Laser Safety - Electrical, Fire and Flood Hazards
When working around or experimenting with
lasers, one should be aware that there are electrical, fire and flood
hazards associated with even low power lasers.
Most medium and high power
lasers operate on 220 or even higher AC voltages; draw
lots of current and frequently use multi-phase electrical
connections. The power supply (exciter) for the laser
typically doubles or even triples the line voltages
before feeding them to the laser head where lethal
voltages can be present. An average of two people per
year die from laser electrocution.
If it become necessary to open the
power supply to diagnose or correct problems, you should
insure that the main power has been disconnected at the
breaker or disconnect switch. With the cabinet of the
laser head or exciter open, terminals carrying lethal
voltages may be exposed. In some systems large
electrolytic capacitors are used for smoothing DC
voltages. Even with 'bleed' resistors these can take
several minutes to discharge fully and should be treated
with caution and possibly discharged manually before
working on the system.
Even small HeNe lasers of the type found in school
science labs operate at very high voltages. While the power
supplies typically don't deliver enough amperage to kill you, they will
deliver a very nasty jolt that could cause heart palpitations. The
jolt could also cause one to drop and smash the laser. Before
connecting the laser to the power supply, insure that the AC power is
Most laser tubes act as a type of capacitor called a "Leaden
Jar". They can story a charge for some hours even after the
power has been turned off. When disconnecting small HeNe lasers
from their power supplies, be careful not to come in contact with the
pins on the Alden connector. You should short those together
briefly on an un-insulated strip of metal to discharge the tube before handling
the connector. Larger laser tubes, such as Argon of Krypton lasers
should be disconnected from the power supply and the leads to the tubes
shorted briefly at the connector before doing any work on or around the
HIGH VOLTAGES CAN
KILL YOU !!
An additional electrical hazard exists where
water cooling of the power supply (exciter) is used.
Minor leaks in the water cooling pipes can cause high
voltages to short to the water or case of the unit both
of which are usually at ground potential.
In high humidity conditions,
condensation can form on the water cooled parts inside
the laser power supply. In combination with dust and
residue in the power supply, the condensation can from a
conductive path shorting components and causing an
explosion. Condensation on water pipes and fittings
inside the laser head can also drip onto vital components
causing problems. Puddles of water on the floor are also
a hazard when working with the high voltages present in
and flood hazards
High power laser beams deflected
onto flammable materials can cause ignition and fires. A 10 watt laser
will drill a hole in cinder block (when focused). Almost any material
except metal is a potential fire hazard, especially wood and drapes (flameproof
drapes make little difference). Nylon or rayon clothing is especially
bad for burns as the plastic fabric melts and can cling to your skin increasing
the burn duration and intensity.
You should be aware of beam path positions and avoid
directing high power beams at dry bushes, drapes or other flammable surfaces.
Watch out for beams when you are around the projector so as to avoid burning
holes in your clothing and setting fire to your fashions.
Hoses connections at the water feed and the hoses themselves
can leak. Water cooled system can also leak in unexpected places inside
the equipment causing flooding and water damage. A further hazard
exists if there is a pool of water or a damp area on the floor as it provides
a good ground for an electrical discharge through your body. When
working around laser it is best to wear shoes that have insulated soles.
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