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Laser Safety: 



1. What is light?


Scientific Definition: ELECTROMAGNETIC RADIATION.   Light travels at around 300,000km per second.   The smallest forms of light are called photons.



2. What is a laser?


A Laser is a device that produces light (or electromagnetic radiation) that is: -


  • Coherent (lightwaves of the same frequency).


  • Monochromatic (lightwaves of the same wavelength or colour).   For lasers, this is measured in Nm or

          one thousand millionth of a metre.


He-Ne lasers                       Typically 632.8 nanometres

Visible beam diode lasers      Typically 635.0 nanometres (Piper ; LMH-600)

Invisible beam diode lasers    Typically 780 nanometres ( Rugby 50)


  • Of the same colour


He-Ne = red

Laser diode = red or green or invisible

Argon = green

Ruby = pulsed red

Carbon Dioxide = invisible


Unlike whitelight (sunlight), which if directed through a prism or diffraction grating breaks into the colours of the spectrum (rainbow), a laser beam subjected to similar conditions retains the same colour. This is because laser light is of the same wavelength whereas with whitelight, there is a continuous change in wavelength from red (the longest wavelength), through orange, yellow, green, blue, and indigo to violet (the shortest wavelength).


  • A narrow intense beam (high irradiance)


  • Of low divergence (well collimated)



3. When was laser light discovered?


  • In 1913 the Danish physicist Niels Bohr pointed out that atoms can exist in a series of states and each state has a certain energy level. Atoms cannot exist between these states but must jump from one to another. An atom at a low energy level can absorb energy to reach a higher energy level. When it changes from a high to a low-energy level, it gives out the surplus energy in the form of radiation. If the radiation is given in the form of visible light, the light will be of the same wavelength (i.e. colour). The atom at a high-energy level may emit this radiation spontaneously, or it may be triggered into doing so by other radiation. It is this latter process, called the stimulated emission of radiation, on which the laser depends.


  • In 1960 an American physicist, T H Maiman, working for Hughes Electronics, built the first laser, using a cylindrical rod of artificial ruby whose ends had been cut and polished to be exactly flat and parallel. It produced brief, penetrating pulses of pure red light with 10 million times the intensity of sunlight.   The pulsed ruby laser is still amongst the most powerful types of laser. Researchers at Bell Telephone Laboratories produced the first gas lasers in the same year, 1960. Although not as powerful as the ruby laser, gas lasers can be left on like a torch, in contrast to the ruby laser which emits its light in very short pulses.


  • The acronym L.A.S.E.R. was coined to reflect the process, i.e.









4. Why the concern for safety?


  • Because exceptionally powerful lasers do exist (e.g. those used for defence uses and those used to cut and/or weld virtually any type of material), the question of safety was raised at an early stage.


  • The more powerful lasers, i.e. those capable of cutting materials, are obviously capable of substantial damage to human tissue. They also introduce the possibility of risk to health arising from the materials being cut (and thus vaporised) containing things such as asbestos, lead, mercury, carbon monoxide etc. Most lasers also make use of high voltages and pulsed lasers are especially dangerous because of the stored energy in their capacitor banks.



5. The aims of this talk?


  • To give those present a reasonable knowledge of the working and potential hazards of lasers - in particular the low powered, visible light, helium-neon and diode lasers used extensively in the construction industry.



6. What is radiation?


  • Radiation in physics is the emission of radiant energy as particles.   The ‚Äúradiation" from construction lasers = LIGHT. i.e. light is electromagnetic radiation.   Light is produced by electrons.   In the process described above, atoms absorb photons (i.e. particles of light) while in their relaxed state.   When the atoms are excited they give up their photons and light is produced. Stimulated emission occurs when an atom, which has already absorbed a photon, is forced to absorb a second photon and then to release them both in the same direction.


  • Construction lasers do not emit x-rays, microwaves, ultraviolet rays, gamma rays or cosmic rays.



7. What then are the dangers?


  • Emitting pure, visible beams of light, the low-powered helium-neon and diode   lasers have been proven to have no effect whatsoever on the skin.


  • There is, however, a potential danger to the eyes.   If the laser beam is powerful enough, is focussed enough, and there is sufficient exposure over a prolonged period of time, then damage to the retina could occur.   This is because the eye will focus light (e.g. a laser beam) on to the retina in much the same way as a magnifying glass can focus the sun's rays on to a piece of paper and eventually burn a hole in it.   It is the fact that laser light is a collimated beam (i.e. all the beams focus together and produce a very small spot) that makes light potentially more hazardous than white light.













The coloured, muscular diaphragm that surrounds and controls the size of the pupil, i.e. it controls the amount of light entering the eye.

The dark, circular aperture at centre of iris through which light enters.

The light-sensitive membrane forming the inner lining of the posterior wall of the eyeball.

Focuses the light on to the retina.



8. Establishing the standards


  • The US Air Force Aerospace carried out well-documented experiments and Medical Research Unit on Rhesus monkeys (animals, which have eye structures very similar to those of human beings).





dilated (enlarged) the monkeys pupils with drugs to simulate dark conditions

strapped the monkeys heads so they couldn't move them

taped their eyelids open so they couldn't blink

directed laser beams directly into their eyes




Until power was increased to 11mW (remember: 1 milliwatt = 1/1000th of a watt), no discernible lesion on the retina occurred

At 10mW no burn could be produced

When the exposure was ceased, the swelling subsequently disappeared

No permanent scar on the retina occurred until power of 50mW was applied




With a safety factor of 10, any laser with an output of less then 1mW is considered totally safe

Under extreme conditions, lasers with outputs of greater than 1mW can potentially cause eye damage




The conclusions assume a pupil diameter of 7mm - a condition that is virtually impossible to achieve, even in total darkness

7mm diameter = an area of 38.5mm2

3.5mm diameter = an area of 9.6mm2 (a safety factor of 5.4 times)

3mm diameter = an area of 7.1mm2 (a safety factor of 4.0 times)



On a building site in normal daylight working hours, a typical pupil diameter is only 2 to 3mm.   Since the area of a circle (i.e. such as a pupil) is proportional to the square of its diameter, the smaller actual pupil sizes produce an additional safety factor of more than 4


9. Lasers in practice


  • After nearly 40 years of use (and no doubt some abuse), there hasn't been one known or documented eye injury to any user or worker from a 2 to 5mW helium-neon laser or any laser-diode construction laser. This is a safety record not equalled in the construction industry by virtually any other item of equipment.


  • Exhaustive research by unions and others has not revealed anything adverse either.



10. The Australian standards


  • AS2211 -       1997 Laser Safety


  • AS2397 -       1993 Guide to the safe use of Lasers in the Construction Industry




11. Classification of Laser under the Standards


  • Class 1 Lasers


Output less than 0.1 mW

Intrinsically safe - maximum permissible exposure level cannot be exceeded under any conditions

No training or certification of operating personnel is required

No label required on laser providing laser class is detailed in other literature


  • Class 2 Lasers


Output between 0.1 and 1 mW

Visible beam, low powered lasers

Generally incapable of causing eye injury within the blink or aversion response period. (Blink response approx.. 1/10th second).   Standard allows 0.25 sec exposure

Originally mainly used as tunnel lasers but now the majority of construction lasers fit into this Class


  • Class 3 Lasers


SUB CLASSES: Class 3A - 1 mW to 5 mW, Class 3B - 5 mW to 500 mW (beam  irradiance or power density < 25W/m2), Class 3BR - 1 mW to 5 mW (beam irradiance <50W/m2)


Standard Construction lasers were once normally 2 to 3 mW and therefore Class 3A units but the majority are now Class 1 or Class 2 lasers.

Australian Standard states:   "Class 3A lasers to not represent an eye hazard from a diffuse reflection, nor a skin or fire hazard from unintentional exposure."

Class 3BR Lasers may be used in daylight conditions where the pupil diameter will not be greater than 5mm under the same safety controls as for Class 3A where used on conditions of lesser illuminance, the appropriate controls are those for Class 3B lasers.



  • Class 4 Lasers


Output in excess of 500 mW

No such lasers in general construction


12. Precautions to be taken with Class 2 & Class 3 Lasers


  • Care should be taken to ensure that people do not stare directly into a stationary laser beam. (This is the prime requirement of Class 2 lasers - the balance of precautions applies to Class 3A and 3BR lasers in the main).


  • It is especially important that operators of lasers are warned not to point these lasers at optical instruments such as dumpies and theodolites, especially if the laser has a stationary laser beam because the laser radiation can be focused to a point.


  • Laser equipment should be correctly located on the site and carefully mounted to ensure that the laser is protected from being bumped, knocked over or severely disturbed.   If a safety strap is supplied, use it.


  • The laser beam should be located well above or below eye level wherever practical.


  • Avoid directing laser beams at reflective surfaces.   (The reflected beam shares the same qualities as the direct beam).


  • Non-rotating beams should be terminated at the end of their useful beam paths.


  • When not in use, the laser beacon and accessories (especially AC/DC converters) should be stored in dry and secure locations.


  • Warning signs are not mandatory but recommended under the Australian Standards. Unfortunately they tend to attract, rather than to discourage, the curious.


  • No laser should be repaired, modified or tampered with by other than the manufacturer or his approved agent.


  • The Laser Safety Officer and Operator should both become familiar with the operation of the laser being used and should read and understand the manufacturer's manuals.


13.      Final Conclusions


  • Modern Class 1,2, 3A and 3BR lasers used in the construction industry for site preparation, building set-outs, formwork, concrete wet screeding; ceiling, computer flooring and partitioning installation; pipe-laying and earth-moving present positively no hazards of possible burns to any bodily tissue whatsoever, with the exception of that within the eye.


  • Laser Safety Officers should satisfy themselves that site conditions are such that the possibility of eye exposure to laser light is within permissible limits.


  • Rotary lasers provide an added safety factor -


Penta-prisms use up about 20% of the available power (2.4mW in/2mW out)

The permissible exposure to the eye is a quarter second -the rotating beam rests on one spot for much less than this

The rated output is that at the emergence from the laser (i.e. with the rotating head removed).


  • Common sense should be practised at all times.


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