Lasers are classified according to their potential to cause biological damage. The pertinent parameters are:
- Laser output energy or power
- Wavelength
- Pulse duration
- Delivery system
- Open or Closed (is the beam exposed to the users, or is there an enclosure to confine the beams?)
Laser classification is marked on the equipment. Laser classes are:
- Class 1: A class 1 laser is safe under all conditions of normal use and poses no more risk than ordinary light. CD-ROM readers and laser printers are class 1 lasers. This class includes high-power lasers within an enclosure that prevents exposure to radiation, and that cannot be opened without shutting down the laser.
- Class 2: A Class 2 laser is safe because the blink reflex limits the exposure to no more than 0.25 seconds. It only applies to visible-light lasers (400-700 nm).
- Class 3R: A Class 3R laser is considered safe if handled carefully, with restricted beam viewing. Visible continuous lasers in Class 3R are limited to 5 mW.
- Class 3B: A Class 3B laser is hazardous if the eye is exposed directly, but diffuse reflections, such as from paper or other matte surfaces, are not harmful. Continuous lasers in the wavelength range from 315 nm to far infrared are limited to 0.5 W. For pulsed lasers between 400 and 700 nm, the limit is 30 megajoules (mJ).
- Class 4: Class 4 lasers include all lasers with beam power greater than class 3B. These lasers pose significant eye hazards as direct beam viewing can cause potentially devastating and permanent eye damage. Class 4 lasers can also cut or burn skin. These lasers may also ignite combustible materials and thus represent a fire risk, in some cases.