Lasers are divided into a number of classes depending upon
the power or energy of the beam and the wavelength of the emitted radiation. Laser
classification is based on the laser's potential for causing immediate injury to the eye
or skin and/or potential for causing fires from direct exposure to the beam or from
reflections from diffuse reflective surfaces. Since August 1, 1976, commercially produced
lasers have been classified and identified by labels affixed to the laser. In cases where
the laser has been fabricated on campus or is otherwise not labeled, Health Physics should
be consulted on the appropriate laser classification and labeling. Lasers are classified
using physical parameters of the laser, power, wavelength and exposure duration.
A qualitative description of laser classes follows:
Class 1 lasers
Class 1 lasers are considered to be incapable of producing
damaging radiation levels, and are therefore exempt from most control
measures or other forms of surveillance. Example: laser printers.
Class 2 lasers
Class 2 lasers emit radiation in the visible portion
of the spectrum, and protection is normally afforded by the normal
human aversion response (blink reflex) to bright radiant sources.
They may be hazardous if viewed directly for extended periods of
time. Example: laser pointers.
Class 3 lasers
Class 3a lasers are those that normally would not
produce injury if viewed only momentarily with the unaided eye.
They may present a hazard if viewed using collecting optics, e.g.,
telescopes, microscopes, or binoculars. Example: HeNe lasers above
1 milliwatt but not exceeding 5 milliwatts radiant power.
Class 3b lasers can cause severe eye injuries if beams
are viewed directly or specular reflections are viewed. A Class
3 laser is not normally a fire hazard. Example: visible HeNe lasers
above 5 milliwatts but not exceeding 500 milliwatts radiant power.
Class 4 lasers
Class 4 lasers are a hazard to the eye from the direct
beam and specular reflections and sometimes even from diffuse reflections.
Class 4 lasers can also start fires and can damage skin.
Safety Manual, page 28-2)
NOTES: Retinal injuries can occur instantaneously
with Class 3b and Class 4 lasers; the damage may be irreparable.
Corneal burns from far-IR and UV lasers may also be irreparable.
Class 4 beams may be of sufficient power intensities to penetrate
through the sclera (white) of the eye and damage the retina and
other structures; thus, turning one's head or not looking directly
at the laser offers little or no protection to high power lasers.
Lenticular damage may also be caused by the beam and by photochemical
reactions from exposure to UV and blue frequencies.
Table 1 and Table
2 show examples of lasers in various classes.