Laser safety for laser operators TUe-TN.doc

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1 Laser safety for laser operators Eindhoven, In the following document the risks related to using or operating lasers are explained briefly. It also describes the safety measures that can be taken to limit these risks as far as possible. An extensive list of work regulations can be found in the laser safety report appropriate to each laser laboratory. 1. Introduction A laser beam of a 1 mw HeNe laser may cause permanent retinal damage if you look directly into the beam! Therefore avoid any eye contact with laser beams! Lasers are coherent light sources. The radiated light source is parallel. This characteristic makes lasers so dangerous. Through a (convex) lens, such as the eye, the parallel light source is focused into one point. At that moment all the energy of the laser light is dissipated onto a small surface. The high energy density of the light source may also be dangerous to the skin. In order to estimate the danger of lasers to some extent, the following is a simple calculation of an HeNe laser with a capacity of only 1 mw and a 1 mm 2 beam diameter. By experimenting you can easily determine that a laser beam with an intensity of 1 W/mm 2 can be felt burning on the skin of your finger. The 1 mw HeNe laser has an intensity of 1mW/mm 2 on the skin, which does not cause any noticeable heating of the skin. In principle, the eye is capable of focusing this beam times (diffraction limit) onto the retina. The intensity on the retina resulting from a 1 mw HeNe laser then becomes 500 W/mm 2, which is much higher than the 1 W/mm 2 that you feel burning on your skin! If you do not move your eye and the beam focuses perfectly on the retina, the laser beam of a 1 mw HeNe laser may cause a severe retinal burn. This damage is irreversible. Besides the light source, there are other dangers when operating lasers, such as the presence of corrosive gases (halogens with regard to some lasers) and solutions of organic substances. As with all equipment, the safe use of electricity is also of paramount importance Laser classification system In terms of radiation danger, lasers are subdivided into four classes. The following is a summary of the classification system. Section Three of the User's guide of the International Standard IEC of 1993, including amendments 1:1997 and 2:2001, drawn up by the International Electrotechnical Committee, as well as the report by Karl Schulmeister should be consulted for an extensive overview of descriptions for each laser class and sub-class. Schulmeister's report also incorporates warning labels that are affixed to each laser (with the exception of Class 1 lasers) Class 1 lasers In this category a distinction is made between lasers of a very low power or built-in laser systems that are intrinsically safe (Class 1), and lasers of a very low power whereby the beam diameter has been made very large or very divergent and which will only constitute a potential danger when using optics (Class 1M). The upper power limit for continuous lasers in the visible area is only 0.5 µw. Copyright TU/e-TN Laser safety for laser operators TUe-TN.doc Page 1 of 6

2 1.1.2 Class 2 lasers In this category a distinction is made between visible, low-power lasers that are safe as long as the beam (Class 2) is looked into no longer than 0.25 s (blinking reflex), and visible, lowpower lasers whereby the beam diameter has been made very large or very divergent and, when using optics, may be dangerous if the eye is exposed to the beam for less than 0.25 s (Class 2M). Visible and continuous lasers ranging from 0.5 µw to 1 mw are classified in safety category II Class 3 lasers In this category a distinction is made between low-power lasers that are considered safe if used with care (Class 3R) and the medium-power lasers that may cause damage if the eye is exposed to the beam (Class 3B), also with regard to specular surfaces such as a glass surface. The upper power limit for visible and continuous lasers is 5 mw in Class 3R and 0.5 W in Class 3B Class 4 lasers High-power lasers that may cause eye injury or skin damage, also in the case of specular or diffuse reflection. This class of lasers may also involve a fire risk The impact of laser radiation on human beings Laser radiation is a specific type of visible (VIS), ultraviolet (UV) or infrared radiation (IR). It therefore has the same impact, which is mainly of a thermal nature. The high capacity of radiation may have effects that will barely be noticeable with other non-ionising beams. Very intensive pulses, for example, can deposit so much energy in a cell, that the fluid within the cell evaporates and the cell explodes due to increased pressure. Non-thermal effects may also occur, such as photochemical activity or the generation of free radicals. The thermal impact, however, is dominant. It is mainly the skin and eyes that are at great risk of being damaged The skin The most pronounced effect of laser beams on the skin may be the occurrence of burns, which can sometimes be really severe. Furthermore, UV lasers may induce skin cancer. The skin, however, can endure higher levels of energy than the eyes, because there is no beam concentration The eyes The eye is the most sensitive organ where radiation is concerned. The lens concentrates the already intense beam of visible or near-infrared rays by a factor of 100 to 500 x This may cause very serious damage, particularly if the beam hits the macula lutea, the yellowish central area of the retina that contains the photoreceptors of the optic nerves. For example, a 40 mw HeNe laser produces approximately a 10 kw/cm 2 radiation intensity on the retina. This radiation intensity almost immediately causes thermal damage of the retina, similar to boiling egg white. Copyright TU/e-TN Laser safety for laser operators TUe-TN.doc Page 2 of 6

3 Illustration 1: Various forms of eye damage to the retina of a monkey, caused by a Nd:YAG laser. The white spots in the centre were caused by thermal charge (burning spots). Craters and haemorrhages (the dark spots) appear when higher power levels are used. Most of the damage is permanent. Accident statistics have identified pulsed lasers and especially Q-switched Nd:YAG lasers as the laser type that causes the most frequent and severe eye damage. Pulse lasers have a relatively high energy peak. Besides direct retinal damage (thermal and optic), this energy peak may also cause shock waves that can result in further retinal injuries. As a result of UV or IR laser radiation, dark spots of a diameter equal to the laser beam may appear on the cornea. If a higher power level is applied, these opacities in the centre of the lens may burst, thereby causing leaks in this body of fluid. A bluish grey cloudy discolouration - cataracts - may appear on the lens. After a few pulses a migration of pigments to the point of impact on the iris can be observed. This concentration of pigment will disappear after a few weeks. After repeated injuries the iris tissue may tear. The damage is almost always irreversible. The radiation level that can be regarded as the theoretical boundary between 'safe' and 'possibly safe' is indicated by means of MPE - Maximum Permissible Exposure - levels. The International Commission on Non-Ionising Radiation Protection (ICNIRP) has determined the MPE levels for the eyes and skin with regard to lasers that have a wavelength ranging from 180 nm to 1 mm and a radiation period ranging from s to s. In this respect it should be noted that the MPE standard does not define a clear-cut limit below which laser radiation may be considered 'safe'. This has to do with the way in which these MPE standards were determined (mainly through vivisection). Section Three of the User's guide of the International Standard IEC of 1993, including amendments 1:1997 and 2:2001 that were drawn up by the International Electrotechnical Committee, as well as the report by Karl Schulmeister can be consulted for additional information about the MPE levels and how to calculate them with regard to particular laser types. The MPE levels appropriate to the laser(s) in a laser laboratory have been incorporated in the laser safety report of the laboratory concerned. The NEN-EN 207 and NEN-EN 208 standards can be consulted for the requirements with which laser safety eyewear should comply Chemical hazards Generally, operating lasers goes hand in hand with chemical hazards. The most well-known hazard is the development of ozone. Ozone originates from oxygen that is exposed to electrical discharge or ultraviolet radiation with a wavelength lower than app. 250 nm. Ozone has a MAC level of 0.2 mg/m 3. Exposure to ozone concentrations that exceed the MAC level may have a severe impact on the mucous membrane. Inhalation may cause respiratory Copyright TU/e-TN Laser safety for laser operators TUe-TN.doc Page 3 of 6

4 problems (pulmonary oedema). In addition, this substance has a highly prickly effect on the eyes. When using solvents in dye lasers, people are advised to work in a fume cupboard as far as possible, also because not all health risks involved in the excessive use of some solvents are known. Generally fluorescent dyes are used in dye lasers or for the visualisation of liquid flows. Many of these chemicals have toxic or carcinogenic characteristics. In particular the powdered form of these fluorescent dyes should be used with due care because these substances are concentrated and could easily be inhaled. The same applies to the very small tracer particles that are often used for flow visualisation Electrical dangers In most cases it requires a lot of energy to start operating the laser. This energy may be derived from high-voltage capacitor banks: kv is not uncommon in this respect. As a result, only staff with sufficient knowledge and experience may work on electrotechnical features. In this respect it should be noted that the metal casing may also have a function with regard to electrotechnical safety. 2. General laser laboratory regulations The laser safety report that relates specifically to the laser laboratory may include different and/or supplementary regulations for positioning and situations present in the laser laboratory. The following are just a number of general requirements to be met by a laser laboratory. - Non-laser operators can only enter the laser laboratory when accompanied by a laser operator or when the emission indicator device ( laser aan / laser on ) is switched off. - With regard to Class 3B and Class 4 lasers, the status of laser aan / laser on is indicated by an emission indicator device outside the laser laboratory. - A sufficient number of laser safety goggles should be present in the laser laboratory. The safety report includes work regulations and procedures with regard to the use of laser safety eyewear that protects against exposures that exceed MPE levels. - In the event of an emergency, each laser in Class 3B and Class 4 can be switched off by means of an emergency stop button, which is situated at a strategically easily-accessible place, i.e. at the entrance door and on the laser table. - Utmost care should be taken that people outside the laser laboratory can at no time whatsoever be accidentally exposed to laser ray levels that exceed MPE standards. - Any emergency or (near) accident should be reported to the capacity group chair. In the event of suspected injury the company medical officer should also be consulted, in accordance with the general Arbo guidelines, which govern health, safety, welfare and environmental matters in the workplace. In cooperation with the laser safety officer an evaluation report should be drawn up stating how the emergency situation or the (near) accident could have arisen and what measures should be taken to avoid a repetition. Copyright TU/e-TN Laser safety for laser operators TUe-TN.doc Page 4 of 6

5 3. Work regulations The following are a number of general instructions for the safe operation of lasers. These, however, should be regarded as guidelines and they most definitely do not exclude every form of risk in all instances where lasers are being used. In the laser safety report concerning the usage and positioning of lasers, this list will be supplemented with work regulations that should be followed with regard to the specific laser position. - Whenever and wherever possible, high-power laser beams should run through a beam tube, or be screened off in another way. - The laser safety report should include a tighter safety regime with regard to alignment operations on the actual high-power lasers (safety cap open). - Unintentional reflections should be avoided. - Unnecessary specular reflection of surfaces should be avoided. - No reflecting rings, necklaces, watches etc. should be worn when working in the laser laboratory. - All optic components should be mounted in a fixed position to a table (in relation to the laser source) or to another surface, so as to avoid sudden changes in the direction of the laser beam. - Laser beams must never run at eye level through the room, but should preferably run along an optical table. - Whenever and wherever possible, beam blockers and black screens should be used to block undesired beam reflections beyond the optical table. - Alignment work should preferably be carried out with a reduced-power laser beam. - If possible, alignment work should be carried out in a well-lit area (small eye pupils reduce the risk of eye injury) - If the laser does not run along an optical table, the beam path should be marked clearly. - Workplaces within the laser laboratory should be set up in such a way that laser beams can never run at eye level range. - The area immediately behind the entrance doors should be safe and cleared. - In laser laboratories where work regulations as set out above cannot be implemented, the use of laser safety eyewear should be mandatory at all times. - These regulations assume that the lasers that are used comply with IEC guidelines and that all the required laser classification labels and interlocks are affixed to the equipment. With regard to self-constructed and highly modified systems, the appropriate IEC requirements should be consulted. - When working with fluorescent dyes a fume cupboard should be used. Appendix: Laser operator application form Copyright TU/e-TN Laser safety for laser operators TUe-TN.doc Page 5 of 6

6 LASER OPERATOR APPLICATION FORM Tue-TN To be completed by the prospective laser operator. Family name: First names: Student: Address: Town: Postcode: Capacity group: Supervisor: Workplace address: Workplace telephone no.: Position/branch of study: Laser worker from: to: - Are you experienced in working with lasers? yes/no If so, which class?: which type of laser?: Please describe the operations in an appendix to this form. - Do you have an eye problems (other than wearing spectacles)? yes/no If so, please briefly describe the eye problems. - You will operate lasers in laboratory (room number): Laser class: - You have received a copy of 'Laser safety for laser operators' and you are committed to compliance with these regulations. To be completed by the laser safety officer. - The prospective laser operator has been given training in operating the lasers specified above and has been referred to the general procedures governing laser safety as set out in the Regulations for Laser Safety of the Faculty for Technical Physics. - Comments by laser safety officer: Endorsed by supervisor: This form has been completed truthfully Applicant's signature: Laser safety officer's signature: Date: Date: Copyright TU/e-TN Laser safety for laser operators TUe-TN.doc Page 6 of 6