ERGONOMICS:ERGONOMICS:

Environmental Issues

Environmental Factors: Environmental Factors: Worksite ConsiderationsWorksite Considerations

The assessment of the working environment needs to include:

The immediate workplaceThe immediate workplace

The physical relationship between the The physical relationship between the work situation and the operatorwork situation and the operator

Impact of temperature, humidity, altitude, Impact of temperature, humidity, altitude, noise, illumination and vibrationnoise, illumination and vibration

Some Points to ConsiderSome Points to Consider

What effect, if any, do sub-optimal What effect, if any, do sub-optimal environmental conditions have on the environmental conditions have on the standard of performance of the worker?standard of performance of the worker?  

Is an individual’s selective attention and Is an individual’s selective attention and concentration disturbed?concentration disturbed?  

Is the operator at risk for injury?Is the operator at risk for injury?  

Do environmental disturbances affect the Do environmental disturbances affect the emotional state of the workeremotional state of the worker

What seems to be the problem(s)?What seems to be the problem(s)?

NOISENOISE VIBRATIONVIBRATION LIGHTINGLIGHTING AMBIENT AMBIENT

CONDITIONSCONDITIONS

What are some of the keyWhat are some of the key

environmental considerations environmental considerations

What factors are likely toWhat factors are likely to

affect the performance affect the performance

of the operatorof the operator

How would you go How would you go

about improving about improving

the work sitethe work site

Operator’s PERCEPTION is an Operator’s PERCEPTION is an important consideration…important consideration…

Active process of looking for meaning in Active process of looking for meaning in the environment in which we live.the environment in which we live.

Involves receiving and interpreting Involves receiving and interpreting sensory information and is unique to each sensory information and is unique to each individual.individual.

Depends on cultural background, user Depends on cultural background, user experience, personal disposition and experience, personal disposition and interest in the particular task.interest in the particular task.

There are 4 mainThere are 4 main

ENVIRONMENTAL CONSIDERATIONS:ENVIRONMENTAL CONSIDERATIONS:

NOISENOISE

VIBRATIONVIBRATION

LIGHTINGLIGHTING

AMBIENT CONDITIONSAMBIENT CONDITIONS

NOISENOISE

The Structure of the Ear – A review!The Structure of the Ear – A review!

External ear: auricle which collects sound waves and transmits them via the external acoustic meatus (auditory canal) to the tympanic membrane (eardrum).

The Structure of the Ear – A review!The Structure of the Ear – A review!

Middle ear: made up of the tympanic cavity in the temporal bone and contains three auditory ossicles (bones): the malleus (hammer), the incus (anvil) and the stapes (stirrup).

The Structure of the Ear – A review!The Structure of the Ear – A review!

Inner ear: this is made up of the bony labyrinth which consists of the: Cochlea (the main organ of hearing), Vestibular Apparatus and the Membranous Labyrinth.

Creating Sounds – The BasicsCreating Sounds – The Basics

An initial disturbance from a vibrating object will force surrounding air molecules to move.

Molecules are squeezed closer together then pulled apart resulting in compression and refraction.

Sound is propagated through an elastic medium such as air or fluid.

Rapid oscillations in air pressure within the ear.

Sound is thus propagated by a pressure wave moving outward from a vibrating body.

Sound definedSound defined

“a complex scramble of many frequencies that is highly likely to have a disturbing

effect on the listener”

Loebs (1986) identified 3 distinct but Loebs (1986) identified 3 distinct but related meanings of noise:related meanings of noise:

1. Sound which varies randomly in intensity and frequency.

2. Sound which interferes with the reception of another sound (masking).

3. Sound which the individual does not want to hear.

Noise leads to two key changes…Noise leads to two key changes…

Distraction:Distraction:

makes it difficult to maintain concentration when there is more than one source of auditory information

Arousal:Arousal:

loud noise is arousing, but whether it has an affect on performance is debatable

Negative Affects of Noise:Negative Affects of Noise:

Damage to hearing

Disturbance of sleep

Poor performance of required task due to increases in muscular tension, accelerated heart rate

Impaired alertness

Increased fatigue, tiredness and irritability

Hypertension, Heart Rate

Damage to hearingDamage to hearing

Intensive noise causes a portion of the organ of Intensive noise causes a portion of the organ of Corti to be separated from the basilar membrane.Corti to be separated from the basilar membrane.

Metabolic theory suggests the depletion of key Metabolic theory suggests the depletion of key enzymes and metabolites in the hair cellsenzymes and metabolites in the hair cells

Sound Intensity:Sound Intensity:

Is perceived as loudness which is generally measured in decibels (dB)  

Frequency:Frequency:

Pitch of the sound measured in Hertz (Hz)

““Normal” response Normal” response of the human earof the human ear

Note that this is a Note that this is a logarithmic scalelogarithmic scale

Protection against Noise:Protection against Noise:  

Design it out before it becomes a factor.

Reduce it at source.

Insulate sound.

Personal ear protection should be worn where exposure exceeds 85 db.

Two “Noise” Two “Noise” Rating ScalesRating Scales

  

Actual Sound Actual Sound (Noise Perception Rating Scale)(Noise Perception Rating Scale)

1. Quiet

2. Conscious Awareness

3. Loud

4. Excessively Load

5. Unbearable

Personal ResponsePersonal Response ((Annoyance Scale)Annoyance Scale)

1. Relaxing2. Not Disturbing3. Disturbing4. Annoying5. Highly Irritating

Hearing Sensitive JobsHearing Sensitive Jobshttp://www2.worksafebc.com/Publications/Multimedia/Videos.asp?reportid=34284

VIBRATIONVIBRATION

VibrationVibration

Defined simply as a movement

which a body makes about a

fixed point (Oborne, 1995).

Whole Body Vibration (WBV)Whole Body Vibration (WBV)

most commonly associated with motor vehicle drivers

can occur in a number of different environments

The effects of vibration are often only considered in one axis (Z).

Need to consider the speed and intensity of the vibration.

UNIT: Hertz (Hz) – cycles.s-1

VibrationVibration

Physiological outcomes from Physiological outcomes from vibration frequencies:vibration frequencies:

(Hz)Tactile sensation 0.1 – 105

Giddiness and instability 0.1 – 103

Motion sickness 0.2 – 1Vibrating hand tool diseases 75 - 100Major body resonances 3, 4-7.5, 11Respiration difficulties 4 - 8Abdominal pain 4 - 14Muscle tone 10 - 20Lumbosacral pain 7.5 - 20Head sensations 9 - 20Disturbances of vision 1 - 95Speech difficulties 7.5 – 20Urge to defecate & urinate 10 – 20

Resonance occurs when the vibrational frequency of an external force matches an organs natural frequency

Pope et al., (1996) state that spinal resonance occurs at 4 - 5 Hz

Coerman (1968) reported that vibrations between 2.5 – 5 Hz generate strong resonance in the vertebrae of the neck and lumbar regions

VibrationVibration

Vibration TermsVibration Terms

Daily vibration exposureThe 8-hour energy equivalent vibration total value for a worker in meters per second squared (m/s²), including all hand-arm vibration exposures during the day.

Partial vibration exposureThe contribution of operation i to the daily vibrationexposure in m/s². The partial vibration exposure relates tothe daily exposure from an individual tool or process, i(where a worker is only exposed to vibration form one toolor process then the daily vibration exposure is equal to thepartial vibration exposure).

Exposure limit value A value for a workers daily vibration exposure of 5m/s²,

above which workers should not be exposed.

Exposure time. The duration per day that a worker is exposure to a vibration source.

Hand Arm Vibration (HAV)Hand Arm Vibration (HAV)

Measurement of vibration is related to acceleration (m.s2) of the surface in contact with the hand.

Depends on the tools used by the operator.

Many tools do not provide the operator with an indication of the dosage of vibration received.

Need exists for detailed analyses of the impacts of continuous/repetitive hand arm vibration.

Total Daily Exposure Duration (Hours)

Maximum Value of Frequency Weighted Acceleration (m.s2) in

any Direction*4 to less than 8 hours4 to less than 8 hours 44

2 to less than 4 hours2 to less than 4 hours 66

1 to less than 2 hours1 to less than 2 hours 88

Less than 1 hourLess than 1 hour 1212

The American Conference of The American Conference of Governmental Industrial Hygienists Governmental Industrial Hygienists

Threshold Limit ValuesThreshold Limit Values

* Directions of Axes in a 3-D System

The effects of vibration on The effects of vibration on performance:performance:

Decreased hand steadiness (important for motor control).

Problems related to sight (for example, blurring and fixation difficulties).

A vibration standard:A vibration standard:

International Standardization Organizations Guideline (ISO) 2631: “Guide for Evaluation

of Human Exposure to Whole Body Vibration”

Vibration-related DisordersVibration-related Disorders

Vascular disordersVascular disorders• dead or white finger,• Raynaud's phenomenon of occupational origin,• vibration-induced white finger.

Neurological disorders Carpal Tunnel Syndrome Musculoskeletal disorders

Jobs and HearingJobs and Hearing

LIGHTINGLIGHTING

Vision and the Role of LightingVision and the Role of Lighting

Problems associated with poor lighting can often be solved by low cost interventions and careful design consideration.

Arrangement of working surfaces, such as placement of machines.

Placement of work benches for natural lighting.

Improved overhead lighting.

Changing the paint colour of walls.

Why is vision so important in Why is vision so important in the working environment?the working environment?

70 – 80% of information entering the brain from the sensory system is visual

Some Lighting Some Lighting TerminologyTerminology

Luminous FluxLuminous Flux (lumen): quantity of energy of the light emitted per second in all directions.

Luminous IntensityLuminous Intensity: ability of a source or illuminated surface to emit light.

LuminanceLuminance: the amount of light emitted by a surface.

Illuminance Illuminance (lux) : amount of light falling on a surface.

Visual AcuityVisual Acuity

a measure of the resolving qualities of the eye (ability to see fine detail).

Affected by physiological factors such as receptive ability of the visual receptors.

Integrity of the nerve pathways to the brain.

CHERNCK (1983) considers the CHERNCK (1983) considers the following visual skills important:following visual skills important:

a)a) Visual acuityVisual acuity

b)b) Near point of convergence (i.e. the closest point to the Near point of convergence (i.e. the closest point to the person along the median line at which he can continue to person along the median line at which he can continue to fixate the target with both eyes).fixate the target with both eyes).

c)c) Stereopsis (i.e. the perception of three-dimensional visual Stereopsis (i.e. the perception of three-dimensional visual space as a result of binocular cues).space as a result of binocular cues).

d)d) Fusion (i.e. the integration of two similar ocular images into a Fusion (i.e. the integration of two similar ocular images into a single precept).single precept).

e)e) Colour VisionColour Vision

f)f) Accommodative facility (i.e. the ability to change focus Accommodative facility (i.e. the ability to change focus efficiently from near to far and back again).efficiently from near to far and back again).

g)g) Eye movement ability (i.e. the ability to follow a moving Eye movement ability (i.e. the ability to follow a moving target smoothly, keeping both eyes on the target).target smoothly, keeping both eyes on the target).

h)h) Visual motor integration (i.e. co-ordinationVisual motor integration (i.e. co-ordination between the eyes between the eyes and the extra-ocular muscles).and the extra-ocular muscles).

Other Factors Influencing Performance:Other Factors Influencing Performance:

Depth Perception

Contrast Sensitivity

Peripheral Awareness

Motion Detection

Eye Movement

Dynamic Visual Acuity

Visuo-motor Integration

Vestibulo-occular Reflex

Reaction Time

Good visual acuity depends on Good visual acuity depends on appropriate lighting conditions based on:appropriate lighting conditions based on:

Good illumination

Sufficient contrast

Adaptation in the central and peripheral visual field

For visual comfort and good optical For visual comfort and good optical performance, the following criteria apply:performance, the following criteria apply:

1. Balanced arrangements of lights.

2. Suitable level of illumination (lux levels).

3. Avoidance of glare and reflection.

Some Lighting Recommendations:Some Lighting Recommendations:

1. No source of light should appear in the visual field of any worker during operation.

2.  The line from eye to light source should be at an angle of more than 30°.

3. Lights should be provided with shades.

4. Rather use more lamps of lower power than fewer high powered lamps.

5. Reflective colours and materials should be avoided.

6. There should be a contrast in colour between working surface and working materials.

Natural Lighting:Natural Lighting:

1. High windows are more effective than broad ones since the light penetrates further into the room.

2. Use clear glass as it has a transparency of 90%.

3. Positioning of work benches to avoid looking directly into the sun.

4. When working at a VDU windows should be at the side of the monitor and lighting should be to the left or right and not directly overhead, or behind.

Signs of Visual Fatigue:Signs of Visual Fatigue:

Painful irritation and reddening of the eyelids

Double vision

Headaches

Reduction in the power of accommodation and convergence

Flickering LightingFlickering Lighting

Flickering light may influence basic brainwave patterns – induce nausea, epileptic seizures.

Stroboscopic effect makes rotating or oscillating machine parts to appear stationary or moving more slowly.

RECOMMENDED ILLUMINATIONS:RECOMMENDED ILLUMINATIONS:

Table 10.3 Examples of recommended naturally occurring illuminancesTable 10.3 Examples of recommended naturally occurring illuminancesArea/activity Illuminance on a horizontal

surface (lux)Clear sky in summerClear sky in summer 150 000 150 000Overcast sky in summerOvercast sky in summer 16 000 16 000Performance of extremely low contrast Performance of extremely low contrast 10 000 10 000

tasks (certain surgical operations)tasks (certain surgical operations)Textile inspectionTextile inspection 15 000 15 000Office work (writing, reading poor quality documents)Office work (writing, reading poor quality documents) 1 000 1 000Precise assembly workPrecise assembly work 1 000 1 000Office work (without VDUs)Office work (without VDUs) 500 500Office work (data entry)Office work (data entry) 500 500Heavy engineeringHeavy engineering 300 300Rough assembly workRough assembly work 200 200Min. illuminance for MMH tasks (NIOSH)Min. illuminance for MMH tasks (NIOSH) 150 150Rarely visited places where little perception of detail is requiredRarely visited places where little perception of detail is required 50 50Good street lightingGood street lighting 10 10Emergency lightingEmergency lighting 2 2MoonlightMoonlight 0.5 0.5

Jobs and VisionJobs and Vision

Climate/Thermal Climate/Thermal EnvironmentEnvironment

  Temperatures

Ventilation Humidity

Poor respiratory function Dehydration

Reduced work capacity!!

Assessing Thermal ConditionsAssessing Thermal Conditions

Six Factors to assess human Six Factors to assess human response to thermal conditions:response to thermal conditions:

1.1. Air temperatureAir temperature2.2. Radiant temperatureRadiant temperature3.3. Air velocityAir velocity4.4. Humidity Humidity 5.5. Activity of the personActivity of the person6.6. Clothing worn by the personClothing worn by the person

WorkWork

Work PaceWork Pace

ClimateClimate

ClothingClothing

Heat Heat StressStress

OperatorOperator

Heat Heat StrainStrain

Criteria:Criteria:HealthHealth

ComfortComfortPerformancePerformance

Individual Factors:Individual Factors:Age/SexAge/Sex

Work CapacityWork CapacityHealth StatusHealth Status

AcclimatizationAcclimatization

CrampsCrampsExhaustionExhaustion

StrokeStrokeSyncope (fainting)Syncope (fainting)

RashRashMiliaria Profunda – inability to sweatMiliaria Profunda – inability to sweat

Heat Balance (homeostasis)Heat Balance (homeostasis)

Optimal human internal (core) temperature is around 37°C

Body under heat stress:Body under heat stress:

Two main mechanisms:Two main mechanisms:

Vasodilation• Where the peripheral blood vessels dilate and

transfer blood (heat) to the surface of the body where it can be lost to the surrounding environment.

Sweating• Heat lost by evaporation

Maximum Core TemperatureMaximum Core Temperature

A maximum core temperature of A maximum core temperature of 38°C is often used as a limit for 38°C is often used as a limit for working environments.working environments.

Death will occur in the region of 42°C Death will occur in the region of 42°C core temperature. core temperature.

Body under cold stress:Body under cold stress:

Two main mechanisms:Two main mechanisms:

Vasoconstriction• Peripheral blood vessels constrict to

reduce the flow of blood to the body surface that reduces heat loss.

Shivering

Psychological Responses to Poor Psychological Responses to Poor Ambient Conditions:Ambient Conditions:

Less Severe:Less Severe:• Decreased Concentration• Decreased Response Time

More Severe:More Severe:• Mental confusion• Unconsciousness• Death due to Ventricular

Fibrillation (heart failure)

Permissible Heat Exposure Threshold Permissible Heat Exposure Threshold Limit Values in Degrees C, WBGTLimit Values in Degrees C, WBGT

WorkloadWorkload

Work/RestWork/Rest(per hour)(per hour)

LightLight ModerateModerate HeavyHeavy

Continuous 30.0 26.7 25.0

75% / 25% 30.6 28.0 25.9

50% / 50% 31.4 29.4 27.9

25% / 75% 32.2 31.1 30.0

Wet Bulb Temperature (WBT):Wet Bulb Temperature (WBT):

Temperature associated with moisture content of the air. WBT is taken by surrounding the thermometer with a wet wick and measuring the reading as the water evaporates. WBT readings are typically lower than dry-bulb temperatures.

• With high relative humidity, little evaporative cooling occurs, and the reading is similar to that of a dry-bulb thermometer.

• On a dry day, significant evaporation occurs from the wetted bulb, which maximized the differences between the two thermometer readings (air velocity is obviously a factor).

Dry Bulb Temperature (DBT):Dry Bulb Temperature (DBT):

Temperature we measure with a standard thermometer that has no water surface on it. When people refer to temperature of the air they are usually referring to this.

Relative Humidity (RH):Relative Humidity (RH):

How saturated the air is with water vapor. The amount of moisture air can hold increases a the dry bulb temperature increases. When referring to the relative humidity it is important to define the dry bulb temperature of the air as well.

Methods of Heat Loss:Methods of Heat Loss: ConvectionConvection

Air flows along the skinAir flows along the skin Heat transferred from skin to airHeat transferred from skin to air

ConductionConduction Heat transferred by touchHeat transferred by touch i.e. working in water, handling cold products, etc.i.e. working in water, handling cold products, etc.

EvaporationEvaporation i.e. sweating.i.e. sweating.

RespirationRespiration Both convective and evaporative heat lossBoth convective and evaporative heat loss Occurs from the lungs by respiration as inspired airOccurs from the lungs by respiration as inspired air

Heat Production/LossHeat Production/Loss

B F

E

C

DA

Heat Production/LossHeat Production/Loss

Conduction

Evaporation (sweat)

Reflected Radiation

Directed Radiation

Respiration

Convection

Heat DisordersHeat Disorders

PreventionPrevention

Slow Moving Fans – increase air circulation

Cooling Jackets

Increased Hydration

Amount and Composition of Clothing

Education about signs and symptoms

Cold DisordersCold Disorders

Cold-related DisordersCold-related Disorders

Frost-nip versus FrostbiteFrost-nip versus Frostbite• With frost nip, there is freezing of the superficial tissues With frost nip, there is freezing of the superficial tissues

commonly diagnosed by a blanching of fingers, noses, commonly diagnosed by a blanching of fingers, noses, ears, etc. Frost bite is significantly more serious. There ears, etc. Frost bite is significantly more serious. There we find freezing of the deep tissues resulting in the we find freezing of the deep tissues resulting in the formation of ice crystals. formation of ice crystals.

HypothermiaHypothermia Trench Foot and Immersion FootTrench Foot and Immersion Foot

• conditions that present much like frost bite; however, they occur at temperatures above freezing when the

foot is continuously immersed in water

PreventionPrevention Apply skin moisturizer to the face, hands, and any other body part that may Apply skin moisturizer to the face, hands, and any other body part that may

be exposed to the cold. be exposed to the cold.

Dress warmly, wear dry clothing, and stay out of the wind. Wear a face Dress warmly, wear dry clothing, and stay out of the wind. Wear a face mask for extra protection. Wear heavy mittens instead of gloves in freezing mask for extra protection. Wear heavy mittens instead of gloves in freezing cold weather. cold weather.

Be extremely careful when pumping gas into your car if the temperature is Be extremely careful when pumping gas into your car if the temperature is below freezing. Gasoline on exposed skin evaporates very quickly, lowers below freezing. Gasoline on exposed skin evaporates very quickly, lowers the temperature of the skin, and makes it more susceptible to frostbite. the temperature of the skin, and makes it more susceptible to frostbite.

When you exercise in below-freezing temperatures, wear layers of clothing. When you exercise in below-freezing temperatures, wear layers of clothing. The innermost garment must be nonabsorbent and loosely woven. The innermost garment must be nonabsorbent and loosely woven.

Go inside, if possible, when you feel too cold. Remember that fatigue, lack Go inside, if possible, when you feel too cold. Remember that fatigue, lack of oxygen in high elevations, and consumption of alcohol may cause you to of oxygen in high elevations, and consumption of alcohol may cause you to disregard discomfort and cold. disregard discomfort and cold.

Avoid smoking or drinking before venturing out into extreme cold. Tobacco Avoid smoking or drinking before venturing out into extreme cold. Tobacco decreases circulation by constricting blood vessels, and alcohol interferes decreases circulation by constricting blood vessels, and alcohol interferes with the body's ability to regulate temperature.with the body's ability to regulate temperature.

Thermal Sensitive JobsThermal Sensitive Jobs

Other Environmental Other Environmental Factors that Affect WorkFactors that Affect Work

Air QualityAir Quality

Indoor environment - inadequate temperature, humidity, lighting, excessive noise

Indoor air contaminants - chemicals, dusts, moulds or fungi, bacteria, gases, vapours, odours

Symptoms – Indoor Air QualitySymptoms – Indoor Air Quality

dryness and irritation of the eyes, nose, dryness and irritation of the eyes, nose, throat, and skin, throat, and skin,

headache, headache, fatigue, fatigue, shortness of breath, shortness of breath, hypersensitivity and allergies, hypersensitivity and allergies, sinus congestion, sinus congestion, coughing and sneezing, coughing and sneezing, dizziness, and/or dizziness, and/or nauseanausea

MotionMotion

•Motion-sickness

•Fatigue

•Motion-induced Interruptions