Aircraft composite materials have been widely used in the aircraft industry and have allowed engineers the ability to create shapes and smoothness that affords greater aerodynamics while maintaining strength.
My first presentation on these hazards was back in the late 1990s with the Aircraft Rescue and Firefighting Working Group (ARFFWG) for a Region 1 seminar hosted at the new Federal Aviation Administration (FAA) funded ARFF Training Facility located on the campus of the New Hampshire Fire Academy. Firefighter safety remains paramount when responding to aircraft accidents. Many times these hazards are not easily identifiable.
There are a few concerns to discuss with these materials. The first is the rapid rate at which some of these composite materials will burn and the second is during the post traumatic damage of these composites, the surrounding air can contain high levels of fiber dispersion. This health and safety concern must be considered by the incident commander (IC), safety officer, company officers, and all firefighters operating on the fireground.
UNDERSTANDING COMPOSITE MATERIALS
Advanced composite (AC) materials include a binder and a matrix. The most simplistic way to explain composite is the use of fiberglass. The composite contains (soft) fiberglass cloth material and a liquid resin. When both materials are in their original state, they are neither usable for aircraft construction nor considered a composite material—until we bind them together. When we apply hardener to the liquid resin, the soft fiberglass cloth begins to form a rigid shape as the physical property of the resin begins to harden. Both materials retain their identities within the finished product but can provide engineered structural shape and strength via the binder.
THE HISTORY OF COMPOSITES
Fiberglass is the most common composite material used today and was first used in boats and automobiles around the 1950s. According to the FAA, composite materials have been around since World War II. Over the years, this unique blend of material has become even more popular and today can be readily found in many different types of aircraft. Some aircraft can be made up of 50 percent or more composite materials.
Fiberglass was first used in aviation by Boeing in passenger aircraft of the 1950s. When Boeing rolled out its new B787 Dreamliner in 2012, it boasted that the aircraft was made up of 50 percent composite materials. New aircraft coming off the line today almost all contain or incorporate some kind of composite material. Although composites continue to be used with great frequency in the aviation industry because of their numerous advantages, some people think using these composite materials may also pose a safety risk to the aviation industry.
ADVANTAGES OF COMPOSITE MATERIALS
Weight reduction is the single greatest advantage of composite material use and the key factor in using it for aircraftstructure panels. Fiber-reinforced matrix systems are stronger than traditional aluminum found on most aircraft, and they provide a smooth surface and increase fuel economy, which is a huge benefit. Furthermore, composite materials don’t corrode as readily as other types of structural materials. They don’t crack from metal fatigue, and they hold up well in structural flexing environments. Composite designs also last longer than aluminum, which means less maintenance for general appearance and reduction in overall repair costs.
COMPOSITE DISADVANTAGES
Because composite materials don’t break easily, it can be hard to tell if the interior structure has been damaged internally. The lack of internal assurance makes this a major concern or disadvantage for using composite materials. In comparison, aluminum bends and dents fairly easily, and it is quite easy to detect structural damage. Additionally, repairs to composite materials can be much more difficult when the surface is damaged, which ultimately becomes very costly. Another concern is the resin used in composite materials will weaken at temperatures as low as 150°F, making it important for composite aircraft to take extra precautions to avoid fire. Fires involving composite materials can release toxic gases in the smoke and microparticles up into the air, posing a serious health risk to emergency responders. Temperatures at or above 300°F can easily cause structural failure.
Take note that you will see different levels of composite materials in the modern aviation industry. Advanced aerospace composites (AAC) materials used on aircraft include carbon, carbon fiber, beryllium, epoxies, thermoplastics, and fiber-reinforced matrix systems. The industry has developed these AACs to better suit the aircraft’s needs and temperatures to which they will be exposed.
Lastly, radar absorbing material (RAM) is a specialist class for which a polymer-based material is applied to the surface of some military aircraft, such as the F-22 Raptor and F-35 Lightning, to reduce their identification by radar, thus making them harder to detect. These materials are also applied in stealth versions of unmanned aircraft. RAM is applied over the entire external skin or to common areas of high radar reflection. RAM works on the principle of the aircraft absorbing the electromagnetic wave energy when targeted to minimize the signature to reduce detection.
WHAT ABOUT FIBER DISPERSION?
After an aircraft accident, traumatic damage (breakup) of the composite materials can produce invisible fibers to be dispersed at the accident site. These fibers are extremely difficult to identify and have been known to cause respiratory illness either acutely or chronically. These fibers can manifest into lung cancer. The human body is unable to filter the fibers. Firefighters and EMS personnel operating at the scene are usually aware of the concerns of toxic gases found in the byproduct of incomplete combustion. Carbon monoxide and hydrogen cyanide are well known gases that firefighters use meters to monitor and measure after a fire is extinguished at a house fire. This air monitoring process is often done to determine if firefighters on scene must continue to wear self-contained breathing apparatus (SCBA) during fireground operations or even during the fire investigation.
In the ARFF industry, there is no meter designed to measure fiber dispersion. Therefore, when you are operating with a known composite material from an aircraft incident, the IC or incident safety officer must maintain the order to use SCBA at all times in and around the aircraft. Wind direction and air speed must be taken into consideration so ARFF responders; ARFF vehicle operators; EMS care providers; patient treatment areas; or any other areas like staging, rehabilitation, or canteens are not positioned in the fiber dispersion zone. Firefighters who must work in this zone should be required to wear SCBA at all times. Acutely, firefighters exposed to fiber dispersion can suffer difficultly breathing, similar to the rapid onset of asthma. They are unable to catch their breath and will have low oxygenation saturation levels. This respiratory threat can also exacerbate other underlying known or unknown medical conditions.
Long-term chronic illnesses from fiber dispersion exposure include microfibers that our body can’t filter. The human body constantly tries to filter the air quality coming into our respiratory system. High levels of microfibers that make it all the way to our lungs can manifest into a mass or tumor. Long term, the foreign body and mass can eventually become lung cancer for many who work in environments with fiber exposures. Our NIOSH-approved respiratory protection equipment—SCBA—will 100 percent prevent fiber dispersion from ever becoming a concern for firefighting personnel.
AIRCRAFT (FIBER DISPERSION) STABILIZATION
The United States Air Force has an aircraft recovery team that can be dispatched when it has a known fiber dispersion hazard. This team of specially trained personnel don hazmat suits and wear respiratory protection when stabilizing an aircraft that has composite materials that have been ripped, have torn, or have broken open. Often the recovery team will use a liquid commercial-grade floor wax to seal the aircraft. This “sealing effect” of fibers is done in a manner similar to painting a vehicle. The aircraft is sprayed with liquid wax and allowed to dry. During this process, the buildup of wax seals any fibers from freely floating into the air during aircraft recovery and during investigation back at the aircraft hangar. This process is not a requirement for civilian aircraft recovery teams, but the practice should be highly considered by all ARFF personnel and the IC if personnel are going to be exposed to any known potential fibers.
When operating around any known composite aircraft and fiber dispersion is a concern, when in doubt, wear your SCBA and protect your respiratory system. This, in turn, will afford you and your family a long, healthy retirement together.
WILLIAM GREENWOOD is a 31-year veteran of fire service, working in both the ARFF industry and municipal structural all-hazard fire departments. He has been an NFPA 1003 ARFF instructor since 1999. He also teaches at FDIC International and has been published in Fire Engineering.