Management of Work Management of Work in Hot Environmentsin Hot Environments“Safety in the Heat” “Safety in the Heat” Trainers PresentationTrainers Presentation

NOTENOTE• This presentation is for training OHS This presentation is for training OHS

professionals and supervisors professionals and supervisors responsible for employees working in responsible for employees working in hot conditions. hot conditions.

• It can be adapted and shortened for It can be adapted and shortened for on-site use and translated into other on-site use and translated into other languages as required.languages as required.

• It should not be used for commercial It should not be used for commercial purposes and remains the property of purposes and remains the property of HAAD. HAAD.

OverviewOverview

1)1) What’s the effect of heat stress on What’s the effect of heat stress on work performance work performance

2)2) The importance of hydrationThe importance of hydration

3)3) Heat stress related health issuesHeat stress related health issues

4)4) How can we measure heat stress How can we measure heat stress and what can we do to manage it?and what can we do to manage it?

IntroductionIntroduction

• The body is required to get rid of excess heat The body is required to get rid of excess heat to maintain a constant internal temperature to maintain a constant internal temperature (37(37°C)°C)

• The bodyThe body’’s best mechanism for removing any s best mechanism for removing any excess heat is through the evaporation of excess heat is through the evaporation of sweatsweat

How does heat alter this?How does heat alter this?

• High humidity stops/decreases the evaporation of High humidity stops/decreases the evaporation of sweat and therefore no heat is lostsweat and therefore no heat is lost

• Muscular strength declines due to increased Muscular strength declines due to increased blood circulation to the skin, resulting in blood circulation to the skin, resulting in decreased flow to musclesdecreased flow to muscles

• Overheating decreases alertness and mental Overheating decreases alertness and mental capacitycapacity

Blood - the key componentBlood - the key component

• Blood has the essential functions of providing Blood has the essential functions of providing oxygen and nutrients to vital organs and working oxygen and nutrients to vital organs and working musclesmuscles

• However it also carries heat from working However it also carries heat from working muscles and the body’s “core” to the skin so heat muscles and the body’s “core” to the skin so heat can be dissipatedcan be dissipated

• The blood volume is about 5 L for males and The blood volume is about 5 L for males and about 4 L for femalesabout 4 L for females

So what happens when I work So what happens when I work in the heat?in the heat?

• Thermal stress results in sweating:Thermal stress results in sweating:– sweat evaporates producing coolingsweat evaporates producing cooling

– all sweat comes from blood supply initially, so all sweat comes from blood supply initially, so increased sweat results in decreased blood increased sweat results in decreased blood volumevolume

Dehydration: the impactDehydration: the impact

• IfIf blood volume decreases you become blood volume decreases you become dehydrated:dehydrated:– there is less blood available to go to the skin there is less blood available to go to the skin

and to ability to dissipate heat is lostand to ability to dissipate heat is lost– heart rate increases because of this smaller heart rate increases because of this smaller

volume, resulting in excessive fatiguevolume, resulting in excessive fatigue– blood supply to the gut is reduced resulting in blood supply to the gut is reduced resulting in

decreased fluid absorptiondecreased fluid absorption– less blood is available to supply working less blood is available to supply working

musclesmuscles– mental capacity is compromised due to mental capacity is compromised due to

decreased blood flow to the braindecreased blood flow to the brain

Dehydration factsDehydration facts

• Single biggest cause of heat illness• “Thirst” only starts at 2% dehydration of body weight

Start drinking fluid immediately, don’t wait until thirsty

• Sweat rate can reach up to 1 litre per hour Drink small amounts and often (program

drinking)

• Typically 40% of workers come to work dehydratedDrink plenty of water before coming to work

• Aim for clear to “straw” coloured urine when at work• Drink so as to urinate frequently (~ 4 times a day)

Dehydration: the impactDehydration: the impact

• 1 to 2% 1 to 2% dehydrationdehydration 6 to 7% 6 to 7%reduction in physical work ratereduction in physical work rate

• 3 to 4% 3 to 4% dehydration dehydration 22% to 50% reduction in 22% to 50% reduction in work rate, for “moderate” and “hot” work rate, for “moderate” and “hot” environmentsenvironments

• Mental performance begins to decrease at 2% Mental performance begins to decrease at 2% dehydration and beyond that decrease dehydration and beyond that decrease proportionally to the level of dehydrationproportionally to the level of dehydration

SummarySummary

• The best way to maintain blood volume and The best way to maintain blood volume and therefore your capacity to stay cool is to prevent therefore your capacity to stay cool is to prevent dehydration by maintaining fluid intakedehydration by maintaining fluid intake

• This is the same as ensuring a radiator is topped This is the same as ensuring a radiator is topped up with coolant before going on a trip. If the up with coolant before going on a trip. If the radiator is full the engine won’t overheat, if its radiator is full the engine won’t overheat, if its only half full its performance will be limited and it only half full its performance will be limited and it will overheatwill overheat

So what exactly is in sweat?So what exactly is in sweat?

• WaterWater

• Sodium (salt)Sodium (salt) larger amountlarger amount

• PotassiumPotassium small amountsmall amount

• Magnesium, CalciumMagnesium, Calcium Virtually noneVirtually none

Fine, but how much fluid do Fine, but how much fluid do you lose?you lose?

Sweat Rate

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Hour 1 Hour 2 Hour 3 Hour 4 Hour 5 Hour 6

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Sweat Rate

(mL.h-1)

•Average sweat rate Average sweat rate ~ 600 mls/hr~ 600 mls/hr•Working for 10 hrs : 6 L lost in a dayWorking for 10 hrs : 6 L lost in a day

Hourly Sweat Rate over 6 Hours at35°C and 50% RH

What about salt?What about salt?Sweat Sodium Concentration per Hour

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Arms Legs

• Average sodium loss: Average sodium loss: ~ 40 mmol/L/hr~ 40 mmol/L/hr• Working for 10 hrs at a rate of 600ml/hr = Working for 10 hrs at a rate of 600ml/hr = 240mmol240mmol• 240 mmol = 5.52 g lost in a day240 mmol = 5.52 g lost in a day

About 13 grams of salt which is about 3 About 13 grams of salt which is about 3 teaspoons!teaspoons!

Sodium Concentration changes in Arms and Legs over 6 hours (Mean+/- SD)

What’s wrong with caffeine and What’s wrong with caffeine and alcohol?alcohol?

• Caffeine and alcohol are diuretics (i.e. they cause Caffeine and alcohol are diuretics (i.e. they cause increased rate of urination)increased rate of urination)

Alcohol : an exampleAlcohol : an example

• If you are dehydrated by 3 Kg (3 L):If you are dehydrated by 3 Kg (3 L):

-And you drink 3 litres of full-strength beer

-you produce 3.5 kg urine

Net LOSS = 0.5 kg

-End up 3.5 kg dehydrated

-And you drink 3 litres of pure water

-you produce 0.0 kg urine.

Net GAIN = 3 kg

-End up hydrated

CaffeineCaffeine• Coffee (per 250 ml mug)Coffee (per 250 ml mug)

– PercolatedPercolated 100-200 mg caffeine100-200 mg caffeine– InstantInstant 70-180 mg 70-180 mg

caffeinecaffeine

• Tea (per 250 ml mug)Tea (per 250 ml mug)– 1 minute brew1 minute brew 15-55 mg 15-55 mg

caffeinecaffeine– 5 minute brew5 minute brew 30-80 mg caffeine30-80 mg caffeine

Caffeine (cont.)Caffeine (cont.)

• Caffeinated drinks (per 375 ml can)Caffeinated drinks (per 375 ml can)– CokeCoke 75 mg caffeine75 mg caffeine– PepsiPepsi 60 mg caffeine60 mg caffeine

• Energy drinksEnergy drinks (per 250ml can) (per 250ml can)– Red BullRed Bull 80 mg caffeine80 mg caffeine– VV 78 mg caffeine78 mg caffeine

What you can do to limit these What you can do to limit these effectseffects

• Drink tea in preference to coffee Drink tea in preference to coffee

• Drink weaker coffee or teaDrink weaker coffee or tea

• Reduce or eliminate intake of cola and energy drinksReduce or eliminate intake of cola and energy drinks

• Drink a cup of water every time you drink a cup of Drink a cup of water every time you drink a cup of

tea or coffeetea or coffee

• When drinking alcohol make sure you are hydrated When drinking alcohol make sure you are hydrated when you startwhen you start

Can hydration status be Can hydration status be tested?tested?

• Simple test ; Urine Specific Gravity using a Simple test ; Urine Specific Gravity using a refractometerrefractometer– Takes less than one minuteTakes less than one minute– Measures concentration of urine compared to Measures concentration of urine compared to

waterwater

Specific Gravity : what it Specific Gravity : what it meansmeans

• 1.000 1.000 1.010 1.010 ExcellentExcellent

• 1.010 1.010 1.015 1.015 OkayOkay

• 1.015 1.015 1.020 1.020 Need fluidNeed fluid

• 1.020 1.020 1.025 1.025 Hypo-hydratedHypo-hydrated

• 1.025 1.025 1.030 1.030 DehydratedDehydrated

So what are the health So what are the health problems associated with heat problems associated with heat stress?stress?• Heat StrokeHeat Stroke

– bodybody’’s system of temperature regulation failss system of temperature regulation fails– body temperature rises to critical levels body temperature rises to critical levels deep deep

body temp. exceeds 40°Cbody temp. exceeds 40°C– primary signs: confusion, irrational behaviour, primary signs: confusion, irrational behaviour,

loss of consciousness, convulsions, lack of loss of consciousness, convulsions, lack of sweating, hot dry skinsweating, hot dry skin

• Heat stroke first aidHeat stroke first aid– call medical attention immediatelycall medical attention immediately– move person to shademove person to shade– remove clothing and wet skinremove clothing and wet skin– increase local air velocityincrease local air velocity– increase fluid intake if possibleincrease fluid intake if possible– can lead to permanent brain damage and can lead to permanent brain damage and

deathdeath

• Heat ExhaustionHeat Exhaustion– symptoms resemble heat stroke and include symptoms resemble heat stroke and include

headache, nausea, weakness, thirst and giddinessheadache, nausea, weakness, thirst and giddiness– caused by loss of large amounts of fluids as sweatcaused by loss of large amounts of fluids as sweat– skin is clammy and moistskin is clammy and moist– complexion is red with rapid pulsecomplexion is red with rapid pulse– body temperature is normal or slightly elevatedbody temperature is normal or slightly elevated

• Heat exhaustion first aidHeat exhaustion first aid– rest in cool placerest in cool place– drink plenty of fluidsdrink plenty of fluids– severe cases could take one or two days to recoversevere cases could take one or two days to recover– no known permanent side effectsno known permanent side effects

• Heat CrampsHeat Cramps– painful muscle spasm that occurs when painful muscle spasm that occurs when

sweating profusely in heatsweating profusely in heat– electrolyte imbalance caused by sweatingelectrolyte imbalance caused by sweating– water may be drunk but person must water may be drunk but person must

replace lost electrolytesreplace lost electrolytes

• Avoidance of heat crampsAvoidance of heat cramps– thirst cannot be used as a guide for the thirst cannot be used as a guide for the

need to drink fluidneed to drink fluid– water must be taken every 15-20 min in hot water must be taken every 15-20 min in hot

environmentsenvironments– drink electrolyte replacement fluidsdrink electrolyte replacement fluids– muscles being used are most susceptiblemuscles being used are most susceptible

• Heat Collapse (fainting)Heat Collapse (fainting)– workers not accustomed to hot environments workers not accustomed to hot environments

who stand upright and immobile for long who stand upright and immobile for long periods of timeperiods of time

– blood poolsblood pools– inadequate venous return resulting in inadequate venous return resulting in

decreased blood pumped to braindecreased blood pumped to brain– prevented by keeping workers moving and an prevented by keeping workers moving and an

acclimatisation programacclimatisation program

• Heat Rash (prickly heat)Heat Rash (prickly heat)– occurs most commonly in hot, humid occurs most commonly in hot, humid

environmentsenvironments– sweat is not easily removed from skinsweat is not easily removed from skin– sweat ducts become blocked, causing rashsweat ducts become blocked, causing rash– prevent by cool breaks and regular bathing and prevent by cool breaks and regular bathing and

drying of skindrying of skin

• Heat FatigueHeat Fatigue– temporary state of mental or psychological temporary state of mental or psychological

strain resulting from prolonged heat exposurestrain resulting from prolonged heat exposure– decline in task performance, coordination, decline in task performance, coordination,

alertnessalertness– reduced by heat acclimatisationreduced by heat acclimatisation

Long term health effects of Long term health effects of heat stressheat stress

• Kidney stones is the most common Kidney stones is the most common

• Cancer of the bladder has recently been reportedCancer of the bladder has recently been reported

• Possibly other effects in certain individuals from Possibly other effects in certain individuals from too much sugar i.e. when sweat replaced with full too much sugar i.e. when sweat replaced with full strength soft drinks and caffeinated drinksstrength soft drinks and caffeinated drinks

What about safety issues?What about safety issues?

• Heat promotes accidents:Heat promotes accidents:– slipperiness of sweaty palmsslipperiness of sweaty palms– dizzinessdizziness– fogging of safety glassesfogging of safety glasses– hot surfaces/steam hot surfaces/steam burns burns– lower mental alertness and individual physical lower mental alertness and individual physical

performanceperformance– physical discomfort promotes irritability, anger physical discomfort promotes irritability, anger

and other emotionsand other emotions

AcclimatisationAcclimatisation

• Within limits, the human body adapts to working Within limits, the human body adapts to working in heatin heat

• In one medically-controlled study:In one medically-controlled study:• Blood volume increased by up to 30% (ave. Blood volume increased by up to 30% (ave.

21%)21%)• Sweated more profusely, up by 50%Sweated more profusely, up by 50%• Sweat started 15% earlierSweat started 15% earlier• Sodium (salt) concentration in sweat down by Sodium (salt) concentration in sweat down by

29%29%• Heart rate fell from 153 to 127 beats per minHeart rate fell from 153 to 127 beats per min• Core temperature fell from 38.80Core temperature fell from 38.80°C°C to 38.10 to 38.10°C°C

The 3 phases of acclimatisationThe 3 phases of acclimatisation• Initial phaseInitial phase - occurs during early consecutive days of - occurs during early consecutive days of

exposure to heat - usually 33% of optimum by day 4exposure to heat - usually 33% of optimum by day 4

• Intermediate phaseIntermediate phase - when cardiovascular stability has - when cardiovascular stability has been assured and surface and internal body temperatures been assured and surface and internal body temperatures are lowered. Usually 44% optimum by day 8are lowered. Usually 44% optimum by day 8

• Third phase Third phase -- decrease in sweat and urine composition, decrease in sweat and urine composition, and other compensations to conserve body fluids and and other compensations to conserve body fluids and restore electrolyte balances.restore electrolyte balances.– Day 10 - 65% of optimumDay 10 - 65% of optimum– Day 18 - 93% of optimumDay 18 - 93% of optimum– Day 21 - 99% of optimumDay 21 - 99% of optimum

• Requires elevated metabolic rate for over 2 hours/dayRequires elevated metabolic rate for over 2 hours/day

Acclimatisation, how long does Acclimatisation, how long does it take to gain and lose?it take to gain and lose?

Gaining acclimatisation:A = Tanh(0.124*D)

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Losing acclimatisation:A = 0.9663 - (Tanh(0.06054(D-0.55626)))

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Acclimatisation benefitsAcclimatisation benefits

• More finely tuned sweating reflexes with increased More finely tuned sweating reflexes with increased sweat production rate at lower electrolyte sweat production rate at lower electrolyte concentrationsconcentrations

• Lower rectal and skin temperatures than at the Lower rectal and skin temperatures than at the beginning of exposurebeginning of exposure

• More stable and better regulated blood pressure with More stable and better regulated blood pressure with lower pulse rateslower pulse rates

• Improved productivity and safetyImproved productivity and safety

Other benefitsOther benefits

Thermal Comfort Thermal Comfort – Improved – Improved Exercise PerformanceExercise Performance – Improved– ImprovedCore Temperature Core Temperature – Reduced– ReducedSweating Sweating – Earlier & – Earlier &

GreaterGreaterSkin Blood Flow Skin Blood Flow – Earlier– EarlierBody Heat Production Body Heat Production – Lower– LowerHeart Rate Heart Rate – Lowered– LoweredThirst Thirst – Improved– ImprovedSalt Losses (sweat & urine)Salt Losses (sweat & urine) – Reduced– ReducedOrgan Protection Organ Protection – Improved– Improved

Air-conditioningAir-conditioning

• Alternating hot and cold conditions:Alternating hot and cold conditions:– Does not cause “colds”Does not cause “colds”– Can result in “chill” to kidney area: thermal Can result in “chill” to kidney area: thermal

“shock”“shock”– Will not cause any permanent problemsWill not cause any permanent problems– Do not set air-conditioning temperature too low Do not set air-conditioning temperature too low – Aim for about 25Aim for about 25°° C inside C inside

What factors will affect our What factors will affect our ability to remove excess heat?ability to remove excess heat?

• Physical factorsPhysical factors– ageage– weightweight– physical fitnessphysical fitness– acclimatisationacclimatisation– metabolismmetabolism– use of alcohol or drugsuse of alcohol or drugs– hypertensionhypertension– general healthgeneral health

Why does my weight matter?Why does my weight matter?• The best measure of your weight “status” is Body Mass Index or The best measure of your weight “status” is Body Mass Index or

BMIBMI

• BMI= weight (kg)/ height (m)BMI= weight (kg)/ height (m)²²

• A “guide” to risk of chronic health problems, life expectancy, and A “guide” to risk of chronic health problems, life expectancy, and likelihood of poor likelihood of poor quality of life in old agequality of life in old age

• BMI : BMI : <<19 19 UNDERWEIGHTUNDERWEIGHT 20 - 25 20 - 25 ACCEPTABLEACCEPTABLE 26 - 30 26 - 30 OVERWEIGHTOVERWEIGHT >>31 31 OBESEOBESE

BMI – the impactBMI – the impact

• 7690 workers injury reports examined7690 workers injury reports examined• 29% where injured over 3 yrs29% where injured over 3 yrs• 85% of these were overweight (25-30) or obese 85% of these were overweight (25-30) or obese

(>30)(>30)• 28% were overweight and 64% obese28% were overweight and 64% obese• Those with BMI >40 were twice as likely to Those with BMI >40 were twice as likely to

sustain an injury sustain an injury (am j epidemiol 2007 pollock et al)(am j epidemiol 2007 pollock et al)

The importance of physical The importance of physical fitnessfitness• Heat stress places additional cardiovascular strain, Heat stress places additional cardiovascular strain,

hence superior aerobic capacity is a big advantagehence superior aerobic capacity is a big advantage

• Workers who are selected for hot jobs that are in good Workers who are selected for hot jobs that are in good general health and physical condition have less general health and physical condition have less chance of getting heat stroke and other heat related chance of getting heat stroke and other heat related illnessesillnesses

• Short term and minor illnesses should Short term and minor illnesses should also be considered - flu, diarrhoea, also be considered - flu, diarrhoea, vomiting, hangovervomiting, hangover

• Workers on medication should seek Workers on medication should seek medical clearancemedical clearance

What else can you do outside What else can you do outside the workplace?the workplace?

• Drink water outside of work Drink water outside of work notnot just caffeine (tea, just caffeine (tea, coffee, Coke) or alcohol (beer, spirits, wine)coffee, Coke) or alcohol (beer, spirits, wine)

• Good dietGood diet

• Good quality sleepGood quality sleep

So what factors are we talking So what factors are we talking about in relation to heat about in relation to heat stress?stress?

• Wet bulb temperature is the most important and Wet bulb temperature is the most important and is measured using a wet bulb thermometeris measured using a wet bulb thermometer

• WB is the temperature at which water evaporates WB is the temperature at which water evaporates into the airinto the air

• Significant when compared to skin temperatureSignificant when compared to skin temperaturebecause of the affect it has how much of anbecause of the affect it has how much of anindividuals sweat evaporatesindividuals sweat evaporates

• Dry bulb temperature (ambient temp.) is not as Dry bulb temperature (ambient temp.) is not as important and is measured using a regular important and is measured using a regular thermometerthermometer

Air Air TemperatureTemperature

Radiant HeatRadiant Heat• Heat energy transmitted by Heat energy transmitted by

electromagnetic waves in contrast to electromagnetic waves in contrast to

heat transmitted by conduction or heat transmitted by conduction or

convectionconvection

• Measured using a “globe Measured using a “globe

thermometer” [a 150 mm diameter thermometer” [a 150 mm diameter

hollow copper ball (painted black) with hollow copper ball (painted black) with

a standard thermometer in it]a standard thermometer in it]

• Significant for deep mines, workers on Significant for deep mines, workers on

or near diesel units and workers in the or near diesel units and workers in the

sun or in smelters sun or in smelters

Relative HumidityRelative Humidity• Relative Humidity is a percentage of the actual Relative Humidity is a percentage of the actual

amount of moisture in the air, compared to the amount of moisture in the air, compared to the maximum moisture that can be taken up by the maximum moisture that can be taken up by the air at that temperatureair at that temperature

• 50% or more of sweat can drop off skin50% or more of sweat can drop off skin

• Only sweat which evaporates off skin Only sweat which evaporates off skin

produces coolingproduces cooling

• Sweat which drops off just adds to Sweat which drops off just adds to

dehydration loaddehydration load

• Dry air means more evaporates and Dry air means more evaporates and

less drips off less drips off keep air dry (low humidity) keep air dry (low humidity)

Wind SpeedWind SpeedThe higher the wind speed the betterThe higher the wind speed the better

• Wind speed increases evaporation of sweatWind speed increases evaporation of sweat

• Use air-movers where possibleUse air-movers where possible

• Ensure ventilation systems are working Ensure ventilation systems are working

effectively at all timeseffectively at all times

• Report any leakage or short-circuitingReport any leakage or short-circuiting

Personal Protection EquipmentPersonal Protection Equipment• PPE is necessary to protect from hazardsPPE is necessary to protect from hazards

• PPE “insulates” the body & adds to heat stressPPE “insulates” the body & adds to heat stress

• Use only the PPE requiredUse only the PPE required

• Wear T-shirts/short sleeves when safe and Wear T-shirts/short sleeves when safe and appropriateappropriate

• Ensure long sleeved shirts are “baggy” [loose Ensure long sleeved shirts are “baggy” [loose sleeves at elbows]sleeves at elbows]

• Use shirts & trousers in preference to overallsUse shirts & trousers in preference to overalls

• Spraying water over you is effective in cooling Spraying water over you is effective in cooling

• Carry plenty of water with you on the job and Carry plenty of water with you on the job and make sure there is close access to cool watermake sure there is close access to cool water

VisitorsVisitors

• We also have a “Duty of Care” towards visitorsWe also have a “Duty of Care” towards visitors

• Visitors need to be told of the hazards they need Visitors need to be told of the hazards they need to be aware of during their visit, including hazards to be aware of during their visit, including hazards from heat, and what to do if the unexpected from heat, and what to do if the unexpected happenshappens

• If applicable, visitors going underground/out in If applicable, visitors going underground/out in the field should complete a self-assessed medical the field should complete a self-assessed medical questionnairequestionnaire

How can we measure the How can we measure the workplace environment?workplace environment?

• Depends on:Depends on:

- - how hot it is where you are working how hot it is where you are working wet bulb wet bulb temp./humidity, air temp., wind speed, radiant temp./humidity, air temp., wind speed, radiant heatheat

- how hard you are working - how hard you are working the harder you work the harder you work the more heat you will generatethe more heat you will generate

- your clothes and PPE - your clothes and PPE these reduce evaporation these reduce evaporation of sweatof sweat

The equation:The equation:

Heat generated by Heat generated by worker + heat worker + heat from the from the environmentenvironment

Cooling due to Cooling due to evaporation & evaporation & other meansother means

Thermal Work LimitThermal Work Limit

The work rate that acclimatised workers can safely

maintain in a particular environment is called the

Thermal Work Limit

So what does it mean?So what does it mean?

• A A HIGHHIGH TWL means TWL means betterbetter working conditions, working conditions,A A LOWLOW TWL means TWL means poorerpoorer working conditions working conditions

• TWL measures TWL measures environmental conditionsenvironmental conditions

• TWL is the metabolic limit measured in Watts/mTWL is the metabolic limit measured in Watts/m22 that can be tolerated before heat storage occurs that can be tolerated before heat storage occurs (hyperthermia)(hyperthermia)

TWL (cont.)TWL (cont.)• Measures all essential environmental parametersMeasures all essential environmental parameters

• Considers clothingConsiders clothing

• Can be used for work rest cyclingCan be used for work rest cycling

• Can be used for calculating maximal duration in a Can be used for calculating maximal duration in a measured environmentmeasured environment

• Has been scientifically validatedHas been scientifically validated

Calculating TWLCalculating TWL

• Can be calculated using instruments (DB, WB, Can be calculated using instruments (DB, WB, Rad., WS)Rad., WS)

i.e. the Heat Stress Meteri.e. the Heat Stress Meter

• Use HAAD Desktop calculator for data input and Use HAAD Desktop calculator for data input and calculation of TWL see www.haad.aecalculation of TWL see www.haad.ae

TWL cut-offsTWL cut-offs• Field studies have suggested the following guidelines:Field studies have suggested the following guidelines:

• < < 115 watts/m115 watts/m22 : : Withdrawal limit for self-paced, self- Withdrawal limit for self-paced, self-supervised workers as below this level even light work is supervised workers as below this level even light work is not continuously sustainable even for fully acclimatised not continuously sustainable even for fully acclimatised workers. Formal “permitting system” with management workers. Formal “permitting system” with management approval required to work. approval required to work.

• 115 - 140 watts/m115 - 140 watts/m22: : “Buffer zone” - work is restricted. A “Buffer zone” - work is restricted. A system of written “corrective action requests” is required to system of written “corrective action requests” is required to ensure rotation of workers and correction of environmental ensure rotation of workers and correction of environmental engineering defects, i.e can improvements be made.engineering defects, i.e can improvements be made.

• 140 - 220 watts/m140 - 220 watts/m22: : Work restricted to acclimatised Work restricted to acclimatised workers. The acclimatisation period lasts for the first 7 workers. The acclimatisation period lasts for the first 7 days back at work after an absence of >14 days.days back at work after an absence of >14 days.

• > 220 watts/m> 220 watts/m22:: Unrestricted work. Unrestricted work.

ConclusionsConclusions

• Hypo/De-hydration is the major factor causing Hypo/De-hydration is the major factor causing heat illnessheat illness

• Fluid replacement is essentialFluid replacement is essential

• Sodium is essential to replace Sodium is essential to replace

• Urine SG is a good indicator of hydration statusUrine SG is a good indicator of hydration status

• Acclimatisation for workers should be consideredAcclimatisation for workers should be considered

• TWL is a valid index to assess the environmentTWL is a valid index to assess the environment