This document discusses heat stress management for workers. It begins by outlining some of the dangers of heat stress, including increased mortality and reduced productivity. It then discusses factors that impact human tolerance to heat like humidity, acclimatization, clothing and health. Several heat stress indices are described, including WBGT, which is the most widely used but has limitations. Guidelines for work-rest regimes using WBGT values are provided. The document emphasizes that heat stress management requires considering both environmental and individual human factors. It suggests weather intelligence tools could help optimize planning to reduce heat risks.

1. Management of environmental
heat stress
Christine Killip
Atmospheric Scientist and
Managing Director of
Katestone

2. 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?

3. 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

4. Which is worse for heat stress?
36°C Temp
28°C Temp
&
&
30% RH
85% RH
42°C Temp
32°C Temp
&
&
20% RH
70% RH
Based on Humidex

5. The human thermal balance
M + W = K + R + C + Cres + E + Eres +S
-ve
Metabolic (M)
Convection (C,
Cres)
Evaporation
(E, Eres)
Ref: ISO 7243
+ve
Conduction (K)
Radiation (R)
Mechanical (W)

6. 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)

7. 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)

8. Overloaded system
Level of heat
tolerance reached
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

9. Guidelines
Metabolic
+
Environment
Ability to
dissipate load
in current
environment

10. 4 elements of our EHL
Wind speed
Radiation
Temperature
Humidity
EHL

11. 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’

12. Factors impacting human
response to EHL
Fitness
Acclimatisation
Age
Dehydration
Clothing
PPE
Weight
Human
response
General health

13. 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)

14. 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

15. Which index?
Solution:
•Pick an index you are
comfortable with
•Understand its limitations
•Use it as a guide only
•Personal awareness is the key

16. 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

17. WBGT reference values from ISO 7243
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.

18. 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

19. 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)

20. 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

21. 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!)

22. 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?

23. 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

24. 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

25. 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

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

27. 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

28. 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

29. 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

30. 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?

31. Weather intelligence

32. 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

33. Overloaded system
Heat stress can cause significant
loss in productivity before we reach
our level of heat tolerance
Body temp rises
Cardiovascular
strain
Sweat increases
(dehydration)
Weak
Dizzy
Clumsy
Sick
Heat exhaustion
Heat stroke

34. 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)

35. 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

36. 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

37. The Katestone forecasting system
Observations
AWS
Ships
Aircraft
Balloons
Buoys
Satellites
Central collection
World Met Office
(WMO) data store
Worldwide
Millions of sites
Decades of data
International
Global Model
GFS
Worldwide
0.5 Deg Resolution
7 Days @ 3 hour
intervals
Katestone
(K-WRF)
BOM AWS Observations
WRF-ARF
12 Km resolution
Australia wide
4 days in 1 hour intervals
Research
On site AWS
Email and SMS
Alerts

39. 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

40. Weather intelligence

41. Thank you
Please e-mail any questions to
christine@katestone.com.au
Katestone
PO Box 2217
Milton, QLD, 4064

42. 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)

43. •
•
•
•
•
•
•
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)