3. Laser Exposure Levels

3.1 MPE

MPE, or Maximum Permissible Exposure, is the the maximum level of laser radiation to which a human can be exposed without adverse biological effects to the eye or skin.

Factors important in determination of MPE

There are two factors involved in the determination of the MPE:

• the wavelength of the laser light
• the duration of the exposure

MPE values for eyes and skin are listed for various combinations of wavelength and exposure duration in Tables 5 and 7 of ANSI Standard Z136.1-2000 (ANSI stands for the American National Standards Institute), which is available from the Laser Institute of America. MPE values for the eye are also listed in Table 6 of the IEC 60825-1 standard, recently arranged in January 2001. (IEC stands for the International Electrotechnical Commission, which deals with international standards.)

3.2 NHZ

NHZ stands for Nominal Hazard Zone, and is the zone inside which laser radiation that is direct, reflected, or scattered exceeds the MPE for the laser. Control measures are not needed outside the NHZ.

3.3 NOHD

NOHD is an acronym for Nominal Ocular Hazard Distance. The NOHD is the distance along the axis of the direct laser beam to the human eye beyond which the MPE of the laser is not exceeded.