New Revision of ANSI Z136.1 (Laser Safety Standards)
Dr. Ami Kestenbaum, Secretary ANSI Z136
(Reproduced with permission from the LIA Today, Volume 8, Number 3, May 2000, Copyright 2000, Laser Institute of America, Orlando, Florida)
Within a few short months a new revision of ANSI Z136.1 will be published by the LIA [Laser Institute of America], the secretariat to the ANSI Z136 Accredited Standards Committee that is responsible for developing laser safety standards for users in the US. This newly revised standard will contain several important additions and changes to the last ANSI Z136.1 document that was published in 1993.
Since the last ANSI Z136.1 standard was published, developments in laser devices and laser applications have prompted research into the bioeffects involving laser parameters not previously addressed. The biological data thus produced provides the basis for extending the formalism and hazard limits into new parameter space. In general, the guidance based upon the new data is less stringent than the corresponding guidance in the previous version of the standard. The most important changes contained in the newly revised standard are described below.
Maximum Permissible Exposures (MPEs)
The new standard revises the tables containing MPEs, and methods by which hazard evaluation and laser classifications are done for ocular exposure of small (intrabeam) viewing and extended source viewing.
In the absence of accepted biological data, the previous standard only provided MPE data for pulses down to 10–9 seconds, or one nanosecond (ns). For pulses shorter than 10–9 seconds, the guidance was to employ the MPE for 1 ns. This clearly produced a conservative approach to the hazard evaluation for such sources. With the emergence of new biological data for sub-nanosecond pulses, more precise and less conservative guidance is provided in the new standard for ultrashort pulses down to 100 femtoseconds in the retinal hazard region of 0.4 mm to 1.4 mm.
Guidance is also offered in the use of laser eyewear in conjunction with ultrashort pulses. The new Class 1 Accessible Emission Limit (AEL) for visible wavelengths is changing to 0.4 mW from a few micro-watts. Thus in the visible part of the spectrum, Class 2 range is 0.4 mW to 1 mW. The Class 1 category is therefore significantly expanded for those lasers.
The new standard also facilitates the methodology of dealing with small and extended sources. Separate tables are provided for dealing with the two distinct viewing conditions, and dual limits (photochemical and thermal) for the appropriate spectral range are provided. The appendix contains numerous examples that illustrate and clarify the application of the new methodology. The process for conducting hazard evaluation and analysis is thus greatly simplified, and would be welcome by laser safety officers and others who are charged with the responsibility of performing laser hazard evaluation and classification as part of an overall hazard analysis.
In the past several years the use of laser pointers has proliferated significantly. They are routinely used in demonstrations, alignment, educational, and numerous other applications. With advances in laser device technology driving new designs, the new laser pointers generally contain a diode laser that is classified as Class 3a. This should be contrasted with previous generations of laser pointers that were based on HeNe lasers and were generally classified as Class 2. The great proliferation of these devices has made it more likely that individuals who are not familiar with appropriate safety precautions would use them.
While it is unlikely that momentary exposure to laser pointers will cause permanent retinal damage, exposure to these devices can cause other visual impairment. Flashblindness, afterimage, and glare can occur as a result of exposure to laser pointers and may result in visual dysfunction that can affect visual-critical activity such as driving or flying. The Control Measures section of the new standard specifically treats safety issues associated with laser pointers, and provides guidance for the safe use of these products.
The ANSI Z136.1 standard specifies that design of signs and labels be in accordance with ANSI Z535 series of standards for Accident Preventing Signs. The ANSI Z535 specifies sign dimension, lettering size, color, and other important sign design elements. The implication on ANSI Z136.1 is that new hazard signs are being specified. The new hazard signs contain an equilateral triangle attention symbol in addition to the familiar sunburst pattern. The new triangular symbol is introduced into both the "Caution" and "Danger" signs. As before, the IEC signs and labels are specified as acceptable alternative to the ANSI signs.
Harmonization with IEC
The ANSI Z136.1 has always striven to have classification guidelines and requirements closely harmonized with the corresponding international laser safety standard issued by the International Electrotechnical Commission (IEC). Currently few differences exist between the two standards.
The IEC recognizes that their current classification scheme is problematic particularly as it relates to evaluations with and without optically aided viewing. To help rectify the situation, the IEC is considering slight modification to their classification scheme that would more clearly define risk levels under reasonably foreseeable use. If this new scheme is approved by the IEC, it is the intent of the ANSI Z136 Committee to adopt a similar scheme and incorporate it in future versions of the ANSI Z136 standards. The newly revised standard of ANSI Z136.1 contains an appendix detailing this new classification scheme, thus alerting the user to these potential future changes. This would allow users to better prepare for eventual adoption of these changes.
Three new classes of lasers are being created 1M, 2M and 3R. Class 1M is composed of lasers, which are incapable of causing eye damage except when viewed with optical instruments. Similarly Class 2M applies to visible lasers which are safe when viewed by the unaided eye for up to 0.25 s due to the aversion response of the eye. Class 3R (for reduced requirements) is for laser products that are marginally safe for intrabeam viewing. The AEL for this class is five times the AEL of Class 1 or Class 2, whichever is applicable.
The ramifications of these changes are relatively small. All current Class 1 lasers will become Class 1 and Class 1M. Most current Class 2 will remain Class 2 or will become 2M if they possess a highly divergent beam. All current Class 3a "Danger" laser pointers will become 3R, and Class 3a expanded beam lasers will become 1M and 2M. Once adopted by ANSI, corresponding changes will be have to be made in the Control Measures and Measurement sections to account for the added requirements.
Visit the LIA website at http://www.lia.org/ or call 1-800-34 LASER for ordering information.
From LIA Today, Volume 8, Number 3, May 2000. Copyright 2000, Laser Institute of America. All rights reserved.