标题: 激光防护标准 [打印本页] 作者: alanick 时间: 2003-8-8 17:35 标题: 激光防护标准 Laser Classifications
Lasers are classified into four broad areas depending on the potential for causing biological damage. When you see a laser, it should be labeled with one of these four class designations:
Class I These lasers cannot emit laser radiation at known hazard levels.
Class I.a This is a special designation that applies only to lasers that are not intended for viewing, such as a supermarket laser scanner. The upper power limit of Class I.A. is 4.0 mW.
Class II These are low-power visible lasers that emit above Class I levels but at a radiant power not above 1 mW. The concept is that the human aversion reaction to bright light will protect a person.
Class III.a These are intermediate-power lasers (cw: 1-5 mW), which are hazardous only for intrabeam viewing. Most pen-like pointing lasers are in this class.
Class III.b These are moderate-power lasers.
Class IV These are high-power lasers (cw: 500 mW, pulsed: 10 J/cm2 or the diffuse reflection limit), which are hazardous to view under any condition (directly or diffusely scattered), and are a potential fire hazard and a skin hazard. Significant controls are required of Class IV laser facilities.
文字作者: solojackie 时间: 2003-8-8 18:43 标题: 激光防护标准 呵呵，alanick，好久没看到你发帖子了。这次要好好顶一下！：）
上面的激光防护标准是：IEC60825-1:1993（International Electrotechnical Commission (IEC)“Safety of laser products Part 1. Equipment classification, requirements and user’s guide”）。后来，由英国进一步完善补充，形成BSEN60825-1:1994 amendment 2。下面是完整的BSEN60825-1:1994 amendment 2标准：
REQUIREMENTS OF THE STANDARD
LASER CLASSIFICATION
The major requirement of the Standard is for laser product manufacturers to correctly classify their products into one of 5 classes depending upon the maximum level of personally accessible radiation. The classification scheme described in the Standard is intended to assist manufacturers and suppliers to meet their duties under section 6 of HSAW. The requirements for each laser product class are summarized below together with a summary of protection requirements.
Class 1
Laser products which are safe either because of the inherently low emission of the laser device incorporated within the product, or because of engineering design which restricts personal access to laser radiation during normal operation.
Protection requirements for Class 1:
None, other than to ensure that the conditions for class 1 operation are maintained.
Class 2
Laser products that emit low levels of visible radiation (ie. wavelengths between 400 and 700 nanometres) which are safe for the skin but which are not inherently safe for the eyes. The class 2 emission limit is set at the maximum level for which eye protection is normally afforded by natural aversion responses to bright light. Accidental eye exposure is therefore normally safe, although the natural aversion response can be overridden intentionally by deliberately staring into the beam, and can also be influenced by the use of alcohol or drugs.
Protection requirements for Class 2:
Avoid staring into the beam (ie. deliberate viewing), pointing the beam at other people, or directing the beam into areas where other people may be present.
Class 3A
Laser products which exceed the permitted accessible emission limits (AEL) for class 1 and class 2 as applicable but which do not permit personal access to laser radiation in excess of the applicable accessible emission limit for class 3A.
As a general rule the class 3A AEL is around five times the class 1 AEL for invisible emissions (180-400nm and 700-106nm) and five times the class 2 AEL for visible (CW) emissions (400-700nm).
Most class 3A laser products on the market are continuous wave (ie. not pulsed ) devices which emit in the visible part of the spectrum and therefore must not have radiant powers above 5mW. The standard also constrains the power density of visibly emitting CW class 3A products to no more than 25 watts per square metre.
For United States products, classified to the equivalent ANSI standard, the above-mentioned power density constraint is not used and so US class IIIa products can, in some circumstances, be more hazardous than products classified to the British Standard.
The key difference between class 3A and class 2 is that viewing aids, such as telescopes and binoculars may make an emission unsafe to view.
Protection requirements for Class 3A:
Avoid the use of magnifying viewing instruments (such as binoculars, telescopes, microscopes and magnifying lenses, but not including correctly-prescribed spectacles or contact lenses). Avoid staring into the beam, pointing the beam at other people, or directing the beam into areas where other people may be present.
Class 3B
Laser products having a level of accessible emission which can be harmful to the unaided eye but generally will not cause injury to exposed skin. Diffuse reflection hazards (ie, those arising from rough surfaces) are generally of low risk.
Protection requirements for Class 3B:
Prevent eye exposure to the beam. Guard against unexpected specular reflections (ie. those arising from shiny, mirror-like surfaces).
Class 4
Laser products having a level of accessible emission which can be harmful to both the eyes and the skin when viewed either directly of following any form of reflection (including diffuse reflection). The laser emission may also be sufficient to ignite materials on which it impinges, and to generate harmful radiation or fume hazards by interaction with target materials.
Protection requirements for Class 4:
Prevent eye and skin exposure to the beam, and to diffuse reflections (scattering) of the beam. Protect against beam interaction hazards such as fire and fume.
PROVISION OF EYE PROTECTORS
36 The Personal Protective Equipment Regulations 1992 require provision of personal protective equipment (PPE) to control personal health and safety risks that can not otherwise be adequately reduced by engineered and administrative controls. For laser applications, the need for protective eyewear depends upon the risk of personal access to potentially hazardous emissions in both routine and reasonable foreseeable use of the laser application. In this regard, PPE would normally be required by users of laser products that exceed class 3B and employers would need to have made a robust risk assessment in order to justify not making such provision. In making such an assessment, design features such as ‘fortress’ enclosure, entry point interlocks, beam path enclosure and focussing systems are all factors that must be taken into account.
37 Assessment of personal exposure risks that arise from the use of high-power lasers is a complex subject and therefore the need for protective eyewear is often a fine judgment to make; employers that use such devices should in the first instance rely upon information provided by the manufacturer. In this regard, the Health and Safety at Work etc. Act, section 6 is relevant. However, under the Provision and Use of Work Equipment regulations 1998, it is the user’s employer that has the overall duty to ensure that work equipment is ‘suitable’ for use. Clearly in many situations it will be necessary to get expert advice from a ‘competent’ person (Management of Health and Safety at Work regulations 1999).
38 If the risk assessment indicates that protective eyewear is needed to adequately control exposure risks, the employer must use eyewear that is CE marked to indicate compliance with the Personal Protective Equipment (EC Directive) regulations 1992. In this context there are two European standards used by protective eyewear manufacturers to demonstrate compliance with this directive: EN207: 1999, which deals with general protective eyewear, and EN208: 1999, which deals with eyewear to be used specifically for laser emission adjustment and alignment.
39 Protective eyewear selection should be made under the direction of competent person appointed by the employer or in accordance with information provide by the laser product manufacturer. Employers should not rely solely on the above-mentioned standards for the purpose of choosing appropriate protective eyewear unless they are satisfied that the measurement conditions these standards use are compatible with the circumstances of use of the laser product for which the protective eyewear is sought.
OPHTHALMIC EXAMINATIONS (EYE TESTS)
40 The Standard advices that the value to laser workers of routine ophthalmic examinations has not been established and that, employers requiring such examinations as part of their safety policy or for medicolegal reasons, should use a qualified specialist. It also recommends that anyone thought to have been exposed to excessive levels of laser radiation should receive urgent medical attention from a qualified specialist who should make a full ophthalmic examination within 24 hours of being notified. A central register of all instances of laser eye damage has been established at the Professional Unit, Moorfields Eye Hospital, London.
41 The advice of HSE is that routine eye examination for medical surveillance purposes is inappropriate because it is not able to provide information on anything other than acute exposure events (in this context, irreversible eye injury). For a medical surveillance practice to be useful, it must be able to provide information about incipient failures in risk management and, in this regard, ophthalmic examination is an insufficiently sensitive technique.
42 There is also the risk that some types of ophthalmic investigation, for example fundal photography and the use of mydriatic drugs to dilate the pupil, may cause photochemical damage to the retina or even severe glaucoma (raised intra-ocular pressure). The need for such examinations therefore needs careful consideration.
LASER SAFETY OFFICERS (LS0s)
43 Employers that use laser products greater than class 2 should appoint an LSO who has sufficient knowledge and training to be able to advise on the user safety precautions that may be necessary. The LSO should also be involved in laser controlled area designation and management, ie. areas where exposure to radiation levels above applicable MPE values is a reasonably foreseeable risk.
WARNING SIGNS FOR LASERS
44 The Standard requires all laser products to bear an appropriate explanatory warning label and those exceeding class 1 to bear the international laser hazard symbol (the so-called ’’star-burst’’ sign). The wording for explanatory labels is class specific and given in the Standard. The labeling requirements set out in the Standard are broadly in line with the requirements of the Health and Safety (Safety Signs and Signals) Regulations 1996.
ENFORCEMENT APPROACH
Class 1 laser products
45 These are generally quite safe under all viewing conditions and require no further controls.
46 However, remember that some class 1 laser products may contain a much higher power ‘embedded’ laser system. This is because the Standard requires the manufacturer to classify in accordance with accessible emissions that could arise in reasonably foreseeable conditions of use rather than in accordance with emissions that could become accessible if the product’s protective housing were dismantled for example. Embedded class 1 laser products therefore need careful inspection in order to determine the adequacy of design features such as protective housings, safety interlocks, beam delivery systems and key control. The maintenance of these features is also a major factor in the ongoing safety performance of this type of laser product.
47 An example of an embedded laser product that inspectors might come across is the supermarket checkout scanner (see LAC60/5).
Class 2 laser products
48 The following points should be noted by enforcement officers.
(i) Employers need to take precautions to prevent continuous direct viewing of the beam; however, momentary exposure (0.25 seconds) is not considered hazardous.
(ii) Where reasonably practicable, laser beams should be terminated at the end of their useful paths and should not be deliberately aimed at people (especially at head height).
(iii) Employers should bear in mind that some people may not have competent eye aversion reflexes that would otherwise stop them from viewing a class 2 emission for more than 0.25 seconds (the safe time limit for a class 2 laser product). Examples of such people would be children, persons under the influence of alcohol and those on some forms of prescribed drug. Therefore if an employer’s work takes place in proximity with such people, appropriate precautions will be needed.
Class 3A laser products
49 These laser products are typically used in survey applications on construction sites and other types of building operation. Generally the precautions that apply to class 3A are those that apply to class 2 with the caveat that emission viewing using optical aids, such as telescopes and binoculars but excluding prescription spectacles, may be hazardous. Employers should therefore take precautions against this risk
50 The following points should be noted by enforcement officers.
(i) Only employees approved by the LSO should be assigned to install, adjust and operate class 3A laser products.
(ii) Warning signs should be posted in any areas where class 3A laser products are used and to which there is access by untrained people (such as members of the public).
(iii) Laser beam alignment should be completed remotely whenever reasonably practicable.
(iv) Systems of work and their operation should ensure that it is not possible for a person to stare directly into beams or through optical instruments which have not been fitted with suitable filters to protect the viewer.
(v) Where practicable, laser beams should be terminated at the end of their useful path.
(vi) Where practicable, laser beam paths should be located well above or below eye level.
(vii) Proper account should be taken of hazardous reflection risks.
(viii) Class 3A laser products should be stored securely when not in use.
Class 3B and 4 laser products
51 These are potentially very hazardous laser products capable of causing severe burns as well as eye injury. Their safety assessment is a specialist area and inspectors are advised to contact HSE or the National Radiological Protection Board (NRPB) for assistance in assessing the safety performance of these types of device.
52 Requests for specialist advice and joint visits should be forwarded to the Area Enforcement Liaison Officer (ELO) who will, where appropriate, transmit the request to the appropriate HSE Regional Support Group (RSG).
Class 3B and 4 laser products may be encountered particularly in the Display and Entertainment industry. HSE guidance document HS(G)95, ‘The Radiation Safety of Lasers Used for Display Purposes’, gives comprehensive guidance to employers, both users and manufacturers/suppliers, on the safety of these installations (see also LAC60/4)).