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Lasers have been classified by wavelength and maximum output power and then divided into four classes with subclasses. The classification categorizes lasers according to their ability to produce damage in exposed people, from class 1 (no hazard during normal use) to class 4 (severe hazard for eyes and skin).
The classification of a laser is based on the maximum power (in Watt) or energy (in Joule) that can be emitted in a specified wavelength range and exposure time. For infrared wavelengths above 4 microns it is specified as a maximum power density (in Watt/metre2). It is the responsibility of the manufacturer to provide the correct classification of a laser, and to equip the laser with appropriate warning labels and safety measures as prescribed by regulations. Safety measures used with the more powerful lasers include key-controlled operation, warning lights to indicate laser light emission, a beam stop or attenuator, and an electrical contact that the user can connect to an emergency stop or interlock.

Class I & IM (Exempt)
      • Exempt from user control measures
      • Incapable of producing damaging radiation levels
Completely enclosed machine with higher powered laser inside & optical communication systems

Class II & II M (Low Power)
      • Almost eye safe
      • Visible portion of the electromagnetic spectrum (0.4 to 0.7 microns)
      • Eye protection is the aversion response (blinking)
      • Continuous wave (CW) with an upper limit of 1 milliwatt (mW)
Supermarket or barcode scanners, low-powered laser pointers, laser printers, CD ROM, compact audio disks, leveling instruments and construction industry lasers

Class III a & now called III R
     • Operate between 1mW and 5mW (if visible) or up to 5 times Class 1 (in infrared and ultraviolet spectral regions)

Many laser pointers and construction alignment lasers

Class III b
A Class III b laser is hazardous if the eye is exposed directly, but diffuse reflections such as from paper or other matte surfaces are not harmful. Normally, Class III b lasers are continuous lasers in the wavelength range of 315 nanometers to far infrared and the power is limited to 0.5 Watt. For pulsed lasers, Class III b falls between 400 and 700 nanometers and the power limit is 30 MilliJoules. Other limits apply to other wavelengths and to ultra short pulsed lasers. Protective eyewear is typically required where direct viewing of a class III b laser beam may occur. Class 3b lasers must be equipped with a key switch and a safety interlock.

    •Operate between 5 mW and 500 mW
    •Not a significant fire or diffuse viewing hazard
    •Hazardous under direct and specular reflection viewing
Some military lasers, lasers used in therapeutic medicine, some research lasers

Class IV
Class IV lasers include all lasers with beam power greater than class III b. Class IV lasers must be equipped with a key switch and a safety interlock.
    • Operate above 500 mW
    • Hazardous to eye and skin from direct viewing and possibly by diffuse reflection
    • Potential fire hazard
    • May produce laser generated air contaminants
    • May produce hazardous plasma radiation
Laser used for cutting, drilling, marking welding materials, outdoor light shows and surgical lasers and many industrial, scientific, military, and medical lasers are found in this category

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