Liquid Sky Lasers

Failure to manage lasers safely can lead to serious irreversible consequences with the damage occurring in a very short period of time. Of particular concern is the serious injury that can be caused to the eyes by the focusing of the radiation onto the retina.

Laser Classification

In BS:EN60825 lasers are classified according to their hazard potential and it is the classification which dictates the engineering and other controls that are necessary for safe use. Safety threshold limits for laser exposure are expressed in terms of the maximum permissible exposure (MPE). There are seven classes of lasers:

(a) Class 1

Laser products, which are safe under reasonably foreseeable conditions of use (i.e. the MPE for the eye cannot be exceeded).

This class may include products incorporating embedded lasers of higher class but which are normally enclosed, so preventing access to the laser radiation. Special requirements are defined in the standard for the interlocking of access panels through which the user could gain access to hazardous levels of laser radiation.

(b) Class 1M

Laser products producing either divergent or large-diameter beams for which the MPE for the eye cannot normally be exceeded unless magnifying instruments are used.

Refocusing the beam may increase the hazard and change the product class.

Laser products producing visible radiation (that is, between 400-700nm) for which direct viewing is not inherently safe, but for which protection is normally afforded by natural aversion responses to bright light, including the blink reflex. The MPE cannot be exceeded in less than 0.25 seconds, but prolonged deliberate viewing may be hazardous.

For continuous wave (CW) emission the limit is one milliwatt.

(d) Class 2M

Laser products producing visible radiation in the form of either divergent or large diameter beams for which the MPE for the eye cannot normally be exceeded in less than 0.25 seconds unless magnifying instruments are used.

The use of magnifying instruments (that is, microscopes and eye-loupes in the case of divergent beams, or telescopes and binoculars in the case of collimated beams) may produce hazardous levels of ocular exposure, otherwise protection is afforded by natural aversion responses to bright light, including the blink reflex.

Refocusing the beam may increase the hazard and change the product class.

(e) Class 3R

Laser products producing up to five times the accessible emission limit for Class 1 (if invisible) or five times the accessible emission limit for Class 2 (if visible).

The MPE can be exceeded but the risk of injury is low. Deliberate viewing of the beam should nevertheless be avoided.

For CW emission at visible wavelengths, the limit is five milliwatts.

(f) Class 3B

Laser products for which the MPE for the eye but not that for the skin may be exceeded.

Direct viewing of the laser beam can present a serious eye hazard. The viewing of diffuse beam reflections (that is, scattering of the beam from a diffusing surface on which it is incident) is normally safe.

For CW emission at wavelengths above 315nm, the limit is 0.5 watts.

(g) Class 4

Laser products for which the accessible emission exceeds that permitted for all other classes. Exposure to the beam can exceed the MPE for both the eyes and the skin.

Direct exposure to the beam can present serious eye and skin hazards, and the viewing of even diffuse beam reflections may be unsafe.

Fire and fume hazards may also exist. Use requires extreme caution.