ECE 796/896ECE 796/896Human Factor Human Factor EngineeringEngineering

Chapters 16,17,18,19

Light,climate,noise,motion

IlluminationIllumination

• 380-780 nm spectrum • Eyes are most sensitive to about 550nm• 2 sources: luminescent + incandescent

bodies• Natural color - color of an object under white

light.• An object’s color - dominant wavelength,

luminance, and saturation

Measurement of LightMeasurement of Light

• Photometry - is the measurement of light.

• Unit is: Candela (cd) 1 cd = 12.57 lm

• 100W bulb = 1740 lm

• 1lm/sq.ft. = 1 (fc) foot candle

• Lluminance(lx) = (cd)/D2

• Dist. In meters =D

Cont.

• Reflectance = luminance(fl)/illuminance(fc)

Tab16.1

Lamps and Luminaires

• Luminaire is a device that consists of lamps and components for distributing the light.

• Lamp is an artificial light source.

LampsLamps

• Two types, Incandescent filament lamp and gas-discharge lamp.

• Gas discharge have three types - high-intensity discharge (HID), mercury, metal halide, high pressure sodium, low pressure sodium and fluorescent lamps.

• Fluorescent lamps produce ultraviolet that excite a phosphor coating.

Cont.Cont.

• Lamp Color: CRI (color rendering index)• As CRI increases color judgment errors

decrease.• Energy Considerations: lamp efficacy

amount of light produced per unit of power consumed.

• Fluorescent vs. incandescent : lasts 20 times longer, uses 41% less energy, and give 30% more light.

Tab16.2

Effect of Lighting on Effect of Lighting on PerformancePerformance

• Both field and laboratory studies.

• Visually difficult tasks are effected more by lighting levels than visually easy tasks.

• Speed improvement noted by over 50% with lighting level changes.

Luminance - Glare

• Glare is caused by brightness in the field of view that is greater than the luminance to which the eye is adapted, so as to cause discomfort and annoyance.

• Direct or reflected glare– Reflected - spread,specular,

diffuse,compound.

Glare - Cont.Glare - Cont.

• Discomfort, disability and blinding.• Discomfort: A measure Borderline

between comfort and discomfort (BCD)The higher the BCD the less glaring was the source or less sensitive was the person.DGR: Discomfort Glare Rating- can be converted to VCP (visual comfort prob)

Disability glareDisability glare

• Glare the directly effects visibility and visual performance is Disability glare.

Reducing GlareReducing Glare

• Reduce direct glare from luminaires.– Select with low DGR, reduce the luminance of

sources, position far from line-of-sight, increase luminance around glare source

• Reduce direct glare from windows– Set above floors, overhang above window outside

• Reduce reflected glare– Keep luminance level low as possible for

luminaries, small light sources, diffuse light, use surfaces that diffuse light

Computer terminalsComputer terminals

• 1. Frosting or etching of front surface to reduce specular reflections.

• 2. Quarter wave thin-film coatings

• 3. Neutral-density filters

• 4. Circular polarizers

• 5. Micromesh filters

Chapter 17Chapter 17

ClimateClimate

Heat ExchangeHeat Exchange

• Avenues of Heat Exchange: – 1. Conduction: Heat transfer by direct contact.– 2. Convection: Transfer of heat by currents of air.– 3. Radiation: Transmission of heat between

objects by electromagnetic radiation.– 4. Evaporation: perspiration converted to vapor.

Heat Exchange EquationHeat Exchange Equation

• DS = (M-W) + - R +- C - E– Where:– DS: = change in body heat content.– M = metabolism, W= work performed, R =

radiative heat exchange, C= Convective, and E= evaporative heat loss

If the body is in equilibrium -> DS=0

Fig 17.1

Environmental Factors Environmental Factors Influencing Heat Influencing Heat

ExchangeExchange• Air temperature, air flow, humidity,

temperature of the surroundings.• Effects of clothing: Insulation provided by air

trapped inside the weavings of the fabric.• CLO: measure of insulation necessary to

maintain comfort - 70F and 50%. 1 CLO can effect a 16 degree temp change. Eskimo = 12.

Measurement of Thermal Measurement of Thermal conditionsconditions

• Dry-bulb temperature, relatively humidity, hydrometer, wet-bulb temperature, mean radiant temperature, and air velocity.

Cont.Cont.

• Effective Temperature: (et - et*) two indices, combinations of temperature, humidity, air movement that has equal sensation of warmth. ET* has a more complex equation shown on the following graph.

17.2

Other FactorsOther Factors

• Oxford Index: WD=.85*WB+.15*DB

• WB: wet bulb, DB: Dry bulb

• Wet-Bulb Globe Temperature:

• WBGT = .7*NWB + .3*GT

• Botsball: BB = WBGT - 3 degrees

The effect of Heat on The effect of Heat on WorkWork

• As external temperature increases, heart rate increases to increase blood flow to the skin to cool.

• This can also cause a shortage of blood to muscles and essentially cause a longer amount of time to recovery from work.

• Sweat is necessary when convection and radiation does not cool a person.

Heat IllnessHeat Illness

• 1. Heat rash: prickly heat

• 2. Heat Cramps: salt loss

• 3. Heat Exhaustion: dehydration

• 4. Heat Stroke: sweat production loss

– Fitness,aging,gender,body fat, alcohol

Cognitive and Cognitive and Perceptual Motor Perceptual Motor

PerformancePerformance• As temperature - WBGT increases the

performance decreases steadily.

17.11

17.12

Reducing Heat StressReducing Heat Stress

• Easiest way to reduce heat stress is cool the environment and lower the humidity.

• Reducing the energy needed for a task is another way of lowering heat stress.

Cold StressCold Stress

• Most workers that work outside in cool weather can dress properly. Most people who have work related cold weather usually have problems when vehicles break down or they are somehow stranded in the weather without protection.

Index of cold Stress - wind Index of cold Stress - wind chillchill

• Wind chill Index or its derivative, equivalent wind chill index temperature.

• Index not used , the modified temp used.

Tab17.3

Cold PerformanceCold Performance

• Manual Performance is related to skin temperature.

• Tactile Sensitivity: adversely effected by cold.

Chapter 18Chapter 18

NoiseNoise

Sound Level Meter Sound Level Meter ScalesScales

• Meters have scales: A,B,C,D– Psychophysical Indicies:

• Physical properties• Psychological properties

• Phon: decibel level of the 1000 hz tone• Ex: 60db sound at 1000Hz = 60 phons

Noise and Loss of Noise and Loss of HearingHearing

• Deafness: Nerve and Conduction.– Nerve deafness is a deterioration of the

hairs in the organ of Corti.– Conduction: some blockage of the

transmission of sound to the inner ear.

Measuring HearingMeasuring Hearing

• 500,1000,2000,3000,4000,6000,8000hz

• Presbycusis: hearing loss due to aging.

• Sociocusis: hearing due to non-normal cause.

Occupational Hearing Occupational Hearing LossLoss

• Temporary loss from continuous noise:2 min after the exposure,

temporary shift (TTS)

. Permanent loss from continuous noise:(PTS) permanent threshold shift

Effects of Noise on Effects of Noise on PerformancePerformance

• General Conclusions: – With the exception of tasks requiring the

use of short-term-memory it takes noise in excess of 95db.

– Performance of routine tasks show no effect of noise.

– If a person has to react to a signal at a definite time, performance will be good even at high noise.

Cont.

• Visual acuity are not effected by noise.

• Motor performance is rarely effected.

• Simple reaction time is unimpaired.

• Noise tends to have the most effect on continuous tasks without rest.

Noise Exposure LimitsNoise Exposure Limits

• OSHA has established noise guidelines

• TWA: 8h time weighted average sound level.

• Noise dose level of 50 percent ( TWA=85dba) as the ACTION level.

Tab 18.3

Tab 18.4

Noise ControlNoise Control

• Control at the Source– Selecting quieter equipment, damping out

noise

• Control along the Path:High frequency noise can be controlled through barriers

• Control at the Receiver:Hearing protection devices

Chapter 19Chapter 19

MotionMotion

Motion SensesMotion Senses

• Exteroceptors: - eyes, ears• Proprioceptors: a class of these are

Kinesthetic receptors.• Semi-circular canals:In each ear that

form a rough 3D coordinate system.• Utricle and Saccule: Utricle(V),

Saccule(H), triggers nerve impulses via hair cells.

Motion - VibrationMotion - Vibration

• Visual data will override other motion/position senses.

• Vibration:Vibration: Attenuation/Amplification and Resonance.

• Human resonance: 3-5hz (neck,back,shoulder), 20-30(head-shoulders),60-90 eyes.

Health Effects of VibrationHealth Effects of Vibration

• Long term effects:– Pain in chest and abdomen (4-10hz)– Backaches, (8-12hz)– Headaches,eyestrain (10-20hz)– Visual performance (10-25hz)– Whole body

19.6

Limits of Body ExposureLimits of Body Exposure

• ISO 2631 (1978,1982a,1982b) Fatigue decreased proficiency at tasks.

• Standard has criticisms: the details

AccelerationAcceleration

• Acceleration can cause vision distortion and blackout.

• Measured in G’s ( times the force of gravity)• 2G - increase in wt. (+Z)• 3-4 Impossible to raise oneself, hard to raise

legs and arms.• 5-6, tunnel vision, after 5 secs loss of

consciousness, convulsions if continued.

Cont.Cont.

• Forward acceleration:• 2-3 abdominal pressure• 3-6 tightness in chest, hard to

breath,blurring of vision• 6-9 increased chest pain, body parts

can’t be lifted• 9-12 fatigue, loss of peripheral vision• 12-15 loss of vision, speaking difficult

19.13

Motion SicknessMotion Sickness

• Connected to most forms of travel.• People who are motion sick with one

form of transportation are most likely susceptible to all others except space sickness.

• Symptoms: Headaches, nausea.• Cause: Sensory rearrangement theory,

incongruity among the spatial senses.

Cont.Cont.

• For it to be considered motion sickness the vestibular (semicircular canals, etc) must be implicated and that implies acceleration.

• 2 classes of sensory rearrangement:– Visual-inertia and canal-otolith– Both these do two things to cause the sickness .– 1. Both systems simultaneously signal

contradictory information.– 2. One system signals the absence of an expected

signal.

Cont.Cont.

• Simulator Sickness:– Non-moving simulators (driving , flying), exhibit

motion sickness like symptoms in users.– Appears to be connected to wide-field-of-view,

realistic out-of-window scenes and visual and simulator-system delays.

– Incongruity between visual and vestibular senses, or what is experienced by the sense vs. what is expected-by-the senses.