Heat stress

How do I calculate heat stress?

The easy answer: Perform a heat stress task hazard analysis. But that doesn’t really give us much more information than the question itself, does it?

As with most workplace hazards, we begin by defining the hazard itself. We identify when, where and to what degree it can be present; what additional factors increase the hazard; what controls are available; what exposure limits (if any) are in place; and what resources are available. Once we gather and document this information, we can begin to calculate the heat stress exposure.

Heat stress can be defined as “physiological stress experienced as a result of excessive heat.” So, what’s “excessive heat?” And what needs to be measured to get a true heat reading?

First, factors outside of just the actual ambient air temperature need to be considered. In other words, no single indicator determines the calculated heat stress exposure. Environmental conditions all play a factor. You’ll need to think about sun, wind, humidity, processes, heat-generating equipment, etc.

We also need to consider both the type of work and level of physical activity being performed. Don’t forget to account for any protective clothing being worn! It could prevent (or assist) in your ability to manage excess heat.

For calculating encompassing environmental heat, we recommend using a wet bulb globe temperature monitor that measures air temperature, humidity, radiant heat and wind. It should be placed in an area that’s representative of the conditions where work will be performed.

However, don’t solely rely on it to determine exposure. Various methods can be used, including examples of physical activity levels, risk of acclimated and unacclimated workers, and adjustments for various types of protective clothing.

You start by calculating your heat stress exposure and determining placement in the respective limits. Then, you can look at engineering controls, administrative controls and personal protective equipment to remove or reduce the exposure. Remember, no one indicator can determine exposure.

It’s best to have a comprehensive heat stress program that includes calculating heat stress along with training, planning, oversight, controls, PPE, symptom awareness, first aid and emergency preparedness.