Chapter 6: Work Environment Chapter 6: Work Environment DesignDesign

Presented by

Andira

Chapter 6:Chapter 6:Work Environment DesignWork Environment Design

LightingNoiseTemperature: heat and cold stressVibrationRadiationShifts to optimize productivityTraining in ergonomics and safety

The value of a good environmentThe value of a good environment

Plants with good working conditions outperform those with poor conditions

Economic return on investment in better conditions is usually significant– Improves safety and morale– Reduces turn-over, absenteeism– Failure to comply results in OSHA fines

OSHA: Occupational Safety and Health Administration

Home environmental designHome environmental design

Many of the same principles that apply to environmental design of the workplace, also apply to design of the home.

Issues such as lighting, heat, ventilation, layout and adequate space for tasks can have great impact on the:– Convenience, – Efficiency– Feeling in one’s home. (Is it a welcoming,

relaxing haven? Or is it a chaotic, stressful pit?)

I. Lighting and IlluminationI. Lighting and Illumination

Lighting intensity is measured in candalas (cd), or lumens, where 1 cd = 12.57 lumens.

Illuminance is the amount of light shining on an object, measured in foot-candles (fc):

Illuminance = intensity / d2

Where d is in feet. Intensity is foot-candles (fc) where 1 fc = 1 lumen/(ft2).

LuminanceLuminance

Luminance is the amount of light reflected from an object, – It impacts our ability to see objects,– It is measured in foot-lamberts (fL):

luminance = illuminance x reflectance

Reflectance is determined by the physical and color properties of an object; how much light is absorbed or thrown back at the viewer?

ReflectanceReflectance

Reflectance is the property of a surface which is determined by both color and surface finish, and expressed as a percentage of light reflected (luminance).

Luminance is measured by a photometer (pointed at surface). Table 6-1 lists reflectances for various colors and surfaces. Reflectance is a ration between:

– The measured reflectance of the target surface,– The measured reflectance of a standard Kodak neutral test card = 0.9

Reflectance = 0.9 x Ltarget / Lstandard

Color or finish Percent of reflected light

Color or finish Percent of reflected light

White 85 Medium Blue 35

Light cream 75 Dark Grey 30

Light grey 75 Dark red 13

Light yellow 75 Dark brown 10

Light buff 70 Dark blue 8

Light green 65 Dark green 7

Light blue 55 Maple 42

Medium Yellow 65 Satinwood 34

Medium buff 63 Walnut 16

Medium grey 55 Mahogany 12

Medium green 52

Reflectances of typical Paint and Wood Finishes

VisibilityVisibility

Visibility is the clarity with which a human can see an object.

There are 3 critical factors in visibility:– Visual angle– Contrast– Illuminance

Yes, but do I have enough light Yes, but do I have enough light on my task?on my task?

The amount of light needed is a function of:– The nature of the task– The worker (age and visual health),– The reflectance of the task background.

Table 6-2, shows how much light (in fC) is needed for different types of tasks.

How much light is needed?How much light is needed?Table 6-2 will give you a range of lighting

levels (low, medium, high) suitable for a general task category:

To choose between low, medium and high use table 6-3.

Task:

Visual task with low contrast, and small size (e.g. pencil writing on low quality paper)

Range of llluminance:

Low Medium High100 fC 150 fC 200 fC

Task Category:

F

Example Lighting ProblemExample Lighting Problem H & R Block (tax preparation company) hires retired

people (60 + years old) to prepare taxes from January thru April.

The task must be done with reasonable speed (particularly in April) and high accuracy.

The notes people give to their tax preparers range from high quality printed receipts, to handwritten pencil notes on yellow notebook paper (low contrast)

Is it sufficient to light the tax preparer’s desk with a single 800 lumen1 incandescent bulb, if the bulb is 5 feet above the worker’s desk, and the surroundings are cream colored?

1. Light output (intensity) in lumens or candelas can often be found on bulb packaging.

Example Lighting Problem (cont.)Example Lighting Problem (cont.)

Consider this question in two parts: How many fc’s are needed? Is a 800 lumen bulb sufficient to provide

that illuminance, if the light source is 5 ft. from the work?

1. How many fc’s are needed?1. How many fc’s are needed?

Find reflectance of surroundings: look in table 6-1, light cream gives you approximately 75% reflectance.

Look in table 6-3 for a weighting factors based on: Task characteristic value weight

– Age of workers, 55 + +1– Reflectance of surroundings, greater than 70% -1– Criticality: speed and accuracy, critical +1

Total Weight = 1 + (-1) + 1 = + 1 Look in table 6-2 to find amount of light needed, use

weighting factor to pick illuminance value:– Low: -3, -2,– Medium: -1, 0, +1– High: +2, +3

1. How many fc’s are needed?1. How many fc’s are needed?

Find reflectance of surroundings: look in table 6-1, light cream gives you approximately 75% reflectance.

Look in table 6-3 for a weighting factors based on: Task characteristic value weight

– Age of workers, 55 + +1– Reflectance of surroundings, greater than 70% -1– Criticality: speed and accuracy, critical +1

Total Weight = 1 + (-1) + 1 = + 1 Look in table 6-2 to find amount of light needed, use

weighting factor to pick illuminance value:– Low: -3, -2,– Medium: -1, 0, +1 => weight = 1 requires medium illumination– High: +2, +3 need at least 150 fc!

2. Is a 800 lumen bulb sufficient?2. Is a 800 lumen bulb sufficient?

Is a 800 lumen bulb sufficient to provide 150 fc on the work surface, if the light source is 5 ft. from the work surface?

1 cd = 12.57 lumens (see Fig. 6.2)

800 lumens * 1 cd/12.57 lumens = 63.64 cd Illuminance (fc) = intensity/d2

63.64 cd/(5ft)2 = 2.5 fc

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2. Is a 800 lumen bulb sufficient?2. Is a 800 lumen bulb sufficient?

Is a 800 lumen bulb sufficient to provide 150 fc on the work surface, if the light source is 5 ft. from the work surface?

1 cd = 12.57 lumens (see Fig. 6.2)

so: 800 lumens * 1 cd/12.57 lumens = 63.64 cd Illuminance (fc) = intensity/d2

63.64 cd/(5ft)2 = 2.5 fc

This bulb at 5 ft is woefully inadequate! (Ok for general lighting in a public area).

Improving VisibilityImproving Visibility

One can improve visability in several ways:– Increase source intensity (increase wattage, change to

more efficient type: florescent, halogen) – Bring target closer to viewer– Bring target closer to light source– Increase contrast– Increase target size (big print books)– Etc.

Factors in VisibilityFactors in Visibility

Visual angle: size of target on retina; the angle the image takes up on retina.

Contrast: relative difference in luminance (light reflected) for two surfaces,

Illuminance: amount of light reaching a surface (most important)

ContrastContrast

Contrast: relative differences in luminance (light reflected) for two surfaces,

Contrast can be defined in several ways,A common definition of contrast (unitless):

contrast = (Lmax – Lmin)/Lmax

Where L is the luminance of each surface.

GlareGlare Any area of excessive brightness, that decreases

visibility:– Causes cornea or glasses to scatter light,– Causes eyes to have to adjust to extreme bright area,

Causes:– Light sources aimed at eyes,– Reflectance off or work surfaces

Solutions:– Change to indirect lighting,– Change lighting angle, or work surface angle,– Use non-glare surfaces,– Use polarizing filters on light sources or eyewear

Other ways of improving visibility:Other ways of improving visibility: Choice of lighting typeChoice of lighting type

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II. Noise and HearingII. Noise and Hearing

Noise: Any unwanted sound.Sound is measured in decibels (dB), which

measure the amplitude of the sound wave.Decibels are measured on a logarithmic

scale

A-weighted Sound Levels (dBA)A-weighted Sound Levels (dBA)

A-weighted Sound Levels:– Measures perceived loudness,– Combines both amplitude and frequency of

noise. (High frequency more annoying and harmful, more powerful.)

– Most widely accepted measure of sound.

Hearing LossHearing Loss

OSHA (1970) limits for noise exposure are shown in Table 6-6.

Duration dBA8 hours 904 hours 951 hour 10515 min 115

Risk of hearing loss increases beyond these exposures.

OSHA Noise Exposure LimitsOSHA Noise Exposure Limits

A worker may not be exposed to anything over 90 dBA for the duration of an 8 hour workday,

Nothing over 115 dBA is allowed at all.

Noise DoseNoise Dose Noise dose is total exposure to any sound above

80 dBA during an 8 hour day.

D = 100 x (C1/T1 + C2/T2 + … Cn/Tn) ≤ 100 %

Where D = noise dose during an 8 hr day, Ci = Hours spent at a given noise level, Ti = Hours permitted at noise level (from

table 6-6). D must be kept below 100 % of permissible noise

dose.

Noise Dose ExampleNoise Dose Example

You are exposed to 3 noise sources during your work day. – 4 hours at 90 dBA– 2 hours at 95 dBA– .5 hours at 105 dBA

Your total noise dose is:D = 100 x (4/8 + 2/4 + 0.5/1) = ? %

Is your hearing at risk?

Noise Dose ExampleNoise Dose Example

You are exposed to 3 noise sources during your work day. – 4 hours at 90 dBA– 2 hours at 95 dBA– .5 hours at 105 dBA

Your total noise dose is:D = 100 x (4/8 + 2/4 + 0.5/1) = 150 %

Is your hearing at risk? Yes.

Noise ControlNoise Control Eliminate noise at its source (best but most

difficult)– Substitute quieter machines (hydraulic for pneumatic

riveter, electric for gas powered mowers) Isolate noise making equipment:

– Rubber feet under equipment– Separate room– Enclosure

Absorb noise (with sound absorbing material on ceiling, walls and floor).

Use hearing protection on workers

Using age-related differences in Using age-related differences in hearinghearing

Mosquito Teen Repellent: product which emits a very loud, high-pitched tone which teens can hear and most people over 30 cannot.

Teens have used the Repellent’s tone as a ring-tone on their cell phones so they can send messages to their friends in class.

You can (try to) listen to the tone at:http://www.npr.org/templates/story/story.php?storyId=5434687http://www.bbc.co.uk/wiltshire/audio/mosquito_sound.mp3

III. Temperature:III. Temperature: heat and cold stress heat and cold stress

Heat and cold can impact workers’– Effectiveness– Safety (Heat exhaustion)– Health

Heat can come from:– The outdoor work environment in summer time (Borax miners in Death Valley)– High temperatures of lack of ventilation

indoors, (Offices in Mechanical Engineering in April, when heat is still on)

– Radiant heat from work (Blast furnace, glass furnace, kitchen oven in restaurant –

“Down and Out in Paris and London,” George Orwell)

Heat Stress MeasurementHeat Stress Measurement

Core temperatures inside body should be:– Normally around 98.6 degrees F; – Above 100 F performance drops sharply. – Above 105 F sweating stops and death may follow.

Thermal comfort zone: 66 to 79 degrees F. Heat exchange between body and environment:

S = M +/- C +/- R - E Where

– M is heat gain from Metabolism; – C is heat gained or lost from Convection; – R is heat gained or lost due to Radiant energy; – E is heat lost through Evaporation of sweat.

For thermal neutrality, S should be zero.

Heat Stress MeasurementHeat Stress Measurement Wet Bulb Globe Temperature (WBGT)

approximates impact of temperature and environment on human body:– Outdoors in the sun:

WBGT = 0.7 NWB + 0.2 GT + 0.1 DB– Indoors or outdoors out of sun

WBGT = 0.7 NWB + 0.2 GTWhere:

NWB – natural wet bulb temperature, measure of evaporative cooling, (thermometer in wet cloth with natural air movement over it)GT – globe temperature – measure of heat from radiation (thermometer in black copper sphere)

DB – Dry bulb temperature – measure of ambient air temperature (regular thermometer shielded from sun)

Heat Stress ManagementHeat Stress Management

Control environment (indoors)– Ventilation (need: 300 cubic feet fresh air per

person, per hour.)– Heating, cooling, humidity control

Administrative:– Limit time in hot or cold situations,– Provide rest breaks at appropriate intervals in a

temperature controlled environment.

Shift WorkShift Work

Shift work: working at times other than daytime hours.

Helps keep factories, trucking and services (fire, police) going 24 hours a day.

Problem: shift work is hard on the circadian rhythms: changes in body temperature, heart rate and energy level over 24 hours.

Impact of Shift Work on the bodyImpact of Shift Work on the body

Most people’s circadian cycle is 25 hours,Circadian rhythms are set by the sun,People on shift work never truly adjust; the

sun keeps their body set on a day schedule even when they have to work at night.

Circadian rhythms of shift workers flatten,

Health and Accident Rates Health and Accident Rates Associated with Shift WorkAssociated with Shift Work

Shift workers experience:– Health problems– Disruption in social life.

Greater accident rate

Types of ShiftsTypes of Shifts

Three shift system (one shift all the time)– Early: 8 AM to 4 PM – Late: 4 PM to 12 Midnight– Night: 12 Midnight to 8 AM

Rapid Rotation: shift change every 2 to 3 days; sleep only disrupted 1/3 of the time.

Weekly Rotation: shift change every week. (very hard on workers – never adjust).

Types of ShiftsTypes of Shifts

Twelve hour shifts (work only 4 days / wk)– Day: 8 AM – 8 PM– Night: 8 PM – 8 AM

Guidelines for Shift WorkGuidelines for Shift Work

Schedule as few night shifts as possibleAvoid shift work for workers over 50Use rapid rotations Use forward rotations (E-L-N)Keep schedule equitable and predictable for

all workers.

OvertimeOvertime

Length of day has a (negative) impact on productivity:– Only 10% increase in productivity

for a 25% increase in hours Scheduling overtime on a

regular basis – NOT recommended!

Shortening the work day can actually result in increased productivity, fewer rest breaks.

Long shifts and safetyLong shifts and safety

Medical residents are allowed to spend 24 hour shifts working with patients; additional time beyond that may be spent on “paper work”

How does this impact medical decision making and patient safety?

RadiationRadiation

The unit of absorbed radiation dose is the rad, The unit of exposure is the roentgen (R). Tissue at the point of exposure of 1 R, absorbs

approximately 1 rad. Radiation sickness is caused by doses of 100 rads or

more. A fatal dose is about 400 rads for 50% of adults,

1000 rad or more is almost always fatal. The annual dose from background sources is

between 0.1 – 0.5 rem/year (100-500 millirem/year)

Radiation from Cell PhonesRadiation from Cell Phones

Radiation from cell phones is close to microwave frequencies.

Cell phone frequencies are non-ionizing.

Non-ionizing radiation, while not necessarily very dangerous, can heat tissues

Sources of Radiation ExposureSources of Radiation Exposure

Visible, ultraviolet and cosmic radiation

Medical & dental treatments

Household products: orangeFiestaware, lantern mantels, kitty litter

Nuclear testing and dumping

Potassium

Radon GasRadon Gas

Radon Gas is naturally occurring. It is the greatest single source of naturally

occurring background radiation.

Radon is responsible for 20,000 lung cancer deaths

per year in the U.S.

EPA recommended limit:4 pCi/L

http://www.yankeerowe.com/images/radiation.jpg

You are always exposed to some level of naturally occurring background radiation.

U.S. nationalaverage: 300 millirem/year

France, near Radon Springs1600 millirem/year

Parts of Brazil:17,500 millirem/year

Background Radiation

Sources:Cosmic rays

Radon

Granite

Etc.

Radioactive Products Radioactive Products

Radioactive heating pad

Radioactive skin cream

Radioactive medicines

Radioactive foods

Marie Curie’s discovery of radioactive elements created excitement worldwide. Radioactive elements were believed to provide energy and healing powers.

Workplace RadiationWorkplace Radiation

Nuclear power plants

Xray & chemo therapy technicians

Uranium mining & processing