C.E. Moss, corning Inc., B. Edwards, Duke University Medical center, and W.J. Ertle, rockwell laser Industries
While the focus of the laser safety community has been dominated by the need to control laser beam hazards, safety professionals are beginning to appreciate the need to similarly address NBH
Safety professionals and organizations confronted by laser related non-beam hazards (NBH)—such as electrical fires, plasma radiation, and explosions—face unique safety and regulatory concerns. The spread of laser technology has increased both the proliferation of NBH incidents and the number of laser users unaware of these hazards.
Laser incident information is available from Rockwell Laser (Cincinnati, OH; www.rli.com), which maintains a Laser Incident Database (LID) containing more than 1300 incidents reported over about 40 years (see Table 1).1 The LID divides laser incidents into Beam (eye and skin) and Non-Beam (other) and indicates (a) that the numbers of reported NBH incidents in the LID now exceeds the number of reported skin incidents and (b) at present, more than 30% of all incidents can be designated as NBH. The LID also reports that the two lasers most involved with NBH incidents are Nd:YAG and CO2 (see Table 2). Unfortunately, not all lasers were identified or reported in the LID, which may skew results. Finally, it was reported by Rockwell2 that the number of NBH incidents in 1998 was 67, which is about 1/3 of the incidents now being reported ten years later.3 The rise of reported NBH incidents clearly supports the need to be more aware of these hazards.
The guidance in the American National Standards Institute (ANSI) Z136 series of standards provides general information on the recognition, evaluation, and control of traditional beam hazards.4 However, the evaluation and control of NBH demands a different knowledge base than what is required for beam hazards, so that laser safety professionals may need to assess their experiences with NBH in order to adequately protect laser users.
Current ANSI guidance
Section 7 of the current ANSI Z136.l-2007 Standard for the Safe Use of Lasers defines NBH as “…classes of hazards that do not result from direct human exposure to a laser beam.” The four general types of NBH covered at present are exposing materials to laser beams (for example, fires), exposure to laser system components (for example, capacitors), materials used to generate the beam (lasing media such as dye and gas), and how the system is used (for example, mechanical, limited space). Some of the specific NBH topics covered in the standard are electrical hazards, plasma radiation, laser disposal, explosions, robotics, fires, and compressed gases. It is to be noted that some of these hazards can be life-threatening (electrocutions). Facilities using lasers must secure sufficient expertise to ensure adequate safety controls for such an extensive array of hazards. As laser technology continues to advance and new workplace safety concerns arise, laser safety professionals must anticipate additional NBH topics.
Balancing beam and NBH guidance
The need for balance in a laser standard between beam and non-beam poses a challenge for laser users. Standards have generally attempted to address the NBH issue by providing enough information to ensure awareness and adequate control measures without overwhelming the users with a comprehensive treatment of each NBH topic. However, this balancing act is difficult because, unlike beam hazards, NBH account for all laser related fatalities and the most severe laser related injuries, which result in a far greater regulatory burden than that associated with eye and skin hazards.
Emerging NBH issues
It is anticipated that future NBH will arise in the coming years either from new applications or resolution of older issues requiring attention by laser safety professionals. Some of these new hazards are associated with nanoparticle production, concerns with gas alarms, ignition/fire sources, and hazards involving ionizing radiation sources.
Nanoparticles—Concern about production of nanoparticles from laser interactions has been voiced from reports in the occupational safety literature.5 One nanometer (nm) is 10-9 meters in length and the term “nanoparticle” generally refers to particles <100nm in at least one of its dimensions. It appears that small size particles (< 0.1 micrometers) may have higher human risks than larger particles due to their increased reactivity issue. While mankind has been exposed to natural nanoparticles for eons, it now appears that enhanced toxicities may exist from engineered (manmade) nanoparticles. A given material’s reactivity is heavily influenced by its surface area, which varies with the square of the particle’s radius (r2), while volume varies with the radius cubed (r3). Therefore, nanoparticles have a greater surface-to-volume ratio, and hence greater reactivity, than the same material in a larger particle size. This increased reactivity has profound consequences for respiratory effects, blood/brain barrier passage, and fire/explosion hazard. Finally, while nanoparticles can travel easily to the deepest parts of the lung (unlike larger particles that are trapped in the upper airway) they may also have the capability due to their small size of traveling to different locations within the body. A potential problem with the production of laser generated nanoparticles is the difficulty of assessing worker exposure and possible subsequent health effects. At the present, there are no occupational standards; appropriate metrics have not been determined; and measurement equipment is not generally available to properly document health effects.Potential ignition source hazard of lower-power lasers—Section 7.2.3 of the ANSI Zl36.l-2007 Standard suggests that enclosure of Class 4 laser beams can result in fire hazards if materials are exposed to beam irradiances >10W/cm2, or beam powers exceeding 500mW. Chapter 5 of the National Fire Protection Association’s NFPA Standard for Laser Fire Protection6 states that laser beams of 0.5W/cm2 shall be considered an ignition source hazard.
Although these irradiance and power values are only intended as a rough guide, they do pose questions on how the laser safety professional should evaluate ignition source hazards. Questions arise when working with Class 3B lasers because while such devices are not generally considered to be an ignition source they may cause smoke or charring without the presence of an actual flame. Under some situations where flammable compounds or substances exist, it may even be possible that smoke could be initiated by Class 3B lasers. The introduction of nanoparticles into the work environment also gives rise to issues concerning possible dust explosions.
Production of ionizing radiation—Section 7.2.2.1 of the ANSI Zl36.l-2007 Standard briefly mentions the possibility of ionizing radiation as a byproduct of laser operation, but provides no discernible guidance on recognition or control of this hazard. While high-voltage (>15 kV) vacuum tubes (used as rectifiers, thyratrons, and so on in power supplies) or electric-discharge lasers can produce X-rays, such devices are almost always appropriately shielded by manufacturers. Solid-state high-voltage components reduce or eliminate X-ray production from power supplies. Free electron lasers have much greater ionizing radiation issues, including X-rays, neutrons (at 10MeV and higher), muons (>1 GeV electron beams), synchrotron radiation (photon fan wherever the electron beam bends); and activation product decay radiation7.
The underreporting of laser beam accidents has long been recognized and is particularly acute for NBH.8 Extensive accident data maintained by various government agencies generally do not indicate whether NBH injuries have occurred with laser use. There have been situations where NBH incidents have been reported as industrial hygiene problems rather than laser related problems.
Several general conclusions can be made regarding worker exposure to laser NBH. First, it is clear that while eye and skin laser bioeffects are still important, they are not the only exposure concern with lasers. Second, newer laser process byproducts such as nanoparticles may increase/complicate occupational exposure to laser NBH. Third, the laser safety community must continue to demand that laser safety training courses contain up-to-date information on NBH. Fourth, safety professionals and laser safety officers charged with managing laser safety programs must not allow NBH to be neglected or emitted from their laser safety program.
C.E. Moss is with Corning Inc., Corning, NY; B. Edwards is with Duke University Medical Center, Durham, NC; and W.J. Ertle ([email protected]) is with Rockwell Laser Industries, Cincinnati, OH.
References
- Information on the Laser Incident Database (LID) is available from Rockwell Laser Industries at www.rli.com.
- R.J. Rockwell, “Laser Incidents: A Summary of Recent Accident Reports,” International Laser Safety Conference, Orlando, FL, 1998.
- C.E. Moss, Update on NBH for the ANSI Z136 Standard, 3rd annual DOE Laser Safety Officer Advanced Training Workshop, Argonne National Laboratory, Chicago, IL, July 17, 2007.
- American National Standards Institute Inc. (2007), Zl36.l-2007 American National Standard for the Safe Use of Lasers, Orlando, FL, Laser Institute of America.
- International Conference on Nanotechnology-Occupational and Environmental Health and Safety: Research to Practice, Sponsored by NIOSH and University of Cincinnati, December 4-7, 2006, Cincinnati, OH.
- National Fire Protection Association (2003) Standard for Laser Fire Protection (NFPA 115), Quincy, MA: National Fire Protection Association.
- B. Edwards and G. Moss, “Unresolved Issue—Laser Ionizing Radiation Hazards,” Proceedings of the 2003 International Laser Safety Conference, Jacksonville, FL, 199-200.
- N. Keeler, J.E. Dennis, A. Figueroa, R.J. Rockwell, B.E. Stuck, and A.L. Wartick, “Investigation of Laser Injuries,” Proc. SPIE, Vol. 4953, p. 61-69, 2003.