Appendix C- Exposure
Limits and Laser Classification
The principle mechanism
for laser injury is thermal. As a result, there is a threshold
for the amount of thermal energy transferred to exposed
tissue below which there will be no injury. In order to
prevent laser injury, a system of exposure limits has been
established. Limits were promulgated as a consensus standard
by the American National Standards Institute (ANSI Z136.1-1993,
"American National Standard for Safe Use of Lasers"). These
limits were incorporated into regulations by the State of
Arizona (Arizona Administrative code Title 12 Chapter 1
Article 14, "Rules for the Control of Non-Ionizing Radiation").
Separate exposure limits exist for direct viewing of the
laser beam, viewing of a diffuse reflection, and for skin
A system of hazard classification
has also been developed and is part of the ANSI Standard
and State Regulations. It is usually more convenient to
establish safety controls based on the laser class than
use of the exposure limits. All lasers fall into one of
6 hazard classes.
Class I (Depends
Any laser or laser system
that cannot emit laser radiation in excess of the maximum
permissible exposure levels (MPE) discussed above is a Class
I laser. There is no hazard.
HOWEVER, it is important
to note that Class I laser systems often imbed more hazardous
lasers in the device. Removal of a protective housing may
result in access to radiation in excess of MPE's and implementation
of the Laser Safety Program for ARRA regulated lasers (IIIb
(less than or equal to 1 mW average power and if applicable
a pulse duration of less than 0.25 seconds)
These are low power lasers
emitting in the visible wavelengths (0.4 to 0.7 mm). These
lasers could result in exposure exceeding MPE's if intentionally
viewed for more than 0.25 seconds. Although, typically
this does not happen because of the normal "aversion response"
people are not allowed to stare at any laser beam. When
people view laser light, the natural response is to blink
and move the head and eye away from the bright uncomfortable
laser beam. An example of a Class II laser is a HeNe pointer
laser of 1 mW or less.
These laser are lasers
emitting light in the visible wavelengths (0.4 to 0.7 mm)
which are not intended for prolonged viewing and will not
produce a hazard if viewed directly for periods not exceeding
1000 seconds. The exposure will not exceed MPE's if viewed
for less than this amount of time.
(1 to 5 mW)
There are medium power
lasers that represent a potential hazard to the eye. Examples
would be visible lasers from 1 to 5 mW.
Note: Class IIIa
includes lasers with an accessible output between 1 and
5 times the Class I AEL for wavelengths shorter than 0.4
Ám or longer than 0.7Ám or less than 5 times the AEL for
wavelength between 0.4 and 0.7 Ám.
(access of IIIa power levels but typically less than 0.5
W average power)
The hazard for IIIb lasers
is potentially greater than that for IIIa. The hazard is
still limited to direct viewing of the laser beam, however.
These are lasers with output less than 0.5 Watt. These lasers
do not produce hazardous diffuse reflections or represent
a skin exposure hazard.
(0.5 W power or higher)
These are high powered
lasers that represent hazards (eye damage, skin injury,
and or potential flammable material ignition source) for
direct viewing, viewing of diffuse reflections, and skin
The power levels for Class
IV lasers are at 0.5 W and higher.