The American standard for laser safety eyewear only requires specification according to the optical density (OD) of the filters. The Optical Density (OD or D(λ)) is the attenuation of light that passes through an optical filter. The higher the OD value, the higher the attenuation. The American standard also allows a Nominal Hazard Zone (NHZ) to be determined by the laser safety officer (LSO). Outside of the NHZ, diffuse viewing eyewear is allowed.
However, in Europe there is a second criteria which must be taken into consideration - the power or energy density (i.e. the power or energy per area = per beam area). The "Diffuse viewing" condition is not allowed and laser safety glasses must protect against a direct laser exposure. Protection due to Optical Density alone is not sufficient when the material itself cannot withstand a direct hit. The European regulations are legal requirements and enforceable. Other legal requirements (e.g. the regulations for industrial safety as well as the medical equipment regulations) also refer to these.
At the area of application of the European laser safety standards laser safety glasses are ment to be lables as personal protective equipment (PPE) acc. to the standard EN 207 and/or EN 208. The marking acc. EN 207 must include the wavelength-/area, the operating mode (D, I, R or M), the protection level (LB-value), the CE-sign and the marking of manufacturer.
In order to achieve a certification according to EN 207 and to receive the CE-mark laser eye protection products require direct hit testing. The safety eyewear (filter and frame) must have to withstand under standardized conditions a direct hit from the laser for which they have been selected for at least 5 seconds (cw) or 50 pulses (pulsed mode). Behind the glasses the critical values of laser class 1 may not be exceeded. In countries which follow the European standard for personal protection it is not acceptable to select laser glasses according to Optical Density alone.
For the reason it is not possible to find a fitting filter for a set of parameters of the laser (wavelength, power or energy, repetition rate and diameter) which meet all requirements acc. DIN EN 207 or DIN EN 208 it is possible to choose a filter acc. a risk assessment which meets the requirements at the closest. This means that at least the optical density must be sufficient to meet the basic norm EN 60825-1. An authorized and certified filter ensures the test time of 5 sec. i.e. 50 pulses which is required from the standard. Up to the stated protection rates only!
For this kind of exceptional cases it is recommended, that the laser safety officer or safety engineer contacts the responsible Employer’s Liability Insurance Association in order to discuss the application in detail.
EN 208:2010-04 (EN)
This norm refers to glasses for laser alignment. They will reduce the actual incident power to the power of a class II laser (< 1mW for continuous wave lasers). Lasers denoted as class II are regarded as eye safe if the blink reflex is working normally. Alignment glasses allow the user to see the beam spot while aligning the laser.
Alignment glasses must also withstand a direct hit from the specified laser for at least 5 seconds (cw) or 50 pulses (pulsed mode) under standardised conditions.