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NOTE-MH01-EN rev05
2.4 Nominal Ocular Hazard Distance
Following the Standard IEC 60825-1, the MPE (Maximum Permissible Exposure), NOHD
(Nominal Ocular Hazard Distance) and OD (Optical Density) are calculated.
The formulas and the numerical coefficients are specified in Section 3, Chapter 13, Table 6,
Figures 1, 2, 5, 6, 7, 8 of IEC 60825-1 standard.
· The MPE level represents the maximum level to which an eye, or skin, can be exposed
without consequential injury, immediately or after a long time. The MPE is related to radiation
wavelength, pulse duration or exposure time, the tissue at risk and, for visible and near infrared
radiation in the 400-1400nm range, to the size of the retinal image.
· The NOHD is the distance at which the beam irradiance or radiant exposure equals the
appropriate corneal maximum permissible exposure.
· The OD of the protective goggles to be worn is defined as:
OD = log
10
(H
0
/MPE)
Where H
0
is the expected unprotected eye exposure level.
Please, refer to previous section 2.6 for further details concerning the protection level in
googles.
Laser system has to be used in a closed area that does not allow the escape of direct, reflected
or transmitted laser radiation.
Doors equipped with a special interlocking system have to be made of a laser non-transparent
material (glass, plastic, curtains, etc.) and windows have to be darkened by using appropriate
laser non-transmissive systems.
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