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A Division of JATCO (Australia) Pty. Ltd
LASER SAFETY WHITE PAPER : UNDERGROUND MINE APPLICATIONS
The use of laser technology in surveying is widespread. This article focusses on the
use of lasers in underground mining applications, and the special considerations for
safe use.
There are regulations for the use of lasers in the building and construction industry,
which are translated into the specific regulations for the coal mining industry, and
often on a State by State basis. Laser Safety relates to the safe use and specification of
laser products apart from the stipulation that products used underground need to also
be Intrinsically Safe or otherwise Ex-approved or Certified. Some laser products used
underground are IECEx Certified, and therefore the Laser Safety Classifications
assigned by the manufacturers are based on international standards, being IEC
60825.1:2011, upon which the Australian Standards are based. Australian Standards
have recently (2011) been updated to match the IEC standard.
Mine sites are required to have a trained Laser Safety Officer who oversees the laser
use on site. Operators of lasers are also required to have training as Operators.
Applied Resolution Technologies has established a substantial Laser Safety Training
package with a special emphasis on underground use. The Training is aimed to
provide the appropriate legislated training and provide an expert reference for
underground miners with regards to Laser Safety.
Infrared lasers, generally Class 1 used in surveying applications, are not such an issue
because they present no perceivable eye hazard. The following discussion relates to
visible lasers, with a special focus on the restrictions and requirements for use
underground. In underground applications where ambient light levels are generally
low, the pupil of the human eye can dilate as large as 7mm in diameter, which is a key
measurement used in Laser Classification. With low ambient light levels,
underground use is an extreme example where Laser Classification and Safety is very
important.
Without going into the acronyms and calculations too deeply, the bottom line in Laser
Safety Classification is that the amount of light that is permitted into the human eye is
set by particular Accessible Emission Limits (AEL) and Maximum Permitted
Exposures (MPE). Laser Safety Standards permit the maximum amount of laser
power within a 0.25 second period (blink response reflex time) to be below 25 Watts
per square metre. For a beam that is less than the 7mm diameter aperture used for
dilated pupil, the maximum power is 1mW. This is Classified as a Class 2 laser for a
visible continuous beam laser.
Lot 521 Sullivans Road, Yamba NSW 2464, Australia
ABN No. 11 052 440 829
Telephone: (02) 6645 8868 Fax: (02) 6645 8875 Mobile: 0407 542 440
Email: [email protected]
www.appliedresolution.com.au
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For more than 1mW of laser power, the beam needs to be expanded in diameter so
that the maximum power allowed within a 7mm diameter of the beam is still 1mW, or
25 W/m2. For a laser to be classified as Class 2M, the maximum classification
permitted under some state regulation for underground mining, the maximum beam
power is 5mW, but the power density still needs to be below 25 W/m2. That is, the
beam needs to be larger at the laser source.
To achieve tighter collimation over distance, laws of divergence tell us that the initial
laser beam needs to start out a larger diameter. As long as the power density within a
7mm diameter does not exceed 25W/m2 , measured 100 from the laser (as per the
Standards) it is then possible to increase the laser power for higher visibility or longer
range, but only up to 5mW.
For example, we chose a 20mm diameter beam in our BLX-635S and BLX-515S
lasers to provide a smaller spot at greater distance (divergence laws), and with 5mW
total power over this aperture the laser power density is only 16 W/m2, well within the
Class 2M classification. A laser with 3mW total power within a 10mm beam
diameter however has approximately 38 W/m2, and would be classified as a Class 3R
laser, not Class 2M. It would not be allowed in an underground mine under State
regulations.
These laser classification arguments apply to visible lasers, however there are
significant reasons why a blue laser should not be used underground. Blue/UV
semiconductor lasers (405nm, 450nm) are now available with high power and even
though they fit the Classification guidelines for visible lasers (400nm to 700nm), the
photon energy of blue lasers may be absorbed by the retina and cause photochemical
change. The “BLUE LASER HAZARD” is well documented in the laser literature,
and as a matter of choice one should avoid blue or UV laser use in situations where
the pupil is dilated (fully open).
For high visibility in underground mine use the best option for is to use green laser
systems where the visibility is approximately 5x that of a red laser.
As you can see from the above discussion, laser safety is a complex field. Although
the onus is on a manufacturer or supplier of a laser to provide the correct classification
for a product, there is also a responsibility for users and sites, especially underground
mines, to have trained operators and the mandatory Laser Safety Officer, so that they
are able to confirm that products are fit for use in their environment, and that
appropriate safety measures are in place.
Lot 521 Sullivans Road, Yamba NSW 2464, Australia
ABN No. 11 052 440 829
Telephone: (02) 6645 8868 Fax: (02) 6645 8875 Mobile: 0407 542 440
Email: [email protected]
www.appliedresolution.com.au
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