of use issues for each of these tasks. Potential solutions to each issue are proposed, and relevant design guidelines are presented.

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What are the issues associated with grasping and lifting a squeeze container?The body of a squeeze container is grasped and lifted during regular use. The following tasks entail grasping and lifting the body of a squeeze container:

Transporting the product Reading instructions and labels Removing the inner and outer safety seals Removing and replacing the closure Dispensing the contents

The squeeze container is too large to be gripped comfortably with adequate force.Detailed Description:Holding a large squeeze container requires the user to adopt a wide grip. Because individuals with arthritis often experience limited range of motion in affected joints, they may be unable to open their hands wide enough to grasp a large squeeze container. Furthermore, strength declines as a user’s grip widens beyond moderate flexion. This means that even if a user is able to stretch his or her hand to fit the squeeze container, he or she may be unable to grasp the squeeze container tightly enough to perform other operations.

The hand is most powerful when it is flexed moderately [26]. When the hand grips a smaller object, grip force is decreased due to inadequate contact with the object and shortening of the muscles. When the hand grips a larger object, grip force decreases due to a decrease in the finger flexor muscles’ moment arm. Furthermore, a larger grip places the thumb and fingers in opposition to one another rather than in opposition to the palm.

Potential Solutions:Provide grasp points that are narrower than the main body of the squeeze container. If the body of the squeeze container is too large to be comfortably grasped with adequate force, an indentation can provide a more narrow grasping point.

Reduce the diameter of the squeeze container. Another solution is to simply decrease the diameter of the squeeze container. This can be done by increasing the height of the squeeze container while decreasing the diameter to preserve the volume. Alternatively, a company can manufacture squeeze containers of several different sizes from which users can choose the most appropriate size for them.

For maximum grip power, what is the optimal squeeze container diameter? The answer depends in part on the user’s hand size and maximum grip diameter, because wider grips are associated with decreased strength. Maximum grip diameter is defined as the maximum diameter of a cylinder that a person can grasp while maintaining contact between the thumb and middle finger. For non-disabled adults, maximum grip power can be exerted on cylinders with diameters approximately 10 mm (0.4 inches) smaller than the maximum grip diameter. Specifically, the average non-disabled adult can exert

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maximum grip power on a cylinder with a diameter of 40 mm (1.6 inches) [26], which is approximately 10 mm less than their median maximum grip diameter ([11]; see Table 4). This diameter allows the thumb and middle finger to slightly overlap and directly oppose the palm.

Table 4: Maximum grip diameters of individuals with and without dexterity disabilities (Source: [11]).

Gender 5th percentile (mm) 50th percentile (mm) 95th percentile (mm)

Non-disabledMale 45 52 59

Female 43 48 53

Dexterity-disabledMale 34 40 47

Female 34 40 48

Note that the relationship between maximum grip diameter and optimal diameter for grip force is somewhat speculative, because the data on these two parameters were derived from two separate studies [11, 26]. A single, systematic study is needed to confirm this relationship. Assuming that such a relationship exists, however, we can infer the diameter of a squeeze container that should yield maximum grip power for dexterity-disabled adults, including those with arthritis. The median maximum grip diameter of dexterity-disabled adults is 40 mm (1.6 inches) (see Table 4). Therefore, they might be expected to exert maximum gripping force on 30 mm (1.2 inches) cylinders, in comparison to 40 mm cylinders for non-disabled adults (see Table 5). Although it might not be feasible to design squeeze containers with diameters of only 30 mm, these data highlight the importance of maintaining a small diameter at the location intended for grasping.

Table 5: Relationships between maximum grip diameter and cylinder diameterfor maximum grip force.

Median Maximum Grip Diameter (male & female)

(mm)

Diameter for Maximum Grip Force (mm)

Non-disabled 50 A 40 B

Dexterity-disabled 40 A 30 C

A: Source [11]; B: Source [26]; C: Inferred.

Applicable Guidelines: Guideline: Ensure that the product is easy to grip and control. The shape of the

product should be easy to hold so that it fits the hand. There should also be a texture to the surface so that it can be gripped and held onto.Sources: Cushman & Rosenberg, 1991 [7]; Haigh, 1993 [17]

Guideline: Allow for alternatives to a standard grip. Size the gripping area and clearances to allow alternatives to the standard grip, including knuckles, the side,

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back and heels of the hand, and two-handed “pinch” grips.Source: Steinfeld & Mullick, 1990 [28]

Guideline: Require a grip span of no more than 2.8 inches for products that are intended to be grasped with one hand. If the size of the container exceeds the maximum grip span recommendations, then add design features such as handles or cutouts to facilitate a reduced grip span requirement.Source: Steinfeld & Mullick, 1990 [28]

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The squeeze container is too small to be gripped comfortably with adequate force.Detailed Description:Small squeeze containers can be just as problematic for users as large squeeze containers. Holding and manipulating a small squeeze container requires the user to have fine motor coordination and dexterity. Because individuals with arthritis often experience limited dexterity and fine motor coordination, they may find it difficult to securely hold a small squeeze container in their hands and perform tasks such as removing the closure.

Potential Solutions:Increase the diameter of the squeeze container. Just as decreasing the diameter of a large squeeze container can make the container more usable, increasing the diameter of a small squeeze container can also make the container easier to use for individuals with arthritis. This can be done by decreasing the height of the squeeze container while increasing the diameter to preserve the volume. Alternatively, a company can manufacture squeeze containers of several different sizes from which users can choose the most appropriate size for them.

Maximize friction between the squeeze container and the hand. Friction can be increased by adding texture to the surface of the container where users are most likely to grasp it. As a result, users will not have to grip the squeeze container with as much force. However, care must be taken to ensure that adding texture does not affect the user’s ability to squeeze the container and dispense the contents.


product should be easy to hold so that it fits the hand. There should also be a texture to the surface so that it can be gripped and held onto.Sources: Cushman & Rosenberg, 1991 [7]; Haigh, 1993 [17]

Guideline: Allow for alternatives to a standard grip. Size the gripping area and clearances to allow alternatives to the standard grip, including knuckles, the side, back and heels of the hand, and two-handed “pinch” grips.Source: Steinfeld & Mullick, 1990 [28]

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The squeeze container may slip in the user’s hand.Detailed Description:Individuals with arthritis typically have weaker grips than those without arthritis. A weakened grip may allow a squeeze container to slide in the hand as the user attempts to lift or manipulate the container. As a result, the user may experience difficulty performing such actions as lifting the squeeze container, removing the closure, and dispensing the product. Factors influencing the user’s ability to grasp a squeeze container include container size, container shape, surface texture, and material composition. The nature of the product and the environment in which it is used can magnify the effects of these factors. For example, users may experience more difficulty holding and manipulating a tube of lotion due to the slipperiness of the lotion. Similarly, products that are to be used in the shower may become more difficult to grasp due to moisture.

Potential Solutions:Increase friction between the squeeze container and the hand. Friction can be increased by adding texture to the surface of the container where users are most likely to grasp it. However, care must be taken to ensure that adding texture does not affect the user’s ability to squeeze the container and dispense the contents.

Use a non-cylindrical shape for the squeeze container. Container slippage can be reduced by using a non-cylindrical container shape. The uniform contour of a cylinder allows it to slide easily in a weak grip. In contrast, elliptical and rectangular containers provide leverage points that can help reduce grip strength requirements.


product should be easy to hold, so that it fits the hand. There should also be a texture to the surface so that it can be gripped and held onto.Sources: Cushman and Rosenberg, 1991 [7]; Haigh, 1993 [17]

Guideline: Allow for alternatives to a standard grip. Size the gripping area and clearances to allow alternatives to the standard grip, including knuckles, the side, back and heels of the hand, and two-handed “pinch” grips.Source: Steinfeld and Mullick, 1990 [28]

Guideline: Require a grip span of no more than 2.8 inches for products that are intended to be grasped with one hand. If the size of the container exceeds the maximum grip span recommendations, then add design features such as handles or cutouts to facilitate a reduced grip span requirement.Source: Steinfeld and Mullick, 1990 [28]

Guideline: Provide a high friction grip surface on cylindrical containers. Tight grasping of the container is required to provide a counter-rotational force when removing a twist off cap. Provide a high friction surface on a cylindrical container to facilitate tight grasping.

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Source: GTRI

Guideline: Provide a non-cylindrical grip feature, such as grip indentions, or use a non-cylindrical container.Source: GTRI

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What are the issues associated with instructions and labeling?Instructions are defined as any textual or graphical information that tells the user how to operate or consume the product. This includes opening instructions, consumption instructions, and dosage information. Labels include warnings, product information, and expiration dates. The ease of use issues associated with instructions and labels are not unique to users with arthritis, but are common to all users. However, older adults, who comprise a large portion of the population with arthritis, often experience a decline in visual acuity. Therefore, the visual design of instructions and labeling are particularly important for many users with arthritis.

The text and graphics are difficult to see.Detailed Description:Some users may have difficulty reading text due to small text size or poor contrast with the background. Textual or graphical instructions for removing a closure are often printed directly on the closure using an inkless embossing process, resulting in very poor visual contrast. Additionally, because of limited space on the squeeze container for labeling, product designers may elect to use a smaller text size, resulting in reduced readability. Users that are unable to read the product labeling may use the product incorrectly or in an unsafe manner.

Potential Solutions:Enhance the readability of all text by increasing font size and contrast. Ideally, all text and graphics should be printed using high contrast ink and a large font size. Previous studies have indicated that 10-point type is perceived as more readable than smaller font sizes by both younger and older adults [27]. If instructions are printed using an inkless embossing process, the poor contrast should be compensated for by increasing the font size and increasing the depth of the embossment.

Provide full instructions either on the product’s outer packaging or as a product insert. If the size of the container prevents the use of a larger font size, provide only the most important warnings and instructions on the body of the squeeze container, and provide a supplement for the abbreviated product labeling. For example, if the product is packaged in a box, the complete set of instructions and warnings could be printed directly on the box or on a piece of paper as a package insert.

Applicable Guidelines: Guideline: Enhance readability and comprehension of labels, critical instructions,

and expiration dates. Print critical text with large print in a sans-serif font with high contrast on a solid background.Source: GTRI

Guideline: It is essential that a warning be as salient as possible to capture the attention of users. The salience of a visual warning can be enhanced using large, bold print, high contrast, color, borders, and pictorial symbols.Source: Wogalter, Conzola, and Smith-Jackson, 2002 [32]

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The text is difficult to find.Detailed Description:Instructions and warnings may be difficult to find if they are not preceded by a prominent title or if they are placed in an unexpected location. For example, dosage information may be difficult to find if all of the product information runs together in a paragraph format.

Potential Solutions:Provide clearly visible, prominent titles for each section. Providing a title or signal word attracts the user’s attention and aids in visual search (see Figure 10). Titles or signal words are perceived as more readable when the difference in title and text size is two points (e.g., 12-point type for titles and 10-point type for text) [27].

Present product information in an outline format rather than as a continuous paragraph layout. Text that is presented as bullets in an outline format allows for faster visual search and maintains attention for a longer period of time (see Figure 10).

Figure 10: To attract the user’s attention, signal words are a larger text size and bolded, and warnings are presented in an outline format.

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Applicable Guidelines: Guideline: A warning should contain a signal word to attract the attention of the

user.Source: Wogalter, Conzola, and Smith-Jackson (2002) [32]

Guideline: To increase effectiveness and salience, warnings should be presented as bullets in an outline format.Source: Wogalter, Conzola, and Smith-Jackson (2002) [32]

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The expiration date is difficult to find, read, or interpret.Detailed Description:Expiration dates may be difficult to find if they are placed in an unexpected location or if the differentiation between the expiration date and the design of the packaging is insufficient. For example, the expiration date can often be found on the crimped ends of squeeze tubes, but the date often appears to be a part of the crimping pattern. The expiration date may also be difficult to find if it is not clearly labeled and cannot be distinguished from the lot number. Once the date is found, it may be difficult to read if it is printed in small lettering or with poor contrast. Often, the expiration date on the product’s box has no contrast at all because the date was printed using an inkless embossing process. Finally, the date may be misinterpreted if its format is ambiguous. For example, “12 07 11” could be interpreted as December 7, 2011 or July 12, 2011.

Figure 11: The expiration date is difficult to read due to the lack of contrast.

Potential Solution:Print expiration dates in a standard location using an unambiguous format, large font, and sufficient contrast. The expiration date should also be labeled appropriately so that it can be distinguished from the lot number. The location of the expiration date should be standardized across products. For squeeze bottles and tubes, consider printing the expiration date in close proximity to the product’s bar code. Previous studies have indicated that 10-point type is perceived as more readable than smaller font sizes by both younger and older adults [27]. To enhance contrast, the expiration date should be printed using high contrast ink on a part of the container that is opaque.

Figure 12: The expiration date is clearly labeled and easy to read.

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Applicable Guideline: Guideline: Enhance readability and comprehension of labels, critical instructions,

and expiration dates. Print critical text with large print in a sans-serif font with high contrast on a solid background.Source: GTRI

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What are the issues associated with removing the outer packaging?The outer packaging of a product is intended to protect product integrity and safety while providing evidence of tampering. It must be removed prior to the first usage of the product. Outer packaging typically consists of a box that encloses the squeeze container or a tamper-evident plastic wrapping on the closure of the container (referred to as the outer safety seal). Because the outer packaging is intended to protect the product and provide evidence of tampering, it can be difficult to remove. Users with arthritis, in particular, may experience difficulty removing the outer safety seal or when opening the packaging. Although this action is only performed once for each item, it can represent a significant barrier to overall ease of use and may discourage users from future purchases.

Removal of the outer safety seal requires the use of a tool.Detailed Description:Tamper-evident plastic wrapping may not have a perforated strip, making it difficult for users to tear the seal and remove it. Instead, users must initiate a tear in the plastic with a tool such as a knife or scissors. However, the use of tools can be problematic for three reasons. First, a tool may not be readily available, so the user may struggle to accomplish the task by hand before searching for a tool. Second, users with arthritis may experience pain in their fingers, hands, and wrists while using the tool. Pain may be caused by the narrow grip required to hold the tool, or by the amount of force necessary to use the tool. Finally, users may resort to using the tool in an unsafe manner, which can lead to serious injury.

Potential Solution:Provide a clearly visible perforation in the seal that will allow users to remove the seal by hand. Perforations in the plastic wrapping allow users to tear the plastic more easily. The perforations should be clearly evident by virtue of their placement and their visual contrast with the underlying material. Note that perforations in clear plastic may be difficult to see, particularly when covering a light-colored squeeze container (see Figure 13). Perforations can be made more visible by using a dark plastic seal or by placing markings on the seal at the perforations. In addition to being clearly visible, the edge of the seal at the perforation should be easy to grip.

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Figure 13: The perforated strip (in the red box) is not helpful to users who cannot see it.



Guideline: Provide at least one mode of operation that does not require fine motor control or simultaneous actions, and that is operable with limited reach and strength.Source: Section 508 1194.31(f) [14]

Guideline: Do not require the use of tools.Source: GTRI

Guideline: Require a pinch force of no more than 3.0 pounds (13.3 N).Source: GTRIDiscussion: Preliminary data collected during GTRI assessments of users with arthritis suggested that pinch force requirements should not exceed 3.0 pounds; however, further research is needed to validate this finding.

Guideline: Ensure that the proper method of removing the outer safety seal is clearly evident, either because of the design of the safety seal or because of instructions printed prominently on the packaging. For example, if the seal is removed by twisting the cap to break the seal, instructions like “Twist cap to break seal” should be provided. If the seal is removed by pulling a perforated strip, the strip should be clearly visible.Source: Vanderheiden, 1997 [30]Discussion: The steps required to open some containers may be intuitively obvious to most users and therefore may not require printed instructions.

Guideline: If the outer safety seal is intended to be torn open, then provide a perforated strip or a starter slit.Source: GTRI

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Guideline: If the safety seal is removed in an independent action (e.g., by pulling a perforated strip), the force required to remove the safety seal should not exceed 5.0 pounds (22.2 N).Source: Section 508 1194.23(k)(2) [14]Discussion: Section 508 sets a broad guideline for maximum linear force requirements for all user actions stating that controls and keys shall be operable with one hand and shall not require tight grasping, pinching, or twisting of the wrist. The force required to activate controls and keys shall be 5 lbs (22.2 N) maximum. The guideline may not be directly applicable to removing a safety seal. Further research will be needed to determine if the 5.0 pound recommendation should be modified for this application.

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The box in which the product is packaged does not have a flap or tab to aid in opening.Detailed Description:A box can be difficult to open if its opening flap does not have a tab for users to grasp. Flaps without a sufficient grasping surface must be picked at with a tool or a fingernail until there is a large enough area for the user to grasp. This may be difficult for users with arthritis because it requires relatively fine motor control. A user might simply tear the box open by inserting a finger under the flap’s edge, but the force required to do so might cause pain for users with arthritis.

Potential Solutions:Provide a perforated strip that users can easily peel off. A perforated strip can be peeled away easily, provided that the force required is not excessive (less than 5 lbs (22.2 N)). The end of the strip should have a sufficiently large tab for grasping.

Provide a large tab under which the user can insert a finger. If a tab is provided with no perforated strip, the tab should be large enough to accommodate most of the tip of the finger. The force required to pull open the tab should not exceed 5 lbs (22.2 N).

Applicable Guidelines: Guideline: If the safety seal is removed in an independent action (e.g., by pulling

a perforated strip), the force required to remove the safety seal should not exceed 5.0 pounds (22.2 N).Source: Section 508 1194.23(k)(2) [14]Discussion: Section 508 sets a broad guideline for maximum linear force requirements for all user actions stating that controls and keys shall be operable with one hand and shall not require tight grasping, pinching, or twisting of the wrist. The force required to activate controls and keys shall be 5 lbs (22.2 N) maximum. The guideline may not be directly applicable to removing a safety seal. Further research will be needed to determine if the 5.0 pound recommendation should be modified for this application.

Guideline: If the outer safety seal is intended to be torn open, then provide a perforated strip or a starter slit.Source: GTRI

Guideline: Require a pinch force of no more than 3.0 pounds (13.3 N).Source: GTRIDiscussion: Preliminary data collected during GTRI assessments of users with arthritis suggested that pinch force requirements should not exceed 3.0 pounds (13.3 N); however, further research is needed to validate this finding.

Guideline: Offer redundant modes of operation utilizing the next larger set of motor movements (finger to hand, hand to arm). Offer different ways to accomplish the same task using increasingly larger motor movements. For

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example, a tab on a seal should be large enough to grip between the thumb and knuckle, rather than between the tips of the finger.Source: Pirkl, 1995 [24]Discussion: By allowing redundant modes of operation, users might have the option to avoid using joints in which swelling and pain are most severe.


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What are the issues associated with using a continuous thread closure?To remove a continuous thread closure, users must grip the squeeze container in one hand while tightly gripping and applying rotational force to the closure with the other hand. Grasping the closure while simultaneously rotating it may be especially difficult for some individuals with arthritis. Following is a discussion of issues related to the usability of continuous thread closures.

Removing a factory sealed closure may require too much force.Detailed Description:Many individuals with arthritis experience pain and difficulty exerting the amount of force required to remove the closures on some squeeze containers. The factory sealed continuous thread closures that have been tested at the GTRI Accessibility Evaluation Facility have required from 1 pound-inch of torque to over 20 pound-inches of torque to remove. In laboratory tests conducted at GTRI with a variety of closure designs, individuals with arthritis have typically been able to exert approximately 2 to 30 pound-inches of torque on the closures before experiencing pain. This wide range is the result of differences among the functional abilities of the participants and variations in closure design.

When a high amount of torque is required to remove a closure, high grip force is also required. In order to prevent a closure from slipping in the hand, the user must apply sufficient grip force. Thus, users with arthritis may experience pain in the wrist as they apply torque and in the hand and fingers as they apply grip force.

Potential Solution:Limit the amount of torque that is required to remove a factory sealed closure to 10 pound-inches (1.1 N-m) or less. To make a closure easier to remove, the amount of torque required to remove it must be decreased. However, product safety and integrity must also be considered. To accommodate approximately 90% of users with arthritis, torque requirements should not exceed 10 pound-inches (1.1 N-m) for closures that are at least one inch in diameter. Reducing the diameter of the closure to less than one inch also reduces the amount of torque that a user can exert, so the maximum torque requirement is lower for smaller closures. Reducing the amount of torque necessary to rotate the closure also reduces the amount of grip force that is required to prevent the closure from slipping in the hand.

Applicable Guidelines: Guideline: Minimize rotational force required to remove the cap from the factory

sealed position.Sources: Berns, 1981 [3]; Langley, Janson, Wearn, and Yoxall, 2005 [20]; Voorbij and Steenbekkers, 2002 [31]

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Removing a closure may be difficult after it has been tightened by a user.Detailed Description:After the initial opening, closures can be retightened with a variable amount of torque, and this may affect the ease of future openings. Hence, even if a factory sealed squeeze container is easy to open for a user with arthritis, it may be difficult on subsequent uses. A friend or family member might tighten the closure too much, or an individual with arthritis might tighten it too much on a day when he or she is not experiencing severe symptoms. Symptoms of arthritis can vary dramatically on a daily basis, as can the individual’s functional abilities.

Potential Solution:Use steep threading rather than shallow threading. The tendency for users to overtighten a closure might be reduced by using steep threading (causing the closure to rise more rapidly as it is unscrewed). Preliminary testing at GTRI with 6 different bottles suggests that closures with steep threading cannot be tightened onto the bottle as tightly as those with shallow threads. After tightening closures with 15 pound-inches (1.7 N-m) of torque, those with steep threading (average incline 4.5°) required approximately 33% less torque to open than those with shallow threading (average incline 1.8°).

Figure 14: Steep threading causes the closure to rise more rapidly as it is unscrewed.

Applicable Guideline: Guideline: Provide at least one mode of operation is that does not require fine

motor control or simultaneous actions, and that is operable with limited reach and strength.Source: Section 508 1194.31(f) [14]

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The closure may slip in the user’s hand as he or she attempts to twist it.Detailed Description:When a closure is tightly secured to a container, users’ hands may slip around the closure as they attempt to twist it. To prevent slippage, users may be required to exert considerable grip force on the closure while simultaneously twisting the closure. Users with arthritis typically have weaker grip strengths, so they are more likely to experience problems with closures slipping in their hands.

Potential Solutions:Reduce the required grip force by increasing the friction between the closure and the hand. A common method of increasing friction is to incorporate ridges or serrations into the closure’s surface. These should be large (deep and wide) enough to provide friction, but not so wide as to produce discomfort on the skin. Surface friction can also be introduced by using different types of materials other than plastic. For example, a rubber surface coating can provide excellent grip.

Reduce the required grip force by providing leverage points on the closure. Knurled, square, and elliptical closures provide leverage points that may reduce grip strength requirements. Individuals with and without arthritis are able to generate more torque on knurled objects than smooth objects [10]. Knurl contours should be smooth and gradual because small or sharp points of contact can create uncomfortable pressure points. In one case of laboratory testing at GTRI, some users preferred a traditional round closure over a knurled closure, because the later caused painful pressure points. The discomfort that some users experienced was most likely due to the abrupt edges in the knurling pattern. To prevent painful pressure points, knurls should be rounded. However, further laboratory testing is needed to determine the optimal knurling style.

Figure 15: Elliptical closures provide leverage points that aid the user in removing the closure.

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Guideline: Avoid sharp edges. Knurls on twist-off closures should be rounded.Source: GTRI


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The diameter and height of the closure prevents a strong grasp.Detailed Description:The size of the closure, both in diameter and height, greatly affects how tightly users can grasp it. Very large diameter closures afford weak grips because the fingers are weaker when they are near full extension [26]. Likewise, closures with very small diameters afford weak grips due to muscle shortening. Small diameter closures also require users to have sufficient dexterity and fine motor control in their hands.

In addition to the diameter, the height of a closure affects how tightly users can grasp it. Short closures, such as those less than 0.5 inches, may be difficult to grasp for users with arthritis due to the requirement for dexterity. Additionally, users may find it difficult to adopt the hand position necessary to use the closure. A shorter closure limits the variety of possible hand positions users can adopt when grasping and removing closures. Taller closures allow for more flexibility in how the user grasps the closure.

Potential Solutions:Use a moderate closure diameter. Because the hand is most powerful when it is moderately flexed [26], the diameter of closures should be determined by the user’s grip span when the hand is moderately flexed. For non-disabled individuals, maximum force can be generated on closures with diameters between 1 and 3 inches (25-75 mm) [23]. This is a relatively wide range, and users with arthritis may experience pain at the extremes, so more moderate closure diameters are preferable (e.g., between 1.5 and 2 inches).

Increase the height of the closure. Increasing the surface contact between the fingers and the closure by increasing the height of the closure allows users to grasp the closure with more force and greater ease. More laboratory testing is required to determine the optimal height of a closure. Additionally, the height of a closure may be limited by the design of the dispensing orifice (e.g., elongated nozzles require a taller closure).

Applicable Guidelines: Guideline: Require a grip span of no more than 2.8 inches (71 mm) for products

that are intended to be grasped with one hand. If the size of the container exceeds the maximum grip span recommendations, then add design features such as handles or cutouts to facilitate a reduced grip span requirement.Source: Steinfeld and Mullick, 1990 [28]Discussion: This guideline applies to a standard power grip (like grasping a cylinder) and may not be directly applicable to the key pinch grip commonly used to grasp a closure.


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The amount of angular rotation required to remove the closure may be too great.Detailed Description:Some closures require a large degree of rotation to remove from the container (e.g., 270° of rotation). Because many individuals with arthritis are limited in their range of motion in the hands and wrists, they must make several small movements rather than a few large movements to remove a closure from the container. If rotating the closure slightly causes pain or discomfort for users with arthritis, then the product may not be usable if several small rotations are required to remove the closure.

Potential Solution:Use a steep and short threading so that the closure can be removed with a limited amount of rotation. Ideally, removing a closure should require no more than a quarter turn. This can be accomplished by using a steep and short threading design which allows the closure to rise rapidly from the container as it is rotated.

Applicable Guidelines: Guideline: Screw top caps should fit in the hand. Their removal should require

no more than ¼ turn for each angular movement, and no more than two angular movements should be required.Source: Haigh, 1993 [17]

Guideline: Minimize user actions.Source: HFDS 2.6.8 [13]

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What are the issues associated with removing the inner safety seal?Inner safety seals are located directly beneath the closure, covering the orifice. They maintain product freshness and provide an additional level of tamper-evidence. Like the outer packaging, the inner safety seal is removed only once for each product, yet it can represent a significant barrier to the overall ease of use of the product. For squeeze containers, the inner safety seal may be in the form of a traditional foil seal that users either peel off or puncture. Alternatively, the user may have to create the dispensing orifice by removing the top portion of the nozzle.

The user cannot peel the seal from the squeeze container.Detailed Description:The inner safety seal can be difficult to remove from the squeeze container’s orifice if the seal does not provide a sufficient grasping surface. The seal may have a pull tab that is too small, or there may be no tab at all. If a tab is not provided, users may attempt to pinch the tiny edge of the seal, likely resulting in pain and frustration for users with arthritis. Alternatively, the user may attempt to puncture the seal using a finger or tool and then peel away the remnants of the seal. In this case, the user is forced to perform multiple physical actions rather than the single, simple action of pulling the entire seal off at once. Even if a tab is provided, the tab may be too small for some users to easily grasp. Given their smaller size, this is a common issue when using squeeze tubes. Additionally, the surface of the tab may be too slippery and require a pinch grip strength exceeding the capabilities of some users with arthritis. Finally, even if the user is able to securely grasp the pull tab, the amount of force required to peel the seal off may be too high.

Potential Solution:Provide a large tab on the edge of the seal with a sufficient grasping surface that can be removed with less than 5 pounds (22.2 N) of force. If a smooth, non-textured tab is provided, it should be at least 0.47 inches (12 mm) wide by 0.79 inches (20 mm) long so that users can grasp it between the thumb and lateral aspect of the index finger. Smaller tabs may be difficult to grasp and may slide from users’ fingers, especially if the tabs are not textured. The optimal pull tab would be large, located on the edge of the seal, with a textured surface that reduces slippage (e.g., a foil tab with raised bumps). The amount of force required to peel the seal away from the container should not exceed 5 lbs (22.2 N). However, due to the small size of many squeeze tubes, it is not possible to provide a tab that is at least 0.47 inches wide by 0.79 inches long. In these cases, consider using an alternative inner safety seal design, such as providing a piercing device on the closure.

Applicable Guidelines: Guideline: Minimize user actions.

Source: HFDS 2.6.8 [13]

Guideline: Do not require the use of tools.Source: GTRI

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Guideline: On smooth inner seal tabs, provide a sufficiently large grasping point. A tab that is at least 0.47 inches (12 mm) wide by 0.79 inches (20 mm) long is recommended.Source: Department of Trade and Industry, UK, 2003 [12]Discussion: The study was based on a smooth tab. The study only looked at one tab width and two tab lengths (0.47 and 0.79 inches). The tabs were rectangular. The test population included people with disabilities, but the sample was relatively small and included a variety of disabilities.

Guideline: Provide texture on the grasp point that facilitates gripping the tab. The grasp point should be textured with a series of bumps or raised strips that are perpendicular to the peel direction.Source: Department of Trade and Industry, UK, 2003 [12]

Guideline: On inner seals that are intended to be grasped and peeled from the container, place the grasp point in a location selected for the application of optimum force. The tab should be located along the edge of the seal if the seal is designed to be peeled from the edge. A tab located along the top centerline of the seal can also be used, provided the tab runs across the diameter of the seal.Source: GTRI

Guideline: Do not glue the grasp point to the inner seal or other surface.Source: GTRI


Guideline: Offer redundant modes of operation utilizing the next larger set of motor movements (finger to hand, hand to arm). Offer different ways to accomplish the same task using increasingly larger motor movements. For example, a tab on a seal should be large enough to grip between the thumb and knuckle, rather than between the tips of the finger.Source: Pirkl, 1995 [24]Discussion: By allowing redundant modes of operation, users might have the option to avoid using joints in which swelling and pain are most severe.

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The user cannot puncture the seal with either a finger or the piercing device provided.Detailed Description:If no tab is provided on the inner safety seal and the seal is of sufficient size, users may attempt to puncture the seal with their fingers or a sharp tool. However, users with arthritis may struggle to puncture the seal with their fingertip and resort to using a tool such as a knife or scissors. Some users may have had difficulty puncturing the inner safety seal on other products that lacked a tab and, assuming that all seals are difficult to puncture, will not even attempt to puncture the seal with their fingertip. Using a tool to puncture the seal can be problematic if a tool is not readily available, if use of the tool causes pain in affected joints, or if the tool is used in an unsafe manner (e.g., stabbing with a knife). Additionally, depending on the type of product that is packaged in the squeeze container, using a tool to puncture the inner safety seal can contaminate the product and possibly lead to infection.

On some squeeze containers, no tab is provided on the inner safety seal because a puncturing tool is provided as a molded integral feature of the closure (see Figure 16). This type of design avoids many of the aforementioned issues. Users do not have to attempt to puncture the seal with their fingertip and can avoid the associated pain and frustration. Furthermore, users can avoid using a sharp tool in a potentially unsafe manner since a tool is provided. However, users with arthritis may experience difficulty puncturing the inner safety seal with the provided tool if the puncturing device and the orifice are small and require too much dexterity to use. Also, users with arthritis may have difficulty using the puncturing device if the closure is too small or has a poor grasping surface.

Figure 16: A tool for removing the inner safety seal is provided as a molded integral feature on this squeeze tube closure.

Potential Solutions:Limit the amount of force required to puncture the seal. The amount of force that is required to puncture the seal, as measured with a blunt object that simulates the fingertip or an object that simulates the provided puncturing device, should not exceed 5 pounds (22.2 N) (but see Guideline Discussion below).

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If the product requires a small orifice diameter for dispensing purposes, use a seal with a tab rather than providing a puncturing tool in the closure. If the viscosity of the contents necessitates the use of a small diameter orifice, then the puncturing device must also have a small diameter. This makes it more difficult for users with limited dexterity in their hands to line up the puncturing device with the inner safety seal.

If a puncturing device is provided on the closure, ensure that the closure can be easily grasped. This can be accomplished by increasing the coefficient of friction between the closure and the user’s hand and by ensuring the closure is sufficiently large. For more information, see the section on issues associated with using a continuous thread closure.

Applicable Guidelines: Guideline: Do not require the use of tools.

Source: GTRI

Guideline: Minimize safety seal removal force. The force required to remove the safety seal (e.g., by puncturing the seal or by pulling to remove it) should not exceed 5.0 pounds (22.2 N).Sources: GTRI; Section 508 1194.23(k)(2) [14]Discussion: Section 508 sets a broad guideline for maximum linear force requirements for all user actions stating that controls and keys shall be operable with one hand and shall not require tight grasping, pinching, or twisting of the wrist. The force required to activate controls and keys shall be 5 lbs (22.2 N) maximum. The guideline may not be directly applicable to puncturing a safety seal. Further research will be needed to determine if the 5.0 pound recommendation should be modified for this application.


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The user cannot break the seal off.Detailed Description:Rather than a traditional foil seal, the inner safety seal on some squeeze containers is a small piece of plastic molded to the orifice of the container. To remove this type of inner safety seal, users must break the seal off using their hands, a tool such as scissors, or the molded integral feature provided on the closure. All three methods for removing the inner safety seal have potential ease of use issues for individuals with arthritis. First, the amount of force required to break the seal off may be outside of the functional limitations for some users. Additionally, the portion of the seal that breaks off may be too small for users to easily grasp. Inner safety seals that require the use of tools such as scissors are also problematic if the tool is not readily available, use of the tool causes pain in the affected joints, or the tool is used in an unsafe manner. If a molded integral feature is provided on the closure, users with arthritis may have difficulty removing the inner safety seal with the provided tool if the safety seal and the removal tool are small and require too much dexterity to use. This is especially true if users are required to line up the pattern of the seal with the pattern of the removal tool. Finally, removing this type of inner safety seal can be difficult if the closure is too small or is difficult to grasp.

Potential Solutions:Reduce the amount of force required to break the seal off and ensure the seal can be easily grasped. To remove the seal, users must first be able to tightly grasp the seal. This can be difficult, especially for individuals with arthritis, if the grasp point is too small or slippery. Ensure that the seal is large enough for users to grasp, and consider providing a texture that would increase the coefficient of friction between the seal and the hand.

If a removal tool is provided on the closure, ensure that the closure can be easily grasped, and reduce the requirement for fine motor control. The design of most removal tools requires the user to line up the pattern on the removal tool with the pattern on the safety seal. Sometimes, the pattern is small and difficult to see for some users who are farsighted. Additionally, due to the fine details, aligning the removal tool with the inner safety seal requires a relatively high degree of dexterity and fine motor control. Instead of using a detailed pattern, consider using a simpler pattern that is also larger and easier to see. Furthermore, ensure that the closure is sufficiently large and the coefficient of friction between the hand and the closure is high enough to facilitate grasping.



Guideline: Allow for alternatives to a standard grip. Size the gripping area and clearances to allow alternatives to the standard grip, including knuckles, the side, back and heels of the hand, and two-handed “pinch” grips.

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Source: Steinfeld and Mullick, 1990 [28]

Guideline: Minimize safety seal removal force. The force required to remove the safety seal should not exceed 5.0 pounds (22.2 N).Sources: GTRI; Section 508 1194.23(k)(2) [14]Discussion: Section 508 sets a broad guideline for maximum linear force requirements for all user actions stating that controls and keys shall be operable with one hand and shall not require tight grasping, pinching, or twisting of the wrist. The force required to activate controls and keys shall be 5 lbs (22.2 N) maximum. The guideline may not be directly applicable to removing a safety seal. Further research will be needed to determine if the 5.0 pound recommendation should be modified for this application.

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What are the issues associated with using a hinged top lid?Closures with a hinged top lid can offer an easy-to-use dispensing solution for many users with arthritis. Using a hinged top lid to dispense a product alleviates the concerns associated with gripping and twisting a traditional continuous thread closure, but also introduces additional usability issues to be concerned with.

The amount of force required to lift the lid open is too great.Detailed Description:To open a hinged top lid, users must either pull the lid up using the lift tab or push the lid open using the thumb recess. Due to the smaller size of most squeeze container closures, users often can only use one finger or thumb to open the lid, which greatly limits the amount of force the user can exert. Individuals with arthritis who have limited strength in their hands will experience pain and difficulty when attempting to lift a hinged top lid if too much force is required.

Potential Solutions:Decrease the amount of force required to lift the lid. By decreasing the amount of force required to lift the tab, more users with arthritis will find the product easy to use.

Increase the size of the lift tab and thumb recess. Users can apply force more easily to larger surface areas. The area where the force is applied (i.e., the lift tab and/or thumb recess) should be large enough to accommodate a variety of methods for operating the product. Accordingly, increasing the size of the lift tab and thumb recess allows users to exert more force when attempting to lift the lid open, and it also allows them to use more than one finger, or even the palm of the hand, to complete the task.

Applicable Guidelines: Guideline: Provide a sufficient area for users to apply force.

Source: GTRIDiscussion: Additional research is required to quantify what constitutes a “sufficient” area for applying force.

Guideline: Offer redundant modes of operation utilizing the next larger set of motor movements (finger to hand, hand to arm). Offer different ways to accomplish the same task using increasingly larger motor movements. For example, a tab on a seal should be large enough to grip between the thumb and knuckle, rather than between the tips of the finger.Source: Pirkl, 1995 [24]Discussion: By allowing redundant modes of operation, users might have the option to avoid using joints in which swelling and pain are most severe.


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The lift tab is too sharp.Detailed Description:Hinged top lids typically have a thumb recess and/or lift tab that provides a surface for the user to push up on and lift the lid to expose the orifice. On some hinged top lids, the lift tab creates a sharp edge where users would typically place their finger or thumb to lift the lid. This can be very painful for some individuals with arthritis, especially if the edge of the lift tab makes contact with swollen, inflamed joints. As a result, users cannot exert as much force when attempting to lift the lid before experiencing pain.

Figure 17: The sharp lift tab may cause pain for some users.

Potential Solution:Provide a surface with a smooth edge for the user to push against. If the lift tab has a sharp edge, users will not be able to exert as much force when lifting the lid before experiencing pain. By providing a smooth edge, users will be able to lift the lid more easily and without pain.

Applicable Guideline: Guideline: Avoid sharp edges.

Source: GTRI

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The lid does not stay open.Detailed Description:Once the user has lifted the lid to expose the orifice, the lid should remain open until the user closes it. If the lid does not stay open, the user will have to use one hand to hold the lid out of the way of the orifice while using the other hand to squeeze the container. However, some individuals with arthritis may need to use two hands to squeeze the container with sufficient force. If the amount of force required to dispense the contents of the squeeze container is too high, then some users with arthritis will not be able to use the product.

Potential Solution:Use a biased hinge to connect the lid to the body of the closure. By designing the closure with a hinge that is biased to stay open, users will not have to hold the lid open while simultaneously squeezing the container to dispense the product. This will allow users to squeeze the container with both hands if necessary.

Applicable Guideline: Guideline: Provide at least one mode of operation that does not require fine

motor control or simultaneous actions, and that is operable with limited reach and strength.Source: Section 508 1194.31(f) [14]

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What are the issues associated with using a disk top lid?Like a hinged top lid, closures with a disk top lid offer an easy-to-use dispensing solution for many users with arthritis. Using a disk top lid to dispense a product alleviates the concerns associated with gripping and twisting a traditional continuous thread closure, but new usability concerns arise.

The amount of force required to push the disk down is too great.Detailed Description:To open a disk top lid, users must press down on the actuator at the finger recess with sufficient force so as to expose the orifice. The amount of force required to open the disk top lid is determined by the size of the actuation rib (see Figure 18). The actuation rib creates friction against the body of the closure, and the bigger the actuation rib is, the greater the coefficient of friction becomes. Accordingly, the greater coefficient of friction results in a higher opening force. Many disk top lids also have a ship post on the body of the closure that prevents accidental opening during shipping by further increasing the coefficient of friction, and therefore, the opening force. Although the ship post breaks away upon initial opening to lower the opening force requirements, the amount of force required to initially open the disk top lid is relatively high by comparison. As a result, some users with arthritis may not be able to press down on the finger recess with sufficient force to break the ship post.

Figure 18: Components of a disk top lid.

Potential Solution:Reduce the size of the actuation rib. A smaller actuation rib reduces the coefficient of friction between the rib and the body of the closure which in turn reduces the opening force requirements. The presence of a ship post will still increase the amount of force required to initially open the lid, but the baseline opening force requirement will be lower.

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Applicable Guidelines: Guideline: Require no more than 3.3 pounds (14.7 N) to push in a push tab.

Source: Berns, 1981 [3]

Guideline: Minimize the forces required to open and close disk top lids. The forces required to flip the closure open and closed should not exceed 5.0 pounds (22.2 N).Source: Section 508 1194.23(k)(2) [14]Discussion: Section 508 sets a broad guideline for maximum linear force requirements for all user actions stating that controls and keys shall be operable with one hand and shall not require tight grasping, pinching, or twisting of the wrist. The force required to activate controls and keys shall be 5 lbs (22.2 N) maximum. The guideline may not be directly applicable to opening a disk top lid. Further research will be needed to determine if the 5.0 pound recommendation should be modified for this application.

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What are the issues associated with dispensing the contents?To dispense the contents of a squeeze container, users must squeeze the container with sufficient force to deflect the shape of the container, causing a rise in pressure in the container. The amount of force required to dispense the contents of a squeeze container depends on several factors including the material composition of the container, the geometry of the orifice, and the viscosity of the contents.

The contents of the squeeze container are not near the orifice.Detailed Description:If the contents of a squeeze container are not close to the orifice, the user has to do more work to dispense the contents. This can be accomplished by shaking the container so the contents move closer to the opening or, in the case of squeeze tubes, squeezing the tube flat moving from the crimped end to the orifice.

Potential Solution:Design the closure with a flat top so it can act as the base. The contents of a squeeze container will naturally flow down to the bottom of the container. Rather than requiring users to do more work to dispense the contents, take advantage of the gravitational forces with an inverted container design with the closure and dispensing orifice on the bottom of the squeeze container. Ensure that the closure is flat and large enough to act as a stable base for the container.

Figure 19: An inverted squeeze container design makes it easier to dispense contents.

Applicable Guideline: Guideline: Minimize user actions.

Source: HFDS 2.6.8 [13]

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Squeezing the container to dispense the contents requires too much force.Detailed Discussion:The amount of force required to squeeze the container and dispense the product depends on the geometry and material composition of the container, the geometry of the orifice, and the viscosity of the container contents. In general, high viscosity products such as toothpaste are more difficult to dispense than low viscosity products such as shampoo. This is why toothpaste is traditionally packaged in a soft squeeze tube while shampoo is traditionally packaged in a more rigid squeeze bottle. Research on the usability of squeeze containers has indicated that, to dispense the same volume of product as younger adults, older adults have to exert more work (i.e., squeeze the bottle more often) [33]. This is especially problematic for users with arthritis who may not have the strength to squeeze a container with enough force multiple times.

Potential Solutions:Reduce the thickness of the walls of the squeeze container, or change the material composition to a more flexible material. To successfully dispense the contents of a squeeze container, users must squeeze the container with enough force to deform the container and cause a rise in pressure within the container. The amount of force that users can apply when squeezing a container is determined in part by the stiffness of the container; specifically, users can apply more force to a flexible (less stiff) container than to a rigid (stiffer) container.

Increase the size of the orifice. Dispensing high viscosity products from a squeeze container requires more work as compared to low viscosity products. To achieve the same efficiency for a low viscosity product and a high viscosity product, the diameter of the orifice must be increased for the high viscosity product. Research also indicates that the geometry of the orifice has an effect on the amount of force required to dispense a product, but there is too little information to provide suggestions on the optimal orifice geometry [4].

Applicable Guideline: Guideline: Minimize the forces required to squeeze a container and dispense the

contents. The operating forces should not exceed 5.0 pounds (22.2 N).Source: Section 508 1194.23(k)(2) [14]Discussion: Section 508 sets a broad guideline for maximum linear force requirements for all user actions stating that controls and keys shall be operable with one hand and shall not require tight grasping, pinching, or twisting of the wrist. The force required to activate controls and keys shall be 5 lbs (22.2 N) maximum. The guideline may not be directly applicable to dispensing the contents of a squeeze container. Further research will be needed to determine if the 5.0 pound recommendation should be modified for this application.

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Controlling the amount and rate at which contents are dispensed is difficult.Detailed Description:Depending on the type of product, users may want to dispense only a small amount of the contents of a squeeze container (such as when applying a topical medication), or they may want to dispense a larger amount but in a controlled manner (such as when decorating a cake with icing packaged in a squeeze tube). For some users with arthritis, this task is difficult because it requires the user to squeeze the container with a consistent amount of force over a period of time.

Potential Solutions:Reduce the size of the orifice. By reducing the size of the orifice, the amount of force required to squeeze the container and dispense the contents increases, thereby reducing the amount of product that is dispensed when the container is squeezed. If the contents of a squeeze container should be dispensed slowly, then reducing the size of the orifice will accomplish this goal. However, doing so may make it more difficult if not impossible for users with arthritis to dispense any amount of the product.

Use an aluminum tube rather than a plastic or laminate squeeze container. Users can control the amount and rate at which contents are dispensed more easily with aluminum tubes than with either plastic or laminate squeeze containers. One reason is that there is no “suck-back” effect; that is, the aluminum tube collapses to prevent air from being pulled back into the tube after it has been squeezed. As a result, no air bubbles that could cause splattering of the product on subsequent uses are formed.

Applicable Guideline: Guideline: Verify that the requirement for constant, uninterrupted actions is

minimized by investigating the required actions for each control.Source: Vanderheiden, 1997 [30]

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Design GuidelinesThe design and evaluation of squeeze containers can be informed by guidelines that have been suggested by researchers. Note, however, that the number of published studies addressing human performance in using squeeze bottles is limited, and the quality of existing research may be questionable if a small subject sample was used or if the experimental designs were flawed. Therefore, it is important to document the sources for the guidance offered in this report. Careful review of the sources may lead to a better understanding of how to interpret the guidelines presented here and of how to allocate future research resources. The squeeze container guidelines referenced in this report are shown in Table 6.

Table 6: Ease of use guidelines for squeeze container design.

Guideline Guideline Source(s) Discussion Applicable

Components

Ensure that the product is easy to grip and control. The shape of the product should be easy to hold so that it fits the hand. There should also be a texture to the surface so that it can be gripped and held onto.

Cushman & Rosenberg, 1991 [7]; Haigh, 1993 [17]

- Container body- Closure- Outer packaging- Inner safety seal

Allow for alternatives to a standard grip. Size the gripping area and clearances to allow alternatives to the standard grip, including knuckles, the side, back and heels of the hand, and two-handed “pinch” grips.

Steinfeld & Mullick, 1990 [28]

By providing alternatives to a standard grip, users with arthritis can adopt a grip that does not create pressure points on inflamed joints.


Require a grip span of no more than 2.8 inches for products that are intended to be grasped with one hand. If the size of the container exceeds the maximum grip span recommendations, then add design features such as handles or cutouts to facilitate a reduced grip span requirement.

Steinfeld & Mullick, 1990 [28]

This includes products that must be grasped with one hand while opening the closure with the other hand. This guideline is especially important for heavy containers and for containers with a low coefficient of friction on the surface.

- Container body

Provide a high friction grip surface on cylindrical containers. Tight grasping of the container is required to provide a counter-rotational force when removing a twist off closure. Provide a high friction surface on a cylindrical container to facilitate tight grasping.

GTRI Tight grasping of the container is required to provide a counter-rotational force when removing a continuous thread closure.

- Container body- Closure

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Components

Provide a non-cylindrical grip feature, such as grip indentions, or use a non-cylindrical container.

GTRI Non-cylindrical grip features enhance grip while removing a closure and while dispensing the contents of a squeeze container.

- Container body

Enhance readability and comprehension of labels, critical instructions, and expiration dates. Print critical text with large print in a sans-serif font with high contrast on a solid background.

GTRI - Labeling

It is essential that a warning be as salient as possible to capture the attention of users. The salience of a visual warning can be enhanced using large, bold print, high contrast, color, borders, and pictorial symbols.

Wogalter, Conzola, & Smith-Jackson, 2002 [32]

- Labeling

A warning should contain a signal word to attract the attention of the user.


- Labeling

To increase effectiveness and salience, warnings should be presented as bullets in an outline format.


- Labeling

Provide at least one mode of operation that does not require fine motor control or simultaneous actions, and that is operable with limited reach and strength.

Section 508 1194.31(f) [14]

- Closure- Outer packaging- Inner safety seal

Do not require the use of tools. GTRI Tools may be used in an unsafe manner leading to injury.

- Outer packaging- Inner safety seal

Require a pinch force of no more than 3.0 pounds (13.3 N).

GTRI Preliminary data collected by GTRI suggests that pinch force requirements should not exceed 3.0 pounds for users with arthritis. Further research is necessary to validate this finding.

- Closure - Outer packaging- Inner safety seal

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Components

Ensure that the proper method of removing the outer safety seal is clearly evident, either because of the design of the safety seal or because of instructions printed prominently on the packaging. For example, if the seal is removed by twisting the cap to break the seal, instructions like “Twist cap to break seal” should be provided. If the seal is removed by pulling a perforated strip, the strip should be clearly visible.

Vanderheiden, 1997 [30]

The steps required to open some containers may be intuitively obvious to most users and therefore may not require printed instructions.

- Outer packaging

If the outer safety seal is intended to be torn open, then provide a perforated strip or a starter slit.

GTRI - Outer packaging

Offer redundant modes of operation utilizing the next larger set of motor movements (finger to hand, hand to arm). Offer different ways to accomplish the same task using increasingly larger motor movements. For example, a tab on a seal should be large enough to grip between the thumb and knuckle, rather than between the tips of the fingers.

Pirkl, 1995 [24] By offering redundant modes of operation, users have the option to avoid using joints in which pain and swelling are most severe.


Minimize user actions. HFDS 2.6.8 [13] Packaging should be designed to minimize hand and eye movements, thus maximizing efficiency.

- Container body- Closure- Outer packaging- Inner safety seal- Labeling

On smooth inner seal tabs, provide a sufficiently large grasping point. A tab that is at least 0.47 inches (12 mm) wide by 0.79 inches (20 mm) long is recommended.

Department of Trade and Industry, UK, 2003 [12]

This study was based on a smooth tab. The study looked at only one tab width and two tab lengths (0.47 inches and 0.79 inches) and only used rectangular tabs. The test population included individuals with disabilities, but the sample was relatively small with a wide variety of disabilities.

- Inner safety seal

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Components

Provide texture on the grasp point that facilitates gripping the tab. The grasp point should be textured with a series of bumps or raised strips that are perpendicular to the peel direction.

Department of Trade and Industry, UK, 2003 [12]

- Outer packaging- Inner safety seal

On inner seals that are intended to be grasped and peeled from the container, place the grasp point in a location selected for the application of optimum force. The tab should be located along the edge of the seal if the seal is designed to be peeled from the edge. A tab located along the top centerline of the seal can also be used, provided the tab runs across the diameter of the seal.

GTRI - Inner safety seal

Do not glue the grasp point to the inner seal or other surface.

GTRI - Inner safety seal

Minimize rotational force required to remove the closure from the factory sealed position.

Berns, 1981 [3]; Langley, Janson, Wearn, and Yoxall, 2005 [20]; Voorbij and Steenbekkers, 2002 [31]

The research available on this topic is very limited. The amount of rotational force that a user can apply to a continuous thread closure is depending on the diameter and height of the closure, the coefficient of friction of both the closure and container, the shape of the container, and the type of grasp users adopt.

- Closure

Avoid sharp edges. GTRI The lift tab on hinged top lids should be beveled and devoid of sharp edges. Knurls and serrations on continuous thread closures should also be rounded.

- Closure

Screw top caps should fit in the hand. Their removal should require no more than ¼ turn for each angular movement, and no more than two angular movements should be required.

Haigh, 1993 [17] The study referenced did not address replacing the closure.

- Closure

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Components

Provide a sufficient area for users to apply force.

GTRI The force required to complete a task, such as flipping a lid open, can be applied more easily when the force is applied to a larger surface area. Additional research is required to quantify what constitutes a “sufficient” area for applying force.

- Closure- Inner safety seal

Require no more than 3.3 pounds (14.7 N) to push in a push tab.

Berns, 1981 [3] This study included people from the general population as well as people with a variety of disabilities including individuals with arthritis, multiple sclerosis, Parkinson’s disease, cerebral palsy, hemiplegia, and amputees.

- Closure

Verify that the requirement for constant, uninterrupted actions is minimized by investigating the required actions for each control.

Vanderheiden, 1997 [30]

- Container body (dispensing)

- Closure

Controls and keys shall be operable with one hand and shall not require tight grasping, pinching, or twisting of the wrist. The force required to activate controls and keys shall be 5 lbs (22.2 N) maximum.

Section 508 1194.23(k)(2) [14]

Section 508 sets a broad guideline for maximum linear force requirements for all user actions. The guideline may not be directly applicable to the tasks involved in using a squeeze container. Further research is needed to determine if the 5.0 pound recommendation should be modified for this application.

- Container body (dispensing)

- Closure- Outer packaging- Inner safety seal

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Appendix A: GTRI Squeeze Container Closure EvaluationParticipants were asked to rate their arthritis symptoms at each major joint on the day of the evaluation. They were asked to classify their symptoms in terms of pain, swelling, or stiffness on a 5-point scale. Figure 20 illustrates the distribution of symptoms of the participants on the day of the evaluation.

Figure 20: Distribution of arthritis symptoms.

Prior to testing, participants were asked if they experienced any difficulty using squeeze tubes in general that could be related to symptoms of arthritis. Participants were told that using a squeeze tube included grasping the tube, removing the closure, removing any safety seals, dispensing the product, and replacing the closure. Following is each participant’s response.

“Sometimes, to open toothpaste initially, I have to use my teeth. To squeeze, I use both hands or put the tube on a countertop and squeeze forward. The smaller the tube, the smaller the cap – and that makes it harder to open.”

“I sometimes have difficulty taking the cap off.” “It can be easy, but it’s always difficult to get the last of the product out.” “I don’t have so much trouble grasping the tube, but when the toothpaste gets

dried up at the cap, it gets hard to open. Small caps are harder to use. Also, as the tube gets emptier, it gets harder to squeeze so I use a tool to squeeze it out.”

“Sometimes I have difficulty using tubes. Once they are open though, I keep it open or just barely close it. With toothpaste, you have nothing to grip when holding the tube.”

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“With toothpaste, I don’t always have the strength to squeeze it out – also with my facial cleaner. I don’t really have problems with the caps though.”

“Sometimes I have difficulty with the little caps. I bought a container with an inner safety seal over the opening and could not get the cap off so I had to poke a hole in it. I also have trouble with toothpaste.”

A torque assessment was performed with a Mark-10 Torque Meter (MGT50 Serial #44350). Five samples of closures from squeeze tubes were utilized for this assessment. Users were instructed to turn each closure in a clockwise (CW) direction as much as possible without experiencing excessive discomfort. Users were instructed to turn each closure in the counter-clockwise (CCW) direction as well. Both left and right hands were tested; however, all of the users that participated in the evaluation reported that they were right-handed. Following are the results of the torque assessment for each sample tested, as well as any user comments recording while testing the closures for individuals with arthritis.

Closure A

Figure 21: Closure A – GTRI Squeeze Tube Closure Evaluation.

Figure 22: Torque Pain Threshold Results – Closure A.

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On average, participants were able to exert 5.53 lb-in of rotational force when removing closure A with their right hand. Following are the user comments recorded during the evaluation.

“The edges are too sharp – not real comfortable.” “My hands slid right off of that cap. Even the third cap was better.” “That’s good – it fits nicely and you feel like you have a good grip.” “It’s too slick for me – it didn’t give me anything to grip.” “It’s smooth so I can’t get a good grip. In terms of size though, it’s okay.” “I would have liked grips on this so your hand doesn’t slide off.”

Closure B

Figure 23: Closure B – GTRI Squeeze Tube Closure Evaluation.

Figure 24: Torque Pain Threshold Results – Closure B.

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On average, participants were able to exert 3.91 lb-in of rotational force when removing closure B with their right hand. Following are the user comments recorded during the evaluation.

“There’s not much to grip.” “I like the ridges, but the leverage is not as good. I’m not so sure the ridges gave

me more gripping power.” “Very slippery. I don’t feel like I can get a good grip.” “I don’t like the lack of a grip.” “To open this, I would put it between my thumb and finger or in the palm of my

hand.” “It was okay. It felt comfortable.”

Closure C

Figure 25: Closure C – GTRI Squeeze Tube Closure Evaluation.

Figure 26: Torque Pain Threshold Results – Closure C.

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On average, participants were able to exert 11.84 lb-in of rotational force when removing closure C with their right hand. Data is available for only five participants because the original closure sample broke during testing and had to be replaced. Following are the user comments recorded during the evaluation.

“This one is easier to twist – I can put more leverage on it since it is a flat shape.” “I like this one.” “I like the shape – it gives me more leverage, and there’s more surface to grasp.” “That’s good. It’s a nice grip even though it’s smooth. I like the shape. The

shape helped make it easy to grip.” “It gives you something to push against because of the shape, but it’s still slick.” “I can easily put it in the palm of my hand to turn it.”

Closure D

Figure 27: Closure D – GTRI Squeeze Tube Closure Evaluation.

Figure 28: Torque Pain Threshold Results – Closure D.

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On average, participants were able to exert 2.71 lb-in of rotational force when removing closure D with their right hand. Following are the user comments recorded during the evaluation.

“Not much to grab. The ribs help me grip it, but they are almost too sharp.” “I prefer a bigger cap.” “The deeper ridges are better, but it’s so small that it’s harder to grip.” “That’s a good grip. It’s better than cap E because it’s not rounded at the top.” “I like the grips, but they hurt.” “It’s difficult because it’s not very big.” “I liked that one.”

Closure E

Figure 29: Closure E – GTRI Squeeze Tube Closure Evaluation.

Figure 30: Torque Pain Threshold Results – Closure E.

On average, participants were able to exert 3.36 lb-in of rotational force when removing closure E with their right hand. Following are the user comments recorded during the evaluation.

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“There’s not nearly as much to grip, but the ridges do help. The edges aren’t so sharp so it’s comfortable, but it’s still too small.”

“I don’t like that.” “I don’t like it any better with the dome shape. It’s still so small.” “It’s difficult because you can’t get a good grip. It’s too little.” “Just looking at it, I know I wouldn’t buy a product with this cap. It’s too small.

Your hand slides across the top because of the dome shape.” “I don’t like the size of that. There’s not enough surface to grip.”

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