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Department of Computer Science and Technology


Laser radiation can cause severe eye and skin damage, potentially even at large distance. To manage this risk, the University has established rules for the safe use of lasers on its premises.

Laser-safety classes

Lasers vary greatly in output power and other parameters. They are categorised by the relevant safety standard (BS EN 60825) into seven classes of increasing risk level:

  • Class 1 lasers are considered generally safe, either because of their low output power, or because they are embedded into an enclosure that prevents any person from being exposed to the laser beam during normal operation. (Example: CD/DVD writer, laser printer)
  • Class 1M lasers are considered safe if optical viewing aids are not used (binoculars, telescope, microscope, magnifying glass, etc.). The hazard arises from a large area beam or a widely diverging beam, which may be focussed onto a smaller area of the skin or eye if an optical instrument is used.
  • Class 2 lasers are considered safe as long as nobody deliberately stares into the beam. Class 2 lasers emit only visible light with a maximum power of 1 mW, which will not cause eye damage within the time (0.25 s) that the eye needs to protect itself via the natural aversion reflex that closes the eyes under bright light. (Example: most laser pointers)
  • Class 2M is as safe as Class 2 if no optical instrument is used by the exposed viewer.
  • Class 3R lasers can potentially damage the eye if the beam is viewed directly or via specular (mirrored) reflection, but are considered safe to the skin.
  • Class 3B lasers will normally damage the eye if the beam is viewed directly. Specular (mirrored) reflection may also be hazardous, but diffuse reflections are normally safe. The upper power limit is 500 mW. (Example: the laser diode inside a CD writer)
  • Class 4 lasers are harmful to eyes and skin, even diffuse reflections are hazardous. Class 4 lasers may also present a fire hazard. (Examples: laser welding machines)

Equipment sold in the United States declares instead classes I, II, IIa, IIIa, IIIb, IV according to ANSI Z136.1, which are roughly similar, but not identical.

Laser equipment usually comes with a yellow sticker on which the manufacturer identifies its safety class. In case of doubt, ask the Departmental Laser Safety Officer.

Departmental Laser Safety Officer

The Departmental Laser Safety Officer (LSO) is the first contact for advice on the safe use of lasers. For the Computer Laboratory, this is currently Dr Markus Kuhn (phone 34676, room GE16).


Authorized use of lasers in the department


  • use or new use of Class 3R, 3B or 4 lasers,
  • modifications, repairs or servicing of lasers (any class),

at the Computer Laboratory requires the written authorization of the Departmental Laser Safety Officer (laser authorization form) and a risk assessment.

The Departmental Laser Safety Officer should also be kept informed of any planned

  • not yet classified prototypes or experiments involving lasers,
  • servicing of lasers,
  • experiments with high-intensity UV or IR sources.

There is no need to report normal office equipment with lasers (laser pointers, laser printers, barcode scanners, CD/DVD drives, fiber-optical transmitters, etc.), as long as it is declared by the manufacturer to be a Class 1 or 2 laser device and it is used as described in the manual (i.e., nobody opens, repairs or modifies it).

Laser controlled areas

Class 3B and 4 lasers in the department must be operated only by authorized and registered laser users who have received the required training and are who familiar with the local rules for the use of this equipment. These local rules are developed during the risk assessment. In addition, Class 3B and 4 lasers must only be used in dedicated rooms, as advised by the LSO. These dedicated rooms must be marked on the outside with the black-on-yellow star-shaped laser warning sign (see graphic above), usually next to the room-number sign.

In case of an accident

If there is any laser incident or accident at the department, inform the Departmental Laser Officer (Dr Markus Kuhn) and the Departmental Safety Officer (Dr Piete Brooks).

If an eye injury is suspected, the injured person should consult Occupational Health if possible and see a specialist ophthalmologist within 24 hours (at Addenbrookes Hospital or Moorfields Eye Hospital). The injured person must not drive.

See Safe Use of Lasers, Section 11.9 (page 58) for more information and emergency contact details.

For more information on laser safety and related topics, see