How Lab & Field Testing made the CDF's PPE safer & more comfortable

By Galen McCray

PHOTO SHARI MORRIS

Each fire department or agency, regardless of its mission statement, has unique requirements for providing the appropriate level of personal protective clothing and equipment (PPE), including structural turnouts, hazardous material suits and wildland firefighting gear. Regardless of what gear you wear, a number of outside variables factor into PPE selection and purchase: Is your PPE purchased by your employer? Do you obtain your PPE from a commissary, or do you pick and choose from the various manufacturers and vendors? The PPE of volunteer fire companies varies widely, from personal blue jeans and Dickies workshirts to OSHA-approved ensembles to PPE that's fully NFPA 1977-compliant. Some fire departments use their station work uniform as their wildland PPE.

The California Department of Forestry and Fire Protection (CDF) is no different. When I started as a seasonal firefighter in 1970, we wore blue jeans, a khaki shirt, a tin hat, leather boots and gloves. The CDF provided the hardhat and gloves, and I was expected to show up to work with my boots, jeans and khaki shirt. Today, when I don my wildland PPE, I wear a helmet, gloves, a jacket and trousers — all of which are NFPA-compliant and meet the requirements of our state OSHA, known as Cal/OSHA.

It took many years and lots of testing for the CDF to arrive at its current PPE specifications. The central issue behind the modifications made over the years: the conflict between maximizing thermal protection from fire and minimizing metabolic heat stress. Simply stated, we can achieve good thermal protection by wearing multiple layers and thick materials, but such PPE can prevent good ventilation and create high heat stress. The evolution of the CDF's PPE is the result of continued attempts to find the right balance between thermal protection and heat stress. The lessons we learned, and continue to learn, through PPE testing apply to all departments that fight wildland fires.

A Concern with Heat Stress
In the late 1980s and early 1990s, firefighters involved in burnover situations on wildland fires exhibited characteristic burn patterns: Those wearing single-layer NOMEX material received significantly more burns, and more serious burns, than those wearing NOMEX outerwear and an additional layer of protective underclothing. As a result, the CDF implemented a two-layering policy in the early 1990s to minimize or at least lessen the degree of burn injuries. Although a two-layered approach to wildland PPE is not unique to the CDF, it is more the exception than the rule in fire departments/agencies that respond primarily to wildfires.

However, the CDF was also aware of the physiological impact multiple layering could have on firefighters: increased heat stress. In 1996, the CDF contracted with the University of California, Davis, (UCD) to determine the safest combination of thermal protection and heat dissipation. Since the start of these studies, the CDF has made some significant changes to its wildland PPE.

Why would the CDF undertake such studies when statistics on heat-related deaths in the wildland firefighting community are quite low (less than 1 percent)? Although heart attacks and burnovers account for the greatest percentage of fatalities, the impact of heat stress is not always measurable, and certainly not in fatality statistics alone. Heat stress is felt in lost productivity, lost work time, overtime costs and workers' compensation costs.

In addition, we must consider the cumulative effect on the firefighter: Studies have shown that those who experience heat stress once are more prone to experiencing it again, posing a potentially higher personal health risk. The CDF wanted to maintain its two-layer wildland PPE requirement and at the same time ensure its PPE provided the best protection from the fire environment and from the metabolic heat generated by the firefighter. Another motive behind the testing: Firefighters in the field had several complaints about the comfort, usefulness and durability of the CDF gear at that time.

As of April 2006, the CDF has completed five PPE studies; another study is near completion. These studies have primarily focused on developing PPE with better heat dissipation qualities, but with little, if any, loss in burn protection.

Note: Since the inception of the CDF/UCD studies, NFPA 1977 (Standard on Protective Clothing and Equipment for Wildland Fire Fighting) requirements have changed. For example, when we conducted our first tests on radiant protective performance (RPP), NFPA 1977 (1993 edition) required a value of 8 (the number of seconds before a second-degree burn injury occurs when the fabric/textile material is exposed to a preset radiant heat source). The current NFPA RPP requirement (2005 edition) is 7. Without going into analytical detail, this reduction essentially allows for lighter weight fabric.

The Properties Tests
Under the direction of Dr. Margaret Rucker of the UCD Textile and Clothing Division, the CDF reviewed and tested 39 different fabrics and more than 22 layer combinations, measuring physiological and mechanical properties such as vapor evaporation, air permeability, tensile strength, abrasion resistance, fabric density, RPP and total heat loss (THL). THL measures thermal resistance or thermal conductivity, a reflection of the fabric's ventilation ability.

To meet the CDF's two-layer policy, recommendations generated by this first study focused on making the two-layer configuration safer and developing a better PPE design. But whether your department requires a single-layer or multiple-layer ensemble, the data generated is still useful when selecting PPE. Remember: This testing was done in accordance with the 1993 edition of NFPA 1977; performance standards have changed since these tests were completed.

Findings from this first study include:

• In a single-layer configuration, NOMEX, Fire Resistant (FR) cotton twill, Firewear twill, cotton and polyester/cotton blend fabrics scored acceptable RPP values;
• FR cotton has a much lower abrasion resistance than the NOMEX fabrics; and
• Color had no impact on RPP or THL values.
• Based on the findings, the study resulted in these recommendations:
• The outer layer of PPE should not be constructed of Firewear, cotton or polyester/cotton blend fabrics, due to the fabrics' low melting points and/or decomposition when exposed to radiant heat;
• Fabric weight should be a minimum of 5.5 oz/yd2 (today, that value is considerably lower);
• Woven fabrics should be chosen over knit fabrics. Both exhibited good RPP values, but researchers were concerned that the higher air permeability values of knit fabrics made their abrasion resistance relatively low; and
• Polyester/cotton fabrics should not be used as a secondary layer, as they became molten during RPP tests. In 1996, the primary CDF uniform trousers featured a 50/50 polyester/cotton blend. As a result of these tests, the CDF soon changed its trousers requirement to match the requirements of NFPA 1975: Standard on Station/Work Uniforms for Fire and Emergency Services.

The Thermal Mannequin Tests
In addition to measuring the mechanical properties of wildland PPE on the market at the time, the first CDF PPE tests also included surveys and group interviews of firefighters to identify their comfort and use concerns. These interviews identified the following concerns:

• The inability to don/doff the trousers over boots;
• Difficulty in accessing either the trouser or PPE pockets, and pockets too small to carry anything;
• The crotch seams were too weak and constantly ripped; and
• The jacket sleeve liners were too stiff, hot, bulky and tight, and did not wick water when firefighters became soaked by a helicopter drop or conducted hoselay operations.

Dr. Rucker and her staff at UCD developed two PPE prototypes that addressed these concerns. After the CDF's review, a third prototype was developed for future studies.

The researchers then set about evaluating the comparative thermal protection offered by three sets of PPE:  CDF PPE, U.S. Forest Service (USFS) PPE and the UCD prototype PPE. Each garment configuration was tested in a thermal mannequin chamber at the University of Alberta (UA) in Edmonton. UA's testing facilities include a thermal mannequin that features 110 skin-stimulant sensors to measure the rate of heat transfer.

Tests are conducted inside a fire exposure system that produces a flame temperature of 1,800 degrees F to 2,000 degrees F for 4 seconds. This temperature and time duration closely simulates a wildland fire flame front.

PHOTOS COURTESY PROTECTIVE CLOTHING & EQUIPMENT RESEARCH FACILITY, UNIVERSITY OF ALBERTA

The Flash Fire Facility at the University of Alberta features a thermal mannequin with 110 skin-stimulant sensors to measure the rate of heat transfer. The facility produces a flame temperature and duration similar to that of a wildland fire flame front.

The results of the thermal mannequin tests are not all that surprising: Wearing the CDF PPE, 12.53 percent of the mannequin surface reached burn criteria (second- and third-degree burns), compared with 53.10 percent of the mannequin surface when wearing the USFS PPE. The prototype developed by UCD scored slightly better than the CDF PPE.

One unexpected result of the testing: The CDF jacket sleeves did not shrink appreciably, whereas the USFS jacket did shrink substantially, both in the arms and the torso area around the waist. As a result, Dr. Rucker recommended that jackets be lined in the back with FR cotton to minimize shrinkage and increase thermal exposure.

The Physiological Tests
Concurrent with the thermal mannequin tests, Dr. William Adams of the UCD's Department of Exercise Science performed physiological evaluations on the three wildland PPE ensembles in a controlled environmental chamber. Eighteen CDF firefighters between the ages of 29 and 51 performed 90-minute protocols while wearing each PPE type in two different temperature environments (86 degrees F/32 percent relative humidity and 103 degrees F/23 percent relative humidity). The protocols included walking, simulated hoselays and handline construction.

Again, the results were not earth shattering: The single-layer USFS PPE created less thermal stress than both of the two-layer configurations. However, the UCD prototype (two-layer) provided better sweat evaporative efficiency.

Recommendations resulting from this study included:

• The CDF should use the USFS single-layer trouser; and
• If the CDF continued to use a two-layer ensemble for the upper torso, it should consider using a long-sleeved T-shirt. Dr. Adams believed the T-shirt had the potential to increase evaporative heat loss due to increased bellows ventilation (i.e., the movement of the arms allows air to enter and escape between the T-shirt and the NOMEX jacket).

PHOTOS COURTESY MARGARET RUCKER, UCD Working with researchers from the University of California, Davis, the CDF used the thermal mannequin to test three types of PPE. These photos show the burn results. From left to right: USFS PPE, CDF PPE and the prototype.

In 2001, Dr. Adams conducted another physiological study in a controlled environment comparing the CDF sleeve liner against a long-sleeved T-shirt. He found that the FR cotton liners provided a good deal more protection than the long-sleeved T-shirts.

Dr. Adams also tested heat stress occurring with fully closed apertures (collar, sleeves, cuffs) vs. open apertures. The recommendation: When it is safe to do so, firefighters should open their PPE at the apertures; if at all possible, firefighters should remove outerwear during rest periods to enhance cool-down. Keeping apertures closed significantly increased thermal stress and recovery times. While in theory these results are not surprising, the recommendation may go against our perception of PPE policy.

Many chief officers and company officers insist firefighters wear their PPE fully closed — close the cuffs of the jacket, band the trouser cuffs (to protect from insects such as ticks), zip up your jacket and close your shroud. I have seen numerous training exercises and fireground operations where firefighters exit the apparatus encapsulated in PPE, even when flame lengths are but a few inches. Dr. Adams' heat stress tests indicate this may not be the best approach. That said, I still see firefighters, both on the fireline and in photographs, wearing PPE with the sleeves rolled up and not wearing gloves, when facing flame lengths of 3 to 4 feet. This is not an appropriate use of PPE either.

PHOTO ED SHERMAN Although two-layer PPE like that worn by CDF firefighters provides increased thermal protection, it can also increase heat stress for firefighters in the field.

The Field Tests
Following these lab tests, the CDF decided to field-test the UCD prototype PPE for a full fire season. Design features included pass-through pockets in the trousers, longer leg openings, cargo pockets, a gusset in the crotch to prevent tearing, a two-zipper jacket and a variety of Velcro® closures at the apertures.

Most firefighters expressed favorable comments on the UCD prototype. They especially liked the longer leg openings to facilitate donning/doffing their trousers over work boots, the two-zippered jacket, the pass-through pockets and the cargo pockets. Less favorable comments were received on the Velcro® fasteners and the radio (handi-talkie) pocket on the jacket. Most of those who wore the UCD prototype were pleased that the trousers did not rip at the crotch as the previous PPE had been quick to do (in other words, the gusset and a different stitch were greatly appreciated!). In addition, the field testers found that the FR liner wicked water quickly and dried quickly when it became soaked.

10 Years & 5 Studies Later…
What does CDF wildland PPE look like today? The CDF switched from a poplin weave to a modified basket weave on both the jacket and the trousers, maintaining the same weight of fabric; the trousers are NFPA 1975-compliant.

Changes resulting from the tests include:

• Jacket: Larger collar with a Velcro® closure strap, two zippers, larger front pockets and reflective stripping along the forearms and the bottom edge of the jacket. We still use the 7 oz/yd2 FR cotton sleeve liner stitched into our NOMEX jacket sleeves.
• Trousers: Cargo pockets on the thighs, pass-through pockets, longer leg openings with zippers, reflective stripping and the all-import gusset in the crotch.

In addition, the CDF is currently completing a final set of thermal mannequin tests, which compare the effects of relative humidity and sweat on the transfer of radiant heat and the effects of silk-screening on heat transfer to the firefighter's skin. The impetus behind the tests were a couple of incidents where portions of the "CDF" lettering on the back of T-shirts or NOMEX jackets were burned onto firefighters' backs. Note: One of these incidents involved a firefighter inside a burning structure. Wildland PPE was never designed to withstand the temperature and heat extremes of a fully involved structure, and the projected temperature exposures inside the home were well over the 2,000 degrees F used in the thermal mannequin tests.

The Practical Application
If all of this seems somewhat academic and analytical, it is. But there is also a practical application. Just as you can go to any car dealership and pick out a new car, you can look in a variety of PPE catalogs and pick out the clothing you believe will suit your department's or your personal needs. But making a decision on accessories alone is not good enough. Amenities such as CD players and sunroofs are nice, but we cannot compromise on our car's ability to stop in emergency situations. Wildland PPE is no different: Your life depends on wearing the best PPE that meets the mission of your department. Kneepads and radio mic holders are convenient accessories, but it's more important that our PPE protects us from radiant heat, convective heat and direct flame impingement, while also dissipating body heat and enhancing evaporation of sweat.

Strive for Balance
Is the CDF's PPE the best wildland PPE? It works for the CDF, and it balances protection from fire with protection from metabolic heat stress. Like many fire departments/agencies, we fight fire aggressively only after having provided for safety first.

The studies conducted by the CDF, along with your agency's regulatory requirements and specific departmental polices, can assist you in finding the right PPE. While these studies were designed in scope for the CDF's two-layer policy, the information and results have application for all PPE configurations. Fires have no concept of jurisdiction and do not discriminate based on the identification patch or logo worn on the PPE. Burns hurt, and if you can prevent or minimize them, you are on the path to a long and successful career.

Finally, one note of caution: No matter how well designed, no PPE is a substitute for maintaining physical fitness, acclimating yourself to the heat and staying hydrated.

To obtain copies of the completed CDF PPE studies, contact the author at Galen.McCray@fire.ca.gov.

Galen McCray is a 37-season career employee with the CDF and a member of the NFPA 1977 technical committee. Currently a field battalion chief in Northern California, he served as the CDF's departmental safety officer for almost six years. Throughout his career, he has held positions as a fire apparatus engineer, station captain, law-enforcement captain, conservation camp captain, emergency command center fire captain and helitack fire captain.