This section has been reviewed and updated as needed: April 2014
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. The manufacturer provides the classification for most lasers. For custom-built and modified lasers, the Laser Safety Officer can assist with classification.
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: some 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 3a 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; some laser pointers.
Class 3b Lasers
Class 3b lasers may cause severe eye injuries through direct or specular exposure. Examples: continuous lasers not exceeding 500[mW] for any period greater than 0.25[s]; pulsed visible lasers not emitting more than 30[mJ] per pulse; pulsed IR or UV lasers not emitting more than 125[mJ] during any period less than 0.25[s].”
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. Example: Lasers operating at power levels greater than 500 mW for continuous wave lasers or greater than 0.03 J for a pulsed system.