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Appendix B Laser Safety Information
Classification of Lasers
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sue. Damage to the retina occurs only when one looks at the light sufficiently
long that the product of the retinal irradiance and the viewing time exceeds
the damage threshold. Optical energies above 1400 nm cause corneal and
skin burns but do not affect the retina. The thresholds for injury at wave-
lengths greater than 1400 nm are significantly higher than for wavelengths
in the retinal hazard region.
Classification of Lasers
Manufacturers of lasers and laser products in the U.S. are regulated by the
Food and Drug Administration's Center for Devices and Radiological Health
(FDA/CDRH) under 21 CFR 1040. These regulations require manufacturers
to certify each laser or laser product as belonging to one of four major Classes
I, II, IIa, IIIa, IIIb, or IV. The International Electrotechnical Commission is an
international standards body that writes laser safety standards. Classification
schemes are similar with Classes divided into Classes 1, 2, 3A, 3B, and 4.
Lasers are classified according to the accessible emission limits and their
potential for causing injury. Lightwave systems are generally classified as
Class I/1, because, under normal operating conditions, all energized laser
transmitting circuit packs are terminated on optical fibers, which enclose the
laser energy with the fiber sheath forming a protective housing. Also, covers
are typically in place over the circuit pack shelves. The circuit packs them-
selves, however, may be FDA/CDRH Class I or IIIb or IEC Class 1 or 3B.
Lightwave Safety Precautions for Optical Fiber
Telecommunication Systems
In its normal operating mode, a lightwave system is totally enclosed and pre-
sents no risk of eye injury. It is a Class I/1 system under the FDA and IEC
classifications.
The lightguide cables that interconnect various components of a lightwave
system can disconnect or break, and may expose people to lightwave emis-
sion. Also, certain measures and maintenance procedures may expose the
technician to emission from the semiconductor laser during installation and
servicing. Unlike more familiar laser devices, such as solid-state and gas
lasers, the emission pattern of a semiconductor laser results in a highly diver-
gent beam. In a divergent beam, the irradiance (power density) decreases
rapidly with distance. The greater the distance, the less energy will enter the
eye, and the less potential risk for eye injury.
Inadvertently viewing an unterminated fiber or damaged fiber with the
unaided eye at distances greater than 5 to 6 inches normally will not cause
eye injury provided the power in the fiber is less than a few milliwatts at the
shorter wavelengths and a few tens of milliwatts at the longer wavelengths.
However, damage may occur if an optical instrument such as a microscope,
magnifying glass or eye loupe is used to stare at the energized fiber end.