HEAT Stress Presentation - HAAD

8/13/2019 HEAT Stress Presentation - HAAD

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Management of Work inHot Environments

Safety in the HeatTrainers Presentation

With thanks to Dr Graham Bates, Dr John Schneider and DrVeronica Miller Health Authority - Abu Dhabi 2009


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Health Authority - Abu Dhabi 2009

NOTE

This presentation is for training OHSprofessionals and supervisors responsiblefor employees working in hot conditions.

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

It should not be used for commercialpurposes and remains the property ofHAAD.


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Overview

1) Whats the effect of heat stress on workperformance

2) The importance of hydration3) Heat stress related health issues4) How can we measure heat stress and

what can we do to manage it?


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Introduction

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

The bodys best mechanism for removing any excessheat is through the evaporation of sweat


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How does heat alter this?

High humidity stops/decreases the evaporation of sweatand therefore no heat is lost

Muscular strength declines due to increased bloodcirculation to the skin, resulting in decreased flow tomuscles

Overheating decreases alertness and mental capacity


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Blood - the key component

Blood has the essential functions of providing oxygenand nutrients to vital organs and working muscles

However it also carries heat from working muscles andthe bodys core to the skin so heat can be dissipated

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


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So what happens when I work inthe heat?

Thermal stress results in sweating: sweat evaporates producing cooling

all sweat comes from blood supply initially, soincreased sweat results in decreased blood volume


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Dehydration: the impact

If blood volume decreases you become dehydrated: there is less blood available to go to the skin and

to ability to dissipate heat is lost

heart rate increases because of this smallervolume, resulting in excessive fatigue

blood supply to the gut is reduced resulting indecreased fluid absorption

less blood is available to supply working muscles mental capacity is compromised due to

decreased blood flow to the brain



Dehydration facts

Single biggest cause of heat illness Thirst only starts at 2% dehydration of body weightStart drinking fluid immediately, dont wait untilthirsty

Sweat rate can reach up to 1 litre per hourDrink 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 impact

1 to 2% dehydration6 to 7%reduction in physical work rate

3 to 4% dehydration22% to 50% reduction in workrate, for moderate and hot environments

Mental performance begins to decrease at 2%dehydration and beyond that decrease proportionally tothe level of dehydration



Summary

The best way to maintain blood volume and thereforeyour capacity to stay cool is to prevent dehydration bymaintaining fluid intake

This is the same as ensuring a radiator is topped up withcoolant before going on a trip. If the radiator is full theengine wont overheat, if its only half full its performancewill be limited and it will overheat



So what exactly is in sweat?

Water Sodium (salt) larger amount

Potassium small amount Magnesium, Calcium Virtually none



Fine, but how much fluid do youlose?

Sweat Rate

0

100

200300

400

500

600

700

800

900

1000

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

Hour

Sweat Rate

(mL.h-1

)

Average sweat rate ~ 600 mls/hrWorking for 10 hrs : 6 L lost in a day

Hourly SweatRate over 6Hours at35C and50% RH



What about salt?Sweat Sodium Concentration per Hour

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

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

Sodium

(mmol.L-1

)

Arms Legs

Average sodium loss: ~ 40 mmol/L/hr

Working for 10 hrs at a rate of 600ml/hr = 240mmol240 mmol = 5.52 g lost in a day

About 13 grams of salt which is about 3 teaspoons!

SodiumConcentrationchanges in

Arms and Legsover 6 hours

(Mean+/- SD)



Whats wrong with caffeine andalcohol?

Caffeine and alcohol are diuretics (i.e. they causeincreased rate of urination)



Alcohol : an example

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

-And you drink 3litres of full-

strength beer-you produce 3.5kg urine

Net LOSS = 0.5 kg

-End up 3.5 kgdehydrated

-And you drink 3litres of pure

water-you produce 0.0kg urine.

Net GAIN = 3 kg

-End uphydrated



Caffeine

Coffee (per 250 ml mug) Percolated 100-200 mg caffeine Instant 70-180 mg caffeine

Tea (per 250 ml mug) 1 minute brew 15-55 mg caffeine 5 minute brew 30-80 mg caffeine



Caffeine (cont.)

Caffeinated drinks (per 375 ml can) Coke 75 mg caffeine

Pepsi 60 mg caffeine Energy drinks (per 250ml can)

Red Bull 80 mg caffeine

V 78 mg caffeine



What you can do to limit theseeffects

Drink tea in preference to coffee

Drink weaker coffee or tea

Reduce or eliminate intake of cola and energy drinks

Drink a cup of water every time you drink a cup of tea orcoffee

When drinking alcohol make sure you are hydrated whenyou start
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Can hydration status be tested?

Simple test ; Urine Specific Gravity using a refractometer Takes less than one minute

Measures concentration of urine compared to water



Specific Gravity : what it means

1.000 1.010 Excellent 1.010 1.015 Okay 1.015 1.020 Need fluid 1.020 1.025 Hypo-hydrated 1.025 1.030 Dehydrated



So what are the health problemsassociated with heat stress?

Heat Stroke bodys system of temperature regulation fails

body temperature rises to critical levels deep bodytemp. exceeds 40C

primary signs: confusion, irrational behaviour, loss ofconsciousness, convulsions, lack of sweating, hot dryskin


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Heat stroke first aid call medical attention immediately

move person to shade

remove clothing and wet skin

increase local air velocity

increase fluid intake if possible

can lead to permanent brain damage and death


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Heat Exhaustion symptoms resemble heat stroke and include headache,

nausea, weakness, thirst and giddiness caused by loss of large amounts of fluids as sweat

skin is clammy and moist

complexion is red with rapid pulse

body temperature is normal or slightly elevated

Heat exhaustion first aid rest in cool place

drink plenty of fluids severe cases could take one or two days to recover

no known permanent side effects


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Heat Cramps painful muscle spasm that occurs when sweating

profusely in heat

electrolyte imbalance caused by sweating

water may be drunk but person must

replace lost electrolytes

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

need to drink fluid

water must be taken every 15-20 min in hotenvironments

drink electrolyte replacement fluids

muscles being used are most susceptible


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Heat Collapse (fainting) workers not accustomed to hot environments who

stand upright and immobile for long periods of time blood pools

inadequate venous return resulting in decreasedblood pumped to brain

prevented by keeping workers moving and anacclimatisation program


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

sweat is not easily removed from skin sweat ducts become blocked, causing rash

prevent by cool breaks and regular bathing anddrying of skin

Heat Fatigue temporary state of mental or psychological strain

resulting from prolonged heat exposure

decline in task performance, coordination, alertness

reduced by heat acclimatisation


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Long term health effects of heatstress

Kidney stones is the most common

Cancer of the bladder has recently been reported

Possibly other effects in certain individuals from toomuch sugar i.e. when sweat replaced with full strengthsoft drinks and caffeinated drinks


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What about safety issues?

Heat promotes accidents: slipperiness of sweaty palms

dizziness

fogging of safety glasses hot surfaces/steamburns

lower mental alertness and individual physicalperformance

physical discomfort promotes irritability, anger andother emotions


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Acclimatisation

Within limits, the human body adapts to working in heat

In one medically-controlled study: Blood volume increased by up to 30% (ave. 21%)

Sweated more profusely, up by 50%

Sweat started 15% earlier

Sodium (salt) concentration in sweat down by 29% Heart rate fell from 153 to 127 beats per min

Core temperature fell from 38.80C to 38.10C


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The 3 phases of acclimatisation

Initial phase- occurs during early consecutive days ofexposure to heat - usually 33% of optimum by day 4

Intermediate phase- when cardiovascular stability hasbeen assured and surface and internal body temperatures

are lowered. Usually 44% optimum by day 8

Third phase -decrease in sweat and urine composition,and other compensations to conserve body fluids andrestore electrolyte balances.

Day 10 - 65% of optimum Day 18 - 93% of optimum Day 21 - 99% of optimum

Requires elevated metabolic rate for over 2 hours/day


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Acclimatisation, how long does ittake to gain and lose?

G a i n ing acc l im a t isa t i on :

A = Ta nh (0 .124*D )

0

0 .2

0 .4

0 .6

0 .8

1

0 5 10 15 20 25 30Day (D )

Acclim'nlevel(A

)

Los i ng ac c l im a t isa t i on :

A = 0 .9663 - (T anh(0 .06054 (D -0 .55626 )) )

0

0 .2

0 .4

0 .6

0 .8

1

0 5 10 15 20 25 30Day (D )

Acclim'nlevel(A

)


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Acclimatisation benefits

More finely tuned sweating reflexes with increased sweatproduction rate at lower electrolyte concentrations

Lower rectal and skin temperatures than at the beginningof exposure

More stable and better regulated blood pressure with

lower pulse rates

Improved productivity and safety


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Other benefits

Thermal Comfort Improved

Exercise Performance Improved

Core Temperature Reduced

Sweating Earlier & GreaterSkin Blood Flow Earlier

Body Heat Production Lower

Heart Rate Lowered

Thirst ImprovedSalt Losses (sweat & urine) Reduced

Organ Protection Improved


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Air-conditioning

Alternating hot and cold conditions: Does not cause colds

Can result in chill to kidney area: thermal shock

Will not cause any permanent problems

Do not set air-conditioning temperature too low

Aim for about 25C inside


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What factors will affect our abilityto remove excess heat?

Physical factors age

weight

physical fitness

acclimatisation

metabolism

use of alcohol or drugs hypertension

general health


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Why does my weight matter?

The best measure of your weight status is Body MassIndex or BMI

BMI= weight (kg)/ height (m)

A guide to risk of chronic health problems, lifeexpectancy, and likelihood of poor

quality of life in old age

BMI : 31 OBESE


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BMIthe impact

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

28% were overweight and 64% obese Those with BMI >40 were twice as likely to sustain an

injury

(am j epidemiol 2007 pollock et al)


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The importance of physical fitness Heat stress places additional cardiovascular strain, hence

superior aerobic capacity is a big advantage

Workers who are selected for hot jobs that are in goodgeneral health and physical condition have less chanceof getting heat stroke and other heat related illnesses

Short term and minor illnesses shouldalso be considered - flu, diarrhoea,vomiting, hangover

Workers on medication should seekmedical clearance


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What else can you do outside theworkplace?

Drink water outside of work not just caffeine (tea,coffee, Coke) or alcohol (beer, spirits, wine)

Good diet

Good quality sleep


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So what factors are we talkingabout in relation to heat stress?

Wet bulb temperature is the most important and is

measured using a wet bulb thermometer WB is the temperature at which water evaporates intothe air

Significant when compared to skin temperaturebecause of the affect it has how much of an

individuals sweat evaporates

Dry bulb temperature (ambient temp.) is not asimportant and is measured using a regular

thermometer

Air Temperature


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Radiant Heat Heat energy transmitted by electromagnetic

waves in contrast to heat transmitted byconduction or convection

Measured using a globe thermometer [a

150 mm diameter hollow copper ball(painted black) with a standard thermometer

in it]

Significant for deep mines, workers on or

near diesel units and workers in the sun or

in smelters

Relative Humidity


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Relative Humidity Relative Humidity is a percentage of the actual amount of

moisture in the air, compared to the maximum moisture

that can be taken up by the air at that temperature

50% or more of sweat can drop off skin

Only sweat which evaporates off skin

produces cooling

Sweat which drops off just adds to

dehydration load

Dry air means more evaporates and

less drips off keep air dry (low humidity)


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Wind SpeedThe higher the wind speed the better

Wind speed increases evaporation of sweat

Use air-movers where possible

Ensure ventilation systems are working effectively at

all times

Report any leakage or short-circuiting


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Personal Protection Equipment PPE is necessary to protect from hazards

PPE insulates the body & adds to heat stress

Use only the PPE required

Wear T-shirts/short sleeves when safe and appropriate

Ensure long sleeved shirts are baggy [loose sleevesat elbows]

Use shirts & trousers in preference to overalls

Spraying water over you is effective in cooling

Carry plenty of water with you on the job and makesure there is close access to cool water


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Visitors

We also have a Duty of Care towards visitors Visitors need to be told of the hazards they need to be

aware of during their visit, including hazards from heat,and what to do if the unexpected happens

If applicable, visitors going underground/out in the fieldshould complete a self-assessed medical questionnaire


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How can we measure theworkplace environment?

Depends on:

- how hot it is where you are working wet bulb

temp./humidity, air temp., wind speed, radiant heat

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

- your clothes and PPE these reduce evaporation ofsweat


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The equation:

Heat generated byworker + heat fromthe environment

Cooling due toevaporation &other means


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Thermal Work Limit

The work rate that acclimatised workers can safely

maintain in a particular environment is called the

Thermal Work Limit


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So what does it mean?

A HIGH TWL means betterworking conditions,A LOW TWL means poorerworking conditions

TWL measures environmental conditions

TWL is the metabolic limit measured in Watts/m2thatcan be tolerated before heat storage occurs(hyperthermia)


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TWL (cont.)

Measures all essential environmental parameters

Considers clothing

Can be used for work rest cycling

Can be used for calculating maximal duration in ameasured environment

Has been scientifically validated


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Calculating TWL

Can be calculated using instruments (DB, WB, Rad., WS)i.e. the Heat Stress Meter

Use HAAD Desktop calculator for data input andcalculation of TWL see www.haad.ae


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TWL cut-offs

Field studies have suggested the following guidelines:

< 115 watts/m2:Withdrawal limit for self-paced, self-supervisedworkers as below this level even light work is not continuouslysustainable even for fully acclimatised workers. Formal permittingsystem with management approval required to work.

115 - 140 watts/m2:Buffer zone - work is restricted. A systemof written corrective action requests is required to ensure rotationof workers and correction of environmental engineering defects, i.ecan improvements be made.

140 - 220 watts/m2: Work restricted to acclimatised workers.The acclimatisation period lasts for the first 7 days back at workafter an absence of >14 days.

> 220 watts/m2:Unrestricted work.


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Conclusions

Hypo/De-hydration is the major factor causing heatillness

Fluid replacement is essential

Sodium is essential to replace Urine SG is a good indicator of hydration status Acclimatisation for workers should be considered TWL is a valid index to assess the environment

HEAT Stress Presentation - HAAD

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