Environmental Factors

Effects of Temperature

Hardianto Iridiastadi, Ph.D.

Introduction

• Cases– Manufacturing plant– Mining– Military– Emergency responders

Introduction

• Comfortable environment– Temperature– Humidity– Air distribution

• Also affected by– Seasons of year– Dry and wet bulb temperature– Cultural practices and habits

Introduction

• Comfortable environment– Chart for certain populations– E.g., ASHRAE Handbook

• Increased heat– Environment– Physical activities

Heat Transfer

• How it occurs– Object with higher temperature to

that with lower temperature

• Mechanisms– Conduction (typically not a significant

factor)– Convection– Radiation

Heat Exchange

• Sources of heat– Metabolic (internally generated)– Environmental (externally imposed)

• Net heat exchangeH = M + R + C – E

H = heat storageM = metabolic heat gainR = radiant/infrared heat C = convection E =

evaporative

Problems with Heat

• Heat stress– Common across industries– Total heat imposed on the body

• Heat strain– Physiological responses to the body– Reflects the degree of heat stress– Varies from discomfort to disorders

Problems with Heat

• Influencing factors– Heat stress intensity– Age– Physical fitness– Degree of aclimatization– Dehydration level– Alcohol intake– Obesity

Problems with Heat

• Heat disorders– Can be distinguished clinically– Rangin from heat syncope (fainting)

to complex heatstroke

Problems with Heat

• Effects on the workers– Faint while standing erect– Painful muscle spasms (during or after

work)– Impaired performance

• Mental• Vigilance• Sensorimotor• Reduced capacity• Poor behavior

Problems with Heat

• Central nervous system– Hypothalamus of the brain acts as a

control/thermostat– Initiates to cool/heat the body, if

temperature difference exists

Problems with Heat

• Heat illnesses– Heat stroke

• Thermoregulation fails• Core temperature exceeds 41oC• Fatal if untreated• One may collapse and disoriented• Skin is hot, red, and dry• Active cooling is needed

Introduction

• Heat illnesses– Heat exhaustion

• Combined strain (thermoregulatory and cardiovascular)

• One feels weak and un-coordinated• Shallow breath• Rapid, weak pulse• Treatment via removing from the heat,

removal of clothing, and fanning

Introduction

• Heat illnesses– Heat syncope

• Fainting due to inadequate venous return• Common for unacclimatized person• Need to lie down

– Heat hyperventilation• Excessive loss of carbon dioxide• Can occur while wearing protective

clothing

Introduction

• Heat illnesses– Prickly heat

• Fine, superficial skin rash• Due to excessive sweating• Often occurs on areas of skin covered by

clothing or protective equipment

Thermoregulation

• Human thermoregulation– Ability to tolerate heat– Balance between metabolic heat

produced and heat loss– Objective to maintain core temp. at

36 – 37oC – Stability needed for most biochemical

reactions

Thermoregulation

• Human thermoregulation– Temperature outside the range

• >39.5 – disabling• >42 – fatal• 35.5 – lower acceptable limit• <33 – onset of cardiac disturbances• < 25 - fatal

Human Thermoregulation

• Human thermoregulation– Heat gained

• Metabolic energy production• Radiation• Convection• Conduction (minimal)

– Heat loss• Evaporation, Radiation, Convection

– Balance between the two

Human Thermoregulation

• Human thermoregulation– Evaporation

• Sweat production and evaporation as means to loose heat to the environment

– The importance of maintaining the balance via a variety of methods

Sweating

• What it is…– Sweat glands stimulated by the nerves– A dilute solution of various electrolytes

(sodium, potassium, and chloride); mainly salt (sodium chloride)

– Potential loss of 500 g/sq.m– Loss of 100g/hour; can be up to 1 – 2

kg/h– Loss of 1 l/hr is frequently found

Sweating

• What it is– Sweat cools the body (only if

evaporates)– Less efficient in humid environment– Result in dehydration and loosing salt– Affected by air humidity and

movement

Sweating

• Sweat and dehydration– 1 liter fluid loss ~ 1 kg drop in body

weight– Workers can be weighed before and

after– Dehydration increases risk of heat

exhaustion

Sweating

• Risk of dehydration– 1% of body weight (max) – use this as

maximum of work period– 2% loss – performance decrement

and unpleasent– 4% loss – maximum allowed– 4 liter sweat (max) / 8 hr (WHO)– 6% loss – threat to health

Measurement

• Dry bulb temperature– Common thermometers

• Wet bulb temperature– Thermometer with wet cloth “sock”

• Globe temperature– Measure the effects of radiant heat

Measurement

• Climatic factors– Humidity?– Relative humidity?– Water vapor pressure?– Dew point?

Measurement

• Five key variables– Relative humidity (rh)

– Dew point temperature (tdp)

– Dry bulb temperature (DBT)– Wet bulb temperature (WBT)

– Vapor pressure (pa)

• Psychrometric chart

Measurement

• Relative humidity– % water vapor pressure (against

saturated pressure)

• Air movement– Affects evaporation

Measurement

• Heat stress indices– Dry bulb temperature– Wet bulb temperature– Effective temperature– WBGT index

Measurement

• WBGT index– Web bulb globe temperature (WBGT)– WBGT (out) = 0.7WB + 0.2GT +

0.1DB– WBGT (in) = 0.7WB + 0.3 GT

Measurement• Heat stress monitor

– Place where workersdo the job; but with noworkers

– Measure once/hr– Sampling, if workers

move around– Also measure outdoor

temp (wet and dry)

Factors to Consider

• Worker– Tolerance– Aerobic capacity– Age, gender, body fat– Acclimatization

• Max 1 l/h for un-acclimatized person• Less blood flow need, more blood

volume, less salt concentration, and max 2 l/h for acclimatized person

Factors to Consider

• Environment– Humidity (RH), heat, shade– Wind speed, etc.

• Task requirements– Work rate, rest schedule, protective

clothing

Recommendation

• OSHA monitoring techniques– Pulse > 110 bpm? Reduce work cycle

to 1/3– Oral temperature > 37.6oC? Shorten

work period by 1/3– Body weight loss > 1.5% during shift?

Increase fluid intake– Limit of 38oC (deep body temp) for

prolonged work (WHO)

Recommendation

• General control methods– Acclimatization– Fluid replacement– Engineering controls– Administrative controls and work

practices– Worker monitoring program

Recommendation

• Acclimatization– Lower heart rate– Lower body temperature– Higher sweat rate– More dilute (less salt) sweat– 2 hrs/day (for a week or two); incrase

gradually– Acclimatization lost in days (traces in 2 –

3 months)

Recommendation

• Preventing dehydration– Plenty of drink before work (50 – 60F)– One cup of fluid every 20 min (OSHA)– Avoid caffeine (& drugs) while working– Provide fluid-rich foods (soup, yoghurt,

etc.)– Provide only water (no energy drink)

• Juice and milk absorbed slower• Salt provision in a separate diet (enough)

Heat Stress Management

• Basic steps• Use dehumidifiers, increase air movement• Remove heavy clothing• Reduce work rate• Frequent rest pauses• Job rotation• Outdoor work during cooler times• 2-week of acclimatization• Rest, water, shade, cool spots

Heat Stress Management

• OSHA Guidelines – Permissible Heat Exp. TLV

Work/Rest Regimen

Workload

Light Moderate Heavy

Continuous 30 26.7 25

75% work/h 30.6 28 25.9

50% work/h 31.4 29.4 27.9

25% work/h 32.2 31.1 30