This article is excerpted from ACGIH Today! Vol. 6, No. 2 of April 1998.

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 Threshold Limit Value (TLV, a commonly accepted occupational exposure limit) 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. 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.

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 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. 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 pointers to see who can do it longer. Permanent retinal lesions almost certainly would result from such a practice.

It is the responsibility of users and owners of Class 3 or 4 lasers to register their laser equipment with the Government Laser Safety Officer of the Electrical and Mechanical Services Department (EMSD) of Hong Kong.

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In, order to fulfill this responsibility, the HKUST safety policy requires that all supervisors of all laser operations submit laser use information to the HSEO Laser Safety Officer (LSO). Furthermore, those using class 3 and class 4 lasers must also:

1. Receive an eye exam prior to the work assignment and following any accidental exposure (suspected or confirmed).
2. Attend the general Laser Safety training course offered by HSEO as well as receiving specific on-the-job training for each specific laser operation.
3. Supervisors of Class 3B or 4 lasers must submit an Operational Safety Procedure(OSP) to the LSO, preferably prior to the commencement of laser operation. The OSP should include as a minimum:
   1. specific safety procedures
   2. necessary and recommended engineering controls
   3. necessary and recommended administrative controls
   4. necessary and recommended personal protective equipment

The OSP should be suitable for preparing the laser users to protect themselves from laser beam hazards including those encountered during the use of optical devices such as beam splitters and lenses, as well as non-beam hazards such as high voltages, toxic dyes, target emissions, etc.

If you are supervising or working with a Class 3B

or Class 4 laser please be certain that:

1. All laser users have received their eye exams
2. All laser users are registered
3. All Class 3 or Class 4 lasers are registered
4. A thorough OSP has been generated and submitted to the LSO
5. All workers are fully trained in the equipment operation and hazards, and in all of the elements of the OSP

You are referred to Chapter 11 ("Laser Safety") of the HKUST Safety and Environmental Protection Manual for more detailed discussions concerning laser use and safety. Chapter 2 ("Work Planning & Procedures") of the Manual provides additional information and a sample format for OSP.

Please contact HSEO for assistance in scheduling medical exams, registering equipment and workers, training workers, and/or OSP preparation.

Laser Protective Eyewear

A - Goggles with separate glass lenses 8 - Spectacles with side shields C - Headrest coverall-4W goggles D - Coverall-type with hard rubber or soft vinyl frames, glass and/or plastic flat filter plates E - Plastic wrap-around lens in ski-type frames F - Full-view soft vinyl goggles

(This article has been taken from March, 94 issue of SafetyWise)

Despite their size, availability, and the fact that most pen size laser pointers are powered by small, widely obtainable batteries, these pointers devices can cause eye damage if used improperly. The potential hazard is limited to looking directly into the laser beam with unprotected eyes. No hazard to the skin exists. Users of laser pointers should never aim the pointer into the audience. When storing pointers, remove the poser source or unscrew the case/ housing enough to disable the power source.

Pen size laser pointers have become common presentation aids in recent years. These battery powered laser pointers that produce a narrow, bright red beam are convenient to carry and use, relatively inexpensive, and readily available through mail-order catalogs and magazines.

ANSI Classification Addresses Possible Eye Hazard

Two types of these pointer devices are widely used in visual presentations-he/ium-neon (HeNe) and diode lasers. The American National Standards Institute (ANSI) has defined the HeNe technology as a Class 2 laser, indicating that momentary or accidental viewing of the direct beam will not cause eye injury. A "CAUTION" label for these Class 2 devices is appropriate. On the other hand, ANSI has classified mist diode lasers as Class 3a lasers, indicating that direct viewing into the beam has the potential to cause eye injury.

Class 3a lasers may be labeled "CAUTION" if they present the same risk as a Class 2 laser to the naked eye. However, if a Class 3a diode laser has a very small beam diameter (less than 7 millimeter (mm)) and has a power rating between 1 and 5 milliwatt (mW), it must have a "DANGER" label. It poses a risk if viewed at close distance where the beam is less than 7mm.

HeNe laser pointers have been available for several years. On a relatively low power level (typically less than 1.0 mW), they produce a bright red (632.8 manometer (nm)) spot that is easily noticeable on a bright screen. The more recently developed diode lasers are smaller in size and more rugged. The fact that they cost only about one-third as much as HeNe lasers makes them popular.

The diode lasers, however, produce a light that is darker (670 nm) than the HeNe lasers. To achieve the same effect as the HeNe lasers, the diode laser power levels are increased (typically to 5 mW). ANSI has assigned the safety classifications described above to these Laser pointers in accordance with the level of danger to the eye.

Recommendation for Use

Because of safety considerations, laser pointers with a "CAUTION" label should be purchased as opposed to those with a "DANGER" label. In other words, Class 2 lasers are recommended. If a Class 3a laser is preferred, users should ensure that its use complies with all the safety requirements of ANSI Zl 36.1 -1993, and Chapter 11 of HKUST Safety Manual as well as the Hong Kong Electrical and Mechanical Services Department laser code of practice. Users should also be aware of the manufacturer's safety precautions.

Note:

On a related subject, users should not tamper with the laser emitting device in compact disc (CD) player, laser disc (LD) player, or CD-ROM drive. These laser sources emit beams of similar energy as laser pointers but in the infra-red range, which are invisible to naked eyes, thus increasing the chance of accidental injury.

HeNe laser pointer (above) and diode laser pointer (below).

(Extracted in part from SAFETY& HEALTH NOTE Issue No. 94-10, Oct 1994, US Dept of Energy)