LASER is an acronym which stands for Light Amplification by Stimulated Emission of Radiation. The laser produces an intense, highly directional beam of light. The human body is vulnerable to the output of certain lasers, and under certain circumstances, exposure can result in damage to the eye and the skin. Research relating to injury thresholds of the eye and skin has been carried out in order to understand the biological hazards of laser radiation. It is now widely accepted that the human eye is almost always more vulnerable to injury than human skin.

In order to regulate laser safety, the Center for Devices & Radiological Health (CDRH) classifies lasers into different categories based on wavelength and output power:

• Class 1

  A Class 1 laser is considered safe based upon current medical knowledge. This class includes all lasers or laser systems which cannot emit levels of optical radiation above the exposure limits for the eye under any exposure conditions inherent in the design of the laser product. There may be a more hazardous laser embedded in the enclosure of a Class 1 product, but no harmful radiation can escape the enclosure.

• Class II

  These lasers cannot cause eye injury under normal circumstances, they can produce injury if viewed directly for extended periods of time. Class 2 lasers only operate in the visible range (400 – 700 nm) and have power output equal or less than 1mW.

• Class IIIa

  Class 3a lasers cannot damage the eye within the duration of the blink. However, injury is possible if the beam is viewed through binoculars or similar optical devices, or by staring at the direct beam. Power outputs for Continuous Wave (CW) lasers operating in the visible range are between 1 – 5 mW.

• Class IIIb

  Class 3b lasers can produce accidental injuries to the eye from viewing the direct beam or a specularly reflected beam. Class 3b laser power outputs are between 5 – 500 mW for CW lasers.

• Class 4

  A Class 4 laser or laser system is any that exceeds the output limits (Accessible Emission Limits, AEL’s) of a Class 3 device. As would be expected, these lasers may be either a fire or skin hazard or a diffuse reflection hazard. Very stringent control measures are required for a Class 4 laser or laser system.

International Classification

The International Electrotechnical Commission (IEC) is a global organization that prepares and publishes international standards for all electrical, electronic and related technologies. The IEC document 60825-1 is the primary standard that outlines the safety of laser products. Classification is based on calculations and determined by the Accessible Emission Limit (AEL) as with the ANSI standard, but the IEC standard also incorporates viewing conditions:

• Class 1

  Lasers are very low risk and “safe under reasonably foreseeable use”, including the use of optical instruments for intrabeam viewing.

• Class 1M

  Lasers have wavelengths between 302.5 nm and 4000 nm, and are safe except when used with optical aids (e.g. binoculars).

• Class 2

  This class contains the low power sources whose spectrum is fully in the visible range (400 nm – 700 nm), with powers up to 1 mW. These sources are harmless for the eye because of the action reflex (i.e., when the eye is hit with a bright light, the eye lid will automatically blink or the person will turn their head to escape the bright light). This reaction to visible light ensures a sufficient protection in standard conditions of use, even if the user needs optical instruments to look at the beam.

• Class 2M

  Lasers have wavelengths between 400 nm and 700 nm, and are potentially hazardous when viewed with an optical instrument. Any emissions outside this wavelength region must be below the Class 1M AEL.

• Class 3R

  Lasers between 1 to 5mW of output power, are potentially hazardous but the risk is lower than that of Class 3B lasers. The accessible emission limit is within 5 times the Class 2 AEL for wavelengths between 400 nm and 700 nm, and within 5 times the Class 1 AEL for wavelengths outside this region.

• Class 3B

  This class is made of medium power laser sources, from 5 mW to 500 mW. they are normally hazardous under direct beam viewing conditions, but are normally safe when viewing diffuse reflections.

• Class 4

  Lasers are hazardous under both intrabeam and diffuse reflection viewing conditions. They may cause also skin injuries and are potential fire hazards. A continuous source of this class emits more than 500 mW.