"Two Firefighters Succumb to Heat" were the headlines of a newspaper article the day after a chemical spill at a loading dock. The firefighters were entry team partners of mine from our hazardous material response team when we responded to a spill of formalin, a liquid consisting of formaldehyde, water, and methanol. A dock worker at a central facility at our local university dropped a cardboard box containing four-one liter bottles and the leak quickly soaked and spilled around the box. Being highly toxic and a carcinogen the workers cleared the area and called for help. Our fire department responded and the hazmat team decided to suit-up in Level A to make an entry and make an assessment.
The critical factor in this incident was the weather. We were in the middle of a heat wave that not only brought high temperatures but also high humidity. The day of the spill the temperature was well into the 90's by 1100 hours with a 40% humidity level. When our entry was made shortly before noon the heat index, a value that combines heat and humidity, made the environment feel like 95F. Still, we forged ahead by suiting up our three-person entry team. As we entered the hot zone and before we were in the building one of our team members motioned that he had to exit. The entire team abruptly turned and exited the hot zone. Shortly after we peeled off our Level A suits we learned that our teammate was suffering from extreme heat exhaustion. As he was attended to by paramedics the other teammate and I re-suited and re-entered the hot zone.
We located the spill area and began to containerize the broken bottles when my partner communicated to me that he also had to exit. We hurriedly left the area and underwent decontamination. We both doffed our suits and my partner was promptly treated by other paramedics. As a result of wearing Level A suits and in response to the extreme heat burden both of my partners were treated on location with intravenous (IV) fluids and cooling measures. Both entry members were transported and kept overnight at a hospital because of heat exhaustion. I was lucky-in comparison: I endured minor heat stress from the hazmat emergency. Another factor that contributed to these heat injuries was that the two firefighters who were transported were dehydrated from alcohol consumption the day before from attending a golf outing.
The time of year to raise our awareness to the signs of heat stress is upon us. The effects of heat on the human body can be devastating and life threatening for both firefighters and hazmat personnel. For firefighters heat stress causes more demand on the heart and the body's cooling system and if heat is not dissipated can lead to severe health problems such as heart attack. Likewise, hazmat personnel in chemical suits also endure a high heat load during hot weather. In fact, many more injuries occur to hazmat personnel as a result of heat stress than from chemical exposure each year. To better enable responders to avoid and manage heat stress, prevention measures and strategies need to be developed and employed.
Perhaps the first place to start is with the signs and symptoms that are displayed by a person under heat stress or hyperthermia. The following is the progression of heat stress if undiagnosed or untreated.
A minor form of heat stress resulting from clothing irritating skin due to moist and hot conditions. Easily treated by good personal hygiene and clean, dry clothing.
Moderate dehydration can cause muscles to cramp or have spasms. Treatment includes proper hydration and a diet with adequate salt can assist in preventing cramps.
This is the most common type of injury incurred by hazmat personnel. It occurs with loss of fluids by perspiring and can also result in cramps. Profuse sweating and lack of energy are also signs of early heat exhaustion. Treatment is with proper fluid replacement and cooling of the body.
This is the most dangerous form of heat stress with complete failure of the body's ability to cool itself. Signs include extremely elevated body temperature, hot, dry, and red skin, disorientation to unconsciousness, and muscle spasms to convulsions. Treatment includes rapid fluid replacement including IV's, cooling, and transport to the hospital.
Recognition of each stage of heat stress can prevent a dire emergency from occurring. Proper response can avert a bigger problem later.
It is also important to monitor the weather and keep an eye on heat stress conditions. Particularly, weather with high temperatures along with high humidity increases the cooling load on the body. Dew points, the temperature at which atmospheric water condenses, above 70F are very humid days that should activate aggressive personnel cooling techniques.
Weather conditions above 80F and 40% humidity make the apparent temperature feel warmer. For this reason heat indexes have been developed to better indicate the heat load on a human. These charts are available from many sources and they should be accessed by responders to better monitor heat stress to personnel.
Probably the best method of controlling heat stress is through prevention measures. The following are some methods that can be employed to avoid heat stress problems.
1. Personal Conditioning.
A physically fit person can tolerate heat stress better than a person who does not exercise and eat properly. In short the physically fit have better circulatory systems and can dissipate heat better.
To help ensure only medically fit personnel are allowed on-duty for firefighting many departments have mandatory medical monitoring programs. The National Fire Protection Association Standard for Fire Department Health and Safety Programs (NFPA 1500) recommends annual physical exams for all firefighters. The exams include several tests that provide a basis for good health and should assist personnel in heat tolerance. Additionally, all personnel who belong to a hazmat response teams are mandated by federal law to participate in a annual medical monitoring program.
On-scene Medical Monitoring
Even though no federal mandates or national standards exist to do so many hazmat response teams conduct pre-entry medical monitoring for entry personnel at each emergency. These screenings are designed to determine if personnel are fit for duty in chemical clothing. (Since these screenings contain medical information they must remain confidential between the medical care-giver and the entry person.) The medical care-giver makes a determination as to whether an entry person is fit to wear chemical clothing usually based on accepted guidelines. These guidelines would preclude entry or the wearing of chemical clothing by any person if values are above the following:
Source; National Fire Academy (NFA) Hazardous Materials Site Practices, Hazardous Materials Strategies and Tactics by David M. Lesak
Also, all personnel need to be medically evaluated after work missions using the same parameters as above and this is when heat stress problems need to be aggressively corrected. Additionally, many hazmat response teams check for weight loss and EKG's to monitor personnel. The EKG interpretation is at the discretion of HazMat EMS and the guideline for weight loss should not exceed 1.5% body weight of an individual. Finally, personnel who are actively taking antihistamines such as Actifed or Benadryl may have an impaired ability to sweat and may not be suited for entry in chemical clothing. It is the responsibility of the entry person to inform medical control with this information.
In order to endure heat it is recommended to be in the heat for prolonged periods to get "used" to it. The human body adapts to its environment in a short period of time and heat adaptation is no exception. So, rather than remain indoors during hot weather it behooves responders to endure the hot weather conditions, at least for short durations, to better adapt. A heat acclimated responder is less prone to encounter heat related problems.
3. Pace Reduction
Hot weather saps energy so a consistent pace of work activity, at least slower than normal, will help to prevent heat stress. When it comes to hazmat response where personnel will work in chemical clothing many teams decrease the work duration period according to the heat stress. Quite often Level A attire utilizes one-hour capacity air bottles with the self-contained breathing apparatus (SCBA). While one-hour bottles provide up to 40 minutes of air duration while working many teams limit the on-air time to 20 minutes maximum for safety reasons. With this in mind heat stress situations would further decrease the maximum time in order to avoid undue heat related problems to the wearers of chemical clothing.
The following is an accepted guideline for decreasing on-air time in respect to the heat burden;
Source; National Fire Academy Hazardous Materials Site Practices, Hazardous Materials Strategies and Tactics by David M. Lesak
Hot weather could find teams limiting their personnel to 10 minutes while inside a suit. This limitation may require more responders to rotate entry and back-up assignments to complete strategic objectives. Finally, the NFA also recommends that entry personnel rest and rehabilitate for the following periods after an entry for a specified temperature.
Monitor your Input
The intake of water is critical in response to heat stress, not only before being in the heat but also during an activity. Since the human body is largely made up of water good hydration must be maintained to perform critical bodily functions. Drink plenty of water and often is the key! The National Institute of Safety and Health (NIOSH) recommends ingesting up to 16 ounces of water before a heat inducing activity and then 8 ounces every 20 to 30 minutes during the activity to maintain good hydration. Do not depend on thirst to indicate when fluids should be taken; at the point of feeling thirsty a person is already playing catch-up. Water is best, especially for short duration activities, but sports drinks can assist with rehydration. Sports drinks, as a result of their ingredients, are critical for long duration activities that last more than 60 to 90 minutes.
Avoid fluids that contain alcohol and caffeine as they are diuretics and can cause depletion of water through the kidneys. Also avoid carbonation because it can cause gastric distress and inhibit the absorption of water in the intestines. Fruit juices or drinks high in sugar and carbohydrates can also prevent the absorption of water in the body. Research has indicated that a lightly salted and low carbohydrate solution is best at rehydrating the body. The Gatorade Sports Science Institute indicates the ideal rehydration drink would be one that has about 6% or 14 grams of carbohydrate per 8 ounces, a blend of sucrose, glucose, or fructose for flavor, approximately 100-110 milligrams of sodium, and no caffeine or carbonation. Obviously, in the absence of a sport drink water will be adequate.
One last precaution with fluid intake is that too much water can be ingested and cause a problem known as hyponatremia. While more common in log distance runners and cyclists this condition lowers the blood sodium levels and can lead to heart malfunctions.
Monitor your Output
A well hydrated person will urinate often and the color of the urine should be straw colored or light yellow. A dehydrated person may not urinate for several hours and the urine will most likely be deep yellow in color. If this is the case hydration needs to be increased. The dehydrated person is also at extreme risk of a heat related illness if called upon for emergency service. Drinking proper fluids should be undertaken immediately. In extreme cases IV's may be the best and fastest course of action to rehydrate a person. Personnel who have recently consumed alcoholic beverages are prime candidates for heat related problems as alcohol is a diuretic. Alcohol consumption stimulates the kidneys to produce urine and this body fluid loss can produce a 3% loss of body weight within four hours of ingestion. The resulting dehydration has a negative effect on performance and endurance and greatly increases the risk of heat illness. Personnel should notify team leaders if their personal hydration is a question.
5. Engineering Controls
The last line of defense to prevent heat stress problems with personnel is with engineering controls. These are outside of the body devices that assist with the cooling process. They include;
- Fans-the moving of air is very effective at cooling skin through the evaporation process. However, the movement of hot air can actually increase heat stress of personnel so the addition of a water mist can aid in the cooling affect.
- Air conditioning-Artificially cool environments obviously aid in cooling personnel.
- Cold packs- can be used to cool personnel by application under arm pits and can be used in cooling vests.
- Cooling vests-can be useful for short term cooling of personnel.
- Cooling suits-effectively cool the whole body (thorax and extremities) of the wearer for long periods of time. One drawback is they are expensive and add to the weight burden but their use has been proven to be effective for heat stress prevention.
Outside of the obvious methods of controlling heat stress such as staying out of the sun, wearing clothing that shields the sun, avoiding hot surfaces such as asphalt, and others the above methods, when employed regularly and consistently, should greatly decrease the chance of heat stress problems to personnel. Well hydrated personnel should be able to withstand heat stress better and stay on the job longer without health consequences.