Published In May 2000
If you look into the end of a fiber, the powerful laser signal transmitting through it will burn your eyeball. The effect is like a medical fiber optics gadget that burns warts off your finger or an endoscope used in laser surgery, right? This is the second most popular myth about fiber, and it is wrong on two counts. First, most fiber optic links pose no eye damage danger. Second, there are other dangers that you must be concerned with to install or use fiber optics safely. Let's start with the eye safety issue. Most fiber optic systems have power levels too low to damage the human eye. Instead of lasers, they use light-emitting diodes (LEDs) for sources that are thousands of times less powerful than medical lasers. Only a handful of very specialized cable access television (CATV) and telephone networks use lasers that are powerful enough to be harmful, and trained personnel are only allowed in these areas during scheduled maintenance periods. Untrained personnel are not going to be allowed within a city block of those networks! Also, the light comes out of fiber in an expanding cone, caused by various modes (e.g., rays of light) travelling in the fiber. The further the end of the fiber is away from the eye, the less the danger. In fact, the exposure goes down by the square of the distance - twice as far means one-fourth as much exposure to the eye. The expanding light from fiber also means the eye cannot focus it on the retina, further reducing the risk of damaging the retina. Most fiber optic systems also operate with light over 1,000nm wavelength. The liquid in your eye absorbs these levels of light heavily, preventing retinal damage. However, corneal damage is still possible if you get the fiber that close and keep it there for a long time! It's silly to look into a fiber when you don't know what is being transmitted through it. Most fiber-optic networks use light invisible to the human eye, no matter what the power level. And if the power is high enough to be a problem, the damage is most likely irreversible. So don't look into fibers! Use a power meter to determine if power is present, especially if looking at the end of a connector with a microscope. So what are the real safety issues of dealing with fiber optics? The two major ones are: proper disposal of the glass shards created by cleaving the fiber or accidentally breaking it during termination and safe use of cleaning chemicals and adhesives during work with fibers. Always dispose of fiber scraps carefully. We recommend a disposable paper cup for all fiber scraps and other dangerous materials. Be careful about getting fiber scraps on the floor or on your clothes. Identify and dispose of every scrap fiber, no matter how small. Be careful in handling all chemicals. Some cleaners and adhesives used for fiber optic terminations are flammable, and some are hazards to breathe or may cause allergic reactions. Always work in well-ventilated areas, keep these chemicals off your skin, and carefully clean up and dispose of any spilled chemicals. Simple rules for safe handling of fiber optics - Keep all food and beverages out of the work area. If fiber particles are ingested, they can cause internal hemorrhaging. - Do not smoke while working with fiber optic systems. - Always wear safety glasses with side shields. Treat fiber optic splinters as you would glass splinters. - Never look directly into the end of fiber cables until you are positive that there is no light source at the other end. Use a fiber optic power meter to make certain the fiber is dark. When using an optical tracer or continuity checker, look at the fiber from an angle at least 6 inches away from your eye to determine if the visible light is present. - Only work in well-ventilated areas. - Contact wearers must not handle their lenses until they have thoroughly washed their hands. - Do not touch your eyes while working with fiber optic systems until your hands have been thoroughly cleaned. - Wear disposable aprons to minimize fiber particles on your clothing. Fiber particles on your clothing can later get into food, drinks, and/or be ingested by other means. - Put all cut fiber pieces in a safe place and dispose of properly. - Thoroughly clean your work area when you are done. HAYES, a frequent contributor to Electrical Contractor, is president of Fotec in Medford, Mass. He has provided fiber optics training and has written widely on fiber optics, including The Fiber Optics Technician's Manual. He can be reached at firstname.lastname@example.org.