1. Laboratory Design
A laboratory in which Class 3B and Class 4 lasers are used must display a laser hazard warning sign on entrance doors to warn people entering the laboratory. It is highly recommended practice that in addition, an illuminated ‘Laser Active – Do Not Enter’ warning light is fitted to the entrance door, in a clearly visible position, electrically linked to the laser(s) such that the warning is illuminated when the laser is switched on.
Protective measures should be considered at the design and lay-out stage of a laser laboratory. For example:
- There should be access control to the laboratory which must be properly managed e.g. secure key/PIN control
- Access prevention to hazardous parts of the laser equipment must be considered e.g. the use of enclosures, physical barriers, fixed guards or moveable guards with interlocks.
- Interlocks must be robust and reliable and consideration must be made for the type of conditions and treatment the devices will likely be subject to in the laboratory. Interlocks such as electro-mechanical, magnetic and proximity switches are examples, which will be suitable in different situations.
- Appropriate incorporation and use of remote viewing (e.g. CCTV), viewing windows and filters should be considered.
- Provision and use of operation limiting protection such as photo-electric light curtains, passive infra-red detectors, pressure-sensitive mats and edges should be considered.
- Provision of emergency stops should be considered.
If practicable a laser laboratory should have a high level of illumination that will minimise pupil size and reduce the risk of stray laser light reaching the retina. Windows should be kept to a minimum and may need to be covered or protected by blinds. These should be non-reflective and may need to be fireproof where higher-powered lasers are used.
Walls, ceilings and fittings should be painted with a light coloured matt paint to enhance illumination and minimise specular reflections. Reflecting surfaces such as the use of glass-fronted cupboards should be avoided.
Ventilation is important especially with higher-powered lasers if cryogens are used, or if toxic fumes are produced that need to be extracted and in this case it is important that the extraction is very close to the source. Facilities may also be needed for the handling of toxic chemicals that are associated with some dye lasers. Handling of toxic chemicals and fumes must be covered under COSHH risk assessment.
The laboratory should be equipped with appropriate fire fighting equipment.
Electrical supplies, switch and control gear should be sited in order to:-
- enable the laser to be shut down by a person standing next to the laser;
- enable the laser to be made safe in an emergency from outside the laser area if reasonably practicable;
- prevent accidental firing of a laser;
- provide an indication of the state of readiness of the laser;
- enable personnel to stand in a safe place;
- provide sufficient and adequate power supplies for all ancillary equipment and apparatus so that the use of trailing leads is minimised.
2. Experimental set-up
Before starting work with a laser there are a number of basic risk reduction measures that should be considered.
- Can a lower powered laser be used?
- Can output power of laser be restricted if full power is not needed?
- Can intra-beam viewing be prevented by engineering design?
- Can the laser be used in a screened-off area, limiting the potential for others to be affected?
- Can work be carried out in a total enclosure?
- Beam paths should be as short as possible, optical reflections should be minimised and the beam terminated with an energy absorbing non-reflective beam stop.
- Laser should be securely fixed to avoid displacement and unintended beam paths.
- If practicable, align powerful lasers with low-power devices that are safe for accidental viewing, or reduce the power of the laser by turning it down or introducing neutral density filters. The aim should be to get the output power <1mW. (some kW lasers will only be able to be turned down to a few watts). Alternatively remote viewing techniques can be used.
- Eliminate chance of stray reflections - use coated optical components or shroud them so that only the intended beam can be refracted or reflected. Keep optical bench free from clutter and remove jewellery, wristwatches etc.
- Point the laser away from the laboratory entrance.
3. Laser alignment
About sixty percent of laser accidents in research settings occur during the alignment process. Laser alignment guidelines to help prevent accidents should include:
- Restricted access, unauthorised personnel must be excluded from the room or area.
- The wearing of laser protective eyewear when appropriate.
- The training and instruction of Class 3B/4 laser users.
- Instructions to remove watches and reflective jewellery before any alignment activities begin.
- The lowest possible/practical power must be used during alignments.
- The use of a He-Ne or CW diode alignment laser, when possible, for a preliminary alignment.
- Identifying individual responsibilities - the individual who moves or places an optical component on an optical table is responsible for identifying and terminating each and every stray beam coming from that component.
- Identifying when the beam is directed out of the horizontal plane.
- Checks on the stability and rigidity of all optical mounts, beam blocks and stray beam shields.
- Use of beam paths at a safe height, below eye level when standing or sitting and not at a level that tempts one to bend down and look at the beam.