Safety In Working With
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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
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.
Light In Most Fiber Optic Networks Is Invisible To The Human Eye
First, there is an issue of
wavelength. Your eye cannot see many of the
used in fiber optics because the eye is sensitive
in the blue to red region of the spectrum while
optic systems operate in the infrared. If there is
dangerous levels of power in a fiber, you cannot see it in time to
avoid it; you must test for power with a power meter or some some device
that measures infrared light or converts it to visible light. The
liquid in your
eye which is mostly water, which absorbs light in
infrared heavily. Light from most fiber optic
be absorbed by this liquid, so any potential harm
likely to come to the lens or cornea, not the
Power In Fiber Optic Networks
Most fiber optic systems communications 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 (see below).
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 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,
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
Safety In High Power OSP Links
Two types of links have high power, as
much as 100 times more than other communications systems,
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
WDM (wavelength division multiplexing) networks have many
wavelengths of light and the total power in the fiber is the sum of all
the power from all the wavelengths.
Fiber amplifiers used in many WDM networks can increase the power by 20 dB - 100 times - or more.
Is it safe for fiber techs repairing cut fiber optic cables to splice OSP networks that use fiber amplifiers as repeaters?
The answer is not a simple yes/no! The short answer is YES; the long answer is more technical and includes details that every OSP tech needs to know.
Fiber amplifiers have been around for decades, replacing electronic
repeaters that convert a signal from the optical domain back into the
electrical domain, remove some noise and retransmit it as an optical
signal. Fiber amps replaced them because they used too much power and
were unreliable. Fiber amplifiers
are used in WDM systems where there can be power from a number of
different wavelengths, increasing the total power, or in analog systems
like CATV HFC systems where high power DFB lasers are used.
The most common fiber amp (EDFA - erbiun-doped fiber amplifier) uses
some complex physics that allows light entering a special fiber
(generally erbium-doped fiber) to be amplified by the light from a high
power "pump laser" at a different wavelength (980 or 1480 nm). Pump
lasers can be as powerful as 10 watts, +40 dBm! Fiber amplifiers have
gains of around 20 dB, so a "0 dBm" laser (1 mw) input will be amplified
to +20 dBm (100 mw). That is a LOT of optical power.
A second type of fiber amp (RAMAN) uses the transmission fiber to
amplify the signal using high-power pump lasers, sometimes at both ends
of the fiber, at particular wavelengths. These are less common.
The problem that field techs need to worry about is whether a fiber amp
will shut down if the link is broken. Transmission equipment generally
shuts down the transceiver if the receive sees no input and initiates an
alarm. If there are fiber amps in the link, will they shut down if
there is no input? The answer is maybe.
The problem seems to be a lack of standardization in fiber amp design.
Some amps have sensors on the input that shuts down the pump laser when
there is no input. Those should be safe. But most designs, it seems, do
not have that feature. We talked to two manufacturers and two users and
the consensus is that fiber amps will have the output of the pump laser
on the output fiber even with no signal at the input.
One user tested a unit with an input sensor. With a range of inputs from
-12 to -4 dBm, the output was a constant at around +20 dBm. Below, -12
dBm, the output was zero - no light at all - even though the EDFA was
switched on. However, when the EDFA was switched off, the unit was
simply a passive component and would transmit signals at 1490 nm but not
at 1550 nm, probably due to a WDM component in the output.
We talked to a manufacturer who mentioned that some EDFAs are
designed this way and some are just amps. For example, he told me their
products will produce ~20 dB gain, so an input of 1 mw will yield ~100
mw output. But if you remove the input, the amp will amplify the noise
and transmit the pump laser on the output which will be about 30 mw,
with the bulk of the power in the pump laser wavelength. A WDM will
filter out the pump laser, but if a tech looks at a broken fiber with
this fiber amp as an input, he will still be looking at a 30 mw optical
It appears that the fiber tech doing restoration on broken OSP
fibers needs to have assurance that either the network does not have any
fiber amps in the link being repaired or the network has been
completely powered down - including the amps.
Never look into a fiber end or get it near your eye since a broken fiber can emit light at an angle.
Before working on any fiber, test it with a power meter to see if power is present.
And the tech probably should wear special laser safety glasses, but we
have not found any yet that cover the entire wavelength range needed.
Focusing Light Into The Eye Can Be Dangerous
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
Hint: The camera in many early cell
phones is sensitive to light in
the infrared. So if you think a fiber has light being
transmitted through it, use an old cell phone to take a
picture of it. But try your cell phone first - here are
photos of a test source taken with an older Motorola Razor
phone from the early 2000s. Here
is a video showing how it works.
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
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 may eventually work themselves out.
X-Ray showing fiber shard imbedded in finger.
courtesy Brian Brandstetter, Mississauga
Training Consultants, www.fiberoptictraining.com
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
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.
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
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
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
all food and beverages out of the work area. If fiber
particles are ingested they can cause internal
on a black work surface as it helps to find fiber
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
wear safety glasses with side shields and protective
gloves. Treat fiber optic splinters the same as you
would treat glass splinters.
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..
work in well ventilated areas.
lens wearers must not handle their lenses until they
have thoroughly washed their hands.
not touch your eyes while working with fiber optic
systems until your hands have been thoroughly washed.
all combustible materials safely away from the curing
all cut fiber pieces in a properly marked container
clean your work area when you are done.
not smoke while working with fiber optic systems.
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!
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