Health and Safety: FibersDateline: 10/06/98
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.
In this series, I will give a brief overview of the health and safety issues involved in working with composites. Please remember that this is only an introduction: before using any material or process, you should fully investigate the potential hazards.
Part 1 of this series covered resins and related materials. In this current installment, I discuss the effects of fibers.
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").
Finally, carbon fibers are electrically conductive. Although this doesn't pose a direct health hazard, airborne fibers can short out electrical equipment. We just lost a 2000 amp breaker in an explosion last week; an accumulation of carbon fibers may have been responsible.
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).
I'm curious about how different people react to fibers. If I just briefly handle a bare carbon tow, my hands will itch like crazy for the rest of the day. On the other hand, fiberglass is only a mild irritant, and Kevlar doesn't affect me at all.
How would you describe your sensitivity to the common fibers?
- None: No irritation after skin contact.
- Mild: Irritation for an hour or two after contact.
- Moderate: Irritation for several hours after contact.
- Severe: Irritation for the rest of the day or longer after contact.
So far, seven people have responded to the survey. The following tables show the results (not everyone answered every question).