Virtually all of the U.S. and international standards divide all lasers into
four major hazard categories called the laser hazard classifications.
The basis of the classification scheme is the ability of the primary or reflected
primary beam to cause biological damage to the eye or skin during intended use.
The criteria is established relative to the Maximum Permissible Exposure (MPE)
levels that are accessible during operation of the laser.
The laser hazard classes are given as:
- Class I: Cannot emit laser radiation at known hazard levels (typically CW:
0.4 micro-watts at visible wavelengths). Users of a Class I laser products are generally
exempt from radiation hazard controls during operation and maintenance (but not
necessarily during service). Since lasers are not classified on beam access during
service, most all Class I industrial lasers will consist of a higher class (high
power) laser enclosed in a properly interlocked and labeled protective enclosure.
In some cases, the enclosure may be a room (walk-in protective housing) which
requires a means to prevent operation when operators are inside the room.
- Class II: Low power visible lasers which emit above Class I levels but emitting
a radiant power not above 1 mW. The concept is that the human aversion reaction
to bright light will protect a person.
Note: Class IIA is a special designation that is based upon a 1000 second exposure
and applies only to lasers that are "not intended for viewing" such as a supermarket
laser scanner. The upper power limit of Class IIA is 4.0 micro-Watts. These are products
whose emission does not exceed the Class I limit for an emission duration of 1000
seconds.
- Class IIIA: Intermediate power lasers (CW: 1-5 mW). Only hazardous for intrabeam
viewing. Some limited controls are usually recommended.
Note: There are different labeling requirements for Class IIIA lasers with a beam
irradiance that does not exceed 2.5 mW/cm(2) (Caution logotype) and those where
the beam irradiance does exceed 2.5 mW/cm(2) (Danger logotype).
- Class IIIB: Moderate power lasers (CW: 5-500 mW, pulsed: 10 J/cm(2) - or
the diffuse reflection limit, which ever is lower). In general, Class IIIB lasers
will not be a fire hazard and are not generally capable of producing a hazardous
diffuse reflection except for conditions of intentional staring done at distances
close to the diffuser. Specific controls are recommended.
- Class IV: High power lasers (cw: 500 mW) are hazardous to view under any
condition (directly or diffusely scattered) and are a potential fire hazard and
a skin hazard. Significant controls are required of Class IV laser facilities.
- Embedded Laser: A Class II, Class III, or Class IV laser or laser system
contained in a protective housing and operated in a lower classification (Class
I, Class II or Class III). Specific control measures may be required to maintain
the lower classification.
