Laser Classification. Laser Classes

Transcription

1 LASER SAFETY Laser Classification It is the responsibility of the laser manufacturer to provide the correct classification of a laser product. This classification is made on the basis of a combination of output power(s) and wavelength(s) of the accessible laser radiation over the full range of capability during operation at any time after manufacture which results in its allocation to the highest appropriate class. Maximum Permissible Exposure Levels (MPE) Maximum Permissible Exposure limits are those levels of laser radiation to which, in normal circumstances, persons may be exposed without suffering adverse effects. A guide to MPE levels are given in BS EN They are based upon biological data collected to date. Laser Classes Lasers are grouped according to ability to do harm, the higher the number the greater the harm. The current laser classes are 1, 1M, 2, 2M, 3R, 3B and 4 Class 1 Safe under reasonably foreseeable conditions of operation. The most limiting MPE values cannot be exceeded and no specific safety controls are required. For CW (Continuous Wave) visible lasers, the maximum limit is 70 microwatts. Class1 operation cannot be claimed for a product containing an embedded laser of a higher class unless full-interlocked high-integrity enclosures using fail-safe interlocks are incorporated. Class 1M is a large diameter or widely divergent beam ( nm). As Class 1, but not safe when viewed with optical aids such as binoculars or eye loupes. Class 2 Visible lasers only, for which the MPE cannot be exceeded in less than 0.25 seconds. The eye is protected by the aversion responses, including blinking reflex and head movement. For CW (Continuous Wave) laser the limit is 1 mw. Class 2M is a large diameter or widely divergent beam. As class 2, but not safe when viewed with optical aids such as binoculars or eye loupes. safetyunit@gre.ac.uk April 2009 Page 1 of 5

2 Class 3R (Previously Class 3A) NB: where reference is made to Class 3R, the same applies to the previous classification of 3A. Wavelength nm Lower risk than 3B, but direct viewing of beam potentially hazardous. Visible lasers up to five times the Class 2 limits and invisible lasers up to five times the Class 1 limits, for which specific H (Jm -2 ) or E(Wm -2 ) values are not exceeded. Class 3B Visible and invisible lasers not exceeding specified limits, which are 0.5W for CW (Continuous Wave) lasers and 10 5 Jm -2 for pulsed lasers (less for ultraviolet wavelengths). Direct beam viewing not safe to the eye, specularly reflected beams e.g. reflected from shiny surfaces may also be harmful to the eye; diffusely reflected beam usually safe to the eye, assumed to be safe to the skin. Class 4 Those that exceed the limits of Class 3B. Viewing a direct beam or a reflected beam is always harmful to the eye and skin, diffusely reflected beams should be assumed harmful to the eye or skin unless proven otherwise, both scattered and reflected beams can present a fire hazard. Laser System A laser system is a system containing one or more lasers associated with a single application or process and under the control of a single operator, i.e. lasers that are exchanged on the same system or are running simultaneously on the same experiment (e.g. pump laser and main laser). There is more than one laser system if the lasers are not operating together or are used by different operators although mounted in the same area. Laser Product A laser product is a piece of equipment containing a laser system. The product may be given a low classification even though it contains a higher classification system, provided that there are engineering controls to prevent access to the totally enclosed embedded system. Common examples are CD players, laser printers and some scientific analytical equipment. Risk Assessments and Written Procedures The Management of Health and Safety at Work Regulations require a risk assessment of all work activities. The risk assessment should identify the key hazards at all stages of the work. The risk the likelihood and severity - of harm occurring to those carrying out the work, and any others who may be affected by it, must be assessed and suitable precautions identified and implemented to minimise the risk of those hazards causing harm. The risk assessment must be recorded in an approved format (see Code of Practice on risk assessment and School/Office procedures). Page 2 of 5

3 Hazards associated with laser equipment Risk assessments must be carried out where use of work equipment involves possible exposure to significant hazards. In carrying out a risk assessment for work with lasers, consideration must be given to the optical and skin hazards of the laser radiation itself due to open beam paths, misalignment problems and the mounting of optics. This applies to the use of all classes of laser but particular attention is required in the case of Class 3 and 4 lasers due to the level of hazard. However, the risk assessment must also consider other hazards associated with use of the equipment, the main ones being:- 1. Electrical high voltages 2. Chemical/Fume sample preparations, use of dyes and solvents, fumes produced by cutting and engraving (apply COSHH Regulations) 3. Mechanical manual handling materials and gas cylinders, falls when accessing high parts of the equipment, slips and trips on cables, cryogenic liquids, noise, vibration 4. Fire high power, direct and reflected beams, ignition of cut materials 5. X-rays/electromagnetic interference All stages of the installation, use, routine maintenance, periodic servicing, and disposal of the equipment must also be considered in the risk assessment, whether this is carried out by staff, students or contractors. The complexity of the risk assessment should be relevant to the class of laser, i.e. for Class 1 and 2 lasers, the risk assessment will be far simpler than for a Class 3B or 4 laser. Summary of Manufacturer s and User Requirements for Lasers (From the AURPO Guidance Note No ) Remote interlock - Safety interlocks - Key control Emission indicator - Beam stop or attenuator/shutter - connection provided by the manufacturer for door or enclosure interlock for Class 3B and Class 4 lasers required for access panels on Class3R, 3B and 4 laser systems a key or similar device is required to control unauthorised operation of Class 3B and Class 4 lasers an audible or visible indicator should be provided by the manufacturer for each Class 3R laser ( except wavelengths nm) and each Class 3B and Class 4 laser system should be provided by the manufacturer for each Class 3B or Class 4 laser system Beam termination - the user should ensure that all beam paths are terminated at the end of their useful path. (Does not apply to Class 1 devices) Beam level - avoid eye level Beam enclosure - to guard against specular reflections from Class 3R, Class 3B and Class 4 lasers - can mean anything from screening the experimental area or piping the beam up to a total enclosure. Eye protection - required for open beam work with invisible beam Class 3R and all Class 3B and Class 4 devices. Page 3 of 5

4 Protective clothing Eye examinations - Training - Laser labels - mainly required for Class 4 lasers but be careful with Class 3B UV lasers as well, may need fire resistant material for some lasers only required after an accident but may be important to people with poor eyesight working with Class 3B or Class 4 lasers required for people working with any Class 3 or Class 4 laser and any modified Class 1M or Class 2M devices. required for all lasers except low power Class 1 ( though need not be directly affixed if the size of the laser product does not permit this) Door/Area signs - required for Class 3B and Class 4 lasers indoors and also for Class 1M, 2M and 3R if used outdoors Summary of precautions for each laser classification Precautions 1M 2 2M 3R 3B 4 1(E) Remote Interlock n/a n/a n/a n/a n/a Safety interlocks n/a n/a n/a Key Control n/a n/a n/a n/a Emission indicator n/a n/a n/a Beam Stop/Shutter n/a n/a n/a n/a n/a Beam Terminator n/a n/a Beam Level n/a Beam Enclosure n/a n/a n/a Eye protection n/a n/a n/a n/a Protective Clothing n/a n/a n/a n/a n/a Eye Examinations n/a n/a n/a n/a n/a Training n/a Laser Labels Door/area signs n/a n/a n/a n/a n/a NB Class 1(E) indicates a Class 1 totally enclosed system Designated Laser Area A Designated Laser Area (DLA) is an area or room where one or more Class 3B and/or Class 4 lasers are in use. Signage is mandatory at the entrance to the area/room. Eye Protection Protective eyewear is a common and important aspect of personal laser protection wherever there is some risk of laser exposure above the specified MPEs. However, it does not replace a full risk assessment and consideration of all alternative means of affording protection such as total enclosure of the beam, interlocks, beam dumps etc. Page 4 of 5

5 Laser safety eyewear, safety glasses, are the last line of defence and not a convenient alternative to avoiding any engineering controls that it may be possible to implement. Laser safety eyewear incorporates optical filters to reduce the laser radiation to below the level of the MPE, whilst at the same time maintaining a reasonable level of visible light transmission. The filter damage threshold must be sufficiently high to withstand the maximum possible exposure long enough for appropriate avoiding action to be taken. The absorbance of the filters must be appropriate to the wavelength of the laser(s) used. Clear information must be available to identify the eyewear that is suitable for each laser and whether it is for alignment work or full protection. Standards for laser eye protection are BS EN 207 (for normal use) and BS EN 208 (for maintenance and adjustment work). Eye protection must conform to these standards and be clearly marked to indicate the protection that is provided. Users are responsible for exercising care in the use and storage of eye protection. These items are expensive and easily scratched, degrading performance and comfort. Any defects must be notified to the user s supervisor and work requiring the defective item should cease until a safe replacement is made. Relevant Standards and Guidance University sector guidance is given in the Association of University Radiation Protection Officers (AURPO) Guidance Note No.7 Guidance on the safe use of lasers in education and research. This can be downloaded from It replaced the CVCP Notes of Guidance Part 2.1 Lasers, More detailed guidance on best practice in the use of lasers is given in: British Standard BS EN :2007 Safety of laser products - Part 1: Equipment classification and requirements. PD IEC TR :2004 Safety of laser products Part 14: A user s guide (originally included in Part 1 of the British Standard) BS EN ISO :2005 Safety of machinery Laser processing machines Part 1: General safety requirements sets out requirements for equipment such as cutting and engraving machines used in design and technology workshops. BS EN :2004 Safety of laser products Part 2: Safety of optical fibre communication systems (OFCS) defines requirements covering the safety of fibre optic networks. IEC/TR :2008 Safety of laser products Part 3: Guidance for laser displays and shows sets out the precautions which should be observed by organisers of events. INDG224 Controlling the radiation safety of laser display installations is available together with other information on the Health and Safety Executive website The Health Protection Agency website includes information about laser hazards and precautions, including laser pointers. See Page 5 of 5