Safety concerns about laser pointers

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<ul><li><p>Safety concerns about laser pointersDavid H. Sliney and Jerome E. Dennis Citation: Journal of Laser Applications 6, 159 (1994); doi: 10.2351/1.4745352 View online: View Table of Contents: Published by the Laser Institute of America Articles you may be interested in Green Diode Laser Pointers Have Now Dropped in Cost to About $10 Phys. Teach. 47, 479 (2009); 10.1119/1.3225522 Safety recommendations for laser pointers J. Laser Appl. 10, 174 (1998); 10.2351/1.521848 How to modulate a pointer laser Phys. Teach. 33, 58 (1995); 10.1119/1.2344137 Diffraction photographs with a Laser Pointer Phys. Teach. 32, 174 (1994); 10.1119/1.2343949 AAPT concerned about FDA lasersafety rules Phys. Today 27, 63 (1974); 10.1063/1.3128825 </p><p> This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: Downloaded to IP:</p><p> On: Sat, 20 Dec 2014 20:09:52</p><p>;option1=author;option1=author</p></li><li><p>JOURNAL OF LASER APPLICATIONS (1994) 6, 159-164</p><p>LASER SAFETY</p><p>Safety concerns about laser pointers</p><p>DAVID H. SLINEYI AND JEROME E. DENNIS2</p><p>1Laser Microwave Division, US Army Environmental Hygiene Agency, Aberdeen Proving Ground, MD 21010-5422, USA, and 2LightProducts Branch, Division of Standards Enforcement, Office of Compliance and Surveillance, Center for Devices and RadiologicalHealth, Food and Drug Administration, Rockville, MD 20857, USA</p><p>Accepted for publication 7 Apt111994</p><p>In the past two years considerable concerns have been expressed about the safety of Class 3A laserpointers. The concern has been that Class 3A diode-laser pointers have replaced the saferheliumneon (HeNe) Class 2 laser pointers. Hundreds of thousands of small HeNe visible-wave-length lasers have been traditionally used for alignment and pointing, laser demonstrations andlaser displays in science, education and industry, but can the diode laser be as safe and effective?Not infrequently, some people associate "lasers" with Buck Rogers and "Star Wars", and areconcerned whether their use in pubic is safe. This safety issue is raised and the risks of viewingsmall lasers are'compared with viewing the sun or bright spotlights. It is shown that HeNe lasersthrough Class 3a (up to 5 mW power) are not a significant eye hazard; however, Class 3A diodelasers may not elicit a strong "aversion response" in some individuals, and greater precautionsmay be necessary than with HeNe lasers of the same power.</p><p>KEYWORDS: laser safety standards; diode-laser pointers</p><p>INTRODUCTION 1</p><p>With the advent of relatively low-cost visible laser diodesover the past few years, laser pointers for use in lecturesand demonstrations have become very popular. Sales inthe US alone are now of the order of many thousands ofunits annually. Recently, however, concern has been ex-pressed by some experts in the laser safety communityabout the safety of these products and the effectiveness ofexisting standards in addressing the hazards. The safetyconcerns stem from the facts that these products: (a) aretypically used by persons who cannot be expected to bereasonably familiar with the appropriate user precautionsnecessary to ensure the safe use of the products, and (b)are Class 3A, since they emit radiant powers of a fewmilliwatts (i.e. above the Accessible Emission Limit(AEL) of Class 2) at wavelengths of approximately 670 nm[1, 2].</p><p>Comparable visibilities of laser spots</p><p>At a diode wavelength of 670 nm the eye's visual sensitiv-ity is considerably reduced. At 670 nm the CIE photopicvisual sensitivity is 0.032 compared to 0.24 at 633.8 nm or1.0 at 550 nm. This is illustrated in Fig. 1. In other words,the apparent brightness of a pointer's spot from a 1 mW,</p><p>Disclaimer: The opinions or assertions herein are those of the authorsand should not be construed as reflecting official governmental positions.</p><p>0.8</p><p>0.2</p><p>0350 400 450 500 550 600 650 700 750 800</p><p>Wavelength, (nm)</p><p>FIGURE I. CIE photopic (daylight color vision) relativespectral sensitivity function V. Note the significant differencein visibility of the HeNe versus the 670 nm diode laser.</p><p>670 nm beam is only 3% of a 1 mW, 555 nm beam of thesame spot size or 13% of the brightness of a 632.8 nmHeNe laser of the same size. The yellow-green wave-length of 555 nm is the peak of the photopic (daylight)sensitivity function. To achieve the same brightness of a0.8 mW Class 2, HeNe laser pointer, the manufacturer of</p><p>1042-346X 1994 LASER INSTITUTE OF AMERICA</p><p> This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: Downloaded to IP:</p><p> On: Sat, 20 Dec 2014 20:09:52</p></li><li><p>160 SLINEY AND DENNIS</p><p>a 670 nm diode laser pointer must achieve an outputpower of 6 mW, which would place the laser product inClass 3B! In fact, most 670 nm laser pointers measured bythe authors do not exceed 4 mW, which corresponds invisibility to a 0.53 mW HeNe laser.</p><p>Pointers used with firearms</p><p>In addition to their use as pointers, similar products aremarketed as aiming aids for firearms. However, becausefirearms have lethal potential, it is hoped that a similarlevel of caution would be practised to that taken with thefirearms to which these lasers are attached.</p><p>HE NE AND DIODE LASER USE</p><p>Until recently, the most common visible-wavelength laserhas been the HeNe laser which emits a beam of red lightat 632.8 nm. Because the HeNe laser was consideredrelatively efficient and can be readily constructed to emita low power of 1-5 mW, it has been by far the mostcommon visible-wavelength continuous-wave (CW) laserused in teaching, displays and alignment. However, duringthe past years, a family of GaAlAs visible, red-light emit-ting diode lasers have been rapidly replacing the Class 3AHeNe laser in many applications. The diode lasers areless expensive and more compact than their more visibleHeNe gas laser counterparts, but the beam is less visible.Laser pointers are generally either Class 2 or Class 3A.</p><p>VISIBLE -BEAM LASER HAZARD</p><p>Class 2 and Class 3 visible-wavelength lasers are a safetyconcern only if one looks directly into the collimated laserbeam. Since the beam of some of these lasers may be only1-3 mm in diameter, most, if not all, of the beam canenter the pupil of the eye which itself normally has adiameter of 2-7 mm. However, for most laser applicationsit is easy to see that it is highly unlikely for such a smalllight beam to be so perfectly oriented as to be directedunintentionally into someone's eye. But if the small beamshould enter the eye, the viewer will be surprised by such abright light and immediately blink and turn his or herhead. This is the normal physiological response to brightlight, and occurs if one suddenly turns one's head intothe sun. It is referred to in laser safety standards as theaversion response [3]. The blink reflex is normally con-sidered to take place in less than 0.2 s, and certainly lessthan 0.25 s. Therefore, if one unexpectedly looks directlyinto the sun when it is not near the horizon, the longestexposure duration should be 0.25 s. The same aversionduration applies to looking at a bright spotlight at a veryclose distance. It is not normal to continue to look (i.e. tostare) at the sun or other very bright lights. If one forcesoneself to stare at the sun for more than 2 min, the result</p><p>can be a permanent injury to the retina, with loss of vision.When people force themselves to look at the sun during aneclipse, the result is referred to as "eclipse blindness" [3].</p><p>APPLICABLE LASER SAFETY STANDARDS</p><p>There are two general types of laser standard in the USA.One is designed for the user [2]. It was developed byconsensus and is strictly voluntary but, because of itswidespread acceptance, many companies and organiza-tions consider it regulatory. Thus when a dispute arises, itis considered the accepted standard of safety in manycourts of law. The second type of standard is a regulationof the Federal Government, but applies only to lasermanufacturers and commercial laser products [1]. Thestandards themselves are complicated, and a detailed ex-planation cannot be presented here. However, some gen-eral explanation of how these standards relate to low-power visible lasers can be provided. Both of thesestandards are relevant to the concerns raised here, andmake use of hazard classifications in order to specify safetycontrol measures.</p><p>Lasers are grouped into several hazard classes based upontheir potential for injury. Class 1 is considered safe underany viewing conditions, whereas Class 4 at the other endof the scale includes very powerful lasers used in weldingand cutting, for which stringent safety measures apply.Class 2 lasers are those visible lasers which have an outputpower of 1 mW or less. Class 2 lasers do not pose a realhazard under conditions of prudent use. These lasers, likethe sun or a slide-projector lamp, are not a realistic hazardwhen used sensibly, but they represent a theoretical poten-tial hazard. If one were to force oneself to stare directlyinto the laser beam ("intrabeam viewing"), one couldexceed the appropriate Maximum Permissible Exposure(MPE) limit A critical assumption is that any Class 2 laseris of a visible wavelength sufficient to be seen as toodazzling to view. Class 3 is divided into two groups: a andb. Class 3b lasers require safety measures to precludehazardous intrabeam viewing, since the direct beam ishazardous to the eye. For visible-wavelength lasers, Class3a is currently defined in the US (but not internationally)[4] as those with an output power greater than 1 mW butless than 5.</p><p>Class 3a represents a narrow transition range betweenClass 3b and Class 2. Initially it was to include only those1-5 mW lasers which had an expanded beam to be saferby emitting less than 1 mW within a 7 mm aperture (i.e.within a dilated pupil). This definition is still used in theinternational standard [4]. A Class 3a warning label similarto that for Class 2 cautioned one not to "stare into beamor view with optical instruments." The Center for Devicesand Radiological Health (CDRH), which is responsible for</p><p>JOURNAL OF LASER APPLICATIONS 6(3) (1994)</p><p> This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: Downloaded to IP:</p><p> On: Sat, 20 Dec 2014 20:09:52</p></li><li><p>LASER SAFETY 161</p><p>the Federal laser performance standard for manufacturers,later revised the definition of Class IIIa (the Federalstandards use Roman numeral notation to designate theclasses; the IEC standards use upper-case letters to desig-nate classes 3A and 3B). The revised CDRH definitionincluded all 1-5 mW lasers since there had never beena report of eye injury in years of use of hundreds ofthousands of 1-5 mW HeNe lasers (Federal Register,Vol. 48, No. 231, pp. 54164-54182, Nov. 30, 1983, andVol. 50, No. 161, pp. 33682-33702, August 20, 1985). Theuser standard (ANSI Z136.1-1993) soon followed suit, butthe old distinction stijl exists in the international lasersafety standard [4]. To the user of a HeNe laser [4] theimportant fact is that there is no reason to expect thatactual eye injury could occur until the laser power enteringthe eye exceeded 5 mW [5]. A 5 mW laser might becapable of injuring a small part of the retina and cause ablind spot if an individual forced himself or herself to stareinto the bright light for more than 10-20 s. One shouldremember that the 1-5 mW HeNe laser has been usedwidely in the construction industry for alignment of pipe,etc., for more than 15 years without any known eyeinjuries.</p><p>The American National Standard [2] requires that Class 3aand Class 2 lasers used for display and alignment be usedso as not to expose people to the direct beam unless thebeam irradiance has dropped below the MPE. The beamshould not be directed at the eye, and in an unsupervisedlocation steps should be taken to prevent access of thepublic to the direct beam. Of course diffuse reflectionsfrom a screen or scattered light from smoke are not thedirect beam and are considered completely safe (and com-fortable to view). It should be remembered that if visiblelaser light from a HeNe laser is comfortable to view, it isfar below safe exposure limits (MPEs) [3].</p><p>Federal Laser Product Performance Standard</p><p>Laser pointers and aiming devices, as well as all otherproducts containing lasers that are sold or imported intothe US, are subject to the Federal Performance Standardfor Laser Products that is administered by the Center forDevices and Radiological Health (CDRH) of the UnitedStates Food and Drug Administration [1]. This standardrequires that all lasers be put into a hazard class deter-mined by the output radiant power level. This class, inturn, determines the requirements for controls, indicatorsand warnings on the product and in its supportingliterature such as promotional brochures and instructionsfor use. However, this standard impacts on the manufac-turers and importers of these products and on the productsthemselves, but can do nothing to ensure (by regulation)that the products will be used safely once the laser hasbeen purchased.</p><p>ANSI Standard for the Safe Use of Lasers</p><p>Safety during use is the scope of-the American NationalStandard for the Safe Use of Lasers, published by theLaser Institute of America (LIA) and the AmericanNational Standards Institute (ANSI Z136.1-1993) [2].However, because these products are sold without restric-tion to the general public, it would be unrealistic toassume that the purchasers would be aware of the exist-ence of this standard, much less of its requirements. Someof the states and the Federal Occupational Safety andHealth Administration (OSHA) of the US Department ofLabor base their laser safety requirement on the ANSIstandard, but the authority is generally restricted to safetyin the workplace. Although the ANSI standard does con-tamn requirements for laser product safety, it defers to theCDRH standard for products sold commercially and thatare certified by their manufacturers under the CDRHstandard.</p><p>International Standard...</p></li></ul>