Chemical Education Today
Letters Take Care When Using That Laser Pointer In the experimental procedure of the Tested Demonstration, “The Use of an Inexpensive Laser Pointer To Perform Qualitative and Semiquantitative Laser Refractometry” (1), the authors give the following warning: “Avoid looking directly at the laser beam.” This warning is insufficient. A year ago I was working in the lab trying to test for the presence of CO2 by bubbling a gas mixture supposedly containing this gas into limewater. Since the precipitate produced was extremely scarce (it looked more like a colloidal suspension), I thought of using a laser pointer to take advantage of the Tyndall effect and thus visualize it. I was using a conicalbottom vial (Ace Glass) and a commercial laser pointer. After using the laser for this purpose for a few minutes, and even though I never looked at it directly, I realized that perhaps the reflections and refractions from the vial had somewhat hurt my vision. For the next few days, I was very often seeing large “white spots” and this so worried me that I went to see an ophthalmologist. After careful examination, he said that nothing of consequence had happened to my vision. Unfortunately, my retina became very sensitive to bright light for several months. I have recovered, but I wanted to warn users of laser pointers for purposes such as those mentioned above, that in spite of not looking directly at the laser light, some side effects may derive from inadvertent reflections and refractions at glassy or other materials. Literature Cited 1. Neder, A. F.; García, E.; Viana, L. N. J. Chem. Educ. 2001, 78, 1481–1483. Jorge G. Ibanez Centro Mexicano de Quimica en Microescala Departamento de Ciencias Universidad Iberoamericana Prolongacion Paseo de la Reforma 880 Delegacion Alvaro Obregon 01210 Mexico, D.F., Mexico
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The Tested Demonstrations Editor replies: The concerns expressed by Jorge G. Ibanez are real, according to an apparently authoritative and very informative essay, “Safety Recommendations of Laser Pointers” by R. J. Rockwell, Jr., W. J. Ertle, and C. Eugene Moss, available on the Web (1). This article notes that Class IIIA laser pointers are available in the U.S., even though they are banned in the UK. These lasers may be hazardous even if viewed for a very short time, and little research has been done on the chronic exposures like those reported by Ibanez. Lasers are classified from I (least dangerous) to IV, which requires strict control measures. Up to class II are allowed as laser pointers in the UK. According to the Laser Institute of America cited by Metrologic (2), a Class II laser is defined as follows: A Class II laser or laser system must emit a visible laser beam. Because of its brightness, Class II laser light will be too dazzling to stare into for extended periods. Momentary viewing is not considered hazardous since the upper radiant power limit on this type of device is less than the MPE (Maximum Permissible Exposure) for momentary exposure of 0.25 second or less. Intentional extended viewing, however, is considered hazardous.
Literature Cited 1. Rockwell Laser Industries: Safety Recommendations. http:// www.rli.com/resources/pointer.asp (accessed Oct 2002). 2. Metrologic Instruments Inc. http://www.metrologic.com/corporate/techfaq.htm (accessed Oct 2002). Ed Vitz Department of Chemistry Kutztown University Kutztown, PA 19530
[email protected] Journal of Chemical Education • Vol. 80 No. 1 January 2003 • JChemEd.chem.wisc.edu
