Laser Safety Information
Personal Protective Equipment
A. Laser Protective Eyewear
The exclusive use of laser protective eyewear has, in the
past, often been stressed as the best method of eye safety
in the laser laboratory. Laser protective eyewear is only
one of many required laser safety control measures. In general,
it is better to control laser hazards through the use of engineering
controls (enclosures, beam blocks, etc.) and administrative
controls (posting, procedures, etc.) rather than to rely solely
on laser protective eyewear.
Laser protective eyewear is essential during the beam alignment
process. Most laser accidents occur during beam alignments
and these can be prevented by wearing the appropriate laser
protective eyewear. The laser protective eyewear selected
must allow proper viewing of the beam at or just below the
MPE. Laser users commonly suffer eye injury when they remove
their eyewear because they cannot properly view the beam.
NOTE: The intensity of a visible beam at the MPE is, by definition,
sufficient to trigger the human aversion response. This means
a diffuse reflection off a card is more than bright enough
to view in a lighted room. The visible light transmission
(VLT) of the laser protective eyewear must be sufficient (35%
or more) to eliminate the need to remove the eyewear while
working in the lighted laser facility. ORS recommends that
the lights be kept on in the laser facility. Working in a
darkened room will increase the potential hazard of eye injury
by increasing the pupil size while increasing the need to
remove the laser protective eyewear to be able to see.
All laser protective eyewear must be marked with the absorption
wavelength and the optical density (OD) at that wavelength.
It is recommended that laser protective eyewear be color-coded
to the laser of concern with colored tape. This can prevent
mishaps when several lasers of different wavelengths are being
used.
Selection of appropriate laser protective eyewear is very
important. Several different laser protective eyewear styles
are available depending on the needs of the user (see Appendix
H). The laser protective eyewear selected must have the appropriate
OD at the wavelength(s) of concern and must be comfortable
enough to wear as required. Contact the Radiation Safety Officer
(RSO) if you need additional information on laser protective
eyewear.
B. Skin Protection
UV laser systems or UV excitation sources can present severe
hazards to exposed skin surfaces. If the UV source cannot
be enclosed to prevent scattered radiation exposure, it may
be necessary to wear appropriate coverings to protect the
skin. These coverings may include gloves, UV face shield,
lab coat, etc.
Ancillary Hazards and Control Methods
A. Toxic Dye Hazards
The fluorescent dyes (used with dye lasers) can present substantial
hazards due to their toxicity. Some of these dyes are suspected
of being carcinogenic or mutagenic. The solvents used for
mixing the dyes may be flammable, toxic, or present other
health hazards. Material Safety Data Sheets (MSDS) on dyes
or solvents are available from your department or by contacting
the RSO.
Because the dyes normally come in a dry power form, they
are readily dispersible and should be handled and mixed with
great care. A lab coat, disposable gloves, safety glasses
or goggles, and a properly functioning chemical fume hood
must be used when handling or mixing the dyes. Good housekeeping
should be maintained before, during, and after the mixing.
Use double containment adequate to contain the entire volume
of the dye solution when they are being mixed, stored, and
used. Clean up any spills immediately using the appropriate
protective equipment. Contact the RSO if you need additional
information.
B. Hazards from Laser Generated Air Contaminants (LGAC)
The interaction of the laser beam with target materials may
produce toxic dusts, vapors or gases called LGAC. This is
particularly true during material processing (welding, cutting,
vapor deposition, etc.). Toxic products resulting from laser
processing must be properly controlled through the use of
adequate ventilation and filtration. The RSO should be consulted
whenever LGAC may result from the laser use.
C. Cryogen Hazards
Some lasers and laser systems may require the use of cryogenic
liquids (liquid nitrogen, oxygen, hydrogen, etc.). These liquids
present skin and eye hazards from their extremely low temperatures
and should not be handled without insulated gloves, goggles
and a face shield. The dewars used for transport and storage
of cryogens may present implosion hazards if they are made
of glass. Glass dewars should be carefully wrapped with strong
tape to contain glass fragments should they implode.
If the cryogenic liquid is allowed to warm to room temperature,
the resulting gas will expand to more than 600 times the volume
in the liquid state. Once it expands to become a gas, the
gas may present an additional hazard (toxic, asphixiant, etc.).
The specific hazards of the cryogen can be found in the MSDS.
Your department safety contact should be consulted whenever
cryogenic liquids are being used.
D. Compressed Gas Hazards
The use of compressed gases is common in the laser laboratory.
Some lasers use both pure gases and gas mixtures as the lasing
media. The high pressure of the gas translates into substantial
potential energy stored in the cylinder. If this pressure
is released in an uncontrolled manner (such as broken nozzle)
the cylinder can become an unguided missile. Compressed gas
cylinders must be properly restrained to prevent damage to
the nozzle or regulator.
The gases themselves may present a variety of hazards if
they leak from the cylinder. Depending on the gas, it may
be toxic, corrosive, flammable, etc. Again, refer to the MSDS
for detailed information on the gas in question. If the hazards
are sufficient, it may be necessary to provide a gas cabinet
under negative pressure to control the hazard in the case
of a leak. Inform your department safety contact if compressed
gases are to be used in the laser facility.
E. High Voltage Power Hazards
The high voltage power supplies associated with laser systems
have been responsible for serious injuries and electrocutions.
For this reason, it is important to know the hazards associated
with your laser and the laser's power supply. Capacitor systems
are of particular concern because they can remain hazardous
long after the main power is disconnected. Capacitor systems
should be safely discharged several times with the main power
off to reduce the hazard before beginning work.
Only qualified persons should perform high voltage laser
or power supply maintenance or repair. As a precaution, a
second person (knowledgeable in high voltage safety and CPR) should always be in attendance when high voltage work
is being performed.
F. Collateral Radiation Hazards
Laser excitation systems and power supplies may produce hazardous
collateral radiation of various types. These hazards are normally
controlled by the equipment housings, and are usually a problem
only if the protective housings are removed.
The laser excitation device may produce very intense UV/Visible/IR
radiation that can be hazardous. Collateral ultraviolet radiation
may injure both the eye and the skin if the exposure duration
is long enough. Blue light presents a special hazard because
of it's ease of absorption in the retina. This "Blue
Light Hazard" is thought to create photochemical injury
in the retina. Exposure to any very intense visible light
source can seriously degrade color vision and night vision
capabilities. Exposure to these intense light sources should
be carefully controlled or eliminated by leaving the housings
in place.
Laser power supplies capable of creating energies greater
than 15 kVp may be a source of x-rays if they contain high
voltage vacuum tubes. Electric discharge excitation sources
in lasers may also be a source of x-rays. Generally, these
x-rays are low energy and are shielded by the equipment housings.
G. Fire and Explosion Hazards
As mentioned before, Class 4 lasers can present fire hazards.
Lasers being operated in a CW mode with a beam power that
exceeds 0.5 Watt can ignite or cause off-gassing in combustible
materials left in the beam path. Beam stops, barriers, and
curtains used with Class 4 lasers must be made of non-combustible
materials. All Class 4 laser labs should have an ABC Type
extinguisher readily available as a fire precaution. Laser
users should receive fire prevention training. Contact the
EH&IS Fire Prevention Group at Ext. 7233 for information
on fire prevention training.
Explosion hazards in the laser lab include: the storage and
use of flammable solvents and gases (both compressed and cryogenic)
and the implosion potential from dewars and excitation flashlamps.
Proper storage and control of these sources should reduce
the potential hazard.
H. Noise Hazards
Some laser systems create significant levels of noise in
the laser laboratory. If the noise level seems unpleasant
or painful, contact EH&IS (Ext. 7233) to have a noise
survey done.
All of the above information is from Dewey Sprague, Laser
Safety Officer, at the University of California, Berkeley.
He is a highly respected authority in laser safety and we
are grateful for the information that he provides to laser
users around the country and worldwide.
Revised: 7/2001