ergonomics and environment- 2008 (1)

8/14/2019 Ergonomics and Environment- 2008 (1)

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ENVIRONMENTALENVIRONMENTAL

ERGONOMICSERGONOMICS

SITI ZAWIAH MD. DAWALSITI ZAWIAH MD. DAWAL

Dept. of Engineering Design andDept. of Engineering Design andManufactureManufacture

Faculty of engineeringFaculty of engineering

University of MalayaUniversity of Malaya


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Workstation EnvironmentWorkstation Environment


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TEMPERATURETEMPERATURE

Most workers are exposed to excessive heat at one time orMost workers are exposed to excessive heat at one time oranother. In many situations, artificially hot climates areanother. In many situations, artificially hot climates arecreated by the demands of the particular industry. Minerscreated by the demands of the particular industry. Minersare subjected to hot working conditions due to the increaseare subjected to hot working conditions due to the increase

of temperature with depth, as well as a lack of ventilation.of temperature with depth, as well as a lack of ventilation.

Textile workers are subjected to the hot, humid conditionsTextile workers are subjected to the hot, humid conditionsneeded for weaving cloth. Steel and aluminum workers areneeded for weaving cloth. Steel and aluminum workers aresubject to intense radioactive loads from open hearthsubject to intense radioactive loads from open hearthfurnaces and refractory ovens. Such conditions, whilefurnaces and refractory ovens. Such conditions, whilepresent for only a limited part of the day, may exceed thepresent for only a limited part of the day, may exceed theclimatic stress found in the most extreme, naturallyclimatic stress found in the most extreme, naturallyoccurring climates.occurring climates.


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THEORYTHEORY

The human is typically modeled as aThe human is typically modeled as a

cylinder with a shell, corresponding to thecylinder with a shell, corresponding to theskin, surface tissues, and limbs, and with askin, surface tissues, and limbs, and with a

core, corresponding to the deeper tissues ocore, corresponding to the deeper tissues o

the trunk and head.the trunk and head.

Core temperatures exhibit a narrow rangeCore temperatures exhibit a narrow range

around a normal value of 98.6 Faround a normal value of 98.6 F (37(37C). AtC). Atvalues between 100-102 F (37.8-38.9 C),values between 100-102 F (37.8-38.9 C),

physiological performance drops sharply.physiological performance drops sharply.


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At temperatures above 105 FAt temperatures above 105 F

(40.6C), the sweating(40.6C), the sweating

mechanism may fail, resulting in amechanism may fail, resulting in arapid rise in core temperature andrapid rise in core temperature and

eventual death.eventual death.


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The heat exchanges between the body and its environmentThe heat exchanges between the body and its environmentcan be represented by the following heat balance equation:can be represented by the following heat balance equation:

S = M C R ES = M C R E

Where:Where: MM= Heat gain of metabolism.= Heat gain of metabolism.

C = Heat gained (or lost) due to convection.C = Heat gained (or lost) due to convection.

RR= Heat gained (or lost) due to radiation.= Heat gained (or lost) due to radiation.EE= Heat lost through evaporation of sweat.= Heat lost through evaporation of sweat.

S = Heat storage (or loss) of the body.S = Heat storage (or loss) of the body.

For thermal neutrality, S must be zero. If the summation ofFor thermal neutrality, S must be zero. If the summation ofthe various heat exchanges across the body result in a heatthe various heat exchanges across the body result in a heatgain, the resulting heat will be stored in the tissues of thegain, the resulting heat will be stored in the tissues of thebody, with a concomitant increase in core temperature andbody, with a concomitant increase in core temperature anda potential heat stress problem.a potential heat stress problem.


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Measurement Of ThermalMeasurement Of ThermalConditionsConditions

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There are five basicThere are five basic

components:components:

Air Temperature or Dry-Bulb TemperatureAir Temperature or Dry-Bulb Temperature

Relative HumidityRelative Humidity

Wet-Bulb TemperatureWet-Bulb TemperatureRadiant TemperatureRadiant Temperature

Air VelocityAir Velocity

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WBGTWBGT

Probably the most commonly used index inProbably the most commonly used index inindustry today establishes heat exposure limitsindustry today establishes heat exposure limitsand work-rest cycles based on theand work-rest cycles based on the wet bulbwet bulbglobe temperature,globe temperature, oror WBGTWBGT (Yaglou and(Yaglou and

Minard, 1957), and the metabolic load. In slightlyMinard, 1957), and the metabolic load. In slightlydifferent forms it is recommended by ACGIHdifferent forms it is recommended by ACGIH(1985), NIOSH (1986), and ASHRAE (1991). For(1985), NIOSH (1986), and ASHRAE (1991). Foroutdoors with a solar load, the WBGT is definedoutdoors with a solar load, the WBGT is definedas:as:

WBGT = 0.7 NWB + 0.2 GT + 0.1 DBWBGT = 0.7 NWB + 0.2 GT + 0.1 DB

and indoors or outdoors with no solar load, theand indoors or outdoors with no solar load, theWBGT is:WBGT is:

WBGT = 0.7 NWB + 0.3 GTWBGT = 0.7 NWB + 0.3 GT


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Thermal ComfortThermal Comfort

Many attempts have been made to combineMany attempts have been made to combineinto one index the physiologicalinto one index the physiologicalmanifestations of these heat exchanges withmanifestations of these heat exchanges withenvironmental measurements. Suchenvironmental measurements. Such

attempts have centered around designingattempts have centered around designinginstruments intended to simulate the humaninstruments intended to simulate the humanbody, or devising formulas and modelsbody, or devising formulas and modelsbased on theoretical or empirical data tobased on theoretical or empirical data to

estimate the environmental stresses or theestimate the environmental stresses or theresulting physiological strains.resulting physiological strains.


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Once the WBGT is measured it can beOnce the WBGT is measured it can be

used with metabolic load of workers toused with metabolic load of workers to

establish the amount of time anestablish the amount of time an

unacclimatized worker and acclimatizedunacclimatized worker and acclimatized

worker are allowed to work under theworker are allowed to work under the

given conditionsgiven conditions

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AcclimatizationAcclimatization

Continuous or repeated exposure to hot orContinuous or repeated exposure to hot or

cold conditions bring about a gradualcold conditions bring about a gradual

adjustment of body functions, resulting inadjustment of body functions, resulting in

a better tolerance of the climatic stress.a better tolerance of the climatic stress.

Acclimatization to heat is demonstrated byAcclimatization to heat is demonstrated by

increased sweat production, lowered skinincreased sweat production, lowered skin

and core temperature, reduced heart rate.and core temperature, reduced heart rate.

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The process- acclimation is veryThe process- acclimation is very

pronounced within about a week and fullpronounced within about a week and full

acclimatization is achieved within aboutacclimatization is achieved within about

two weeks.two weeks.

Interrupting heat exposure for just a fewInterrupting heat exposure for just a few

days reduces the effects of acclimatizationdays reduces the effects of acclimatization

and return to a moderate climate isand return to a moderate climate isentirely lost after about two weeks.entirely lost after about two weeks.

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A healthy person can adjust to dry orA healthy person can adjust to dry or

humid heat.humid heat.

Acclimatization to heat does not dependAcclimatization to heat does not depend

on the type of work performed or whetheron the type of work performed or whether

the work is heavy and of short duration orthe work is heavy and of short duration or

moderate and continuous.moderate and continuous.

A healthy and well trained personA healthy and well trained person

acclimates more easy than someone inacclimates more easy than someone in

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Effect of heatEffect of heat

Cardiovascular effectsCardiovascular effects

- increase blood flow from core to skin- increase blood flow from core to skin

- increase heart rate- increase heart rate

Effects on musclesEffects on muscles

- competition for blood b/w skin and- competition for blood b/w skin andmuscle lack oxygen- lactic acid build up muscle lack oxygen- lactic acid build up

muscle fatiguemuscle fatigue

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DehydrationDehydration

-loss water sweating dehydration rise-loss water sweating dehydration rise

of core tempt muscles crampof core tempt muscles cramp

Effect of mental performanceEffect of mental performance

- ?- ?

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EXERCISEEXERCISE

Consider an unacclimatized constructionConsider an unacclimatized construction

worker at 400kcal/hr with a thermal loadworker at 400kcal/hr with a thermal load

of WBGT = 25of WBGT = 25 OO C. How long the workerC. How long the worker

would be able to work in such condition?would be able to work in such condition?

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ILLUMINATIONILLUMINATION

The basic theory applies to a point source of light (such as a candle) of aThe basic theory applies to a point source of light (such as a candle) of agiven luminous intensity, measured in candelas (cd)given luminous intensity, measured in candelas (cd)

Light emanates spherically in all directions from the source. The amountLight emanates spherically in all directions from the source. The amountof light striking a surface, or a section of this sphere, is termedof light striking a surface, or a section of this sphere, is termedilluminationillumination ororilluminanceilluminance and is measuredand is measured in foot-candlesin foot-candles (fc).(fc).

The amount of illumination striking a surface drops off as the square ofThe amount of illumination striking a surface drops off as the square of

the distance (d) in feet from the source to the surface:the distance (d) in feet from the source to the surface:

illuminance = intensity/dilluminance = intensity/d22

Some of that light is absorbed and some of it is reflected (for translucentSome of that light is absorbed and some of it is reflected (for translucentmaterials, some is also transmitted), which allows humans to "see" thatmaterials, some is also transmitted), which allows humans to "see" that

object and provides a perception of brightness.object and provides a perception of brightness.The amount reflected is termedThe amount reflected is termed luminanceluminance and is measuredand is measured infoot-infoot-lambertslamberts (fL). It is determined by the reflective properties of the surface,(fL). It is determined by the reflective properties of the surface,known asknown as reflectance:reflectance:

luminance = illuminance X reflectanceluminance = illuminance X reflectance


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Illustration of the distribution of light sourceIllustration of the distribution of light source

following the inverse-square lawfollowing the inverse-square law


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Recommended Illumination Levels for Use inInterior Lighting Design


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Weighting factors to be consideredWeighting factors to be considered

in selecting specific illuminationin selecting specific illumination

level within each categorylevel within each category


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Show in table 6-3. These weights are thenShow in table 6-3. These weights are then

summed to obtain the total weighing factor.summed to obtain the total weighing factor.

Note that since categories A, B, and C do notNote that since categories A, B, and C do notinvolve visual tasks, the speed/accuracyinvolve visual tasks, the speed/accuracycharacteristic is not utilized for thesecharacteristic is not utilized for these

categories, and overall room surfaces arecategories, and overall room surfaces areutilized in place of task background. If theutilized in place of task background. If thetotal sum of the two or three weighting factorstotal sum of the two or three weighting factorsis -2 or -3, the low value of the threeis -2 or -3, the low value of the threeilluminance is used; if - 1, 0, or + 1, the middleilluminance is used; if - 1, 0, or + 1, the middle

value is used; and if + 2 or + 3, the high valuevalue is used; and if + 2 or + 3, the high valueis used.is used.


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Example 1Example 1

For highly critical inspection for small sizeFor highly critical inspection for small size

assembly task and workers age below 40assembly task and workers age below 40with critical accuracy and reflectance.with critical accuracy and reflectance.

What will be the specific illumination?What will be the specific illumination?

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Example 2Example 2

For surgical operation with surgeons ageFor surgical operation with surgeons age

of between 40 55 with critical accuracyof between 40 55 with critical accuracyand reflectance. What will be theand reflectance. What will be the

illumination?illumination?

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GLAREGLARE

GlareGlare is the excessive brightness in theis the excessive brightness in thefield of vision. This excessive light isfield of vision. This excessive light isscattered in the cornea, lens, and evenscattered in the cornea, lens, and evencorrective lenses (Freivalds, Harpster,corrective lenses (Freivalds, Harpster,and Heckman, 1983), decreasing visibilityand Heckman, 1983), decreasing visibilityso that additional time is required for theso that additional time is required for theeyes to adapt from light to darkeeyes to adapt from light to darker

conditions.conditions.


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Also, unfortunately, the eyes tend to beAlso, unfortunately, the eyes tend to bedrawn directly to the brightest lightdrawn directly to the brightest lightsource, which is known assource, which is known as

phototropism.phototropism.

Glare can be either direct, as causedGlare can be either direct, as caused

by light sources directly in the field oby light sources directly in the field ofview, or indirect, as reflected from aview, or indirect, as reflected from asurface in the field of view.surface in the field of view.

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Reflected glare can be reduced by usingReflected glare can be reduced by using

non-glossy or matte surfaces andnon-glossy or matte surfaces and

reorienting the work surface or task, inreorienting the work surface or task, in

addition to the modificationsaddition to the modificationsrecommended for direct glare. Also,recommended for direct glare. Also,

polarizing filters can be used at the lightpolarizing filters can be used at the light

source as part of glasses worn by thesource as part of glasses worn by theoperatoroperator

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The other areas of the room should reflect lowerThe other areas of the room should reflect lower

and lower percentages of the light as one movesand lower percentages of the light as one movesdownward from the ceiling until the floor isdownward from the ceiling until the floor is

reached, which should reflect no more than 20-reached, which should reflect no more than 20-

40 percent of the light, to avoid glare. To avoid40 percent of the light, to avoid glare. To avoid

excessive luminance, the luminaires should beexcessive luminance, the luminaires should be

evenly distributed across the ceiling.evenly distributed across the ceiling.

Direct lightingDirect lightingde-emphasizes the ceiling surfacede-emphasizes the ceiling surfaceand places more of the light on the workand places more of the light on the work

surfaces and the floor. Direct-indirect lighting issurfaces and the floor. Direct-indirect lighting is

a combination of both.a combination of both.


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Reflectances recommend for roomReflectances recommend for room

and furniture surfaces in officeand furniture surfaces in office


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Reflectance of typical paint andReflectance of typical paint and

wood finisheswood finishes


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LIGHT DISTRIBUTIONLIGHT DISTRIBUTION

LuminairesLuminaires for general lighting are classified infor general lighting are classified inaccordance with the percentage of total light outputaccordance with the percentage of total light outputemitted above and below the horizontal (see Figureemitted above and below the horizontal (see Figure6-4).6-4).

Indirect lightingIndirect lighting illuminates the ceiling, which in turnilluminates the ceiling, which in turnreflects light downward. Thus, the ceilings should bereflects light downward. Thus, the ceilings should bethe brightest surface in the room (see Figure 6-5),the brightest surface in the room (see Figure 6-5),

with reflectance above 80 percent.with reflectance above 80 percent.


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LIGHT SOURCESLIGHT SOURCESTwo important parameters related to artificial lighting areTwo important parameters related to artificial lighting are

efficiencyefficiency (light output per unit energy; typically,(light output per unit energy; typically,lumens/watt) andlumens/watt) and color rendering.color rendering.

Efficiency is particularly important, since it is related to cost;Efficiency is particularly important, since it is related to cost;efficient light sources reduce energy consumption.efficient light sources reduce energy consumption.

Color rendering relates to the closeness with which theColor rendering relates to the closeness with which theperceived colors of the object being observed match theperceived colors of the object being observed match theperceived colors of the same object when illuminated byperceived colors of the same object when illuminated bystandard light sources.standard light sources.

The more efficient light sources (high- and low-pressureThe more efficient light sources (high- and low-pressuresodium) have only fair to poor color renderingsodium) have only fair to poor color renderingcharacteristics and consequently may not be suitable forcharacteristics and consequently may not be suitable forcertain inspection operations where color discrimination iscertain inspection operations where color discrimination is

necessary.necessary.


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Types of industrial ceiling-mounted luminairesTypes of industrial ceiling-mounted luminaires


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COLORCOLOR

Both color and texture have psychologicalBoth color and texture have psychological

effects on people. For example, yellow iseffects on people. For example, yellow isthe accepted color of butter; therefore,the accepted color of butter; therefore,margarine must be made yellow to appealmargarine must be made yellow to appealto the appetite.to the appetite.

Perhaps the most important use of colorPerhaps the most important use of coloris to improve the environmental conditionsis to improve the environmental conditionsof the workers by providing more visualof the workers by providing more visualcomfort. Analysts use colors to reducecomfort. Analysts use colors to reducesharp contrasts, increase reflectance,sharp contrasts, increase reflectance,highlight hazards, and call attention tohighlight hazards, and call attention tofeatures of the work environment.features of the work environment.


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Sales are also affected or conditioned by colors.Sales are also affected or conditioned by colors.

People recognize a company's productsPeople recognize a company's products

instantly by the pattern of colors used oninstantly by the pattern of colors used on

packages, trademarks, letterheads, trucks, andpackages, trademarks, letterheads, trucks, andbuildings.buildings.

Some research has indicated that colorSome research has indicated that color

preferences are influenced by nationality,preferences are influenced by nationality,

location, and climate. Sales of a productlocation, and climate. Sales of a productformerly made in one color increased whenformerly made in one color increased when

several colors suited to the differences inseveral colors suited to the differences in

customer demands were supplied.customer demands were supplied.4141


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Bright light entering from a windowBright light entering from a window

Solution ?Solution ?


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Glare from overhead light sourceGlare from overhead light source

(Figure 3)(Figure 3)


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Monitor with a glare screenMonitor with a glare screen

(Figure 4)(Figure 4)

ergonomics and environment- 2008 (1)

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