Chapter_11 No Pics

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Chapter 11: Allowances

ME 5211 Human Factors


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A word about your

presentations Presentations will be split into two

days:

Wed, 12/8/07

Mon, 12/13/07

Each presentation will be no more than 12

minutes, with 1 min for questions at the end,and 2 min for change-over to next group at theend.

Give me your preferences today!


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Presentations

No more than 10 power point slides, less ifyou plan to include a video or softwaredemonstration. (All must fit into your 12minute slot).

If you will be bringing a prototype(cardboardor otherwise) as part of your presentation, letme know in advance


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Turning in your

presentation: E-Mail me the .ppt file before5:00 PM

the day before your presentation, and

I will put it on my desktop.Alternatively, you can come 10 min

early to class on the day of your

presentation with your presentation ona flash drive, and load it beforeclass.


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Special presentation

needs If you have a videoor softwareto

present, you may use your own

laptop, but you need to let me know inadvance so I can sequence thepresentations.

Otherwise, we will be spending toomuch time switching laptops!


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Standards: Using data to

set a standard There is no one size fits all

procedure for setting standards,

Standard must be set to meet thecontext, and the particular goals of theorganization,

Setting an appropriate standard mayrequire data collection, detectiveworkand experimentation.


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Allowances

Allowances compensate for fatigue andnecessary delays in the workplace

Allowances can be determined throughobservation and work sampling,

Provide minimum of 9 10 % constantallowance for personal needs and basicfatigue,

One can add these fatigue allowances tonormal time as a percentage of the normaltime to complete the task.


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Two methods to collect data forestimating the need for allowances

Production Studies: observation ofall activity in an extended interval

(record duration and reason for all idletime).

Work sampling studies (chapter14): take a large number of randomsamples of the work. Walk in to workarea at random times, record totalnumber of delays, and productive

work.


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Estimating Allowances is

an inexact science It is difficult to estimate appropriate

allowances exactly from scientific

principles, However, appropriate and fair

allowances can be estimated from

data and from agreements developedover time between management andlabor across many industries.


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Collecting data to

determine allowances Collect data to determine:

Normal time (NT)

Range of operator abilities (if severaloperators are observed)

Estimate frequency and duration of

foreign operations Fatigue over time

Look at environment to identify fatigue

factors


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Division of Allowances:

Fatigue:

Constant

Variable Special Allowances (related to process,

equipment, materials, etc.)

Unavoidable

Avoidable

Extra

Policy


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Allowances


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Constant Allowances

Personal needs: to maintain generalwellbeing of the worker Trips to drinking fountain, restroom, etc.

5% allowances for personal time are typical.(4.6 6.5% were found across many industries)

Basic Fatigue: (rest needed to recoverfrom energy expended, relieve monotony,

stress, etc.) 4 % allowances are appropriate for a seatedworker doing light work, under good conditions,no special demands on sensory of motorsystems.

Harder work may require more allowances.


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Variable Fatigue

Allowances Additional allowances may be given beyond

the basic fatigue allowance of 4%.

Fatigue may be the result of: Physical stress Psychological stress

A combination of both.

Fatigue can result in a loss of: Muscle strength,

Attention and concentration.


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Major factors affecting

fatigue: Working conditions

Noise

Heat

Humidity

General health of

the worker

Nature of work

Posture

Muscularexertion

Tediousness

Stress


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To determine whether

workers need more rest: Examine the speed at which they perform

work cycles at: Start

End of a long period of continuous work.

Calculate a coefficient of fatigue:

F = (T t) x 100/TWhere:

F = Coefficient of fatigue

t = Ave. time required to perform one cycle of work at thestart of the period of continuous work,

T = Ave. time required to perform one cycle of work at theend of the period of continuous work.


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Example

At start of work, 1 cycle takes 2.3 min = t

At end of work, 1 cycle takes 2.5 min = T

Coefficient of Fatigue:F = (2.5 min 2.3 min)

------------------------ x 100 = 8 %

2.5 min

Fatigue has slowed the worker down by 8 %


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Coefficient of Fatigue

Note: this coefficient does notsayanything about:

How long the period of work is, How large an allowance should be given

for rest

It only indicates whether there is abuild-up of fatigue.

Tasks can be compared relativelytodetermine if some are more fatiguing

then others.


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Methods for calculating variableallowances for additional rest

Use ILO* recommended allowances (Table 11.9, pg. 456).

This table was developed in the late 1950sthrough consensus agreements betweenmanagement and workers across manyindustries .

Compute allowances Based on equations learned in Chapters 4 7.

* IL0 is the International Labor Office.


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ILO

Recommended

Allowances

(pg 456)


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Allowances

Total allowances time = NT (normal time) * total percentage of allowances


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Computing Variable

Fatigue Allowances Physical fatigue, Temperature and humidity, Noise,

Illumination Visual strain: size, contrast of text and materials

handled, and exactness of task Mental stress: complexity, danger and anxiety level

of task Monotony:Associated with mental repetitiveness

and vigilance tasks Tediousness: associated with repetitive motions


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Computing perceived mentaland physical workload

NASA-TLX: Task Load Index (Hartand Staveland)

A subjective measure of workload inwhich subjects performing a task rateits difficulty according to 6 properties

(shown on next slide).


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NASA-TLX

Task Load Index Demands imposed on the subject:

Mental

Physical

Temporal Interaction of subject and task:

Effort

Frustration

Performance

Subjects ratings in each of these areas are combinedto create an overall weighted workload score.


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For more information on

NASA-TLX see: Google to find PDF article on web:

Development of NASA-TLX (TaskLoad Index) Results for Empirical andTheoretical Research, Sandra G. Hart

and Lowell E. Staveland.


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Allowances



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Special allowances

Unavoidable delays: Interruptions from supervisor

Material irregularities

Interruptions from other duties (cant attend to onemachine while servicing another).

Avoidable delays(one may or may not give allowances forthese things personal phone calls, social visits, etc.)

Extra allowances for special conditions,

Bad lot of material, many rejects Broken lifting equipment, need more time for material

handling


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Special Allowances

Policy allowances: exceptional allowancesfor exceptional circumstances:

New employees, Temporarily injured employees,

Differently abled (visually impaired, hearingimpaired, physically impaired, etc.)

Often negotiated between management,worker and union.


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Allowances



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Computing Standard Time

Standard time (ST):

ST = NT + NT * allowances

Where: NT = normal time

Allowances are expressed as a percentageof the normaltime (NT).

Alternatively,ST = NT * (1 + allowances)


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Allowances Summary

If allowances are too high: costs are unnecessaryinflated,

If allowances are toolow, labor relations suffer,

illness and absenteeism may rise (also increasingcosts) By combiningobservational dataand analysis,

one can obtain a more certain estimate ofappropriate allowances,

Total timefor allowances should be in line withdata from observational studies, once avoidabledelays are subtracted (particularly with worksampling study of more than 2 weeks).

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