Heat Stress in Construction  


By: Barry A. Cole, President
Cole-Preferred Safety Consulting, Inc. and
Preferred Safety Products, Inc.

Just about now, across the country, we hear of healthy young men, dropping, and sometimes dying on high school and college football fields somewhere around the country. We don’t hear about the many men (and sometimes women) on our construction sites that faint, have seizures, get cramps, and/or become comatose, nor even the ones that die, on our millions of construction job-sites, annually. And, while it is more common to see heat related illnesses and accidents (HRI) in warmer months, it has been my experience that the hotter environments we see less affects from the heat than we do in the climates that have wider swings in temperature and climate. Arguably, this is because the workers in the warmer climates have a bit of acclimatization always, where the cooler climates with the suddenly warm or hot day, catch more people by surprise. Also, it could be argued, that persons in hotter climates may have inherently gained some insight to their body signals, in that they are exposes so often to heat related stress.  Make no mistake, though, all humans, in all regions, have far too many heat related ailments, and there is a reasonably good, practical way to stop this in our industry.

Heat illnesses are a serious medical concern for all constructors, and each contractor should pay attention to simple rules to predict and prevent heat related illnesses. Nearly everyone can tell you about the types of ailments, but not many can give you a basic understanding of how it all works in our bodies, and how to prevent it (and still get some work done) in hot environments, nor when to predict it. These are important elements of this medical problem that supervisors and employees need to know, to prevent this sometimes-deadly ailment.

A lesser concern is heat rash, which is just the skins reaction to open pores clogged with dirt or bacteria, very sensitized skin with vascular swelling rubbing on fabrics or enclosed places, or more than the usual amount of work contaminants reacting with salty water of sweat causing a skin reaction. Cooling, drying powders, antibiotic creams, cool compresses, and over the counter cortisone cream is often all that is necessary for this non-serious annoyance related to hot environments.

The American Conference of Governmental Industrial Hygienists has established Threshold Limit Values to identify heat stress condition under which it is believed that nearly all workers may be repeatedly exposed without adverse health effects. These Threshold Limit Values are based on the assumption that nearly all acclimatized, fully clothed workers with adequate water and (and any necessary electrolyte replacements) should be able to function effectively under the given working condition without exceeding a core body temperature of 100.4 degrees Fahrenheit.  A raise in your core body temperature above this mark is a plain indication that your cooling system is broken down, and the only way to go is up from there.

In order to understand the basics of heat injuries we must review the factors. Obviously, heat, in the form of external exposure to the skin and body and internally made heat. This is ambient heat – the true temperature of the air around you; solar gain –  the amount of heat absorbed from direct exposure to the sunlight;  radiant heat – heat radiated of other objects that have gained more heat from the sun or from motors etc., that is absorbed by your body; and metabolic heat – the heat your body makes whenever it does work.  Regardless of whether you have one, two or all four of these heat sources, you can and will be overcome with heat related injury if you do not pay attention to the following.

The second factor is your body’s ability to control or rid itself of heat. The body does this is three basic ways. First, we sweat, and the evaporating water takes the heat out of and of the outside of our body. Second we breath, and the huge amount of air volume that comes into contact with a huge amount of blood, picks up heat, and sends it out of our body as we exhale. Third, our peripheral veins and capillaries swell open and allow substantially more blood to flow on our surface, as another way to rid our body of heat. (The cooling effect of the sweating is more meaningful if the surface area of the blood vessels are larger).

It is easy to see, then that we must offer the outside and inside of our body something to help it out! Particularly an environment that is dryer than our skin, in order to encourage sweat evaporating, a temperature that is cooler than our body in order to allow heat from our body to transfer to the environment, and sufficient extra volume of moisture to compensate for the pooling in our skin, and the extra amounts lost from the sweating. It is obvious to most then, that when working in a high humidity, high heat environment, the ability to cool your body is very low. Combine that with extra metabolic heat load from working hard, and sun or radiant heat loading on your body, and it could spell trouble.

Lets look at the easiest methods to prevent some of the heat sources. In most construction situations, engineering controls for air temperature, moisture content of the air, are either ineffective or not feasible. However air movement to increase cooling and increase airflow to remove moisture from your body is readily available with fans. Radiant heat can be repelled from a person by blankets over top of the heat source, or reflective curtains. For instance workers welding on top of or next to black iron vessels outdoors, would be well served to have silver backed welding blankets places over the black surfaces around where they work. In some instances, compressed air blown through “Blow-Joes” will move air and cool the air temperature (rapidly expanding compressed air is cooling. (Do not use compressed air directly on a person with out a device to reduce pressure, as air, fluid, or debris embolisms could be forced into their blood stream, or into their skin.)    Further, light colored, lightweight cotton or synthetic fabrics (wicking fabric) enhances cooling by collecting fluid and increasing your surface area, and reflecting significant amounts of sunlight light. A hard hat reflects significant heat from your scalp which not only gains heat but loses heat faster than most of the body, due to its high blood flow and vascular surface area.

The human body attempts to regulate the core body temperature at nominal 98.6 degrees Fahrenheit – considered ‘normal – your body may be lower, and sometimes slightly higher, for its ‘normal’. In order to maintain the core body temperature, equilibrium is established where the amount of heat gained or produced by the body equals the heat lost by the body. The heat generated by the metabolism of the body is lost through evaporative cooling due to sweating. In cooler climates, our body still loses heat, but it may be sufficient to lose it through convection alone without sweating. (Cool air takes the heat from the skin and blood just through passing over the skin, without any water to increase the cooling efficiency.)  Air conditioning is especially effective because it is not only cool, moving air, but also dryer air, so evaporation and convection are maximally efficient.

With improper balance between bodily cooling and heat production/absorption, there is heat stress. Too much internal heat, causes the body systems to begin to fail. Heat stress injuries are basically caused by three things. Sweating (when your body is not acclimated) takes with it too many bodily electrolytes, so the loss of important bodily chemicals causes muscle cramps, and generalized weakness. ) Heat Cramps then, are often the first sign of heat stress, and are a sure sign that your employees are exposed to substantial heat load, and have not been acclimated. Remember heat load might simply be a lot of physical work, without rest, in what seems like a mild environment, just as it may a rather passive or low effort job in a high heat environment, or anything in between. Many times, cramps are alleviated (or prevented) with electrolyte drinks (Gatorade, PowerAde, and similar “sports” drinks, are a good curative or preventative for cramps and treatment is easy on the job, but most have a fairly high salt content). Newer electrolyte drinks and tablets have less sodium (salt) and still have the potassium, magnesium, calcium, chloride, and sometimes iodine, commonly lost through sweating. In the old days, salt tablets (concentrated sodium chloride) were given routinely and workers were allowed to take as many as they liked to prevent or treat cramps, without much concern by first aid personnel. This is now not allowed in most places and not recommended at all due to our knowledge of how the body acclimates, and our understanding of the damage concentrated salt can do to persons with cardiac and blood pressure problems. It should be noted that healthy people without cardiac, circulatory, urinary/kidney, spleen,  or endocrine problems, and without to much excess weight generally will self adjust to electrolyte loss in a few days of working in high heat, and sweating (and losing electrolytes) for several days. Thereafter, the taking of any supplemental salt or other electrolytes is generally unnecessary and often results in less efficient sweating. By this we mean that a body that loses salts and electrolytes in the first few days of hard labor or sweating to keep cool, self adjusts, and limits the amount of salt getting out in the sweat. By retaining the salt in the cells, it also forces the body to hold more water to keep the salt diluted properly. By holding more water, more water is available to sweat, so the volume of cooling capacity actually goes up after acclimatization! (Also called acclimation.) Then the only factor left is water, water, water, – the number one preventative for heat related illnesses.  So the best treatment for heat, is to allow the body to acclimate (acclimatize) and then to keep it continually stocked and restocked with water.

While heat cramps are often passed without noticing, or are prevented by taking some electrolyte drink or tablets, the danger really begins with the next stage, and unfortunately, the cramps might have been a helpful indicator to tell you to stop!  The next two phases are almost always about water, or lack of it, and the bodies inability to cool itself. There can be no mistaking the value of huge amounts of water, to allow the body to properly function. As the body loses a quart or more of fluid an hour, it is necessary to take that much, or more to keep the volume up. The body will begin to rob tissue and organs of water during high sweating phases, and that can cause other issues, so water replacement at the same speed or more that it is being used for cooling is imperative. For instance, most workers report a concentration of urine during high heat loads – this is simply notice that you are not taking in enough cooling water! Your body is stealing it from your blood and waste stream to send to the skin to cool you. Highly concentrated urine is not advisable.   One doctor consultant that associates with my firm, said urine should always be clear, or nearly clear, otherwise you are not taking in enough liquids.

Once the body cannot properly cool itself, often because of low volume of water, the body temperature rises,  and two types of events can happen quite rapidly. The first, is Heat Exhaustion. The body will be sweaty, often bright red in color, but cool and clammy. The employee may be disoriented, confused, dizzy, have rapid heart beat, high or low blood pressure, have headaches, body aches, nausea, vomiting, or dry heaves.  The employee may or may not express thirst but cool water should be given as much as tolerated.   The employee can pass out.   If removal from the heat, stoppage of the work, cooling of the body, (cool drinks, cool towels and cool environment such as air conditioned area), and constant monitoring of the employee with heat exhaustion does not promptly relieve the symptoms, then the worker should be taken to a medical facility for continued observation, and likely some fluid replacement (IV fluids are commonly given because dehydration is a common part of this problem.)

If heat exhaustion is not noticed, or the symptoms are ignored, or a worker manages to stay in the hot environment without relief and treatment, then Heat Stroke is the next logical and now extremely critical event that can be expected. Heat stroke is always critical, always a severe medical emergency. Heat stroke is defined as occurring when the core body temperature rises above 105-106.0 degrees Fahrenheit. The body systems are in failure at this point. Sweating ceases to occur, and the victim is often red and dry, or pale, blueish, and dry. Generally semiconscious, or unconscious,  the victim’s defense mechanisms that the body uses to provide evaporative cooling have completely shut down, minimal heat transfer occurs, and the body fails to protect the individual from the excess heat. The skin becomes dry and pale.  Breathing may be very shallow or stopped. Cardiac rhythm may be very slow, weak/thready, irregular or ceased.  Coma and death are imminent unless immediate intervention occurs.

In both cases of severe heat exhaustion and heat stroke, the individual must be removed from the hot environment; restrictive or dense covering clothing must be completely removed. Do not hesitate to dump coolers of ice water on the whole upper body and groin area, and/or place icy or cool towels in the armpits, groin, neck, face and head area. Hoses with running cool water can be used to douse the individual. Fans, or air movement to keep the surface of his skin cooling is important, and maintaining cool temperatures around him by moving him to air conditioning, after icing or hosing down has had an effect. In the case of heat stroke, or heat exhaustion with sustained unconsciousness, the paramedics should be called, and infusion of cooled fluid is helpful.    The individual must be placed in an ice bath to reduce the core body temperature to less than 103.0 degrees Fahrenheit; and body fluids must be replenished. If these procedures are not accomplished, and h eat load continued to mount or be maintained, brain damage would begin to occur in just four to six minutes. However with prompt recognition and treatment of heat exhaustion and proper medical attention and emergency reaction to cool the heat stroke victim, both sets of workers, will survive and live a perfectly normal life.

Following a severe heat related episode, it is best for the victim to have a check up for his dehydration, and electrolyte needs, and if the employee has any cardiac or endocrine system issues. Note that employees with preexisting endocrine issues, cardiac issues, or neurological issues, their bodies may have a problem with heat and cooling abilities already. Anticipate heat related ailments in any situation where high heat environments, and workers that have not been routinely exposed and trained to maintain body temperature and acclimatization.

A worker should be warned that caffeine drinks, (especially the newer power or energy drinks) alcoholic drinks, and electrolyte drinks may have a undesirable effect on his/her bodies ability to cool itself.

Also, supervision should have recognized by now, that a worker in heat over 101, high humidity, still air, high reflectivity surfaces (increases radiant and absorbed heat from the sun on the worker), or high radiant environments (dark colored surfaces,  or motorized equipment, steam rooms, boilers, etc.), will need to be monitored extremely closely, because the conditions are not likely to allow normal bodily cooling to work very efficiently. Rest breaks, cool fluids taken in large quantities and often, air movers, insulation or reflection of radiant heat sources, water sprays, cool and reflective (light colored) work clothes, light colored hard hats, and air conditioning if possible. In serious, high heat jobs, piped in air conditioned air may have to be directed on the workers, and ice water cooling work suits are available to help keep bodies from overheating.

In on case, I had workers in the ceiling area of a paper mill with humidity of virtually 100% and temperatures of 125 – 145, working only 20 minutes and then retreating to an air conditioned trailer with monitoring of their core temperature and mandatory fluid intake. Over 60 workers, were well trained, allowed to acclimate, and warned about off duty alcohol and caffeine. The project ran 4 months without incident. A sister job, this time with cool suits (frozen canisters and pumped fluid in a cotton work suit)  allowed the workers to manage about 40 minutes on duty, before a 20 minute break, nearly doubling production. Again, there were no heat related injuries.

Note that many industrial hygiene, enforcement,  and safety personnel talk about the heat indexes and favor a mandatory program to mimic the presumed results based on these theoretical data, and these are often restrictive and unrealistic – especially when you take into account thousands of boiler workers, bakers, engine room mechanics, ironworkers, shipbuilders, roofers, decking crews, and other trades with constant exposures well above the “allowable” in most of these data models.  If strictly followed, many heat index work tables would not allow any (or only very little)  work in many parts of the United States on many days. While the models certainly give us an awareness of the risk of heat related injuries, we should be aware that workers can be overcome with heat in cooler settings, and can also continue to function adequately in very hot and hostile environments, when we acknowledge the methods of acclimatization, and the benefits of bodily and environmental controls that must be monitored to adequately prove what has the best results on a particular job site.

Virtually all heat related incidents are preventable. Understand the mechanisms of cooling, and heat loading in the body, and train workers to practice good ‘keep cool’ techniques and acclimatization, and the risk of heat injuries will be small on your projects.