Laser Safety Seminar

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Laser Safety Seminar

• Marc Vrakking
• FOM Instituut for Atomic and Molecular Physics
  (AMOLF)
• LCVU, 10/12/2002

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165 Frequency doubled NdYAG in a research
lab. A visiting professor from China lost part
of the sight in his left eye after he removed his
safety goggles during a test with a frequency
doubled NdYAG laser. The professor was in he
research lab of a university. He was working on
an experiment with a crystal he had grown. He had
removed his goggles so he could see better and
the laser reflected into his eye, burning the
retina.
http//www.rli.com/accident/case_studies/
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255 Beam blinds scientist doing alignment of a
NdYAG laser. During optics alignment involving
a 30 mJ pulsed NdYAG laser (10 Hz) on a target
using a prism, the beam exceeded the prism's
critical angle and struck the scientist in the
eye resulting in a permanent retinal burn.
Unfortunately, no protective eyewear was worn at
the time. An ophthalmologist was consulted and
confirmed retinal burns. Blurry vision resulted
especially when reading.
http//www.rli.com/accident/case_studies/
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307 Backscatter from mirror causes hemorrhage
and foveal blindspot. A 26 year old male
Student aligning optics in a university chemistry
research lab using a "chirped pulse"
Titanium-Sapphire laser operating at 815 nm with
1.2 mJ pulse energy at 1 KHz. Each pulse was
about 200 picoseconds. The laser beam
backscattered off REAR SIDE of mirror (about 1
of total) caused a foveal retinal lesion with
hemorrhage and blind spot in central vision. A
retinal eye exam was done and confirmed the laser
damage. The available laser protective eyewear
was not worn.
http//www.rli.com/accident/case_studies/
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280 Graduate student receives macular lesion
from picosecond laser. A picosecond NdYAG
pulsed laser operating at 1064 nm was on a laser
optics table. The beam was directed from one
table to another across an isle. The beam went
onto the second table, where it was directed onto
a liquid sample holder. Here, apparently, the
beam was bigger than the liquid sample holder, so
the edges of the beam went pass the sample bottle
and then off that table into the room area where
a Strip Chart Recorder (SCR) was located. A
graduate student working on the experiment looked
at the SCR and received about 10 of the beam
into the eye. The student reportedly a "heard a
popping sound" which was followed by a white spot
in the vision center. The professor took the
student to an eye doctor for a retinal exam which
confirmed the burn exposure. The student did not
experience shock. The beam caused a retinal burn.
The student now complains that his "eyes get
tired" while reading.
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274 Technician receives retinal burn with a
single Ti-Sapphire laser pulse. A laser lab
technician was working without laser protective
eyewear. He was exposed to a single 7 ns pulse at
a pulse energy of 10-50 µJ. In the setup, the
beam was directed onto a metal "test slide" from
the power meter manufacturer. This was used to
test whether the beam would harm the power meter.
The slide was accidentally tilted so-as-to
reflect the beam into technician's eye (assume
about 4 reflection). At time of exposure the
person perceived a bright flash that persisted
(with eyes closed) as if he had looked at the
sun. There was no pain nor did the person go into
shock. There was eyewear was available but not
for the 806 nm wavelength in use.
http//www.rli.com/accident/case_studies/
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Ask yourself
Could any of these accidents happen in my lab?
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Dangers associated with the use of lasers

• Beam hazards
• - eye damage
• - skin damage
• Non-beam hazards
• - electrical hazards
• - toxic/carcinogenic laser dyes
• - hazardous gases (e.g. excimer lasers)
• - fire

In some of our labs at LCVU, where the emphasis
is on TiSapphire technology we have to be
especially concerned with the beam hazards
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The majority of injuries involve the eye and, to
a lesser extent, the skin
Summary of reported laser accidents in the United
States and their causes from 1964 to 1992
http//www.adm.uwaterloo.ca/infohs/lasermanual/doc
uments/section11.html
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The majority of injuries occur during alignment
procedures, or because the protective eyewear was
either inappropriate or not used
Summary of reported laser accidents in the United
States and their causes from 1964 to 1992
http//www.adm.uwaterloo.ca/infohs/lasermanual/doc
uments/section11.html
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Laser eye damage
a short introduction
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Basic layout of the human eye
www.yorku.ca
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Eye transmission
http//www-training.llnl.gov/wbt/hc/LaserRefresh/E
yeTransmission.html
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The effects of the laser depends strongly on the
wavelength
http//www.adtdl.army.mil/cgi-bin/atdl.dll/fm/8-50
/INTRO.htm
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Potential eye damage
The biological damage caused by lasers is
produced through thermal, acoustical and
photochemical processes. Thermal effects are
caused by a rise in temperature following
absorption of laser energy. The severity of the
damage is dependent upon several factors,
including exposure duration, wavelength of the
beam, energy of the beam, and the area and type
of tissue exposed to the beam. Normal focusing
by the eye results in an irradiance amplification
of roughly 100,000 therefore, a 1 mW/cm2 beam
entering the eye will result in a 100 W/cm2
exposure at the retina. The most likely effect of
intercepting a laser beam with the eye is a
thermal burn which destroys the retinal tissue.
Since retinal tissue does not regenerate, the
damage is permanent.
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Potential eye damage
Acoustical effects result when laser pulses with
a duration less than 10 microseconds induce a
shock wave in the retinal tissue which causes a
rupture of the tissue. This damage is permanent,
as with a retinal burn. Acoustic damage is
actually more destructive than a thermal burn.
Acoustic damage usually affects a greater area of
the retina, and the threshold energy for this
effect is substantially lower. Beam exposure may
also cause Photochemical effects when photons
interact with tissue cells. A change in cell
chemistry may result in damage or change to
tissue. Photochemical effects depend strongly on
wavelength. N.B. the severity of the eye damage
depends strongly on whether it occurs by
intrabeam exposure or scattered laser light
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Skin Hazards

• Skin can suffer thermal burns and photochemical
  changes from laser exposure. These effects are
  almost entirely independent of the coherent
  nature of the laser light, but are aggravated by
  the high power density of lasers.
• In the literature two types of skin damage are
  emphasized
• prolonged exposure to UV laser light leads to
  erythema (sunburn)
• high intensity exposure to laser light burns the
  skin
• In the literature there is very little mention of
  damage below the skin due to high intensity
  lasers.

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Example of eye damage
Experience has demonstrated that most laser
injuries go unreported for 2448 hours by the
injured person. This is a critical time for
treatment of the injury.
http//www.adtdl.army.mil/cgi-bin/atdl.dll/fm/8-50
/INTRO.htm
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Exposure Limits Laser Classification
Class 1 Lasers Class 1 lasers do not emit harmful
levels of radiation . Class 2 Lasers (lt 1mW,
commonly found in alignment applications) Capable
of creating eye damage through chronic exposure.
In general, the human eye will blink within 0.25
second when exposed to Class 2 laser light,
providing adequate protection. It is possible to
stare into a Class 2 laser long enough to cause
damage to the eye. Class 2a Lasers (special
purpose lt 1mW, e.g. barcode readers) Class 3a
Lasers (1-5 mW) Not hazardous when viewed
momentarily with the naked eye, but they pose
severe eye hazards when viewed through optical
instruments (e.g., microscopes and binoculars).
Class 3b Lasers (5-500 mW or less than 10 J/cm2
for a ¼-s pulsed system) Injury upon direct
viewing of the beam and specular reflections.
Specific control measures must be
implemented. Class 4 Lasers (gt 500 mW or greater
than 10 J/cm2 for a ¼-s pulsed system) They pose
eye hazards, skin hazards, and fire hazards.
Viewing of the beam and of specular reflections
or exposure to diffuse reflections can cause eye
and skin injuries. All control measures to be
outlined must be implemented.
At LCVU we use almost exclusively Class 3 and
Class 4 lasers!
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Exposure Limits Retinal Injury Thresholds - I
At 10-12 seconds the threshold for a retinal
injury is appr. 10-7 J/cm2 (i.e. 105 W/cm2).
Because of the x 105 enhancement in the eye this
value is elevated to 10-2 J/cm2 (i.e. 1010 W/cm2)
on the retina. These exposure levels are further
enhanced by self-focussing.
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Exposure Limits Retinal Injury Thresholds - II
Numerical example A 4 reflection from a 2.5 mJ
laser in a 2 mm beam, gives an exposure of
(10-4 J)/(0.78 x (0.2)2 cm2) 3.2 10-3 J /cm2
, exceeding the threshold value on the cornea
of appr. 10-7 J/cm2 by a factor 3.2 104.
To be adequately protected against this exposure,
protection with an optical density (OD) of
log(3.2 104) 4.5 is required
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Prevention
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Some common unsafe practices that are causes of
preventable laser accidents
Not wearing protective eyewear during alignment
procedures Not wearing protective eyewear in
the laser control area Misaligned optics and
upwardly directed beams Equipment malfunction
Improper methods of handling high voltage
Available eye protection not used Intentional
exposure of unprotected personnel Lack of
protection from nonbeam hazards Failure to
follow Activity Hazard Document Bypassing of
interlocks, door and laser housing Insertion of
reflective materials into beam paths Lack of
pre-planning Turning on power supply
accidentally Operating unfamiliar equipment
Wearing the wrong eyewear
http//ehs.lbl.gov/ehsdiv/pub3000/CH16.html
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Guidelines to help prevent accidents during
alignment
No unauthorized personnel will be in the room
or area. Laser protective eyewear will be
worn. The individual who moves or places an
optical component on an optical table is
responsible for identifying and terminating each
and every stray beam coming from that
component. To reduce accidental reflections,
watches and reflective jewelry should be taken
off before any alignment activities begin.
Beam blocks must be used and must be secured.
When the beam is directed out of the horizontal
plane, it must be clearly marked. A solid stray
beam shield must be securely mounted above the
laser use area to prevent accidental exposure
to the laser beam. All laser users must receive
an orientation to the laser use area by an
authorized laseruser of that area. The lowest
possible/practical power must be used during
alignments. When possible, a course alignment
should be performed with a HeNe alignment
laser. Have beam paths at a safe height, below
eye level when standing or sitting. Not at a
level that tempts one to bend down and look at
the beam. If necessary, place a stepplatform
around optical table.
http//ehs.lbl.gov/ehsdiv/pub3000/CH16.html
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Control measures for Class 3 or 4 laser systems,
an example - I
http//ehs.lbl.gov/ehsdiv/pub3000/CH16.html
All commercial lasers require a protective
housing and interlock systems that prevent
emission of laser radiation when the housing is
opened. Removable master key switch. All lasers
are controlled by an area interlock system and
remote shut-off device. When the terminals are
open-circuited, the laser must not emit any
radiation in excess of the Maximum Exposure
Limit. It is recommended that the plane of the
laser beam be above or below the level of a
seated or standing person. Each Class 4 laser or
laser system must have a shutter that prevents
the emission of laser light in excess of the MPE
when the beam is not required. Class 3b and
Class 4 lasers may only be operated in laser
control areas. All personnel who require routine
entry into a Class 3B laser controlled area shall
undergo an appropriate training program.
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Control measures for Class 3 or 4 laser systems,
an example - II
http//ehs.lbl.gov/ehsdiv/pub3000/CH16.html The
area must be posted with appropriate warning
signs that indicate the nature of the hazard.
Only personnel who have been authorized may
operate the laser. All laser beams must be
terminated within the control area. Beam stops
provide protection from misaligned beams, and
should be placed in all appropriate and practical
locations. Appropriate eye protection must be
provided for all personnel within the laser
control area. The eye protection must have an
appropriate optical density and/or reflective
properties based on the wavelengths of the beams
encountered, the beam intensity, and the expected
exposure conditions. The need for laser eye
protection must be balanced by the need for
adequate visible light transmission. Access to
the area by spectators or visitors must be
limited and controlled by the laser user.
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Control measures for Class 3 or 4 laser systems,
an example - III
http//ehs.lbl.gov/ehsdiv/pub3000/CH16.html Light
levels in excess of the MPE must not pass the
boundaries of the control area. Class 4 laser
control areas must be equipped with interlocks or
alternate controls to preclude the entry of
unprotected personnel while Class 4 laser
radiation is present in the control area. There
must be provisions for rapid escape from a laser
control area under all normal and emergency
conditions. Wherever possible, lasers should be
monitored and fired from remote locations. A
visible or audible signal must be provided at the
entrance to the control area to indicate when the
laser is energized and operating.
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Special Requirements for Invisible Lasers
Since IR and UV lasers produce no visible light,
this can contribute to their hazard potential At
LCVU near-IR laser radiation generated in
TiSapphire lasers is present in several laser
rooms Therefore anybody entering the area of
those experiments should wear goggles providing
protection around 800 nm (available near the
entrance). These goggles can only be taken off
in the room when its explicitly stated by the
users inside that all IR beams are completely
blocked at the output of the laser.