From the personal protective equipment e-Newsletter, sponsored by
By Ted Nee
Like most firefighters, I used the gear that I was issued and never gave much thought to how it was selected for use by the department. That all changed for me in 1998. While serving as the director of training for the Albuquerque (NM) Fire Department, I was charged by the fire chief to head up our bunker gear specification committee. Since then I have learned what a complex and difficult task protective clothing manufacturers face in providing bunker gear for the fire service.
Bunker gear is a protective ensemble that consists of three basic components: an outer shell, a moisture barrier, and a thermal liner. These components work as a system to provide the necessary protection for firefighters as outlined in National Fire Protection Association (NFPA) 1971, Standard on Protective Ensembles for Structural Fire Fighting and Proximity Fire Fighting, (2007 edition)..
Ideally, we want gear that protects us from the radiant, convective, and conductive heat of structure fires while at the same time dissipating the internal body heat generated while working in it. We want gear heavy enough to withstand the rigors of firefighting but light enough to reduce heat stress. We want gear that allows sweat generated during firefighting to quickly route from the inside to the outside, but that also keeps water on the outside from getting inside. Unfortunately, no protective ensemble can meet all of these competing demands without some compromise in weight or performance. The challenge for us in the fire service responsible for the specification and selection of bunker gear is to determine the right compromises based on the climate, call volume, and firefighting culture of our department. Gear that performs well in the desert heat of an Arizona suburb may not work as well for an urban department in Wisconsin. This article presents some of the key factors to consider when selecting bunker gear.
Thermal Protective Performance
Thermal protective performance (TPP) defines how well the protective ensemble protects the wearer from the thermal environment. NFPA 1971 standard requires a TPP average for the ensemble of not less than 35. The TPP test is conducted by having a convective/radiant heat source with a heat flux of 2 cal/cm²/sec impinged on the outer surface of a four-inch by four-inch area of the fabric. Heat is applied for a specified amount of time to reach the equivalent of a second-degree burn (131ºF) at the calorimeter on the other side of the fabric. The time (in seconds) is then multiplied by the heat flux of the exposure, which gives the TPP rating of the system. A 17.5 second exposure multiplied by a heat flux of 2 cal/cm²/sec equals the minimum TPP of 35. The higher the TPP number, the more thermal protection the garment provides.
Several thermal classification systems have been developed to define the types of thermal environments faced by firefighters. The International Association of Fire Fighters (IAFF) developed one system of thermal classification of structure fires under the project FIRES. According to these criteria, structure fires can be distinguished by their temperature range and rate of heat output (heat flux). Each class of fire can be associated with a structural firefighting situation and its expected average duration.
Class I occurs in a room during overhaul. Environmental temperatures up to 100°F and thermal radiation up to 0.05 watts/cm2 are encountered for up to 30 minutes.
Class II occurs when a small fire is burning in a room. In this case, environmental temperatures from 100°F to 200°F and thermal radiation from 0.050 to 0.100 watts/cm2 are encountered up to 15 minutes.
Class III occurs in a room that is totally involved. Environmental temperatures from 200°F to 500°F and thermal radiation from 0.100 to 0.175 watts/cm2 are encountered up to five minutes.
Class IV occurs during a flashover or backdraft. Environmental temperatures from 500°F to 1500°F and thermal radiation from 0.175 to 4.2 watts/cm2 are encountered for approximately 10 seconds.
Bunker gear must protect firefighters over a wide range of thermal environments from the routine to the emergency. To do this, the ensemble works much the same way a goose down jacket. Air is trapped in the thermal liner and creates a “dead” air space. Air is a poor conductor of heat and thus is a good insulator. And like a goose down garment, bunker gear loses some of its thermal protection if the thermal liner is either saturated with moisture or compressed. Water, being a good conductor of heat, can displace the “dead” air space and defeat the system. It’s easy to see why NFPA 1971 standard and the industry have focused so much attention on dissipating moisture generated internally by the wearer and preventing external moisture from penetrating into the thermal liner. Thermal protection can also be compromised when air is compressed out of the garment. Some of the more common burn injuries seen in firefighters (shoulders, knees, and biceps) have been attributed to compression of their gear during firefighting activities.
Once the protective ensemble has absorbed all the heat that it possibly can, any additional heat is passed through the gear to the wearer. This is important to note for several reasons. First, if firefighters are working through multiple work cycles at the same incident (or in training), gear must be opened up and the accumulated heat must be allowed to dissipate before they reenter the hot environment. Second, if a firefighter’s gear is heat saturated, as in the case of exposure to a class IV thermal environment, it is important to get the firefighter’s gear off as soon as possible, even if the gear is burning. Hitting a firefighter with a hose stream or a gloved hand to extinguish flames can compress the thermal layer or cause steam burns to the firefighter. The tragic line-of-duty death of instructor Robert Gallardy from thermal injuries while conducting live fire training at the Pennsylvania Fire Academy on October 23, 2005, highlights the need to allow gear to cool between exposures to high heat levels.
A thicker thermal liner creates a larger dead air space and a more thermally protective garment. There is a trade-off for better thermal performance: a bulkier, less ergonomic garment that may retain more of the heat generated by the wearer.
Total Heat Loss
Total Heat Loss (THL), is a measure of breathability, defined as watts per square meter (W/m2). A higher THL indicates that the bunker gear is more breathable–it allows more flow of heat and moisture to the environment. The 2007 edition of NFPA 1971 requires that the three-layer ensemble provide a total heat loss of 205 W/m2 as a minimum. The higher the THL value, the better the garments breathes. A high THL value should provide some measure of protection from heat stress. It is possible to obtain high THL numbers by using a combination of lighter outer shell materials, thinner thermal liners, and permeable moisture barriers.
Thermal Protective Performance Versus Total Heat Loss
There is an inverse relationship between TPP and THL–as one value goes up, the other goes down. Gear with high TPP values may lead to problems with heat stress, whereas gear with high THL values may not provide adequate thermal protection. The key is to find the correct balance of THL and TPP values for your department. This requires an honest assessment of the thermal environments your department is likely to work in, as well as the local climate. If most of your firefighting operations are conducted from the exterior and you live in a hot and humid area of the country, a higher THL number may be more important than a high TPP value. On the other hand, if you conduct largely offensive interior firefighting in a colder, drier area of the country, a high TPP value may be the better choice. In a perfect world, we would spec out both summer-weight gear and winter-weight gear.
Recent research into moisture transport in bunker gear conducted at the University of North Carolina suggests that what you wear under the gear is an important consideration for firefighters. A non-wicking cotton tee shirt worn under bunker gear tends to lead to high levels of sweat being transported into the thermal liner. Search and rescue personnel call cotton the “killer” fabric, since it robs the body of heat when it becomes wet. There are various weights of synthetic and natural fabrics that don’t absorb sweat and that are flame resistant that may be better choices to wear under your turnouts.
Conductive and Compressive Heat Resistance
The NFPA 1971 requirement is that the Conductive and Compressive Heat Resistance (CCHR) rating of shoulder and knee areas, when compressed, must equal the established base garment rating. This is intended to ensure that the shoulder and knee areas will provide the same level of protection when compressed as the rest of the garment. The CCHR rating is the time in seconds to achieve a temperature rise of 24°C. The minimum requirement established in the 2007 edition was 25 seconds, which was arrived at by testing a garment with a TPP of 35 on a hot plate set at 280°C, under a pressure of 1/2 psi. The shoulder area is tested under a 2 psi load, simulating a firefighter wearing an SCBA. The knee area is tested under an 8-psi load, representing the amount of force that a 180-pound firefighter would exert in the kneeling position. CCHR values are usually achieved by adding additional material to the thermal lining in the knee and shoulder areas.
Weight and Tactile Performance
Performing well in laboratory tests doesn’t guarantee that the gear you select is going to work well for you. Gear that fits and feels right is just as important as having the right balance of test values. The good news is that the personal protective equipment industry has spent a lot of time working on the ergonomics of firefighting ensembles. Each of the manufacturers has developed different strategies to provide better freedom of movement and range of motion in their products. Participants of events like the Firefighter Combat Challenge, who demanded a more athletic cut to their competition gear, have spurred the push for more ergonomic bunker gear.
Lighter weight gear may be more comfortable to wear and less likely to lead to heat stress, but weight alone shouldn’t be the determining factor in gear selection. During one of the bunker gear evaluations we conducted in Albuquerque, one of our evaluators wanted to select one ensemble over another based on a weight difference of a few ounces. I asked the firefighter to bring in his personal bunker gear and to empty all of the pockets. When we finished weighing all of the tools, lights, and webbing he was carrying, the gear topped out at more than 10 pounds. In the big scheme of things, the additional two ounces didn’t seem so important.
July 3, 2007 Close Call
The following incident that occurred in Albuquerque on July 3, 2007, highlights the importance of selecting the right gear for the job and making sure that the ensemble is worn right at every incident. On the morning of July 3, 2007, Albuquerque Fire Department Engine 5 was dispatched to a reported vehicle fire. What the hysterical caller failed to mention was that he had severed a gas meter and that his pickup truck was in the middle of a natural gas-fed fire with a two-story apartment building as an exposure. When the Engine 5 captain realized all this, he requested a first-alarm assignment and proceeded to have his crew evacuate the apartment building. In the course of evacuating the structure, a natural gas explosion occurred and one of the Engine 5 firefighters was enveloped in a ball of flame. Firefighter Brian Barnes was also thrown against a fence by the force of the explosion. Several firefighters then pulled Firefighter Barnes to the safety of the street. Brian Barnes spent one night in the hospital as a precaution and suffered only a minor burn injury to one hand.
I took the following photos the day after the incident. You can see that his firefighting hood suffered thermal damage (photo 1). You can also see where the turnout coat and reflective trim that were not protected by the SCBA cylinder were damaged (photo 2).
Photo 1
Photo 2
References
National Fire Protection Association, NFPA 1971 Standard on Protective Ensemble for Structural Fire Fighting and Proximity Fire Fighting: 2007 Edition, NFPA 1971-2007, Quincy, MA, 2007.
Career officer injured during a live fire evolution at a training academy dies two days later – Pennsylvania, NIOSH F2005-31 Oct 23, 2005
Evaluating the Effects of Moisture on the Thermal Protective Performance of Firefighter Protective Clothing in Low Level Heat Exposures. Annual Report; 94 p. December 2001. North Carolina State University
Fatal Training Fires: Fire Analysis for the Fire Service. Interflam 2007. (Interflam ’07). International Interflam Conference, 11th Proceedings. September 3-5, 2007, London, England, 1-12 pp, 2007. Madrzykowski, D.
Ted Nee is a 25-year veteran of the fire service. He worked his way up the ranks of the Albuquerque (NM) Fire Department to the position of Deputy Chief of Operations before retiring in 2003. He is an instructor with the Emergency Operations Organization at Sandia National Labs, where he conducts proficiency training with the Emergency Response Team. Nee is also a senior instructor with the New Mexico Firefighter’s Training Academy, Socorro, New Mexico.
