Heat Stress Assessment and Control

Only by taking accurate temperature readings will it be possible to quantify the danger so appropriate responses can follow.

The word "stress" seems to be used more and more frequently these days. The economy invokes its use quite often. It comes up a lot when we are talking about workplace or job stress. According to the National Institute for Occupational Safety and Health's NIOSH Publication No. 99-101: STRESS . . . At Work, "Job stress can be defined as the harmful physical and emotional responses that occur when the requirements of the job do not match the capabilities, resources, or needs of the worker." Heat stress is another major issue in many workplaces, and summer is coming soon.

The term job stress could almost be replaced in the definition above by heat stress and still be a decent basis from which to work because stress is stress, and our bodies will respond to it. Our own bodies are our own stressors at times. Clothing, personal protective equipment (PPE), and equipment are potential stressors. Outdoor work sites will have their own intrinsic issues: lack of shade, for instance, or heat reflected from the pavement. Indoor sites such as foundries will have their own sets of stressors, such as heat generated by the furnaces getting trapped inside the building.

Protective clothing or respirators that are intended to improve safety in some cases can worsen heat stress in others. Your site's documented job hazard analyses should have current listings of heat hazards if indeed heat is an issue where you work. Drag these documents out and ensure they are up to date. Revise them as needed to be sure they cover today's working conditions for your site. Performing this step ensures you are in compliance with OSHA's standard 1910.132(d)(2) while simultaneously addressing heat issues.

It's one thing to realize that working conditions are hot, but it's another thing to actually know just how hot. Only by taking accurate temperature readings will it be possible to quantify the danger so appropriate responses can follow. The temperature of the workplace has to be used in conjunction with the added heat our bodies generate as we work so we can set allowable exposure limits. This is so basic it's almost not worth mentioning, but do you have records of temperature measurements, humidity readings, heat indices, or allowable exposure times in your JHAs? Estimates of metabolic work rates for your various jobs? These are the tools you must have in order to define the hazard.

ESP: Predicting the Future

One mathematical equation used in risk management says that risk is a function of exposure x severity x probability, or R=(esp). Using this basic concept can help us predict the future and possibly control heat hazards to a large degree. Identifying exposures means identifying persons who could suffer heat-related injuries while working and understanding how these folks can be harmed. The severity of the injury or harm has to be estimated, as does the probability that injury will occur.

Rank the exposures according to the demands on, and capabilities of, your workers. Exposure is increased by things such as the number of employees exposed, the time they are exposed, and how often they are exposed. Factor in the time required to get medical treatment to an injured worker. Now, assign a number value to the exposure. Let's assume a numerical value of 1 is the lowest exposure and 100 is the highest, or worst case. We'll use a number from this range as the multiplier for "e" in our R=(esp) equation.

Moving on to the severity part of the equation, we will assign a numerical value to "s." We can use the same scale if we choose, 1 to 100, with 100 being the most severe. OSHA's technical manual lists the following conditions as heat disorders or health effects: fatigue, rashes, collapse, cramps, exhaustion, and stroke.

These problems are listed in the order of increasing severity, so we can assign a multiplier value as prudence would allow. Probability is estimated next. No one is immune to heat injury, but some people may be more likely to have a heat strain if they are ill, elderly, obese, have had a previous heatrelated injury, or are on certain medications. Identifying those employees who are at increased risk gives you another tool to use in managing heat strain. The "p," or probability of injury occurring, will now be assigned a numerical value from 1 to 100.

The number value of this and the other two factors in the equation are arbitrary numbers you choose using your judgment and experience so you can assign relative values to the variables in the equation. You could use a 1-5 point value or a 1-1,000 point scale just as easily. (There's a good example of a risk assessment table here.).

Plugging some numbers into the R= (esp) equation, using the 1-100 scale across all three variables, the lowest risk will be:
R=1x1x1 or R= 1
The highest risk is:
R=100x100x100 or R=1,000,000

Real-world results will be somewhere in between; this just gives you a relative risk value of a situation you analyze.

Controlling the Hazard

There's nothing new here. Well, nothing very new. We usually follow the safety and health hierarchy of controls to manage hazards. We identify the critical characteristics we have to control to effectively manage the hazard and implement controls, in order, from most effective to least effective: engineering controls, work practice controls, and personal protective equipment.

Many times, the heat stress we have can be loosely compared to an endothermic reaction, wherein our bodies absorb heat from a hotter object or source. Engineering controls use machinery or equipment that is built into the workplace to disrupt the path the heat takes to apply stress to our bodies. Baffles, barriers, fans, and HVAC systems are some examples that block, divert, modify, or absorb the heat before our bodies do.

Work practice controls are used to further reduce hazards that are not completely removed by engineering controls. Limiting the time workers are exposed to the heat is an effective control in endothermic-type situations where the body absorbs heat. Prohibiting people from working alone in dangerously hot conditions is another work practice control that could help prevent a problem. Controlling the speed of the work and amount of physical effort are other effective, if not entirely popular, work practice controls.

When we use our muscles to perform work, we generate what is called metabolic heat. Metabolic heat is the two-dollar term for the heat generated when we process food and convert it to motion. In this case, we can compare the process to exothermic reactions in which objects (our bodies) give off heat into the environment. If we generate heat faster than we can dissipate it or throw it off into cooler air or objects, we get heat stress and can exacerbate problems in endothermic situations. We increase the chance of getting the strain we want to prevent.

Acclimatization is a management technique that's a little different from most hazard controls. We can't, for example, get acclimatized to receiving high-voltage electrical shocks, but we can get used to working in hot conditions, within reason, if we go about it correctly. Get sound medical advice on how to acclimatize yourself or your workers and be aware that acclimatization wears off when heat exposure is reduced through vacations or other events that take workers out of the hot environment for a few days.

Personal protective equipment is the last choice in the hierarchy of controls, but in managing heat hazards it can be very effective. PPE items are barriers, baffles, reflectors, insulators, etc. that are worn on the worker's body, and not permanently engineered into the workplace. It has to be the right PPE, selected to address specific hazards as identified in your written hazard analysis. Its effectiveness depends largely on the training of the user and its fit, comfort, and ease of use. Like work practices, effective PPE use often depends on managing the site's rules.

Ensure your workers have access to adequate first aid supplies such as cold packs. First aid guidelines say to put cold packs on the victim's neck, armpits, and groin areas in certain heat emergencies. It sounds simple and straightforward in class, but realistically, how long would it take to actually do this in your facility? In the field? Does your first aid kit have a thermometer for taking a victim's temperature? You can assemble a dedicated heat strain first aid kit for hot job sites or can buy one already packaged.

Promoting Awareness

Hazard awareness training is critical for effective hazard management. If workers have a flawed understanding of danger, it is going to be hard for them to avoid it. Training for managing heat stress has to include everyone at the work site. Because first aid is, by default, something that happens after injury occurs, a good start for training is to educate at-risk employees and their management in prevention measures.

One United States military safety alert closed by saying, "Successful management of heat exposure results in optimal work capabilities and prevention of heat illness/injury." This makes sense. Better to manage the exposure than manage the emergency.

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