Composites: Safe handling of modern methods

Airframe Technology


Safe handling of modern methods

By Bill Brinkley

July 2004

Composites have become a way of life in aviation, and the advances made possible by composite technology over the last several years have been nothing short of astounding. Composites have become so commonplace in aircraft that they are taken for granted by both pilots and technicians, without much thought to the fact that not so many years ago they were completely unheard of. For the most part, composites aren’t even considered "new technology" anymore, although they are still relatively "young".

As it is with most things that are commonplace or taken for granted, there are many inherent dangers in composites that are overlooked. Several potential hazards exist that are not even recognized as dangerous by the people who live and work around composite materials. To best illustrate this, let me tell you about an aircraft recovery that I was involved in several years ago.

The aircraft involved was a helicopter that had gone down on an ice flow. The details of the incident are interesting in their own right, but that, of course, is another story. All three persons on board walked away from the incident with no injuries.

The aircraft impacted the ice with landing gear down, practically level, and with a slight yaw to the right, almost a run-on landing. The right main gear slid off into the only spot of open water in 10 miles and the aircraft stopped. The main rotor blades struck the water and the ice rim. A 6-foot portion of one main rotor blade departed the aircraft and landed almost 400 feet away from the aircraft, then skidded across the ice another 400 feet. Another main rotor blade continued to travel along its plane of rotation and locked itself in front of the next main rotor blade. This blade, now bent 180 degrees upon itself, placed the blade root under tremendous tension. The weight and position of the aircraft held this blade in place.

The pilot popped the floats and the crew departed the aircraft. During the aircraft recovery, investigation and maintenance personnel climbed all over the airframe, unsuspecting of the material tensions and stresses that were present. The potentially lethal hazard revealed itself during disassembly of the aircraft prior to hoisting it onto the recovery vessel. As the last securing bolt was removed from the blade that had turned back on itself through 180 degrees, the blade root sprung back into line with the blade. Serious injury, if not death, could have resulted had anyone been in its path.

Composites will return to their original configuration when freed of external forces, and they will do so with amazing force and velocity. This holds equally true for main rotor blades and for smaller composite parts under the right conditions. A small composite part may not have enough latent force to injure a person directly, but it may startle you enough to make you hurt yourself.

Use protective equipment
Another hazard, as potentially dangerous as the stressed blade, was the widespread distribution of composite carbon, graphite, and Kevlar fibrous debris throughout the incident site. Even though investigation and recovery personnel were equipped with skin and respiratory protective equipment during recovery operations, there were numerous injuries. They ranged from respiratory distress caused by inhaling Kevlar, carbon, and graphite fibers; cuts and splinters from handling sharp pieces of composite material; and skin rashes from the composite fiber dust (if you have ever installed fiberglass insulation batting, you know about this one first hand). Surprisingly, the recovery crew suffered far more injuries than the aircrew.

Granted, the odds are that you will never work an aircraft salvage or recovery, but the same conditions can be found in your day-to-day working environment. If you are manufacturing or repairing composite parts, or are in the vicinity of someone who is, you are working under near identical conditions to those described above (Kevlar, graphite, and carbon fibers and dust, sharp composite edges, stress-loaded composite materials, etc.), and the same types of injuries are possible.

Compared to resins, fibers are relatively inert. The primary hazard is mechanical irritation, either of the skin or the upper respiratory tract. Most, if not all, fibers have too large a diameter to be respirable, which means they do not enter the lungs. Carbon fibers are close, and carbon dust created by machining may be respirable. Aramid (Kevlar) fibers are much too large to be respirable, but they can fracture into small fibrils which are respirable.

Mechanical irritation is itching after direct contact. Aramids cause no irritation for most people, but glass and carbon do. Most fibers have a sizing (often an epoxy or other resin) which can also cause chemical irritation, and this can be mistaken for mechanical irritation.

After cure, fibers become very rigid and may stick out from poorly machined or fractured surfaces. Such surfaces should be handled with care, because it is very easy to get fiber splinters (or "snake-bites").

Gloves should always be worn when handling resins, and these will also protect against fibers in uncured composites. Only heavier gloves will protect against sharp fibers on fracture surfaces.

Dust masks and protective clothing should be worn whenever dust is created (such as while machining). Elastic cuffs will keep dust from getting inside protective suits. Of course, dust removal systems are also important (though shop-vacs can be shorted out by carbon fiber dust).

Another factor to consider when working around composites is flammability. We all know that composite materials won’t burn, but the resins used to manufacture them, mold them, and keep them together sometimes will. Even the resins that won’t burn can release noxious or toxic fumes when heated that can range from mildly nauseating to potentially dangerous.

Finally, carbon fibers are electrically conductive. Although this doesn’t pose a direct health hazard, airborne fibers can short out electrical equipment.

Composite materials are not going to go away, and in fact will become even more predominant in aviation in the future. As a technician, you will need to add "chemist" to your list of abilities right alongside "tin bender" if you want to stay competitive.

Composites are here to stay, and as with anything else, you have to work smart and be aware of the potential for injury that exists in working with these materials. Take proper precautions when working with composites, including the use of masks or respirators when necessary. Remember that the sanding dust from composite materials can be irritating to the lungs. Remember that Kevlar splinters can be quite painful, and that the edges of composite materials can be sharp.

Composite materials pose health hazards, both in their uncured and in their cured forms. These hazards, though, shouldn’t scare you away from the materials: with proper precautions, the risks can be minimized and even eliminated.