The World of Laser Safety according to the American Standard (ANSI Z136)
ANSI Z136 standard requires specification according to optical densities (OD) only. 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 mathematic expression of Optical Density (Dλ) is the logarithm to the base ten of the reciprocal of the transmittance and is given by the listed equation (where τλ is the transmittance). ANSI 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. Most Asian countries refer to these ANSI regulations. Australia has adopted new laser safety regulations that are based on the European laser safety regulations (EN 207/EN208).
The World of Laser Safety in Europe (EN 207/208/60825)
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). “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 of the eyewear cannot withstand a direct hit. The following regulations are called the “norm”, but in fact they are legal requirements and enforceable. Other legal requirements (e.g. the regulations for industrial safety as well as the medical equipment regulations) refer to them as well.
