Classification of lasers

All working laser systems purchased from a manufacturer must carry a label stating the class of that system. This should not be removed or altered in any way unless the system is itself modified in such a way as to alter its class. Should this be done, the Laser Safety Service must be consulted over the reclassification of the system.

In line with variously agreed national and international standards (British Standards Institution, International Electrotechnical Commission) all lasers are assigned an appropriate classification. The criteria for the assigning of a class to a laser system are complex. The following is no more than a broad indication of the meaning of the class and the implications for the system it describes.

Class 1: Lasers that are safe under reasonably foreseeable conditions of operation, including the use of optical instruments for intrabeam viewing.

Class 1M: Lasers emitting in the wavelength range from 302.5 nm to 4,000 nm which are safe under reasonably foreseeable conditions of operation, but may be hazardous if the user employs optics within the beam, Two conditions apply:

for diverging beams if the user places optical components within 100 mm from the source to concentrate (collimate) the beam; or
for a collimated beam with a diameter larger than the diameter specified for the measurements of irradiance and radiant exposure

Class 2: Lasers that emit visible radiation in the wavelength range from 400 nm to 700 nm where eye protection is normally afforded by aversion responses, including the blink reflex. This reaction may be expected to provide adequate protection under reasonably foreseeable conditions of operation including the use of optical instruments for intrabeam viewing.

NOTE Outside the wavelength range from 400 nm to 700 nm, any additional emissions of Class 2 lasers are required to be below the AEL of Class 1.

Class 2M: Lasers that emit visible radiation in the wavelength range from 400 nm to 700 nm where eye protection is normally afforded by aversion responses including the blink reflex. However, viewing of the output may be more hazardous if the user employs optics within the beam. Two conditions apply:

for diverging beams, if the user places optical components within 100 mm from the source to concentrate (collimate) the beam, or
for a collimated beam with a diameter larger than the diameter specified for the measurements of irradiance and radiant exposure.

NOTE Outside the wavelength range from 400 nm to 700 nm, any additional emissions of Class 2M lasers are required to be below the AEL of Class IM.

Class 3R: Lasers that emit in the wavelength range from 302.5 nm to 10⁶ nm where direct intrabeam viewing is potentially hazardous but the risk is lower than for Class 3B lasers, and fewer manufacturing requirements and control measures for the user apply than for Class 3B lasers. The accessible emission limit is within five times the AEL of Class 2 in the wavelength range from 400 rim to 700 nm and within five times the AEL of Class 1 for other wavelengths.

Class 3B: Lasers that are normally hazardous when direct intrabeam exposure occurs (i.e. within the NOHD). Viewing diffuse reflections is normally safe.

Class 4: Lasers that are also capable of producing hazardous diffuse reflections. They may cause skin injuries and could also constitute a fire hazard. Their use requires extreme caution.

NOTE For rule-of-thumb purposes, for continuous-wave lasers, Class 2 lasers are powered below 1 mW, Class 3R lasers between 1 and 5 mW, Class 3B lasers between 5 and 500 mW, Class 4 lasers anything above this power.

Classification of lasers

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