Radiation Safety Committee
Visible light lasers used for surveying, levelling and alignment
Some Frequently Asked Questions
- What are the risks?
- How does this equipment operate?
- What are the biological effects?
- What are the Laser classifications?
- What precautions should be taken?
- What regulatory controls are in place?
- What references are available?
What are the risks?
The growth in the number of laser devices used in Australia for surveying, levelling and aligning applications has increased the potential risk of workers being exposed to laser radiation through carelessness, misuse of equipment or ignorance of the hazards involved.
This bulletin is intended to explain the hazards and provide broad guidelines for the safe use of visible light lasers employed for surveying, levelling and alignment purposes.
How does this equipment operate?
Helium/neon gas laser devices which are most commonly used for surveying, levelling and alignment purposes consist of a high voltage gas discharge tube with reflecting mirrors at each end. One of the mirrors is partially transparent and the laser beam emerges from the discharge tube as a fine pencil of red light about 1 millimetre in diameter.
Lenses may be added to expand the beam diameter and to decrease the beam divergence. Helium/neon laser devices usually produce their light continuously and are referred to as continuous wave (c.w.) lasers, but the laser light may be pulsed (either electrically or mechanically).
Surveying, levelling and alignment laser devices all use the property that light travels in a straight line through air over long distances. For pipe laying or tunnelling applications the direction of the laser beam is fixed and used to guide the work; if accurate level measurements over a large area are required (e.g. laying concrete slabs, installing ceiling tiles), a motor driven prism reflector may be used to continuously rotate the laser beam.
A pulsed laser light allows the distance to be measured between a reflecting target and the laser measuring equipment by determining the time taken for a laser pulse to reach the target and reflect back to the laser measuring instrument. (Light travels in air at a constant velocity of about 300 million metres per second).
What are the biological effects?
Most laser damage is due to the heating of the absorbing tissues. This thermal damage is usually confined to a limited area extending either side of the energy absorbing layer and centred on the irradiating beam.
Lasers which produce light in the visible region of the spectrum are potentially hazardous to sight. This is because the eye will focus the laser beam onto the retina and a retinal burn may result, in much the same way as a magnifying glass using the sun’s rays will burn paper. The power density of the laser spot focussed on the retina is typically about 100,000 times the power density incident on the cornea. Therefore, although it may be quite safe to expose the skin to a moderately low power visible laser, it is often hazardous to look into the beam. Laser burns on the retina may cause serious impairment of vision or even blindness in the eye affected.
Where the eye receives minimal exposure to a laser beam, temporary blindness may occur (similar to that caused by a photographic flash unit). The duration of the flash blindness is a measure of the severity of exposure and if the flash blindness lasts for an hour or more, it is an indication that permanent eye damage may have occurred.
What are the Laser classifications?
Australian Standard 2211 - 1981 requires that laser products used for surveying, levelling or alignment purposes should preferably be either Class 1 or Class 2 (refer to section 6.3). The Standard allows use of Class 3A, but more stringent safety precautions are required than with Class 2. Class 3B and Class 4 laser products are too dangerous for general surveying, levelling or alignment purposes and are therefore not allowed for these applications.
What precautions should be taken?
Users and manufacturers of laser devices should consult Australian Standard 2211 - 1981 "Laser Safety" (AS 2211 - 1981) which lists detailed requirements of procedures and requirements necessary to protect persons from laser radiation. Users of lasers employed for surveying, levelling and alignment tasks in the construction industry, should also consult Australian Standard 2397 - 1980 "Guide to the Safe Use of Lasers in the Construction Industry". AS 2397 - 1980 reproduces and supplements the user precautions outlined in AS 2211 - 1981.
Precautions should be taken to ensure that persons do not look directly into the laser beam.
Direct viewing of the laser beam through optical instruments (theodolite, binoculars, telescope, etc.) will generally increase the hazard and should not be permitted.
The laser beam should be terminated at the end of its useful beam path and must in all cases be reduced to less than the recommended maximum permitted exposure (see AS2211 - 1981) if the beam path extends beyond the control area (construction site, etc.).
The laser beam path should be located well above or below eye level wherever practical.
Precautions should be taken to ensure that the laser beam is not directed at specular (mirror-like) surfaces.
When not in use the laser device should be stored in a location where unauthorized personnel cannot gain access.
The laser head should be rigidly fixed in place so that the direction of the laser beam cannot be accidentally altered.
Where laser devices are used indoors, room lighting should be as bright as practical in order to constrict the diameter of the pupil of the eye and consequently lessen the hazard.
A responsible person should be appointed as a Laser Safety Officer to assess and implement controls appropriate to the class of laser, the type of installation and the associated hazards.
Only suitable trained employees approved by the Laser Safety Officer should be allowed to install, adjust and operate the laser equipment.
Warning signs (as designated by AS2211 - 1981) should be placed in conspicuous locations both inside and outside the work area and in locations giving access to the area.
Laser devices used on building construction sites, which employ ROTATING LASER BEAMS, often have a beam rotation rate adjustable from about 6 revolutions per second down to a completely stationary beam. Accidental viewing of a STATIONARY beam must be avoided; however whilst the beam is rotating at more than a few revolutions per second, then accidental viewing should not cause any permanent eye damage (even when Class 3A laser devices are used).
What Regulatory controls are in place?
In Victoria approval for the use of a laser on a construction site must be sought from the Department of Labour and Industry who enforce laser safety regulations.
Department of Labour and Industry
National Bank House
500 Bourke Street
MELBOURNE VIC 3000
What References are available?
Charschan, S.S. (ed.)., Lasers in industry. New York: Van Nostrand, 1972.
Harry, J. E., Industrial lasers and their applications. New York: McGraw-Hill, 1974.
Standards Association of Australia. Laser Safety. North Sydney, 1981. A.S.2211.
Standards Association of Australia. Guide to the safe use of lasers in the construction industry, 1980. A.S.2397.
Sydenham, P. H., Laser gauging - reference guide to the use of laser based measurement systems. Armidale, N.S.W.: Department of Continuing Education, University of New England, 1976.
Victoria. Labour and Industry (Laser Safety) Regulations 1983. Statutory Rules No. 361, Government Printer, Melbourne.