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Fiber optic safety

If the far end of the fiber is not under your control there could be light being radiated from the end being repaired.

If SG3 light emitters are being worked on laser safety glasses of the proper frequency need to be purchased and used.

Fiber is seeing more use in station and transmission facilities as the bandwidth demands of communication channels increase. Because of this it is important to become aware of the high-level issues of fiber use and how to take appropriate safety measures when working with it.

The installation of fiber is simple, but does require some special skills and tools, and training in their use. This is particularly true when installing connectors, as they are sensitive to light-coupling loss. Several companies offer training covering the technology, tools, techniques and safety issues. Safety protection issues while working with or repairing fiber optic cable fall into three general categories: eye protection, fiber fragment control and safe use of chemicals.

Probably the first item that comes to mind is the danger to the eye due to high-intensity light. Light sources for fibers are lasers, Vertical Cavity Surface Emission lasers (VCSEL) and LEDs. Different manufacturers will use different sources depending on the intended use of the product. A laser is typically used in higher-speed and longer-distance applications using single-mode fiber. LEDs are used for cost-sensitive and shorter-distance applications and are popular for lower-bandwidth, multimode requirements.

The light from these emitters is in the near-infrared (800nm to 1400nm) and infrared regions (above 1400nm to 3000nm) and cannot be seen. ANSI Z136.2-1997, a standard on fiber optic safety, classifies the emitters into service groups ranging from SG1 to SG4. An SG1 emitter is considered safe based on current medical knowledge. This is what is normally used in fiber systems for carrying video or data in a broadcast facility, but some amplifiers can employ vision-damaging SG3. Infrared light does not trigger normal visible bright light reactions in the eye, so it is best to develop a habit of never looking into a fiber that may be lit.

Typically, a person is working with fiber to install or repair connectors. Connectors must have low light loss. Air gaps between the fiber ends, angular misalignments, lateral offsets, ends cut at an angle (tapered air gap), core size mismatching, and dirt and scratches can reduce coupling efficiency, causing light to be lost.

When installing connectors, determine what the link is used for and the light emitter at the far end, if there is one. Take note, if the far end of the fiber is not under your control there could be light being radiated from the end being repaired. During the inspection of such a small area, you'll need to use magnifying glasses. This will concentrate and focus any light being emitted from the fiber onto your retina. The ends of the fiber are small, and therefore sharp, so you may be looking closely during an inspection. Beware of any laser or VCSEL emitters. Any emitter that falls into SG3 requires eye protection. Safety glasses that protect the eye from high-intensity light (visible or invisible) are available. These glasses are specified by the frequency and the attenuation of the light. Some glasses are made to cover a range of frequencies. These glasses reduce the light reaching the eye by absorption. This prevents reflections off the glasses into the local environment. While these glasses are expensive, they are required to protect your sight and should always be worn when working with fiber.

Additional equipment is sometimes available that is helpful. A light power meter can indicate whether the fiber is powered up at the instant of being checked. In addition, inspection scopes are available with absorption filters. If you are using such a device, insure the absorption filters are correct for the wavelength of the light source being used. Light radiating from an open fiber will diverge and the energy will decrease rapidly with distance. Using an inspection microscope concentrates and focuses the light onto the retina.

Another hazard encountered when working with fiber is exposure to small glass fragments made during the connectorization process.

In the process of cutting and trimming the strands on fiber optic cables, you'll create small fragments of glass or plastic that can get into the skin and cause irritation. Due to the size and clarity of the fragments, they can be hard to find and remove. Wear gloves and don't rub your eyes.

The best protection is the prevention of the problem in the first place. Use a dark mat as a work surface so fragments can be seen. A resilient mat works better as it will give a bit and make it easier to pick up fragments with tweezers. This mat also should be chemically resistant.

Keep the area work area clean. Use a disposable trashcan for fiber scraps that is designed to be sealed to contain them. This small trashcan could be a plastic bottle with a screw-on cap or something similar that can be tightly closed after the job is done. It need not be expensive, just secure storage for the fragments so you can dispose of used containers and have a new clean one available.

Keep a safety kit containing the necessary tools on hand. Several companies make and sell fiber optic safety kits containing a polishing/work mat, fiber scraps trashcan, tweezers for removing splinters, safety glasses and gloves. Some may contain cleaning supplies as well. You can augment this as needed. The safety glasses in the kits are normally clear and offer mechanical eye protection. If SG3 light emitters are being worked on or if there is the possibility of your encountering them, then laser safety glasses of the proper frequency need to be purchased and used.

In addition to the danger to the eye and skin from light and fiber fragments, another safety issue is exposure to the prep and cleaning chemicals. These are chemicals used for cleaning prior to installing connectors, the chemicals used to install the connectors, and the chemicals used in the installation of the fiber.

To comply with OSHA requirements, Material Safety Data Sheets (MSDS) for the chemicals should be available and referred to for specific precautions and instructions. This sheet should be read and filed with the others for future reference. Before handling a chemical for the first time, you should become familiar with its MSDS.

The typical chemicals used for cleaning will be isopropyl alcohol and acetone. Connectors will come with epoxies or require the use of a particular epoxy in their assembly. Other chemicals could be cable lube and gels. Operators should keep the effects of these chemicals in mind when connecting fiber optic cable.

David Lingenfelter is director of engineering for The Evers Group.