Resources - Safety Info

From February 1993 edition of ‘Crucible’ Volume 24.1

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BACKGROUND
Like many other technological developments of the twentieth century, the laser has moved rapidly from the scientific research laboratory to widespread use in everyday life. It is possible to design a laser for virtually any wavelength in the electromagnetic spectrum from X-ray to infrared. Today, the laser can be found in industry, drilling fine holes and cutting precise shapes in a wide variety of materials including metals, crystals, and cloth. Lasers are at the heart of modern fibre-optic communications systems, as well as the CD player which is replacing the phonograph turntable. In the health care professions, lasers are used for diagnosis and treatment of many conditions, as "bloodless scalpels", and for imaging parts of the body. In the classroom, laser pointers are replacing wood pointers, and small lasers are often used to demonstrate fundamental principles of optics.

TYPES AND HAZARDS
Lasers may emit optical radiation continuously, or in short bursts. In either case, the laser emission is confined to a highly directional beam which spreads very little over long distances. As a result, even a laser with very low power output delivers a large amount of radiant energy to a small area; depending on the wavelength of the laser radiation, the resulting irradiance level may be high enough to damage or destroy the exposed material, including living cells.

Lasers are classified according to the hazard that their emissions present to human eyes and skin. The American National Standards Institute (ANSI) laser hazard classification is summarized in Table 1. While Class IIIb and IV lasers are mainly found in research laboratories and industry, Class I lasers are often used in science classrooms; some laser pointers intended for use in large lecture rooms contain a Class IIIa laser.

Only Class I lasers should be used in Science classes. The 0.5 FW HeNe laser is ideal for demonstrating the principles of optics, because its red light presents no hazard to the eyes and skin. Protective goggles are not required. Nevertheless, safe operating procedures should be followed so that students learn to handle these devices with respect. Remember that the high voltage electrical power supply required to operate the laser can also be hazardous!

PRECAUTIONS

• Only low power lasers (Class I) should be used in school Science labs.
• Laser sources should be kept in a locked storage area when not in use.
• The laser source should be firmly mounted so that the beam direction cannot be changed by an accidental touch.
• Optical components such as lenses, mirrors, filters, etc. should be aligned and firmly positioned before the laser is turned on.
• The laser beam should be aimed at an area of the classroom not occupied by students during the demonstration or experiment. Barriers should be placed to prevent students from gaining access to that area.
• Never look directly into the laser beam or expose your skin to it.
• Whenever possible, do not aim the laser beam at a polished surface which can reflect the light like a mirror. Any reflected laser light should be blocked by opaque screens.
• The laser power supply should be plugged into a Ground Fault Interrupter (GFI) circuit to reduce the electrical hazard to the operator.
  

When handled carefully, the laser is a safe and effective teaching tool, and an excellent example of a high-tech. spin-off into everyday life.

FURTHER READING

American National Standards Institute (1986). American national standard for the safe use of lasers. ANSI Z136.1. New York: ANSI.

Canadian Standards Association (1987). CAN/CSA-W117.2-M87 Safety in welding, cutting and allied processes. A national standard of Canada. Rexdale: CSA.

Sliney DH, Wolbarsht ML (1980). Safety with lasers and other optical sources. New York: Plenum Press.

Table 1 - Laser Hazard Classes

Class I Any laser which presents no eye hazard, even when the beam is directed into the eye for extended periods of time. Visible light lasers in this classification have beam powers less than 0.5 FW.

Class II A laser which may cause eye injury if one suppresses the aversion reflex in order to look at the laser source along the beam. (The aversion reflex causes the eyes to close or turn away from an intense light source.) These lasers have visible light outputs in the range of 1 mW.

Class III A laser which may cause eye injury within the time needed for the aversion reflex to operate. Class IIIa lasers are relatively low risk visible lasers, while specular reflections of a Class IIIb laser may also be hazardous to the eyes. Beam power is typically 5 mW.

Class IV A laser which presents both eye and skin hazards, and can ignite combustible materials upon exposure to the beam. A reflected beam is also dangerous. The power supply for such a source presents a significant electrocution hazard.

Some laser devices carry a low classification, but may contain an "embedded" laser source which would be more hazardous if removed from the device. Operating laser devices should only be disassembled or serviced by a qualified technician.