Laser bar code scanners are used in applications where the accurate identification
of many articles in a short time is necessary, for example, in supermarkets, libraries
and warehouses. These devices use a low powered laser to read the bar code attached
to the article in question.
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.
- The word LASER is an acronym for Light Amplification by Stimulated Emission
of Radiation, which describes the process by which lasers generate this light.
- 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.
