Q I am an occupational health and safety trainer who recently purchased a laser pointer as an aid in my use of slides in presentations. Is there any significant, potential hazard in their use?

A Yes. While most exposures to laser pointer beams result in temporary flash-blinding, a slight retinal lesion also is possible. Exposure above the TLV for lasers is possible, depending primarily on the power of the laser diode and the duration of exposure.

Over the past few years, laser pointers have appeared on consumer markets around the world selling for not much more than US $20. Hence, their use among the general public has been proliferating. Use of such laser pointers by untrained people, who typically are unaware of their potential hazards, occasionally results in the flash-blinding of a student or audience member. Some victims of such flash-blinding have, on occasion, had a furious reaction, leading to coining of the term Laser Rage.  

Many claims of laser injury resulting from exposure to these 635*670 nanometer (nm) wavelength beams with a few milliwatts (mW) of power have appeared in the press and on the Internet. The power output of the laser diodes in these pointers typically is in the 3*5 mW range, although some units are advertised with power greater than 5 mW. By comparison, the TLV for exposure to lasers of this wavelength range is 2.5 mW/cm2 at the cornea, averaged over a 7-mm pupil for a blink reflex limited exposure duration of 0.25 second.(1) This is equivalent to a 1 mW beam entering the eye. So, an exposure to one of these beams may exceed the TLV. However, under most circumstances when the beam is accidentally swept across the face and enters the eye only momentarily, the exposure usually would fall below the TLV.  

Because the TLV has built-in safety factors and a normal exposure to a laser pointer beam is limited by the blink reflex, exposures above the TLV should not result in a retinal injury for most people. Exposure to the 635*670 nm wavelength region is less hazardous than shorter visible wavelengths because these longer wavelengths are less likely to cause photoretinitis or a photochemically induced lesion. However, even if there is no injury, exposure above the TLV can create liability problems.  

The safest laser pointers are those which do not exceed 1 mW output and therefore will not produce exposures above the TLV unless the viewer overcomes his or her blink reflex and purposefully stares into the laser. These are Class 2 lasers and bear a Caution label. Lasers in the range >1 mW to 5 mW are Class 3a, and carry a Danger label. Class 2 laser pointers, which have a power output no greater than 1 mW, are available, but those with 670 nm wavelength have low apparent brightness and may not be satisfactory for all uses. Laser pointers with 635 nm wavelength produce a much brighter-looking orange-red light and are satisfactory for most uses, even when the power does not exceed 1 mW. However, 635 nm pointers are somewhat more expensive and are hard to find.* One company now is marketing a green laser pointer*, but it is even more expensive. This pointer should appear very bright, even at a fraction of a milliwatt. So, when such short wavelength diodes become less expensive and more available, this issue should become self-limiting.   

It is important to remember that ANSI Z136.1(2) requires areas where Class 3 lasers (>1  mW) are used to be posted with a DANGER sign. The ANSI standard strongly recommends that users of Class 3a lasers have laser safety training and requires such training for users of Class 3b lasers(>5 mW). While, for example, there are no U.S. OSHA regulations in 29 CFR 1910 regarding lasers, ANSI often is used by OSHA and other regulatory agencies to evaluate laser hazards. This indicates that anyone using a 2 mW pointer should have laser safety training and one who is using a 6 mW pointer must have it. It also indicates that the classroom or auditorium where either pointer is in use must be posted with DANGER signs. So, in addition to the possibility of exceeding the TLV, using a Class 3 (a or b) laser pointer can impose some very cumbersome requirements.   

It is hard for many people to believe that something which looks like an ordinary penlight and runs on a couple of AAA batteries can be dangerous. However, it is important to realize that the hazard from laser pointers, although low, is not zero, particularly for Class 3 pointers which may cause exposure above the TLV. For example, a 5 mW blink-reflex limited exposure leads to as much as a 10% probability that a retinal lesion will result.(3) However, even eye exposures below the TLV may result in temporarily flash-blinding the victim and should be avoided.  

A special, nonoccupational concern is that these pointers seem to be gaining popularity as gift items for children to use as toys. When children are involved, a brief accidental exposure is not the only likely scenario. One can envision a group of adolescents staring into a laser pointer to see who can do it longer. Permanent retinal lesions almost certainly would result from such a practice.  

For more information, please review the 1998 revision of the TLV for lasers, the documentation for the lasers TLV(1), and the ACGIH publication, A Guide for Control of Laser Hazards(4).  

* A Class 2, 635 nm laser pointer is available from an Australian manufacturer, Laserex, with a U.S. distributor in Scottsdale, AZ. A Class 2, 532 nm laser pointer is available from Lasermate of Walnut, CA. Mention of brand name does not imply endorsement by ACGIH.

References

1. ACGIH Documentation of the Threshold Limit Values for Physical Agents in the Work Environment (Lasers). ACGIH, Cincinnati (1993).
    
2. American National Standards Institute Standard Z136.1, Safe Use of Lasers. ANSI, New York (1986).
    
3. Sliney, D.H.; Wolbarsht, M.L. Safety with Lasers and Other Optical Sources A Comprehensive Handbook. Plenum Press, New York (1980).
    
4. ACGIH A Guide for Control of Laser Hazards, 4th edition. ACGIH, Cincinnati (1990) Answer provided by Gary Myers, CIH, member of the Physical Agents TLV Committee.