Heat Stress during the Summer Months
6/14/2021
Well, it looks like the Summer months have arrived. We passed the unofficial beginning of Summer on Memorial Day and the official beginning is one week away, and now extreme heat has gripped many parts of the Nation.
One of the industrial hygiene tools used to assess worker heat stress load is the Wet Bulb Globe Temperature Heat Stress Meter; often referred to as simply the WBGT (pronounced Web-Get).
The concept of this instrument goes back to the 1950’s at Parris Island; just off the coast of South Carolina, where marine recruits attended boot camp. And during the summer months, the weather was extremely hot and humid while recruits were subject to rigorous conditioning. As a result, many as these recruits suffered severe heat stress conditions including hospitalizations and even death. As a result, the assessment method to determine the severity of heat stress conditions were developed by taking into consideration the actual temperature (known as the dry bulb temperature), wet bulb temperature (which measure evaporative effects), and globe temperature, which took into consideration radiative heat. These three measurements were added together in a very specific weighted formula (0.7 x WB + 0.2 x GT + 0.1 x DB) to provide a heat stress reading which was then used to determine when the recruits needed to rest. Years later, occupational health professionals developed work/rest cycles that were based on the WBGT temperature. This work/rest regimen included workload classifications, expressed as light, medium, heavy and extremely heavy. Thus, a heavy workload cycle would require workers to rest more frequently than when performing light work.
Sounds easy enough, yes? Well, those of us that have worked in heat stress environments and tried to employ this process understand, on a first-hand basis – the drawbacks of this method. First; it does not consider the fact that every person has their specific characteristics; most importantly, individual physical conditioning. In addition, the specific clothing a person is wearing will also play a crucial factor. Therefore, the pure WBGT calculation may not properly indicate how an individual is coping with the extreme hot weather.
Another point to be made is that, under the more severe WBGT calculations, persons may be required to work for a total of 15 minutes, followed by a 45-minute rest period. This may sound like easy work but try telling a heavy equipment operator to take a break after 15 minutes and watch his/her reaction! The point is, within 15 minutes, operators establish a rhythm and breaking this rhythm becomes quite annoying. And they will let you know it as they will insist that they are not feeling any adverse effects from the hot weather (remember, they are probably sitting in a climate-controlled cab).
So, what is the solution? One group that is dedicated to occupational health is the American Conference of Governmental Industrial Hygienist or ACGIH. Instead of using the environmental parameters of ambient temperature conditions, using an oxypulse meter, we can directly measure the body burden of any individual. Oxypulse meters are simple and inexpensive – typically costing no more than $50.00 (although more expensive units ranging upwards of $250.00). Anyone who has been in the hospital or had a recent visit to his/her doctor, would be familiar with this piece of equipment. It is simply is placed on the index finger, while a direct readout (either as a LED or LCD) is displayed within a few seconds. This measurement provides the blood-oxygen concentration -which should be in the high 90 percent, such as 96% to 98 %, while also displaying one’s heart rate. It is this last measurement that provides a direct indication of one’s body burden. Using the equation of “180 minus the persons’ age,” we can obtain the maximum heart rate that is allowed without the individual being placed in a potential heat stress scenario. Should an individual’s target heart rate (based on 180-age) be exceeded, upon leaving the work area or based on a specific time limit; usually 60 minutes, the individual must rest until his/her her rate falls below 120 beats per minute (bpm). At this time, the person may continue work, but may only continue at 2/3 of the initial work period. Thus a 60-minute work cycle, may only be followed by a continued work period of 40 minutes. At this time, the individual’s oxypulse reading is once more checked to ensure his/her heart rate remains within the “180-age” limit. If this number is once again exceeded, then it is time to not have this person continue with this specific work task.
There is no specific Occupational Safety and Health Administration (OSHA) standard that addresses heat stress. However, OSHA frequently refers to the General Duty Clause of the Occupational Safety and Health (OSHA) Act to cite employers who should have a written heat stress program in place. The General Duty Clause states that employers are required to “…provide a place of employment free from recognized hazards that are causing or are likely to cause death or serious physical harm to its employees.” This statement has been used throughout the years, citing employers when adverse work conditions are present and proper protective actions are not implemented.
Avoiding heat stress – under any extreme condition – requires persons drink plenty of water or other hydrating liquid. Experts tell us that we should be hydrating with a glass every 15 – 20 minutes. We should be taking frequent breaks in a shaded area while knowing the signs/symptoms of heat stress so you can recognize when a fellow worker needs assistance. These are simple measures and whether you are at work or doing chores around the house, when it comes to working in a heat environment, we need to take heat stress seriously. Ignoring these steps can result in some very serious consequences!
Concurrently, OSHA has published a Heat Stress Guide (on their Web page” www.OSHA.org”), where practices such as a frequent break in a shaded area, drinking substantial amount of water and maintaining a buddy system are stressed. Persons need to be trained to recognize heat stress conditions, so based on observations, a co-worker may insist his/her buddy should take a break and get fluid replenishment.
It should be noted that while Federal OSHA has not promulgated a heat stress regulation, some states- such as Cal OSHA – have instituted a heat stress standard (for Cal OSHA, that’s 8 CCR 3395 – Heat Illness Prevention in Outdoor Places of Employment).
No heat stress assessment can determine how an individual is truly coping with elevated temperatures, although we can get some important data to help us understand when we need to take heed to extreme heat conditions. As with any prudent S&H plan, a certain amount of ownership belongs to the individual – just like any worker has the responsibility to check their PPE prior to use to ensure there are no defects and that their assigned PPE fits properly.