Management of Environmental Heat Stress
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Transcript of Management of Environmental Heat Stress
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
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)