Hey, it's way too hot in here!
In Harm's Way
Risks to people inside Level A1 full body protective clothing are many, but one of the most dangerous may be heat stress or heat stroke. Heat Stress is a medical condition during which the body's heat control mechanisms cannot cope with the surrounding heat load, causing a rise in the person's core body temperature over 39° C2. Heat Stroke is a medial condition during which key bodily functions shut down, which can lead to death, and usually, if the person does not die, may leave them with a diminished capacity to handle heat in the future. In 2000 in the U.S. 21 workers died and 2,554 experienced heat-related occupational injuries.
It's Not Just in the Summer
Of course the dangers are most prevalent when the outside atmosphere is at high temperature and/or humidity, but inside a Level A suit, the occupant can easily be subject to heat stress during relatively cool or dry outside temperatures. Think for a moment of some of the reasons a Level A suit might be worn. The person inside may be performing cleaning operations at a post office contaminated with a white, powdery substance; cleaning or repair inside a solvent tank; or entering a zone where a fire has taken place, in order to do search and rescue. In all these cases it is easy to see that some range of motion is required, and some caloric output will be used to accomplish the desired mission. The more rigorous work performed inside the suit, the hotter it gets. Level A suits are good at not letting contaminants in, but they are also good at keeping heat generated by the body from dissipating in the atmosphere. The result is their occupants can cook like popcorn in a microwave popcorn bag.
What can be Done?
The outside temperature has some bearing on how long one can work in a Level A suit. With or without protective clothing, the accepted area method for assessment of how much work can be done without the dangers of heat stress calls for a WBGT monitor. That acronym, WBGT, stands for Wet Bulb, Globe, Temperature. The WBGT monitor is an instrument designed to take a weighted average of various heat loads on a body from the surrounding atmosphere. It can take into consideration the ambient temperature, the humidity, and the effect of radiant heat from the sun or other heat source (blast furnace, oven), and yield an overall number which can be used to predict how long people can do certain levels of work in that environment. However, the WBGT instrument by itself cannot take into consideration several personal factors concerning a specific person in a Level A Suit, such as their age, gender, body type, physical conditioning, amount and type of clothing being worn etc. If one needs a good way to assess for those factors as well, it would be wise to turn to a personal heat stress monitor.
In use over the past 10 years, commercially available personal heat stress monitors have allowed people to engage in work inside Level A suits and have some degree of protection from heat stress. There is the type that was developed by The John Hopkins University and which has been used by the astronauts. It is a small pill-size device which is ingested and travels all the way through the digestive system, recording deep body temperature along the way and transmitting it outside the body to a receiver. Although these pills are relatively inexpensive, and do work, not all people want to swallow a radio transmitter.
Another type of instrument utilizes measurements of body temperature in the ear. The theory is the ear is close to the hypothalamus, the part of the brain that regulates deep body temperature. Hospitals often use body temperature measurement done in the ear with infrared devices because they are quick and fairly accurate. A patented device, commercially available and intended for use by people who are occupationally exposed to high heat environments utilizes temperature measurement in the ear. After the device is calibrated, using a conventional oral type thermometer (in the same environment where it will be used), it will record accurately the person's temperature as measured in the ear, and send this temperature along wire connected to a belt-mounted device which can be set for certain temperature levels. When the pre-set temperature maximum for the person being measured is hit, the instrument will set off an alarm in the earpiece telling the person that they are in danger and need to take action to reduce their deep body temperature. These devices have been tested3 by researchers from NIOSH (National institute of Occupational Health and Safety) and found to be effective in that regard.
A third type of instrument was developed by the Electric Power Research Institute (EPRI) who represent workers in power plants and outdoors maintaining transmission lines. It is commercially available under license from EPRI. In the power industry's hotjobs, workers can over heat and cause a heat strain reaction. Research done by the Coast Guard indicated that recovery heat rate was the best physiological measurement of heat strain. Recognizing that, the American Congress of Government and Industrial Hygienists (ACGIH) published in 2000 a Threshold Limit Value or TLV®â calling it the heat stress and strain TLV. The strain portion of this index is computed using the heart rate monitor, which, in conjunction with skin temperature measurements, produces a more composite picture of how the body is reacting (heat strain) to the heat stress environment. This type of instrument, as well as the one with the ear probe, can be used inside a Level A suit, and both can be purchased by Federal government agencies on-line via GSA Advantage.
Fourth, and developed in conjunction with the US Department of Energy, a commercially available system is available which uses wireless technology to send data from sensors inside the suit to a laptop computer attended by a person monitoring workers in the same general area of those working inside Level A suits.
No perfect solution
There is no perfect solution to this problem. The devices mentioned herein are all commercially available and, except for the wireless one, have been used successfully for years to avoid worker injury in hot environments. However, their success is dependent on, like anything else, whether they are properly calibrated, utilized and maintained. They can be a line of defense against the perils of heat induced injury, and can provide some warning against the dangers that lurk inside Level A suits.
Footnotes:
1. Level A personal protective equipment consists of a self
contained breathing apparatus and a totally encapsulating chemical protective suit. Level A personal protective provides the highest level of respiratory, eye, mucous membrane and skin protection.
2. A World Health Organization (WHO) expert panel recommended a peak value of 39C under closely monitored conditions and 38C for steady state exposures. The American Conference of Governmental Industrial Hygienist (ACGIH) recommends 38.5C to allow a margin of safety for peak exposures. Assuming that heat stress exposures are intermittent with time for recovery allowed between exposures, a transient increase in core temperature to 38.5C is safe. The average core temperature for the day, however, should not exceed 38C. See page 10 & 11 of Chemical Protective Clothing, Managing Heat Stress, 2nd edition, 2002 by Thomas E. Bernard and Frank N Dukes-Dobos, published by The AIHA Press.
3. Applied Occupational and Environmental Hygiene Journal, September 1992, "Case Studies, Personal Heat Stress Monitoring", pps. 567-571
About the Author:
Dan Webster is President of Quest Technologies, an employee owned company specializing in industrial hygiene instruments and software for the occupational safety and environmental markets. Mr. Webster has a B.S. in Industrial Distribution from Clarkson University, and an M>B>A> from the University of Albany. He has 20 years of general management experience in instrumentation, and spent 23 years with Perkin Elmer. Mr. Webster served as a US Naval Officer during the Vietnam War, and is a member of the American Industrial Hygiene Association and the American Marketing Association. His email address is dwebster@quest-technologies.com and daytime phone is 262/567-9157 ext. 124
