Management of environmental

heat stress

Christine Killip Atmospheric Scientist and

Managing Director of Katestone

Questions

• Who has experiences excessive heat at

work?

• Who has a Heat Stress management

policy?

• How often is the policy used?

• Which heat stress index is used?

• Who thinks they could be doing more to

manage heat stress?

Is heat stress important for

humans?

• Currently 1100 deaths due to heat per year in Australia

• Small number of workers have died due to heat stress in recent years

• Significant impact on labour rates

• Maloney et al (2011) projected the number of “dangerous” days will increase from 1 to 21 in 2070 for an acclimatised person doing physical labour and 17 to 67 days for an unacclimatised person

Which is worse for heat stress?

36°C Temp

&

30% RH

32°C Temp

&

70% RH

28°C Temp

&

85% RH

42°C Temp

&

20% RH

Based on Humidex

-ve +ve

Mechanical (W)

Metabolic (M)

Convection (C, Cres)

Evaporation

(E, Eres)

Conduction (K)

Radiation (R)

The human thermal balance

M + W = K + R + C + Cres + E + Eres +S

Ref: ISO 7243

How do we keep our balance?

• In light work or cool environments we dump metabolic heat by radiation and convection

• But as work becomes heavier or environments warmer we become increasingly dependent on evaporative cooling

• Result – we are vulnerable to anything that restricts evaporation (e.g. clothing, high humidity, or low air movement)

How do we keep our balance?

“Unrestricted evaporation of sweat lets

healthy people cope — without ill effect or

even marked discomfort — with air

temperatures of 100 ◦C in saunas and 50 ◦C

in deserts, and with more than a kilowatt of

metabolic heat in strenuous activity.”

Budd (2008)

Overloaded system

Body temp rises

Cardiovascular strain

Sweat increases (dehydration)

Weak

Dizzy

Clumsy

Sick

Heat exhaustion

Heat stroke

Adverse effects become likely when our behavioural

responses are not allowed to function normally

Level of heat

tolerance reached

Guidelines

Metabolic

+

Environment

Ability to dissipate load

in current environment

4 elements of our EHL

EHL Temperature

Wind speed Radiation

Humidity

How hot is too hot?

• In 1947 Schickele plotted 157 heatstroke deaths in military training camps against temperature and humidity

• Identified the ‘heat death line’

• Air temperatures ranging from 26 to 49 ◦C and relative humidities of 10 to100%

• She commented that ‘Death can occur at surprisingly low temperatures, provided the evaporative power of the air is sufficiently reduced’

Human response

Clothing

PPE

Dehydration

Acclimatisation

Fitness

Age

Weight

General health

Factors impacting human

response to EHL

Heat Stress Indices

• Rational indices are based upon calculations

involving the heat balance equation (e.g.

Swreq, TWL)

• Empirical indices are based on establishing

equations from the physiological responses

of human subjects (e.g.ET)

• Direct indices are based on measurement

(usually temperature) used to simulate the

response of the human body (WBGT index)

Which index?

• Currently over 67 different indices and

growing

• Each have boundaries for application

• New ones always find ways to criticise the

old ones

• Complex ones are hard to apply

• Easy ones tend to get used – but can be

misused

Which index?

Solution:

•Pick an index you are

comfortable with

•Understand its limitations

•Use it as a guide only

•Personal awareness is the key

Example of using WBGT

• Developed by US Military in 1950’s

• Most widely used heat stress index

• Measures all 4 elements of EHL

• Based on hydrated, fit men in olive green

long pants and t-shirts

Ref: G. Budd WBGT – its history and limitations. Journal of Science and Medicine in Sport (2008) 11, 20—32

Metabolic rate

M (Wm–2 )

Reference value of WBGT (°C)

Acclimatised Not acclimatised

0. Resting M≤65 33 32

1. 65<M≤130 30 29

2. 130<M≤200 28 26

No sensible

air movement

Sensible air

movement

No sensible

air movement

Sensible air

movement

3. 200<M<260 25 26 22 23

4. M>260 23 25 18 20

Note:

The values given have been established allowing for a maximum rectal temperature of 38°C for the

persons concerned.

WBGT reference values from ISO 7243

Work/rest regimes Work Demands

Acclimatised workers

Light Moderate Heavy Very

Heavy

100% work 29.5 27.5 26.0

75% work / 25% rest 30.5 28.5 27.5

50% work / 50% rest 31.5 29.5 28.5 27.5

25% work / 75% rest 32.5 31.0 30.0 29.5

recommended by the ACGIH (1996) based on the WBGT values in °C

WBGT Limitations

• Commonly misused and “estimated” from not standard instruments

• Wind speed is not adequately accounted for as a cooling mechanism

• Underestimates the heat stress in restricted evaporation conditions

• e.g. clothed men alternately exercising and resting for 4 h in hot, humid conditions tolerated ‘with ease’ when WS was 0.8 m/s became incapacitated when WS dropped to 0.1 m/s (only a 0.2 increase in WBGT)

CAUTION:

If WBGT is used as a “screening”

level assessment it may not actually

indicate the extreme level of heat

stress likely if sweating is the only

mechanism to dissipate heat

When WBGT isn’t actually WBGT

• WBGT without the GT is not WBGT

• published in 1980’s by American College

of Sports Medicine, and widely used

including BOM

• Measurement by hand held instruments

(physically impossible to get it right!)

Is heat stress currently being

taken seriously?

• Singh et al (2013) interviewed 20

Australian industries to answer:

– Is excessive heat exposure an existing threat

to health of working people in the Australian

context?

– What are the prevailing attitudes towards heat

exposure and heath protection in high heat

exposure occupational groups in Australia?

Study finding

• 95% experienced excessive heat at work

• 75% experienced heat exhaustion at work

• 35% indicated heat exhaustion was

frequent

• 100% indicated that heat caused a loss in

productivity

Study finding

“During summer most calls to our workers

disputes hotline are related to heat”

Union Representative

“We often hear managers claim that heat

exposure is simply part of working in this

industry, so workers just have to deal with

it and continue”

Union Representative

Heat and Accidents

• Increased accident rate in construction industry during summer months

• Prof Rowlinson et al (2013) proposed that management of heat stress through work rest regimes can result in increased productivity

• Ramsey et al (1983) produced a relationship between unsafe behaviour and temperature

Ramsey et al (1983) Effects of workplace thermal comfort on safe work behavior. Journal of safety Research, Vol.

14, pp. 105-114, 1983

Acclimatisation

• Is a complex physiological process where the body adjusts as a response to the thermal environment

• Physiological changes include:

– cardiovascular stability, fluid and electrolyte balances, sweat rates and temperature responses

• Exposure to heat does not confer acclimatisation

• Elevated metabolic rate for about 2 hours per day, to achieve acclimatisation, is required

How long does it take to

acclimatise?

• Gradually gained over weeks (up to 21

days)

• Can be lost even over a weekend (only

small amounts)

• Acclimatisation to one level of heat stress

does not indicate acclimatisation at a

higher heat stress level

Learnings

• The human response to heat stress is complex with lots of factors to consider

• Heat stress can cause problems before it becomes a serious health issue (e.g. Impaired cognitive ability)

• Heat stress management involves: – environmental heat load

– job requirements (e.g. PPE, radiant heat source, work load)

– human factors (e.g acclimatisation, hydration)

• Heat Stress indices are great in number and have been widely misused

For your consideration

• Are workers in the field as well protected as

those in well documented high heat stress

areas inside?

• What happens when the EHL changes? Are

thermal heat risk assessments updated?

• Do we know when the highest EHL occurs?

• Would better understanding of EHL forecasts

allow you to plan your work schedules?

Weather intelligence

What is

• online environmental management system

• designed to provide state-of-the-art weather and climate analytics

• to assist you to proactively manage activities

• by providing location specific weather forecasts, extended outlooks and climate projections

• tailored to your specific business location and activities

Overloaded system

Body temp rises

Cardiovascular strain

Sweat increases (dehydration)

Weak

Dizzy

Clumsy

Sick

Heat exhaustion

Heat stroke

Heat stress can cause significant

loss in productivity before we reach

our level of heat tolerance

Benefits

• Reduce weather risk

• Optimise operations through better

planning for work/rest regimes

• Protect worker through heat stress

management before it causes additional

problems (e.g. increase in accidents)

• Simplify your workload through easy to

interpret dashboard (red/orange/green)

Features

• High resolution local forecast for anywhere

in Australia (4 days, hourly timestep)

• Extended 14 day outlook

• Seasonal outlook

• E-mail or sms alerts

• Latest situation updated by meteorologist

for high risk events

Behind the scenes

• Customisable index to meet your

application (e.g TWL, DustX, Inversion)

• Increase accuracy by uploading your own

data

• Robust and fully backed up data system

for data security

The Katestone forecasting system

World Met Office

(WMO) data store

Worldwide

Millions of sites

Decades of data

Central collection

AWS

Ships

Aircraft

Balloons

Buoys

Satellites

Observations

WRF-ARF

12 Km resolution

Australia wide

4 days in 1 hour intervals

Katestone

(K-WRF)

GFS

Worldwide

0.5 Deg Resolution

7 Days @ 3 hour

intervals

International

Global Model

Research

Email and SMS

Alerts

BOM AWS Observations

On site AWS

Accurate information

Model Parameter

(1 day out)

Statistic Value

(°C)

Comment

K-WRF Temp RMSE 2.17 2012/13 all sites

K-WRF Temp RMSE 1.61 2012/13 Zone 11

ACCESS-A Temp RMSE 2.2 Bridge et al, 2011

K-WRF Temp MAE 1.68 2012/13 all sites

K-WRF Temp MAE 1.23 2012/13 Zone 11

US-NWS

(Human)

Tmax and

Tmin

MAE 1.47 Wheeler et al

2011

GFS+MOS Tmax and

Tmin

MAE 1.53 Wheeler et al

2011

K-WRF MAE for Temp remains below 2°C out 3 days

Weather intelligence

Thank you

Please e-mail any questions to

christine@katestone.com.au

Katestone

PO Box 2217

Milton, QLD, 4064

References

• Gaughan et al., 2008. A new heat load index for feedlot cattle. Journal of

Animal Science, vol. 86 no. 1 226-234

• Bureau of Meteorology and CSIRO (2010) State of the climate

• Hanna, E.G., Kjellstrom, T., Bennett, C. and Dear, K. (2011) Climate Change

and rising heat: population implications for working people in Australia. Asia

Pacific Journal of Public Health, 23 (2 Suppl.), 14S-26S

• Parson, K (2003) Human Thermal Environments – The effects of hot,

moderate and cold environments on Human Health, Comfort and

Performance. Taylor & Frances, London

• Maloney, S. and Forbes, C. (2011) What effect will a few degrees of climate

change have on human heat balance? Implications for human activity.

International Journal of Biometeorology, 55, 147.

• Ollie, J. and Kenny G. (2010) Heat Exposure in the Canadian Workplace.

American Journal of Industrial Medicine 53:842–853 (2010)

• International Standard (1989) ISO 7243 Hot Environments – estimation of the heat stress on working me, based on the WBGT-index (wet bulb globe temperature)

• Budd, G. (2008) Wet-bulb globe temperature (WBGT) - its history and its limitations . Journal of Science and Medicine in Sport (2008) 11, 20-32

• Schickele E. (1947) Environment and fatal heat stroke - an analysis of 157 cases occurring in the army in the U.S. during World War II. Milit Surg 1947;100:235-56

• Ramsey et al (1983) Effects of workplace thermal comfort on safe work behavior. Journal of safety Research, Vol. 14, pp. 105-114, 1983

• ACGIH (1996) TLVs and BEIs. Threshold Limit Values for chemical substances and physical agents. Biological Exposure Indices. American Conference of Governmental Industrial Hygienists, Cincinnati, OH.

• Singh, S. Hanna, E. Kjellstrom, T. (2013) Working in Australia’s heat: health promotion concerns for health and productivity

• Steve Rowlinson, Andrea Yunuan Jia, Baizhan Li, Carrie Chuanjing Ju (2013) Management of climatic heat stress risk in construction: A review of practices, methodologies, and future research. Accident Analysis and Prevention (unpublished)