Laser Classification, Hazards & Controls Contents
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| Laser Classification, Hazards & Controls
Contents:
LASER CLASSIFICATION Class 1: Safe, max power 0.4 mW CW e.g CD players, printers These lasers cause no damage to both the eyes and skin under reasonably foreseeable circumstances and therefore can be treated as totally safe. Class 2: Low hazard, max power 1 mW CW e.g. supermarket scanner Only emit radiation in the visible region (400-700 nm). These lasers are safe to the skin and cause no damage to the eye as long as the exposure time is less than 0.25 seconds i.e. the aversion response (time it takes to look away). Class 1M & 2M: Both considered low hazard, but contain magnifying optics, class takes into account amount of beam that can enter the eye. Class 3R: Low-medium hazard, max power 5 mW CW e.g. surveying equipment Direct exposure to the beam of a Class 3R laser is potentially hazardous so must be treated with respect, however the risk is lower than that for the Class 3B products. Class 3B: Medium-high hazard, max power 500 mW CW e.g. HeNe These lasers have sufficient intensities to cause eye damage through the direct beam but diffuse specular reflections (see below) are safe, as long as exposure time is less than 10 seconds and the eye is no closer than 13 cm from the diffusing surface. Systems containing Class 3B lasers should be sufficiently interlocked to eradicate any open beam exposure. If it is necessary to override the interlock for alignment purposes, the amount of open beam exposure should be minimized as much as possible and the relevant eye protection must be worn (check that the wavelength range if the eye protection is correct for that laser). Class 4: High hazard, power > 500 mW CW or pulsed (no upper limit) e.g. Nd-Yag These lasers have sufficient intensities to cause eye damage both through the direct beam and specular reflections (see below). These lasers also have an associated fire hazard. Extreme caution must be used when using these lasers. Systems containing Class 4 lasers should be sufficiently interlocked to eradicate any open beam exposure. If it is necessary to override the interlock for alignment purposes, the amount of open beam exposure should be minimized (as described fro Class 3B). Reflections. There are two principle types of laser reflection:
EYE AND SKIN DAMAGE FROM LASERS The damage caused to the eye and skin by a laser varies with wavelength. Users of lasers should be aware of the damage that can be caused by the wavelength region they are working in. The most serious damage to the eye is caused by wavelengths of 400-1400 nm, which affects the retina (known as the Retinal Hazard Region). The skin can be burnt by wavelengths above 315 nm (far UV to IR). The tables below summarise the regions of the eye affected by UV/Vis/IR (Table 1) and the effects that radiation will have on the eye and skin (Table 2). Table 1 – Summary of areas of the eye affected by radiation
Table 2 – Summary of laser beam hazards to the eye and skin
LASER SIGNAGE Every laser product higher than Class 1 should be clearly marked with the laser hazard sign and a label indicating the class, power and wavelength (Table 3) Table 3: Signage required for laser products.
Designated Laser Areas: The points of access to areas in which Class 3B or 4 laser products are used must be marked with warning signs complying with BS 5378 and the Health & Safety (Safety Signs and Signals) Regulations 1996. The signs shall incorporate the following information:
N.B. Warning lights must always be on when lasers are in use . NON-BEAM HAZARDS Many regard laser radiation to be the main hazard of lasers but this is often not the case. The main cause of accidents from lasers is electrocution from exposed electrical parts during repair or adjustment. These associated hazards should not be overlooked and details should be included in all risk assessments for laser based work. A summary of non-beam hazards are summarized in Table 4. Table 4: Summary of non-beam hazards
CONTROL OF HAZARDS The control of hazards associated with lasers is described by a hierarchy of control, the first level of which being the most important in avoiding accidents: - Engineering controls - Administrative controls - PPE
Each will be described with details of procedures that must be followed for any experiments involving lasers. ENGINEERING CONTROLS Laboratory design The following considerations relate mainly to the use of Class 4 lasers but some may be appropriate for Class 3B devices as well, or, as general specifications for a laser laboratory. 1) If practicable the 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 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. 2) 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. 3) The laboratory should be equipped with appropriate fire fighting equipment. 4) Electrical supplies, switch and control gear should be sited in order to:-
Experimental set-up – key control Before starting to use your laser there are a number of basic risk reduction measures that should be considered. 1) If a lower powered laser can be used then it should. The experiment may lend itself to lowering the output power of a laser if full power is not needed. Lasers should be operated so that individuals are not exposed to levels in excess of the Maximum Permissible Exposure (MPE) levels given in the current BS EN document. These are the maximum amounts of laser radiation that are unlikely to cause harm to the eyes or skin and can be established by calculation. In some cases appropriate measurements using specific detectors/instrumentation may be necessary; if this is the case then a suitably qualified person will be required to undertake the measurements. 2) Intra-beam viewing must be minimized by engineering design. This design should include a fully interlocked casing around the laser (see below). EU legislation coming into force in 2010 will mean that any open beam work on Class 3B lasers or above will be illegal, thus the systems with these lasers should be totally enclosed. 3) 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. This includes casing the laser with lead/lamented Perspex. These surfaces will stop any beam escape for a short period of time, after which the laser will start to burn the surface, which can be detected by the user and the laser shut down 4) Lasers should be securely fixed to avoid displacement and unintended beam paths. 5) Powerful lasers should be aligned with low-power devices that are safe for accidental viewing or with reduced power of the laser (by turning it down or introducing neutral density filters). The aim should be to get the output power <1mW, NB some kW lasers will only be able to be turned down to a few watts. If higher power is needed then remote viewing techniques e.g webcam should be used. 6) Eliminate the chance of stray reflections - use coated optical components or shroud them so that only the intended beam can be refracted or reflected. Keep the optical bench free from clutter and remove jewellery, wristwatches etc. 7) Have the laser pointing away from the laboratory entrance. PLEASE NOTE: Eye protection should be a last line of defense in protecting against a direct eye strike. A properly interlocked system should negate the need to wear any eye protection. ADMINISTRATIVE ARRANGEMENTS This section summarises the administrative arrangements that should be in force for the control of laser safety. These arrangements are based on guidance from the Users Guide associated with the BS EN 60825-1 standards (published as PD IEC TR 60825-14). This Users Guide suggests three aspects of the use of lasers that need to be taken into account in the evaluation of a possible hazard and the application of control measures:
Risk Assessments (RA’s): These are required for all laser related work and must cover all details & hazards associated with the laser & experiment, considering the points listed above. Before carrying out any laser-related work, details of the laser (see “Inventory” below) and RA’s must be passed to the DLSO (see “Administrative responsibilities” below). Anyone using the laser must have read & signed a hard copy of the associated RA, which must be kept in the same lab as the laser. Scheme of work: These must be written for all work with Class 2 lasers and above. They must contain as much detail as possible about the protocol of the experiment itself, including:
Signed hard copies of the Scheme of Work must be kept in the lab relating to that laser(s) and must also be passed to the DLSO. Inventory: Details of every laser, including type, power and wavelength, must be recorded in an inventory before any work using that laser can be carried out. This must be updated whenever modifications are made or new laser equipment is added to a set-up. User Registration: Every laser user must be registered with the University and Department. New users must be authorised to use lasers by completing the criteria set out in the Training Record Form. This must be done to make people aware of the hazards of lasers and to ensure that safe systems of work are being practiced. RA’s and Schemes of Work should also identify users of lasers and a list/record must be kept up. All people intending to work with any class of laser, except for inherently safe Class 1 or 2 devices or embedded laser products such as those in laser printers or CD players, should be identified. Persons who could or are going to modify Class 1M or 2M devices should also be identified, as they will require instruction/training. Emergency sheet: A sheet containing details of the laser type, associated hazards and emergency contacts MUST be kept by every laser. In the case of a direct eye strike or burn, this sheet then provides the information on the correct course of action. Emergency procedures must include details of a local Ophthalmic Hospital. Any eye damage must be attended to within 24 hours and must be reported to the HSE if the injury is serious or causes more than a 3 day absence from work. Administrative responsibilities Laser Safety Adviser (LSA) The role of the Laser Safety Adviser is to provide advice and assistance to implement the requirements of BS EN 60825 when Class 3 and 4 lasers are being used. The LSA will liaise with the DLSO (see below) and may be consulted during the planning and specification for the laser application and any related safety issues. Departmental Laser Safety Officer (DLSO) The Departmental Laser Safety Officer (DLSO) is responsible for ensuring that all lasers used in the department are identified and used in compliance with the University policy. The DLSO will ensure that:-
If a survey reveals non-compliance with the standards and a potentially dangerous situation, the laser should not be used until the situation has been remedied by the adoption of additional control measures. Responsibilities of Research Supervisor/Principal Investigator The day-to-day Health and Safety Management of individual research projects is the responsibility of the Principal Investigator (PI). All work involving hazardous lasers MUST be covered by RA’s and where appropriate by written schemes of work and protocols. There should also be procedures to ensure that lasers are made safe prior to disposal and dealt with appropriately if they contain hazardous materials. The PI should also ensure that their laser workers are effectively trained in the operating techniques required and that inexperienced staff are adequately supervised. Responsibilities of Laser Users All users of lasers must have a full eye examination before starting to use any laser application. This is to ensure the eye is in healthy state and allows the assessment of any subsequent damage caused by a laser strike. Laser users have a responsibility:-
PERSONAL PROTECTIVE EQUIPMENT (PPE) Personal protective equipment (PPE) may be necessary when performing work with a laser or associated equipment. However, PPE must always be regarded as a last resort to protect against risks to health and safety. Situations where protective goggles or gloves are necessary do arise, and if these are planned and accounted for, after all other methods of engineering and administrative control have been employed, laser users are not putting themselves at unnecessary risk. Choosing the correct PPE is crucial to ensuring safety. A laser user should be kept informed of changes in standards or designs of PPE by the DLSO and be offered suitable materials for them to undertake tasks safely. A summary of PPE is given in Table 5. Table 5: Summary of Personal Protective Equipment.
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