The fire starts on a sofa or in the wastepaper basket in the corner of a room. It grows exponentially, igniting the carpet, the curtains, the walls and other items. The room starts to get hotter and hotter, the fire bigger and bigger. Surfaces in the room begin to break down and emit flammable gasses. Suddenly and without warning, the entire room bursts into flames.
This is a flashover - an event that occurs when gases produced from the combustion of materials become hot enough to ignite - typically 1,000 to 1,500 degrees Fahrenheit. It is also, as most firefighters know, a danger that has become more prevalent due to new construction practices that trap heat better and the increased use of plastics in homes.
When a flashover or other extreme fire event occurs, the firefighter's last line of defense is his or her personal protective equipment (PPE). Increasingly, however, firefighters and their PPE are being required to do more than just fight fires; work practices now require prolonged use of the PPE in non-structural-fire activities.
"As a fire officer, my first concern in personal protective equipment is to have the best possible protection from fire and burn injuries," said Kristina Kreutzer, assistant fire chief at the Mill Creek Volunteer Fire Company in Marshallton, DE. "However, while I need my PPE to protect against increasingly intense fires, I also need PPE that addresses the unique and often mutually exclusive challenges of non-fire related emergencies."
The threat of extreme fires makes it more important than ever for firefighters to understand how thermal protection is incorporated into turnout gear. However, because of the expanding role of firefighters in non-fire-related emergencies, it is also important to recognize that PPE that only delivers thermal protection is no longer enough. As a result, firefighters also need to understand how new developments, such as the introduction of Nomex On Demand - new "smart" fire-resistant fiber - are helping to create turnout gear that addresses the full scope of the challenges they face.
Today's Challenges
Forty years ago, before DuPont introduced Nomex, the first flame-resistant fiber to be used in firefighter gear, the vast majority of firefighter injuries and deaths were attributable to burns. Today, however, burns account for only 4% of firefighter deaths and related injuries because of technology advances in the PPE and improved work practices. Thirty-nine percent, by contrast, are caused by exertion and stress.
Why has the ratio changed so dramatically? Firefighters are doing much more with the same PPE than just fight fires today. These garments provide excellent protection against the high-temperature environments encountered during structural firefighting, but now must also be functional for longer tasks such as EMS and vehicle extrications.
"Our company responded to 4,250 emergencies in 2008," said Kreutzer. "Only 1,101, or about a quarter, were fire-rescue-related, and only 217 of those were fires."
But while today's challenges place new burdens on firefighters and turnout gear, thermal protection remains the most important factor. "As a practical matter, the threats that kill you quickest are the ones that are most important and need to be dealt with first," adds Kreutzer.
A Look Inside Your Turnout Gear
Every turnout coat features three components: an outer-shell, a moisture barrier and a thermal liner. Advanced flame-resistant fibers such as Nomex and Kevlar are incorporated at each level to help maximize thermal protection, durability and flexibility and to minimize heat stress.
The outer-shell protects the inner components from thermal hazards, abrasion, sunlight and other factors. It accomplishes this through flame-resistant filaments and other fibers engineered together to form composite materials that stand up to heat and are highly durable.
The moisture barrier features a liquid-impermeable composite, bonded to flame-resistant substrate, which protects against the intrusion of water, selected chemicals or viral agents. Moisture barriers are designed to be breathable, allowing metabolic heat to escape and reducing overall heat stress during strenuous activity.
Finally, the thermal liner provides most of a turnout coat's thermal insulation by trapping air in either traditional needle-punched batts or between multiple layers of fire-resistant nonwovens. Face cloths using flame-resistant filament yarns reduce surface friction, improving overall garment mobility and ensuring durability. Additionally, water-wicking or repellent finishes on individual layers of flame-resistant fabric improves moisture management and drying time.
The combination of these components defines the performance characteristics of an entire system. Heavier systems offer high thermal protection, but feature lower breathability, thereby contributing to heat stress. Flame-resistant fibers are also included in other elements of the firefighting ensemble, including a variety of accessory items such as helmets, boots, gloves and hoods. These fibers are also being used to create stationwear - clothing that offers secondary thermal protection and traps additional air layers, improving the thermal performance of the whole system.
Smart Fiber
Over the past 40 years, since the introduction of the first flame-resistant fibers, advances in materials and the design of turnout systems have improved the protective threshold of PPE. However, materials have always remained static, providing a stable level of protection with certain set features in all circumstances.
"My first turnout coat was very difficult to move around in and very heavy," said Kreutzer. "Newer equipment has improved on this immensely, but the gear still takes a one-size-fits-all approach, requiring me to wear the best, most protective PPE for everything from a structural fire to a routine car accident."
However, new "smart" thermal liner technology is emerging that responds automatically to more extreme situations. The nonwoven is the first material of its kind available for firefighters that adjusts and changes properties to provide different characteristics and levels of protection in response to environmental factors. During routine conditions, the technology provides the thermal protective performance of standard liners and remains thin, lightweight, comfortable and breathable - thereby addressing concerns related to heat stress and flexibility. At internal temperatures of 250°F and higher - emergency conditions with the highest potential for burn injury - the fabric senses the increased heat, self-activates and expands to trap more air for up to 20% more thermal protection.
The added thermal protection is critical for situations, such as flashovers, that are occurring with more frequency and require improved thermal protection. However, it does not solve all of the problems, challenges or issues firefighters face. As the first "smart" material of its kind, however, it has the potential to usher in an era of new innovations in PPE that will further address problems related to heat stress, ergonomics and, as always, thermal protection.
RICH YOUNG, Ph.D., is a senior research chemist at E.I. du Pont de Nemours & Co. Inc./DuPont Personal Protection. Of his 23 years with DuPont, he has spent the past 10 working on fabrics and systems for protective apparel. Dr. Young is a senior member of the market support and product development team for thermal protective apparel. He has several patents on fabric and component technologies and has worked with various technical committees on developing new thermal test methods. Dr. Young earned his bachelor's degree in chemistry at California State University, Sacramento, and received his doctorate in organic chemistry from Michigan State University. He is a member of the National Fire Protective Association (NFPA) Technical Committees for Stationwear and Technical Rescue Gear and works with the Technical Committees on Structural and Proximity Gear.
