Limitations of Optical Density Specification

The problems with this approach are graphically illustrated if we consider a high power CO2 laser emitting at 10600 nm, and some polycarbonate eyewear having an OD > 6 at the same wavelength. The Class 1 Accessible Emission Limit for this wavelength is 10 mW and this power is therefore safe under all exposure conditions. We might therefore expect that the eyewear will protect us against 1,000,000 x 10 mW = 10 kW from the CO2 laser. However, if we place the eyewear in a CO2 laser beam of even a few hundred watts we find that it is very quickly destroyed and offers little protection (even a 20 W beam will cause immediate burning of the eyewear).