The Thermal Environment

Physiological monitoring for heat stress – The answer or more questions?

• By Ross Di Corleto
• 23/03/2014
• No Comments

In the three step approach to managing heat stress the third method applied is physiological monitoring. Basically it involves monitoring the heat strain on the individual directly rather than just the physical parameters of the environment via heart rate and/or core temperature etc. A question sometimes asked is whether this is the benchmark or “gold standard” of heat stress monitoring and hence the best approach. This is one of those “yes, however” type answers. Monitoring the individual’s fluid losses, heart rate and/or core temperature is without doubt the most comprehensive way of determining the impact of heat stress on a person, however it may not be the best approach for the scenario. There are some pros and cons.

It would be my method of choice for scenarios that require the use of high levels of PPE such as Hazmat suits, non –breathable disposable coveralls and high levels of military and firefighting turnout gear. The general ambient climate of the working environment is often far removed from the micro-environment experienced within these outfits. Whilst there have been a number of attempts to quantify this over the years using formulae and graphs, the physiological approach is still far superior.  The recent developments in pill telemetry has seen equipment that can also allow remote real time monitoring of the individuals in higher risk scenarios thus providing an extra level of protection.

However,

• the equipment is generally not cheap,
• can be seen as invasive,
• requires specialist interpretation of data collected, and
• the information collected is one individuals physiological response to a specific scenario.

Physiological monitoring also plays an important role in researching the heat stress dilemma. Research involves the collection of as much quality data as possible. This may then be utilised to develop a control methodology across the general working environment. We all know how big a variation exists among healthy individuals (let alone those that may not feel well). Add to that the number of different climatic scenarios people are exposed to and then throw in varying types of tasks and how they are carried out; quite a complex equation. So you can see that in an isolated scenario care needs to be taken when drawing conclusions from smaller data sets. Generalisations made across large groups with the use of limited data of this nature will not only lead to a poor control strategy, it can be dangerous.

We are starting to learn more and more about how the thermal environment effects people thanks to these great tools but it is important to remember that one size does not fit all and the methodology should be used carefully and with discretion.

BOTTOM LINE

Physiological monitoring for heat strain is a valuable tool in the right hands and applied to the right scenario.

KEY POINTS

• Method of choice for scenarios that require the use of high levels of PPE
• Good tool for real time monitoring of an individual in an elevated risk scenario
• It has limitations and should be used carefully
• Should be carried out by individuals with the appropriate knowledge & skills
• Be careful when making control generalisations across large work groups based on limited data

USEFUL REFERENCES

ISO 9886 (2004).  Ergonomics – Evaluation of thermal strain by physiological measurements.  International Organization for Standardization, Geneva.

ACGIH (2013).  Heat Stress and Heat Strain.  In: Threshold Limit Values for Chemical Substances and Physical Agents, pp. 206-215.  American Conference of Governmental Industrial Hygienists, Cincinnati, OH.