The document discusses a mobile phone app called PHS (Predicted Heat Strain) that allows users to conduct heat stress risk assessments based on environmental and worker parameters. The app was developed based on algorithms from ISO 7933 and allows users to input data to predict a worker's heat strain and core body temperature rise. It can be used to assess heat stress risks, analyze the impact of different controls or work/rest schedules, and provide guidance on managing risks from heat exposure.

1. TO ASSESSAND MANAGE THERMAL RISKS
USE OF HEAT
STRESS PHONE
APPS
Dr Kelly Johnstone
The University of Queensland
Dr Ross Di Corleto
Rio Tinto

2. Climate change is expected to continue to raise temperatures and increase the frequency of extreme
heat events
Australia’s temperatures are projected to rise by 0.6 to 1.50C by 2030
The number of extreme heat records in Australia since 2001 has outnumbered the extreme cool by
almost 3 to 1, for daytime temperatures (Australia Bureau of Meteorology and CSIRO, 2014)
Management of workers’ exposure to heat stress will be an ongoing issue for at risk industries
An Increasing Workplace Risk

3. Heat Stress vs. Heat Strain
Heat Stress
Environmental heat and humidity, metabolic work load and clothing, individually or
combined create heat stress for the worker.
Heat Strain
The physiological response to that stress,
– sweating, increased heart rate, elevated core temperature, etc.

4. Humans need to maintain their core body temperature within a very narrow range (around 37oC)
Maintaining the internal temperature requires a heat balance between the body and its environment
A 2-3°C increase in core body temperature can be potentially life threatening
• First symptoms occur at 37oC – 39oC
• Heat stroke at 40oC
• Death at 42oC
Core Body Temperature

5. Heat Stress Parameters
A human’s response to the thermal environment is influenced by six parameters:
Four environmental variables
• air temperature
• radiant temperature
• humidity
• air movement
combined with two worker variables
• metabolic heat from activity
• clothing worn

6. Assessing the work environment in relation to thermal risks has often been seen as a complex process
Numerous tools, methods and concepts to consider
But is it really that difficult?
Heat Stress Risk Assessments

7. Heat Stress Risk Assessment
The assessment process need not always be difficult and should be suited to the
complexity of the environment & task
Don’t over complicate
If the scenario is straight forward and the risks obvious then address them
However, if there are numerous interacting factors or high levels of PPE then take
the time to assess properly

8. 1. A basic qualitative heat stress risk assessment, which can incorporate a simple index
i.e. WBGT, Apparent Temperature, Basic Effective Temperature, (BET), etc.
2. Additional data collection and use of a second level assessment
• ISO 7933: Predicted Heat Strain (PHS)
• Thermal Work Limit (TWL)
3. Physiological monitoring
AIOH Three Step Protocol
Source: AIOH A Guide to Managing Heat Stress
https://www.aioh.org.au/onlinestore/publications/a-guide-to-managaing-heat-stress-developed-for-use-in-the-australian-enviro
nment

9. Basic Thermal Risk Assessment
Basic Thermal Risk Assessment Mobile Phone App, download from:
Android (Google play)
https://play.google.com/store/apps/details?id=com.Gopaldasani.thermalrisk
Apple (iTunes store)
https://itunes.apple.com/us/app/thermal-risk/id867920824?ls=1&mt=8
Windows Phone store
http://www.windowsphone.com/en-us/store/app/thermal-risk/6f3ffccf-fcca-4588-9f3c
-b7bdea119662
Based on AIOH Basic Thermal Risk Assessment

10. WHSQ has an online tool to complete a basic thermal risk assessment (similar to the mobile app)
https://fswqap.worksafe.qld.gov.au/etools/etool/heat-stress-basic-calculator-test/
Basic Thermal Risk Assessment

11. There are over 60 heat stress indices published since the development of the Effective Temperature scale
in 1923 (Brake and Bates, 2002)
The Wet Bulb Globe Temperature (WBGT) is probably the most widely used (easy to use and interpret)
Although useful in basic assessments of the thermal environment, application of work limits based on
WBGT are considered over conservative and therefore not useful in effective risk management
(Holmer et al., 2010). WBGT too simple for a second level assessment
To overcome the recognised issues with the use of the WBGT, a rational heat stress index such as the
Predicted Heat Strain (PHS) index can be used for a second level risk assessment
60+ Heat Stress Indices

12. Predicted Heat Strain (PHS) Index
PHS is a rational index based on the heat balance equation and the concept of
maintaining a thermal equilibrium
It uses measured environmental parameters combined with task parameters in a series
of equations to predict the body’s response to heat stress as a rise in core body
temperature
Useful tool for developing control strategies and assessing the impact of these controls
or changes of environment on the worker

13. Rational heat stress indices (such as the PHS) provide a more accurate assessment of
heat stress scenarios than simpler empirical or direct indices (i.e. ET, WBGT) but
they are complex
Mobile devices provide a readily accessible platform on which to develop such an assessment tool
Why PHS?

14. The Project
A University of Queensland (Dr Kelly Johnstone) and Rio Tinto (Dr Ross Di Corleto)
collaboration to develop a heat stress assessment phone app based on the Predicted
Heat Strain Index as detailed in ISO 7933:2004 Ergonomics of the thermal environment
– Analytical determination of heat stress using calculation of the predicted heat strain
The program is based on algorithms used in ISO 7933 (Annex E) which were validated
on a database including 747 lab experiments and 366 field experiments, from 8
research institutions

15. iOS App only, but there are plans to develop an Android and Windows version
Available from the Apple Store (search for PHS):
https://itunes.apple.com/nz/app/phs/id1148768952?mt=8
User Guide also available from:
http://www.thethermalenvironment.com/the-predicted-heat-strain-mobile-application/
Download the PHS App

16. Using the PHS App
By modelling predicted heat strain in work environments, users are able to alter various
parameters (e.g. air velocity, air temperature, rest cycles, etc.) to determine the resulting
effect on employee thermal strain
The PHS app provides the following interpretive data:
• Predicted heat strain summaries for specified parameters/ scenarios
• Predicted heat strain graphs for specified parameters/ scenarios
• One, two and/ or three work phase analyses
• Predicted water loss values
• Custom reports based on summary information and graphs (which can be emailed)

17. Prior to utilising PHS, users require a thorough understanding of the task being analysed
(e.g. duration, level of physical exertion, frequency of breaks etc.) and the thermal parameters of the
environment the task is performed in (e.g. air and globe temperature, air velocity, humidity)
Employee input should be sought to provide accurate knowledge of task details. Accurate monitoring
data should be used to determine environmental parameters
Using the PHS App

18. Start Screen/ Model List Screen

19. New Model Screen

20. Data Entry
Model variables (individual characteristics of height
and weight) are pre-set to 1.8 metre height and 75kg
weight. These parameters were used to validate the
application against Annex F in ISO 7933
The ‘Phase View’ provides pre-populated toggle fields
but it is possible to enter site-specific data for a
calculation into the “New Value” box
Each parameter field has defined value limits (values
outside the ranges are automatically identified by the
application)

21. Output Views

22. Example: Monitored Parameters
Dry Bulb = 40.9 0C
Globe = 45.3 0C
Relative Humidity = 22.6%
Air Velocity = 0.2 m/s
Metabolic Load = 175 W/m2
Posture = Standing
Clothing is a single layer disposable cotton overalls with an insulation factor of 0.8
clo
Acclimatised worker
Can drink freely
Task takes 120 minutes and is performed twice in a shift

23. PHS Graph
Rectal temperature of 380C exceeded at 79 minutes
into the 120 minute task
Do we need to do anything?
What if we give them a 30 min break in the work
environment?

24. 30 Minute Break
in work environment
What about a 30 min break
in an air conditioned room?

25. 30 Minute break in
air conditioned room
– does this improve
the recovery?
So what happens when
we put the worker back
to work?

26. Back to Work after 30 min
air-conditioned break
We can see a marked reduction in the core
temperature but the core temperature still
climbs quickly back up and exceeds 380C at
31 minutes back at work
Is this acceptable? Workable?
Lets try a rest break after 60 mins instead of
120 mins

27. Break after 60 minutes
then back to work
Design has effectively reduced the strain on the
employee. Caution should be exercised however as
they have not recovered to their baseline level and
if the individual returns to the same work
environment there is potential they may exceed the
limits.
Lets try a different approach - what if we try
increasing the air flow?

28. Increased air flow

29. Volunteers Needed
The University of Queensland, School of Earth and
Environmental Science is conducting a study to evaluate the
in-field use of the PHS App
What is required:
– Workers in at risk thermal environments
– Thermal monitoring equipment
• Air temperature
• Globe temperature
• Humidity
• Air Velocity
– OHS professionals to perform heat stress assessments using the PHS App
– Completion of a survey collecting data on the usability and application of the
tool
Image Source: http://solutions.3m.com/wps/portal/3M/en_EU/PPE_SafetySolutions_EU/Safety/Product_Catalogue/~/3M-QUESTemp-Heat-Stress-Monitor-QT-44?N=5023587+3294756749+3294857473&rt=rud

30. Summary
• A readily accessible level two heat stress assessment tool that looks at
a number of parameters
• Can be used to assess
– the heat stress of a work environment
– the impact of different controls
– work/ rest regimes
• Is free of charge
• Is still only a guide and cannot account for all scenarios