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Laser safety overview

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Laser Science Projects

Laser Safety Overview

Caution Laser In Use sign

    All laser light show systems have intrinsic dangers. Observation of basic laser safety rules and the specific safety regulations of the jurisdiction in which you operate the laser are essential.

    This page is a brief overview of laser safety, for more detailed information see the Laser Safety pages.

    A laser can be considered as a highly collimated source of extremely intense electromagnetic radiation.  Due to the temporal and spatial coherence of the laser beam it can be considered as a point source of phenomenal brightness than can easily exceed the brightness of the sun. Lasers are a more directional light source than any other common fixture such as stage lights or a follow-spot. The higher the optical output power of the laser, the greater the potential hazard.

Laser Hazards

    The danger from lasers can be divided into the following major categories:

  1. Eye hazards such as retinal or cornea burns.
  2. Skin hazards such as burns.
  3. Electrical hazards from high voltage equipment.
  4. Fire and flood hazards.


Eye Hazards
   
The major danger of laser light shows is hazards from beams entering the eye since this is the organ most sensitive to light. The simplest way to explain this is to say, "just as a magnifying glass can be used to focus the sun and burn wood, the lens in the human eye focuses the laser beam into a tiny spot than can burn the retina".
   
The maximum absorption of laser energy in the retina occurs in the range from 550 nM to 400 nM. Argon and YAG lasers operate in this range clearly making them the most hazardous lasers. Wavelengths of less than 550 nM can cause a photochemical injury similar to sunburn. Photochemical effects are cumulative and result from long exposures (over 10 seconds) to diffuse or scattered light.
   
The laws of thermodynamics do not limit the power of lasers. The second law states that the temperature of a surface heated by a beam from a thermal source of radiation cannot exceed the temperature of the source beam. The laser is a non-thermal source and is able to generate temperatures far greater than it's own. A 30 mW laser operating at room temperature is thus capable of producing enough energy (when focused) to instantly burn through paper!
   
Due to the law of the conservation of energy, the energy density (measure of energy per unit of area) of the laser beam increases as the spot size decreases. This means that the energy of a laser beam can be intensified up to 100,000 times by the focusing action of the eye. A one watt laser beam when focused down to a small spot can produce temperatures higher than the surface temperature of the sun! Thus even a low power laser in the milliwatt range can cause a burn if focused directly onto the retina.

NEVER point a laser at someone's eyes no matter how low power the laser.

    Eye damage can also occur when laser beams are scanned across the eye even for very brief periods. The amount of exposure is difficult to estimate as 'dwell' or 'transit' time must be taken into account in your calculations. For example a 1 mW laser illuminating a 7 mm aperture (the average size of the dark adapted iris) for one second is the equivalent of a 10 mW laser illuminating the same 7 mm aperture for 1/10 of a second.  The international laser safety standard, IEC-825, defines a short exposure as 2.5 mW per square centimeter. Each jurisdiction has it's own maximum exposure levels for laser radiation.
  
Symptoms of a laser burn in the eye include a headache shortly after exposure, excessive watering of the eyes, and sudden appearance of many 'floaters' in your vision. Floaters are those swirling distortions that occur randomly in normal vision most often after a blink or when you have had your eyes closed for a couple of seconds.

 

Skin Hazards
   
Exposure of the skin to high power laser beams (1 or more watts) can cause burns. At the under five watt level, the heat from the laser beam will cause a flinch reaction before any serious damage occurs. The sensation is similar to touching any hot object, you tend to pull your hand away or drop it before any major damage occurs.  With higher power lasers a burn can occur even though the flinch reaction may rapidly pull the affected skin out of the beam.

 

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.

HIGH VOLTAGES CAN KILL YOU !!

 

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).
    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.

 

BASIC SAFETY PRECAUTIONS

NEVER point a laser in someone's eyes, even low power hand held units can cause eye damage due to the focusing effect of the lens in the eye.

NEVER use mirrors or watch crystals to deflect static laser beams as you can cause eye damage to yourself or other spectators.

NEVER float Mylar coated balloons these into the beam paths above the audience as they can cause unexpected reflections of the beam into people's eyes.

NEVER deflect laser beams with hand held mirrors as they are difficult to control and can direct beams in unexpected ways causing eye damage.

NEVER track a moving vehicle such as a car or aircraft with a laser, even a very low power hand held HeNe unit or laser pointer. With higher power units you may temporarily blind the operator or destroy their night vision. Even low power lasers may cause a distraction of the driver/pilot leading to an accident.

To eliminate skin burns, don't stick your body parts into high power laser beams.

 

Electrical Safety

   When working on the electrical systems of lasers, use the 'buddy' system. In the event that you come in contact with a live high voltage AC power line, your muscles will spasm making it difficult or impossible to let go of the line. Your 'buddy' should use a broom stick to whack your hand off the power terminals.
   
If you have to operate the laser system with the cabinets open (E.G. when troubleshooting), have an assistant standing by to disconnect the power at the main switch/breaker in case of problems.
    To avoid electrical problems from water in the exciter (power supply), check that all fittings are tight, replace worn washers and keep the floor dry.

    This page is a summary of laser safety information - for more details, see the Laser Safety pages.

 

[ Introduction | Bibliography | Glossary of Terminology | Laser safety overview | Other applications of lasers | Selected laser related web sites | Basic laser science projects | Intermediate laser science projects | Advanced laser science projects | Illustrations for laser science projects ]

 

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