Safety In Working With Optical Fiber
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Safety in the lab or on the job site
must be the number one concern of everyone. Besides the usual safety issues for construction,
generally covered under OSHA rules, fiber optics adds concerns for eye
safety, chemicals, sparks from fusion splicing, disposal of fiber
shards and more. Before beginning any installation, safety rules should
be posted on the classroom wall, lab wall or on the job site and reviewed with all onsite personnel. All
personnel must wear the usual construction safety gear plus everyone
must wear eye protection whenever working with fiber.
Eye Safety
Many people are concerned that the most dangerous part of fiber optic
work was the chance you might get your eyeballs burned out by laser
light in the fiber. They had confused optical fibers to the output of
high powered lasers used in labs. Or perhaps they had been going to the
doctor to get warts burned off their skin using lasers with fiber optic
probes or even seen too many science fiction movies.
In fact, most fiber optic systems do not have sufficient power to cause
harm to your eyes and the light coming out of a fiber is expanding so
the farther you are away from the end of the fiber, the lower the
exposure. Having said that, consider yourself warned. In more recent
times, some fiber optic systems are carrying sufficient power to be
dangerous and some fiber optic inspection techniques increase the
chance of harm. But that’s not the biggest danger facing installers.
Let’s look at the issues.
The key to
understanding the power issue is understanding power levels, wavelength
of the light and the nature of light transmission in optical fiber.
Fiber optic medical laser systems used for surgery and laser machining
systems certainly have enough power to cause harm to your eyes, as well
as burn off warts or machine some types of materials. Those systems use
very high power lasers, often CO2 lasers, which emit radiation at a
wavelength that is really heat not light, around 10 microns wavelength.
This wavelength is readily absorbed by materials and can heat them
quickly, cutting those materials easily.
In
medical applications, the heat not only cuts tissue, but it cauterizes,
stopping bleeding, a major advantage. It also cuts more precisely with
a small focused spot, allowing more exacting work to be done.
Laser machining also takes advantage of the smaller focused spot of the
laser, making it possible to create smaller holes or parts more
precisely than conventional machining. The smaller spot size also
reduces local heating, reducing the need for cooling and preventing
thin materials from warping.
Some of these high
power systems use fiber with focusing lenses on the end for delivery,
allowing use of a flexible probe that increases the flexibility of the
machine’s use. However, the power is so high that any dust or dirt on
the end of the fiber may be vaporized, causing damage to the end of the
fiber probe. 
Fiber optic communications systems use much less power. First of all,
most sources used in fiber optics are optimized for modulation speed,
not absolute power. In fact, in most telephone links, the laser has too
much power, so much it needs an attenuator at the receiver to prevent
overloading. Secondly, it you put too much power in a fiber, it
creates some types of secondary light emission that can add to the
noise in the system, causing problems.
Premises
cabling with multimode fiber and LED sources has very low power levels,
too low to be a hazard. Higher speed premises links use VCSEL lasers,
which are still quite low in power levels, and generally harmless.
Two types of links have high power, as much as 100 times more than
other communications systems, and they are CATV or video links at 1550
nm and telco long distance links using dense wavelength division
multiplexing (DWDM.) The CATV or video links used in fiber to the home
(FTTH - read more) may use fiber amplifiers (read more) that boost the power to very high
levels, potentially dangerous the eye. Telco DWDM links are used on
extremely long distance links (read more). They not only use fiber amplifiers for
boosting the power, but they have many different signals operating at
different wavelengths carried in one singlemode fiber. Any one
wavelength may not be a problem, but the sum of 16, 32 or 64 individual
wavelengths can be very powerful.
The next issue is focusing the light from a fiber into your eye. Light
exiting an optical fiber spreads out in a cone, the angle of which is
determined by the transmission characteristics of the fiber as defined
by the numerical aperture. As your eye is further from the end of the
fiber, the amount of radiation it receives is inversely proportional to
the square of the distance – double the distance and cut the power by
1/4, ten times the distance reduces the power to about 1%. You do not
have to be far away from the fiber for the power to be reduced to low
levels.
Because the light is
exiting the fiber in a cone-shaped beam, your eye cannot focus it on
the retina. This is unlike the typical lab laser or laser pointer that
shines a narrow, collimated beam that does not spread out; a beam your
eye can easily focus on the retina, causing temporary blindness.
Finally, there is an issue of wavelength. Your eye cannot see many of
the wavelengths used in fiber optics because the eye is sensitive to
light in the blue to red region of the spectrum while fiber optic
systems operate in the infrared. The liquid in your eye which is mostly
water, which absorbs light in the infrared heavily. Light from most
fiber optic sources will be absorbed by this liquid, so any potential
harm is likely to come to the lens or cornea, not the retina.
While the expanding beam of the light exiting the fiber makes it less
of an issue for direct viewing, using a fiber inspection
microscope can be a problem. We’ve tested this hypothesis ourselves,
and can confirm that a microscope will focus virtually all the light
back into the eye. Many microscopes used in fiber optics, therefore,
have filters to absorb any infrared (IR) light that could be harmful.
Be wary of inexpensive microscopes like the one shown, however, which may not have IR
blocking filters.
To be certain fibers are safe
to inspect or work with, always check fibers in an operating network
with a fiber optic power meter to ensure no light is present before
inspecting any connector with a microscope.
So to sum up what we have said: 1) Most fiber optic links are harmless
to eyes 2) Some links may be harmful, however, 3)Never take a chance –
check the link before inspecting it!
Bare Fiber Safety
Fiber optics installation, however, is not without risks. The more
common problem is getting scraps of fiber in your eye when working with
fiber. While few fiber optic systems have harmful levels of power,
every termination and splice produces shards (scraps) of optical fiber
which is potentially very harmful to your eyes and skin or may stick in
your clothing and be carried to other locations where it may be harmful
to others.
These shards of fiber are tiny, thin and often very
sharp where they broke off the fiber. They can easily puncture your
skin, burying themselves deep enough to be difficult to pull out, if
only you could see them. Being transparent they practically disappear
once imbedded in your skin. In most parts of your body, they merely
become a nuisance, perhaps infecting or causing an irritating bump,
until they eventually work themselves out.
Around your eye, however,
they can be much more difficult to find and remove. The tears that wet
your eyes make the transparent glass shards practically impossible to
find and remove. The sharp ends of the fiber may cause it to imbed
itself in the eye or surrounding tissue, making it even more difficult
to remove. Unlike metallic particles, they cannot be removed with
magnets,
It is imperative to follow procedures that minimize the
dangers to the eye. Always wear protective eyewear with side shields,
even if you normally wear glasses, to prevent any flying shards from
getting near your eyes. Do not trust normal eyeglasses, since taking
them off for a second allowed a fiber shard to land on my lower
eyelash, where luckily, I found and removed it.
Be
extremely careful whenever handling fibers, especially when stripping
fiber or scribing and breaking fiber extending out of an adhesive
connector. Instead of breaking it, scribe it gently, then slide your
fingers up the connector ferrule, grasping the fiber and pulling it
off. Then dispose of it carefully.
Most
cleavers used for splicing or terminating prepolished/splice connectors
hold the fiber after cleaving, so the only problem is disposing of it.
We recommend using disposable containers like those used for soups at
carry-out restaurants. Use it for all your fiber scraps and then seal
it and dispose of it properly.
You can also set up your workplace
to make it easier to avoid problems. Use a black plastic mat for a work
surface. The dark background will make it easier to see the fibers you
are working with and handle them more carefully. Any broken fibers that
fall on the mat are easily found for disposal.
Some techs like to
place a length of double stick tape or a loop of black electrical tape
on the mat and stick fibers to the adhesive surface, then dispose of
the tape when finished. I prefer to simply use a disposable container
and place every fiber scrap into that container rather than leave them
exposed on the work surface.
Other Considerations for Safety
Chemicals:
Fiber optic splicing and termination use various chemical cleaners and
adhesives as part of the processes. Normal handling procedures for
these substances should be observed. Even simple isopropyl alcohol,
used as a cleaner, is flammable and should be handled carefully.
Manufacturers will supply "material safety data sheets" (MSDS) on request or they
may be found on the Internet.
Splicing hazards: Fusion splicers use an
electric arc to make splices, so care must be taken to insure no
flammable gasses are present in the space where fusion splicing is done.
No Smoking:
Smoking should also not be allowed around fiber optic work. The ashes
from smoking contribute to the dirt problems with fibers, in addition
to the possible presence of combustible substances (and, of course, the health risks.)
This
is all very important – important enough to have a few workplace rules
for all fiber optic techs that can prevent workplace accidents:
Fiber Optic Installation Safety Rules
- Keep all food and beverages out of the work area. If fiber particles are ingested they can cause internal hemorrhaging.
- Work on a black work surface as it helps to find fiber scraps.
- 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.
- Always wear
safety glasses with side shields and protective gloves. Treat fiber
optic splinters the same as you would treat 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 lens 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 washed.
- Keep all combustible materials safely away from the curing ovens.
- Put all cut fiber pieces in a properly marked container for disposal.
- Thoroughly clean your work area when you are done.
- Do not smoke while working with fiber optic systems.
Note: Installation
of fiber optic cabling does not normally involve electrical hazards
unless the cable includes conductors. However, these cables are often
installed in proximity to electrical and conductive cables. Whenever
you are near these cables, there is always a potential shock hazard. Be
careful! If you are not familiar with electrical safety, we recommend
you take a course on the NEC (National Electrical Code) and safety
practices for installers!
Watch a Lecture on Safety on YouTube
Download a safety poster from the FOA!
More reading on safety in FOA Tech Topics
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