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- Class I lasers - Lasers that are not hazardous for continuous
viewing or are designed in such a way that prevent human access to laser
radiation. These consist of low power lasers or higher power embedded
lasers (i.e., laser printers).
- Class II visible lasers (400 to 700 nm) - Lasers emitting visible light which
because of normal human aversion responses, do not normally present a
hazard, but would if viewed directly for extended periods of time. (like
many conventional light sources).
- Class IIa visible lasers (400 to 700 nm) - Lasers emitting visible light not
intended for viewing, and under normal operating conditions would not
produce a injury to the eye if viewed directly for less than 1,000 seconds
(i.e. bar code scanners).
- Class IIIa lasers - Lasers that normally would not cause injury to
the eye if viewed momentarily but would present a hazard if viewed using
collecting optics (fibre optics loupe or telescope).
- Class IIIb lasers - Lasers that present an eye and skin hazard if
viewed directly. This includes both intrabeam viewing and specular
reflections. Class IIIb lasers do not produce a hazardous diffuse
reflection except when viewed at close proximity.
- Class IV lasers - Lasers that present an eye hazard from direct,
specular and diffuse reflections. In addition such lasers may be fire
hazards and produce skin burns.
Here is another description, paraphrased from the CORD
course: "Intro to Lasers". (Cord
Communications. Lasers.) It relates the laser classifications to
common laser types and power levels:
- Class I - EXEMPT LASERS, considered 'safe' for intrabeam
viewing. Visible beam.
Maximum power less
than 0.4 uW. This will not cause damage even where the entire beam enters the
eye and it is being stared at continuously.
- Class II - LOW-POWERED VISIBLE (CW) OR HIGH PRF LASERS,
won't damage your eye if viewed momentarily. Visible beam.
Maximum power less
than 1 mW for HeNe laser.
- Class IIIa - MEDIUM POWER LASERS, focused beam can injure
the eye.
HeNe laser power
1.0 to 5.0 mW.
- Class IIIb - MEDIUM POWER LASERS, diffuse reflection is not
hazardous, doesn't present a fire hazard.
Visible Argon
laser power 5.0 mW to 500 mW.
- Class IV - HIGH POWER LASERS, diffuse reflection is
hazardous and/or a fire hazard.
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