Stanford University Laser Safety Manual

Definitions of Classes of Lasers
Assistance in Laser-Related Problems
Eye Protection
Medical Surveillance
Written Procedures
Engineering Controls for Laser Systems
Control of Laser Areas
Posting and Warning Systems for Laser Controlled Areas
Projection of Beams Outdoors or in Public Areas
Ancillary Hazards
UV Lasers
Inventory, Acquisition and Transfer (Disposal)

Definitions of Classes of Lasers
Table 1
Table 2

Lasers are divided into a number of classes depending upon the power or energy of the beam and the wavelength of the emitted radiation. Laser classification is based on the laser's potential for causing immediate injury to the eye or skin and/or potential for causing fires from direct exposure to the beam or from reflections from diffuse reflective surfaces. Since August 1, 1976, commercially produced lasers have been classified and identified by labels affixed to the laser. In cases where the laser has been fabricated on campus or is otherwise not labeled, Health Physics should be consulted on the appropriate laser classification and labeling. Lasers are classified using physical parameters of the laser, power, wavelength and exposure duration.

A qualitative description of laser classes follows:

Class 1 lasers

Class 1 lasers are considered to be incapable of producing damaging radiation levels, and are therefore exempt from most control measures or other forms of surveillance. Example: laser printers.

Class 2 lasers

Class 2 lasers emit radiation in the visible portion of the spectrum, and protection is normally afforded by the normal human aversion response (blink reflex) to bright radiant sources. They may be hazardous if viewed directly for extended periods of time. Example: laser pointers.

Class 3 lasers

Class 3a lasers are those that normally would not produce injury if viewed only momentarily with the unaided eye. They may present a hazard if viewed using collecting optics, e.g., telescopes, microscopes, or binoculars. Example: HeNe lasers above 1 milliwatt but not exceeding 5 milliwatts radiant power.

Class 3b lasers can cause severe eye injuries if beams are viewed directly or specular reflections are viewed. A Class 3 laser is not normally a fire hazard. Example: visible HeNe lasers above 5 milliwatts but not exceeding 500 milliwatts radiant power.

Class 4 lasers

Class 4 lasers are a hazard to the eye from the direct beam and specular reflections and sometimes even from diffuse reflections. Class 4 lasers can also start fires and can damage skin.

(Reference: LLNL Safety Manual, page 28-2)

NOTES: Retinal injuries can occur instantaneously with Class 3b and Class 4 lasers; the damage may be irreparable. Corneal burns from far-IR and UV lasers may also be irreparable. Class 4 beams may be of sufficient power intensities to penetrate through the sclera (white) of the eye and damage the retina and other structures; thus, turning one's head or not looking directly at the laser offers little or no protection to high power lasers. Lenticular damage may also be caused by the beam and by photochemical reactions from exposure to UV and blue frequencies.

Table 1 and Table 2 show examples of lasers in various classes.