UNDERSTANDING TURNOUT TECHNOLOGY: A MATTER OF HEALTH AND SAFETY
Photo by Becky Gerard.
Protective clothing can be likened to tires on a pumper: Every fire department has them, but how many administrators or firefighters understand differences in tread design, rubber compounds, ply patterns, wheet and rim types, and certified load ratings? About the only time most departments think about tires is when they wear out—and then they simply buy new ones.
Unfortunately, in all too many departments the same is true about fire clothing. How many purchasers understand fabric weaves, TPP ratings, pattern design, heat stress management, dynamic and static firefighter loading, and after-char length of shell materials?
With both tires and fire clothing, firefighter health and safety directly are related to how the product performs. How well a tread pattern grips a wet road may mean the difference between a screeching but safe stop and a multiple-fatality collision. Not evaluating fire clothing materials and gear design and not integrating the evaluation with a particular department’s operations can increase the possibility of firefighter thermal burn injuries and heat stress.
Before making a protective clothing purchase, it is important to define the problems inherent in providing the best firefighter protective envelope possible.
Fire clothing originally was designed to keep firefighters dry as well as warm in cold weather. Long rubber coats and pull-up boots were used by the fire service almost exclusively as the first line of protection until the 1940s. Even though many departments practiced interior attack in those years, clothing was designed simply to keep water from wetting the firefighter. During and after World War II, cotton duck clothing with thin, waterproof liners replaced rubber materials in many departments.
As indirect interior attack tactics became popular in the late 1950s and early 1960s and interior operations became more widely practiced, a rapidly increasing firefighter burn injury rate made officials look at the problem of how to provide effective protective clothing.1 The National Aeronautics and Space Administration (NASA) began an effort in the late 1960s to transfer for commercial use technology developed from its space program research.2 This research made available to the fire service new man-made, fire-retardant fabrics such as Nomex®, FBI®, Durette™, Kynol™, and Kevlar®. They were tested in the marketplace, and by the early 1970s, clothing constructed of Nomex readily was available to the fire service. In 1971, NASA began a program to utilize additional technology to develop state-of-the-art protective clothing for structural firefighters. Along with funding from the U S. Fire Administration, NASA began Project FIRES (Firefighters Integrated Response Equipment System), a program that attempted to address the problems of heat stress as well as develop additional clothing protection from flame and heat.
About the same time, the National Fire Protection Association, along with fire administrators and manufacturers, developed a tentative standard on protective clothing for firefighters, which in 1975 evolved into NFPA 1971, Standard on Protective Clothing for Structural Fire Fighting. While the NFPA standard set minimum recommendations for clothing design and construction, the Project FIRES program focused much of its research on adopting new technology to increase firefighter thermal protection and reduce stress.5
NFPA 1971 addressed the problem of firefighter thermal protection by specifying limits of material flammability and insulation levels. This standard has been adopted by all manufacturers and serves as the benchmark for minimum specifications for practically all fire clothing manufactured in the United States today. The standard was updated in 1981 and 1986, and the present edition was adopted in 1991.4
While the first edition of NFPA 1971 set minimum construction requirements for conventional garments, the Project FIRES program worked to develop a clothing ensemble that performed on a more practical level. In 1983, after a series of garment design changes and inclusive tests, the management of the Project FIRES program was taken over by the International Association of Fire Fighters, which worked in conjunction with clothing manufacturers and the USFA to develop workable clothing designs as well as definitive testing procedures.
Members of the Project FIRES team as well as testing labs worked with the National Bureau of Standards to design a definitive test for thermal protective performance (TPP), which is used to quantitatively evaluate fabrics for thermal protection. This test measures the amount of protection from heat transfer through protective clothing layers in conditions approximating those of a flashover situation. A minimum value of 35 TPP is required by both the Project FIRES and NFPA 1971 criteria. This relates to providing approximately 17 seconds of protection before suffering seconddegree burns in a flashover-like heatloading situation.5
For evaluation purposes, manufacturers test the outer shell, moisture barrier, and thermal insulating liner materials together to determine a garment’s TPP rating. In practical terms, the higher the TPP rating of a garment, the more insulation it provides.
A turning point in the protective clothing industry came in 1985, when the Project FIRES testing advanced the theory that thermal protection alone should not be the only criterion tor fire clothing. While thermal protection is extremely important, the report pointed out that more firefighters are killed and injured as a result of physical stress (heart attacks, heat exhaustion, etc.) than burns.
Firefighter death statistics compiled by the USFA for 1990 show 105 Iine-of-duty deaths but only one caused by thermal injuries sustained in a structural fire. More than 50 percent of the deaths were caused by heart attacks. In a study due to be released this summer, the USFA is examining stress-related injuries and deaths, including heart attacks.
As fire service officials begin to focus on the effects of heat stress, more attention is being paid to engineering turnout clothing to help reduce weight and move more heat away from the firefighter’s body. It is important for firefighters to understand how the body absorbs heat and in turn eliminates it. The body normally generates heat as a product of calorie consumption and dissipates excessive heat by sweating. As sweat evaporates from the skin, it lowers the skin’s temperature.6
In the past, it was general practice to specify garments having high TPP ratings. While high TPP ratings provided a high level of thermal protection, they also caused the firefighter to sweat more. The additional insulation of the garment also tended to hold the firefighter’s body heat inside, making the wearer even more uncomfortable and contributing to a high probability that the wearer would develop heat-stress injuries.
Other factors can work to raise the temperature of the human body. As the body reacts to physical workload, more calories are consumed and more heat is generated as a by-product. Adrenaline release sharply intensifies calorie consumption, resulting in more heat generation. Finally, the body can absorb the excessive environmental heat bombarding it.
Now, we begin to see a problem. Firefighters don turnout clothing and answer an alarm. Heat is being retained around their bodies by the insulating properties of their gear. About a block from the scene, the dispatcher radios the unit that there are multiple telephone reports of peopic trapped. Now the firefighters’ adrenaline begins to flow! The engine rounds a corner, and flames can be seen and screams heard. Another shot of adrenaline. The engine stops, firefighters make a quick size-up, pull a line, don breathing apparatus, and advance the line to the second floor. All these physical activities consume a great amount of calories, generating even more heat. As they push the line down the hallway, members are met with a wall of heat, generating even more heat energy around their bodies.
The firefighters’ minds are racing: How much time do they have before the fire banks down? They can hear the trapped victims’ screams but cannot tell exactly from where they are coming. What about the integrity of the floor or the ceiling? What if they encounter a locked door, requiring a higher level of physical activity in a red-hot hallway as they pound and pull halligan bars?
(Photos by author.)
How is the body reacting to all this punishment? It is attempting to cool itself by sweating. How effective the sweating process will be depends on how much sweat is removed from the body. This is where the protective ensemble comes into play.
Clothing can contribute to heat stress by entrapping body heat, which in turn reduces the body’s attempt to regulate its temperature by sweating. Heat stress becomes critical when the amount of heat generated by the body cannot be dissipated through the clothing. Properly designed turnout clothing can help remove sweat from the body in three ways: vapor transmission into and out of the garment, ventilation of the garment, and sweat absorption by insulating materials.
Many factors enter into the heat stress equation during a fire situation such as the one described above. Studies have shown that an overall reduction in heat stress can be accomplished in a number of ways.
- Reduce static loading (garment weight).
- Reduce dynamic loading (hobbling, or garment’s restriction of movement).
- Use materials that provide high levels of vapor movement along with an acceptable level of insulation. “*
- Provide adequate ventilation of the fire environment to transmit heat away from personnel.
- Provide adequate training so personnel can recognize limitations in protective clothing and operating in marginally survivable firefighting environments.
The first three items relate directly to the design and construction of protective clothing, while the last two deal with operations and training. Because of the scope of this article, we will deal only with the protective clothing aspects of heat-stress protection.
REDUCING STATIC LOADING
The more weight a firefighter carries, the more energy he/she expends making simple movements such as walking, and the more heat the body generates. Wearing the lightest weight clothing possible will begin to reduce body-generated heat in tactical situations. The same clothing must provide a certain level of protection from heat and flame.
Generally, the trend among departments that have extensive testing programs is to reduce garment weight by specifying materials that are lighter in weight and provide a TPP level of around 40. Of course, static loading also includes the weight of boots, helmets, breathing apparatus, and even the equipment the firefighter carries in clothing pockets. Thus, any program to reduce static weight should focus on these items as well.
One example of how manufacturers are attempting to reduce static loading is the introduction of shorthem coats. Worn with matched pants, the combination provides an acceptable level of overlap protection in the waist area without the excessive weight of the additional and unneeded longer coat hem.
REDUCING DYNAMIC LOADING
As the firefighter moves about dressed in protective clothing, any movement restriction induced by the clothing can cause the body to expend more energy to overcome the restriction. This restriction, known as hobbling, is caused by either poorfitting or improperly designed gear. For example, if raising a knee pulls the fabric tight around the knee and further movement requires the garment to ride up, this is hobbling. It may be caused by pants that are too small for the wearer, knee or seat areas that do not have enough material, or a crotch that does not fit snugly to the wearer.
Test for hobbling in the arms by raising them over the head and watching the hem of the coat rise. How much the hem of the coat rises (measured from the floor to the bottom of the coat) from the at-rest to armraised position determines the amount of movement restriction. The more the coat rises, the higher the dynamic loading. Each time the arms are raised, the weight of five inches of overlap materials can add a static weight of about two pounds; the action of raising the arms, such as when pulling a ceiling, adds a hobbled dynamic load to the firefighter’s upper body. If a large amount of ceiling needs opening, the firefighter possibly could reach over his/her head 100 times during the operation. This would cause the firefighter to expend the energy of moving an additional 200 pounds during the course of the operation.
If improperly designed or poorly sized turnout pants cause the leg to bind when the knee is raised, additional energy will have to be generated to overcome the restriction to leg movement and to lift the weight of the leg, boots, and clothing.
Manufacturers are responding to the stress-reducing needs of the fire service by offering a wide array of clothing specifically designed to integrate the design of the pant-and-coat ensemble.
Turnout clothing is constructed of three layers: the outer shell, the moisture barrier, and the thermal liner.
Outer Shell. The outer shell provides the first line of protection against flame and heat as well as wear and abrasion protection for the interior layers. Because of the wide variety of fabrics now offered, selecting an outer shell material can be an intimidating task. You should have a basic knowledge of yarns, weaves, and weights before making a purchasing decision.
Nomex, a popular outer shell material, belongs to a family of syntheticfibers called aramids. It is flexible, strong, relatively lightweight, and offers good protection from heat and flame. Nomex outer shell materials are available in two weights: 7.5 oz. per yd and 6 oz. per yd2 Manufacturers offer the 6-oz. material in a ripstop weave to help prevent tearing. Nomex material also is offered in a version coated with fire-retardant neoprene.
PBI, or polybenzimidazole, of a family of fibers called azoles, was introduced to the fire service about nine years ago. Fabric manufacturers blend PBI fibers with Kevlar fibers (like Nomex, Kevlar is of the aramid family) to enhance strength and then weave the resulting material in a ripstop pattern. PBI outer shell materials are available in weights of 7.5 and 6 oz/yd2. They offer strength, good flexibility, and high flame and heat resistance.
Suppliers now are offering a selection of materials constructed of blended fabrics. One such product, Advance™, blends 50 percent Nomex and 50 percent Kevlar in an effort to improve flexibility after heat exposure. Another product, AraMax™, constructed of yarns with a Kevlar core that are wrapped in a Nomex sheath, was designed to address fabric strength after heat and flame exposure. A new family of fibers, called polyimids, now is being blended with Kevlar to produce a fabric intended to address after-flame shrinking and crisping.
Moisture hairier. The moisture barrier prevents liquids from passing from the fire environment to the wearer. These barriers are available in two types: impermeable and expanded membrane polytetrafluoroethylene (PTFE). Impermeable barriers consist of a coating of fire-retardant neoprene on either fire-retardant poly-cotton or rip-stop Nomex lightweight cloth. Unless punctured or worn, they will not permit vapor or liquid transmission into the thermal liner. They also will not permit sweatladen vapor to diffuse outside the thermal liner.
Expanded membrane PTFE liners such as Gore-Tex® and Tetratex® stop liquid travel into the protective envelope, yet their porous fiber construction will permit the escape of vaporized body sweat to the outside of the coat. They are available laminated on a variety of fabrics that provide additional insulation protection. PTFE liners are about half the weight of impermeable barriers, which helps reduce static loading and aids in diffusing sweat vapor.7
Studies have shown that in a highheat, high-humidity fire environment, for example, when handling the nozzle during interior knockdown, atmospheric conditions may limit the amount of sweat vapor the PTFE can transmit.8 Manufacturers of impermeable barriers have used this research to promote their products, saying that PTFE’s vapor transmission capability is of little consequence in reducing heat stress during a fire situation. But be aware that the limited focus of the research did not take into consideration operations during other fire and emergency scene duties. Searching above the fire floor, outside venting, opening the roof, operating exterior hoselines on exposures, vehicle extrication operations, and hundreds of other situations other than face-toface fire attack within a certain environment are all situations where PTFE liners will help dissipate sweat vapor and body heat, providing more comfort to the firefighter and helping to reduce stress as well.9
Thermal liner. Thermal liners provide the bulk of the insulation needed for an adequate level of protection from heat. Because the liners are fabricated of flame-retardant materials, they also form a second line of defense against flame contact. In the past decade, specifiers and manufacturers placed heavy emphasis on providing a high insulation factor. Inservice experience and further research now have shifted that emphasis to a more balanced approach between heat stress/comfort factors and insulation factors—there are trade-offs.
Thermal liners can be grouped into three basic styles: batt, enhanced batt, and new technology. Perhaps the most common type of thermal liner in the industry today is the batt liner. It is constructed of an insulating material covered by a quilted facecloth. Batt materials offer high insulation values but are relatively heavy in weight.
Batt liner insulation usually is constructed of Nomex or a Nomex/wool blend.
Lighter than batt, the enhanced batt liners nevertheless are thermally efficient. Enhanced batt materials are constructed of fiber blends, usually various combinations of Nomex, PBI, and Kevlar. Enhanced batt was a material industry response to Project FIRES data and other research that underscored the potential benefits of lighter-weight materials.
A second generation of enhanced materials is entering the marketplace. This newer technolgy is addressing enhanced vapor transfer between the body and the liner. It employs the principle that increased dead air spaces in the insulating package augment transfer of sweat moisture away from the body, thereby dissipating heat.
Before purchasing any fire clothing, evaluate the gear to make sure that material, design, and performance criteria will meet your department’s needs. The best indicator of clothing performance is a wear test that lasts through extremes of hot and cold climatic conditions. Many manufacturers allow a department to purchase wear-test garments at a special price or, in some instances, to borrow clothing for evaluation. At the very least, dealers or manufacturers should furnish sample garments for personnel to try on and use to perform simulated firefighting movements to test fit, performance, and comfort.
Wear garments to check for ease of donning; garment weight static loading; amount of discomfort from heat buildup during exercise; and amount of hobbling due to the clothing’s restricting arm, leg, and torso movements. The new edition of the NFPA 1500 safety standard will require that the clothing maintain a minimum two-inch overlap in all three layers while performing the following movements: standing at attention with the arms fully raised over the head and the hands clasped, bending down and touching the toes while keeping the arms extended over the head, and bending the torso completely to the sides and back. Garments designed in compliance with the 1992 edition of NFPA 1500 will be required to provide an overlap between the coat and pants of all protective layers (not just the outer shell) of no less than two inches while performing the above maneuvers.
Another important consideration is the amount of dynamic loading present when moving the arms. This can be gauged by measuring the upward movement of the coat hem from the ground to the hem while in the handsat-sides and hands-over-the-head positions. Also note the amount of sleeve pull-back and wrist exposure while performing the upward and rotational maneuvers.
Very few men feel comfortable wearing a rented tuxedo. That could be because an off-the-rack rented tuxedo was made to fit someone else. Most fire clothing is manufactured to fit average measurements within a given size range. Remember that the better the fit, the less the clothing will hobble the wearer. Purchasing highquality fire clothing is a very’ expensive undertaking. The dealer and manufacturer will provide the best fit possible if they take careful measurements of each wearer before the clothing is custom-manufactured. Purchasers should try on the garments they intend to buy, and their order should reflect any special measurements, such as pant inseam and sleeve length, to ensure a better fit. Female firefighters should insist that their clothing be constructed from women’s patterns. Otherwise, severe hobbling could occur as they try to operate in gear designed to fit only men.
When you decide on the garment’s design, you then can consider pocket placement, trim style and design, and special features such as built-in rescue harnesses and reinforcement.
Remember that when the material layers are compressed or wet, thermal performance suffers.10 It is wise to provide extra thermal protection in the shoulder area, where breathing apparatus straps compress thermal insulation, and in the knee area, where the weight of the body also compresses the material layers. The knees are also a good spot to specify material to reduce abrasion damage. Leather is the most frequently used reinforcement; however, a new fire-retardant synthetic material is now available that offers good abrasion protection and does not absorb water, which adds to the static weight of the garment.
More than ever before, manufacturers are offering the fire service more to choose from in fire clothing materials, design, performance, and options. Wise purchasers can draw on a vast store of new knowledge by evaluating garments they intend to purchase and by asking manufacturers for names of present users they can contact for additional wear-test results.
Only you can determine which clothing is suitable for your particular operation. Evaluate, ask questions, ask users, and make your decision based on facts, not claims. The benefits of your research will be enormous— providing your suppression personnel with an increased level of thermal protection while reducing the possibility of stress-related injuries.
- Fornell, David P., Fire Stream Management Handbook, Fire Engineering Books, 1991, pp. 84-92.
- Grumman Aerospace Progress Report. Project FIRES, 1979.
- Project FIRES, “The Final Report,” International Association of Fire Fighters, 1985, pp. 1-5.
- National Fire Protection Association, NFPA 1971, Standard on Protective Clothing for Structural Fire Fighting, 1991, pp. 1-2.
- Project FIRES, “The Final Report,” pp. 5-7.
- Goldman, Ralph F., “Heat Stress in Firefighting,” Fire Engineering, May 1990, pp. 47-48.
- Project FIRES, “The Final Report,” pp. 5-7.
- Goldman, Ralph F., pp. 49-52.
- Fornell. David P., “Wear Test Report on PTFE Barriers,” Treadway Fire-Safety, 1979.
- 10.Veghte, James H., PhD, “ Thermal Protective Performance Ratings,” Biotherm, Inc., 1984, p. 5.
Advance is a trademark of Southern Mills, Inc Nome* and Kevlar are registered trademarks of I* I. Du Pont de Nemours. Gorr-Tex is a registered trademark of W.l,. Gore and Associates, Inc. Tetratex Is a registered trademark of Tetratec Corporation. PHI is a registered trademark of Hoechst Celanesc Corporation AraMax is a trademark «>f Springs Industries.