The laser beam is rapidly scanned in one or more planes usually by vibrating or rotating mirrors inside the bar code scanner. A sensor detects the time dependent pattern of reflected laser light as the beam is scanned across alternate light and dark bands on a bar code. This information is processed electronically to produce a digital interpretation of the bar code that a computer will understand.

To meet design safety requirements, the scanner incorporates fail-safe detection circuitry that turns the laser off in the event of a component failure or when output limits are likely to be exceeded during a given time interval. Many handheld scanners used for low volume bar code reading (such as in libraries) do not use a laser light source - they use a low power visible or infrared light emitting diode similar to those used in remote controls for TV or video equipment.

This document discusses the special characteristics of laser light and the inherent safety aspects of lasers used in bar code scanners.

Characteristics of Laser Light

A laser1 is a device that can produce an intense beam of either visible or invisible "light" (in scientific terms, light is "electromagnetic radiation"). Laser light is usually almost monochromatic (that is, has a single colour) and can be formed into an intense narrow beam. High power lasers (outputs measured in watts) can emit beams with intensities many thousands of times greater than sunlight. Laser bar code scanners operate at relatively low power levels (outputs measured in milliwatts) and produce visible red beams (most common) or near-infrared beams.

General Laser Hazards

There are no direct hazards associated with the low powered lasers used in bar code scanners.

For other types of laser products, the degree of hazard depends on the power of the laser beam and the circumstances of exposure. A laser beam may be easily focused to a small area on the retina of the eye, resulting in damage to the retina and impairment to vision. High-powered lasers may cause burns to the skin without any additional focussing.

Australian Laser Safety Standard

The potential health hazard of a laser is indicated by its hazard classification. The Australian/New Zealand Standard 2211 Laser Safety defines a hazard classification scheme for lasers. Class 1 lasers are considered safe under reasonably foreseeable conditions of operation. Class 2 lasers are low power devices that are not completely safe, but eye protection is normally afforded by aversion responses including the blink reflex2. They are not capable of causing injury to the skin. Class 3A, Class 3B and Class 4 lasers emit progressively higher levels of radiation and special precautions are required in their use. All lasers other than Class 1 must carry a label indicating their hazard classification. Bar code scanners use only either Class 1 or Class 2 lasers.

Bar Code Scanners - No Significant Hazards

The vast majority of supermarket bar code scanners are classified as Class 1 under ANZS 2211 and so are therefore safe. The risks associated with handheld Class 2 laser bar code scanners, as used in larger variety stores, are small owing to the strong aversion response that normally sighted people have to bright light sources2. However, temporary flash blindness (similar to the effect of an electronic camera flash seen at close range) may occur following a brief accidental exposure to a laser scanner. Such flash blindness will usually occur only within about 500 mm from the scanner head in a dull lighting environment. A person effected by temporary flash blindness could have other accidents while this visual impairment persists.

No injuries from Class 1 or Class 2 bar code scanners used either in Australia or overseas have been reported. In view of the relatively low output power from these devices, this lack of injury reports is not unexpected. By comparison, there have been injury reports from high power Class 3B and Class 4 laser systems used in research, industry or medical surgery around the world.

Conclusion

Currently, there are no mandatory legal requirements in any Australian States or Territories for bar code scanners to comply with Class 1 limits. However, it is highly likely that all supermarket checkout scanners used in Australia are Class 1. Some handheld laser bar code scanners intended primarily for use in warehouse environments (inventory and stocktaking purposes) are classified as Class 2.

THERE ARE NO OCULAR HAZARDS TO USERS OR THE PUBLIC ARISING FROM LASER BAR CODE SCANNERS.

1. The word LASER is an acronym for Light Amplification by Stimulated Emission of Radiation, which describes the process by which lasers generate this light.
2. It is worthwhile noting that viewing the sun so that the image is fixed on a single region of the retina for exposure times of about a second can cause retinal burns. In practice, people avoid solar retinal injury through very strong aversion responses such as blinking, tearing and looking away with rapid eye movements.