Safe Use of Lasers

  1. Lasers in Science Fair Projects
    1. Lasers can be used in science fair projects done at home or school only if:
      1. The beam is protected, so that it can never enter the eye of any observer.
      2. All appropriate safety precautions and eye protection are in place.
      3. All legal, regulatory and industry standard restrictions are observed.
      4. There is an adult supervisor who has sufficient knowledge to enforce safe procedures at all times.
    2. Lasers cannot be brought to the science fair unless the conditions in 1.(a) are in place. 
    3. They cannot be used as pointers at science fairs.
  2. Background.
    1. LASER stands for “Light Amplification by Stimulated Emission of Radiation”. Lasers are devices that emit coherent light.  All the individual photons have exactly the same frequency, and are exactly in phase.  In contrast, the light from the sun or a lightbulb covers a large frequency range and the individual photons vibrate randomly. The beam from a laser is very narrow, and the beam can be focussed into a very small spot on, for example, the retina of the eye. Lasers are now used widely in scanners of all kinds, such as the checkout of grocery stores, and in medicine in a huge range of medical procedures.  They can be found in the home in devices such as DVD players, laser cutters and stereolithography 3D printers.
  3. Sources of Information on Lasers.
    1. How Stuff Works (Weschler, 2000).This article is a basic introduction to how lasers work.  The laser classification scheme is out of date, and there is no mention of laser pointers
    2. Wikipedia’s article on Lasers (Laser, 2015)
    3. Laser Safety Training, Oregon State University (Oregon State University, 2015). The first four or five sections are the most relevant.
    4. Using Lasers in Medicine (Harris, 2011)
    5. General Laser Safety (Murphy, 2014).
  4. Classification of Lasers (Laser Safety, 2015)
    1. Class 1. Less than 1 mW. A class 1 laser is safe under all conditions of normal use. This means the Maximum Permissible Exposure (MPE) cannot be exceeded. This class includes high-power lasers within an enclosure that prevents exposure to the radiation and that cannot be opened without shutting down the laser. For example, a continuous laser at 600 nm can emit up to 0.39 mW, but for shorter wavelengths, the maximum emission is lower because of the potential of those wavelengths to generate photochemical damage. The maximum emission is also related to the pulse duration in the case of pulsed lasers and the degree of spatial coherence.
    2. Class 1M. A Class 1M laser is safe for all conditions of use except when passed through magnifying optics such as microscopes and telescopes. Class 1M lasers produce large-diameter beams, or beams that are divergent. The MPE for a Class 1M laser cannot normally be exceeded unless focusing or imaging optics are used to narrow the beam. If the beam is refocused, the hazard of Class 1M lasers may be increased and the product class may be changed. A laser can be classified as Class 1M if the total output power is below class 3B but the power that can pass through the pupil of the eye is within Class 1.
    3. Class 2. 1 mW. A Class 2 laser is safe because the blink reflex will limit the exposure to no more than 0.25 seconds. It only applies to visible-light lasers (400–700 nm). Class-2 lasers are limited to 1 mW continuous wave, or more if the emission time is less than 0.25 seconds or if the light is not spatially coherent. Intentional suppression of the blink reflex could lead to eye injury. Some laser pointers are class 2.
    4. Class 2M A Class 2M laser is safe because of the blink reflex if not viewed through optical instruments. As with class 1M, this applies to laser beams with a large diameter or large divergence, for which the amount of light passing through the pupil cannot exceed the limits for class 2.
    5. Class 3R. 5 mW. A Class 3R laser is considered safe if handled carefully, with restricted beam viewing. With a class 3R laser, the MPE can be exceeded, but with a low risk of injury. Visible continuous lasers in Class 3R are limited to 5 mW. For other wavelengths and for pulsed lasers, other limits apply. Projects using lasers with a power in excess of 5mW must demonstrate significant safety precautions, eye protection, and appropriate experienced supervision to be permitted to be used in a science fair project.
    6. Class 3B. 500 mW. A Class 3B laser is hazardous if the eye is exposed directly, but diffuse reflections such as from paper or other matte surfaces are not harmful. Continuous lasers in the wavelength range from 315 nm to far infrared are limited to 0.5 W. For pulsed lasers between 400 and 700 nm, the limit is 30 mJ. Other limits apply to other wavelengths and to ultrashort pulsed lasers. Protective eyewear is typically required where direct viewing of a class 3B laser beam may occur. Class-3B lasers must be equipped with a key switch and a safety interlock.
    7. Class 4. Class 4 lasers include all lasers with beam power greater than class 3B. In addition to posing significant eye hazards, with potentially devastating and permanent eye damage as a result of direct beam viewing, diffuse reflections are also harmful to the eyes within the distance called the Nominal Hazard Zone. Class 4 lasers are also able to cut or burn skin. In addition, these lasers may ignite combustible materials, and thus represent a fire risk, in some cases. Class 4 lasers must be equipped with a key switch and a safety interlock.
    8. This newer classification scheme replaces an older system used until 2002. (Laser Safety, 2015)
  5. What is the Power of your Laser?
    1. You may not know, and you can’t easily measure it. Scientists at the National Institute of Standards Technology (NIST) measured the power output of 122 laser pointers purchased commercially. They found that 90% of green pointers and 44% of red pointers were not in compliance with the Code of Federal Regulations. They all had higher powers than stated on the label. In one case, they found that a green laser labelled Class 3R emitted 20mW mostly in the infra–red, which is invisible to the eye (Hadler, Tobares, & Dowell, 2013).
  6. What is the Danger to Eyes from viewing Lasers?
    1. A team from the Mayo Clinic irradiated three patients with Class 3A (roughly equivalent to the more modern 3R classification) red lasers for up to 15 minutes, and could find no damage to any of the eye’s structures (Robertson et al., 2000).
    2. A bus driver suffered observable damage six months after being irradiated by a red laser that reflected in to his eye via the rear view mirror. It was estimated that he was viewing the laser for up to 10 seconds in an attempt to identify the user of the laser. (Solon Thanos, 2015)
    3. Jason Harlow (2012) has published a study on green lasers that shows that class 3R green lasers pose no danger to drivers or pilots as long as they are used responsibly.
    4. In most cases, the eye will blink, limiting the exposure time to about 0.25 seconds. There will be temporary loss of vision, which is dangerous if driving a car or piloting a plane.
    5. Visible lasers are mostly safe if the power is below 5 milliwatts (mW), and they are handled professionally. They must never ever shine directly into a person’s eyes.
  7. Buying a laser.
    1. The rapid development of laser technology has outstripped the ability of governments to regulate them. Canada does not regulate the import of hand held lasers. Many low cost lasers are available to the general public that have powers far in excess of level 3R, and have the potential to do significant harm. The internet lists many suppliers of hand held lasers advertised with powers of up to 2000 watts, for example, the Wicked Lasers’ Arctic brand (http://www.wickedlasers.com/arctic?gclid=CJ7V5eSMqK4CFRIDQAodFR71TQ). These are dangerous instruments that have the ability to blind a viewer who looks directly into the beam. If the user inadvertently blinds someone, or distracts a motorist or a pilot, they will probably face a criminal charge. Under no circumstances may any student involved in a science fair project ever have such a laser in their possession. The paper by the scientists at NIST (Hadler, Tobares, & Dowell, 2013) shows that buyers cannot rely on power stated on the labels provided by the manufacturer. Thus even the red hand held laser pointer bought at the Dollar store may have powers significantly greater than advertised.
      A few manufacturers do state that their lasers have the power stated on the label and that their lasers do meet US government standards. One such company is Laser Classroom in the U.S.A.
    2. http://store.laserclassroom.com/class-ii-1mw-red-laser-pointer/
    3. http://store.laserclassroom.com/super-safe-green-laser-pointer/
    4. This green laser is available from Sargent –Welch in Canada
    5. https://www.sargentwelch.ca/store/catalog/product.jsp?catalog_number=WLS1815-74
  8. Location of the Project.
    1. Students are allowed to use lasers in excess of 5mW as long as the project is carried out in a location where appropriate safety protection is in place. Experienced supervision is mandatory. Safety rules and precautions must be strictly observed.  These will usually include safety glasses that strongly absorb the laser light, a safety interlock switch, professional supervision, and a laser safety course.
  9. Conclusion
    1. Lasers are not toys, and must be treated with respect. Users must be knowledgeable about their uses and potentials for harm.
  10. References
    1. Hadler, J. Tobares, E., & Dowell, M. (2013). Random testing reveals excessive power in commercial laser pointers. Journal of Laser Applications, 25(3). doi: http://dx.doi.org/10.2351/1.4798455
    2. Harlow, J. (2012. Are laser pointers dangerous to pilots? Retrieved from http://www.physics.utoronto.ca/~jharlow/teaching/lasers.html
    3. Harris, S. (2011). Lasers in medicine. Retrieved from http://spie.org/x43738.xml
    4. Laser. (2015). In Wikipedia. Retrieved from https://en.wikipedia.org/w/index.php?title=Laser&oldid=686197952
    5. Laser Safety. (2015). In Wikipedia. Retrieved from https://en.wikipedia.org/w/index.php?title=Laser_safety&oldid=690908551
    6. Murphy, P. (2014) Laser Pointer Safety. Retrieved from http://www.laserpointersafety.com
    7. Oregon State University (2015). Laser safety training. Oregon State University. Retrieved from http://oregonstate.edu/ehs/laser/training/introduction
    8. Robertson, D. M., Lim, T. H., Salomao, D. R., Link, T. P., Rowe, R. L., & McLaren, J.W. (2000). Laser pointers and the human eye: A clinicopathologic study. Archives of Opthamology, 118(12), 1686-1691. doi:10.1001/archopht.118.12.1686
    9. Thanos, S., Böhm, M. R., Meyer Zu Hörste, M., & Schmidt, P. F. (2015). Retinal damage induced by mirror-reflected light from a laser pointer. BMJ Case Reports. pp. 1-3. doi: 10.1136/bcr-2015-210311
    10. Weschler, M. (2000). How lasers work. In How Stuff Works. Retrieved from http://science.howstuffworks.com/laser.htm
    11. All references were accessed on 27 November 2015
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