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Basic 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.

Electrical hazards
    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 turned off.
    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 tube.

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 laser equipment.

Fire 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.