Introduction to Laser Safety

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Introduction toLaser Safety
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Examples of laser accidents
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Overview of the eye
macula or macula lutea (yellow spot on the
retina) allows color vision fovea central spot
of macula allowing for sharp central vision
(necessary for reading, TV, driving, and any
activity where visual detail is of primary
importance
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413 Picosecond pulses cause bleeding/latent
viewing distortion

• Description
• New frequency doubler didn't have AR coatings as
  requested. As person left room, beam hit eye
  corner and transmitted schlera and caused
  interocular bleeding. Resided at 2 wks and eye
  normal at 2 months. Person still complains at 8
  yrs of floaters and vision that looks "like
  looking through a dirty window".
• TypeFD NdYAG Divergence-
• Wavelength1064 nm Energy/PowerMW/cm2
• ClassIV Pulse Rate1 KHz
• Exposure Time60 ps 

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165 Reflected beam caused vision loss

• Description
• Professor from China removed eyewear to "see
  better" while doing an experiment with a crystal.
  Exposure produced retinal burn and permanent
  vision loss. He described seeing a white flash,
  central purple spot surrounded by yellow halo. No
  pain reported.

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223 Retinal burn from beam off rear laser mirror

• Description
• Student WITH EYEWEAR ON (and witness to verify)
  received exposure from the rear mirror of a
  "Continuium" YAG laser. The student was wearing
  Glendale Broadband (OD 4.0) eyewear ANSI
  standard requires OD6.0. Retinal burn resulted
  with permanent damage.
• TypeNdYAG Divergence-
• Wavelength532 nm Energy/Power0.18/0.40
• Class- Pulse Rate5 KHz
• Exposure Time7 ns

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356 Blurred vision from reflected exposure.

• Description
• Student received reflected beam from plastic tool
  box lid from Ti-Sapphire laser. No eye protection
  worn. Student reported blurred vision and seeing
  black spots. He was installing a laser transport
  tube (beam safety tube). The student had not
  received laser safety training. At 1 month
  student still had blurry vision.
• Type Ti-Sapphire Divergence-
• Wavelength800 nm Energy/Power15 mJ
• ClassIV Pulse Rate10 KHz
• Exposure Time120 fs 

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312 Off-axis beam causes macular burn in left eye

• Description
• Scientist bumped mirror mount in a complex
  optical array - causing a stray beam to go
  off-axis. When leaning over the table, he was
  struck in left eye by beam off lower array
  mirror. Exam confirmed macular lesion which he
  states disrupts vision. No eyewear worn and
  safety knowledge was limited.
• TypeTi-Sapphire Divergence-
• Wavelength800 nm Energy/Power6 mJ
• ClassIV Pulse Rate3.3K KHz
• Exposure Time50 ns

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307 Backscatter from mirror causes hemorrhage and
oveal blindspot

• Description
• 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.

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283 Photophobia in right eye after beam
misalignment

• Description
• Received "flash" into eye during alignment where
  he looked back along the beam path to view
  reflection off laser face plate. Result caused
  photophobia with burning sensation. No retinal
  burns detected. Patient used sunglasses for
  photophobia.
• TypeHeNe Divergence-
• Wavelength633 nm Energy/Power6 mW
• Class- Pulse Rate-
• Exposure Time0.25 sec

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Airway Fire

• Description
• During laser surgery on a patients vocal cords,
  the surgeon struck the endotracheal tube with a
  pulse from a CO2 laser. The tube, which carries
  oxygen to the patient and runs through his mouth
  to his lungs, was not made of laser-resistant
  material. Instead, it was made of polyvinyl
  chloride (combustible to both NdYAG and CO2
  lasers). It caught fire and filled the mans
  lungs with toxic smoke, causing burns. The
  patient did not survive the procedure.
• In general the anaesthesiologist has only six
  seconds to recognize that a tube has ignited and
  remove it before the fire peaks. Once ignited,
  the tubes are as hot as an oxygen lance used in
  welding. The flame can reach a length of 5 to 10
  inches. Laser beam interaction with secondary
  materials is a known source of laser incidents.
  This sort of unplanned interaction is a danger
  one needs to think of beforehand.

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Los Alamos Laser Accident

• Description
• A postdoctoral employee received an eye exposure
  to spectral radiation from an 800 nm Class 4
  laser beam. The extremely short pulse (100 fs)
  caused a 100-micron-diameter burn in the
  employee's retina. The accident occurred shortly
  after a mirror was removed from its mount and
  replaced with a corner cube during a realignment
  procedure. Although the beam had been blocked
  during several previous steps in the alignment,
  it was not blocked in this case. The employee was
  exposed to laser radiation from the corner cube
  mount when he leaned down to check the height of
  the mount. Neither of the two employees
  performing the alignment was wearing the
  appropriate laser eye protection. The system had
  two modes of operation 10 Hz and 1,000 Hz. In
  addition, the researcher forgot that the part of
  the 800 nm beam he could see represented only
  1-2 of the beam.

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You have to ask yourselfcan this happen in our
laboratories?
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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

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Majority of injuries involve the eye and to
lesser extend the skin
Summary of reported laser accidents in the United
States and their causes from 1964 to 1992
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Majority of injuries during alignment, or no use
or improper use of eyewear
Summary of reported laser accidents in the United
States and their causes from 1964 to 1992
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Sensitivity to damage eye transmission
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Effect of laser beam depends strongly on
wavelength
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Potential eye damage

• In general terms, in supra-threshold exposures
  the predominating mechanism is broadly related to
  the pulse duration of the exposure.
• Thus, in order of increasing pulse duration, the
  predominant effects in the following time domains
  are
• nanosecond and sub-nanosecond exposures, acoustic
  transients and non-linear effects
• from 1 ms to several seconds, thermal effects
• in excess of 10 s, photochemical effects.

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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
ampli-fication of roughly 100,000 therefore, a 1
mW/cm2 beam en-tering 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 perma-nent,
as with a retinal burn. Acoustic damage is 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 damage
depends strongly on whether it occurs by
intrabeam exposure or scattered laser light
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Skin hazards

• In general terms, the skin can tolerate a great
  deal more exposure to laser beam energy than can
  the eye.
• The biological effect of irradiation of skin by
  lasers operating in the visible and infra-red
  spectral regions may vary from a mild erythema to
  severe blisters.
• An ashen charring is prevalent in tissues of high
  surface absorption following exposure to very
  short-pulsed, high-peak power lasers.
• The pigmentation, ulceration, and scarring of the
  skin and damage of underlying organs may occur
  from extremely high irradiance.
• In the wavelength range 1500 nm to 2600 nm,
  biological threshold studies indicate that the
  risk of skin injury follows a similar pattern to
  that of the eye.

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Example of eye injury
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.
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Retinal Burn

• A range of injuries induced with a NdYAG laser
  on a monkey retina.
• The white spots in the centre are thermal burns,
  i.e. coagulation of retinal layers. With larger
  energies, holes in the retina are produced which
  result either in bleeding into the vitreous (the
  gel-like substance which fills the centre of the
  eye ball), or the bleeding is contained in the
  layers of the retina, which results in functional
  loss in the affected area.
• Photograph courtesy of J. Zuclich, TASC Litton,
  TX, USA.

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Eye Damage FocusingRemember Your Eyes Are
Designed to Focus
With safety rule
Cornea Damage BAD
Retina Damage WORSE
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Laser classification
Class 1 Lasers Lasers that are safe under
reasonably foreseeable conditions of operation,
including the use of optical instruments for
intrabeam viewing. Class 1M Lasers Lasers
emitting in the wavelength range from 302,5 nm to
4000 nm which are safe under reasonably
foreseeable conditions of operation, but may be
hazardous if the user employs optics within the
beam.
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Laser classification

• Class 2 Lasers
• Lasers that emit visible radiation in the
  wavelength range from 400 nm to 700 nm where eye
  protection is normally afforded by aversion
  responses, including the blink reflex. This
  reaction may be expected to provide adequate
  protection under reasonably foreseeable
  conditions of operation including the use of
  optical instruments for intrabeam viewing.
  Outside this wavelength range AEL AEL of a
  class 1 laser.
• Class 2M Lasers
• Like class 2 lasers, however, viewing of the
  output may be more hazardous if the user employs
  optics within the beam. Outside visible range AEL
  AEL of a class 1M laser.

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Laser classification

• Class 3R Lasers
• Lasers that emit in the wavelength range from
  302,5 nm to 106 nm where direct intrabeam viewing
  is potentially hazardous but the risk is lower
  than for Class 3B lasers.
• The accessible emission limit is within five
  times the AEL of Class 2 in the wavelength range
  from 400 nm to 700 nm and within five times the
  AEL of Class 1 for other wavelengths.
• Class 3B Lasers
• Lasers that are normally hazardous when direct
  intrabeam exposure occurs. Viewing diffuse
  reflections is normally safe.

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Laser classification

• Class 4 Lasers
• Lasers that are also capable of producing
  hazardous diffuse reflections.
• They may cause skin injuries and could also
  constitute a fire hazard.
• Their use requires extreme caution

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Retinal injury thresholds
Health Physics October 2000, Volume 79, Number 4
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 injuryexample

• A 4 reflection from a 2.5 mJ laser pulse in a 2
  mm beam, gives an exposure of
• (10-4 J)/(p x 0.12 cm2) 3.2 10-3 J/cm2.
• This exceeds the threshold value of the cornea of
  about 10-7 J/cm2 by a factor of 3.2 104.
• To be adequately protected against this exposure,
  protective eyewear must have an optical density
  (OD) of at least log10(3.2 104) 4.5

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Some common unsafe practices 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 non-beam hazards

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Some common unsafe practices or preventable
laser accidents

• Failure to follow (Laser) Safety Instructions
• 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

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Guidelines to help preventaccidents 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 jewellery 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.

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Guidelines to help preventaccidents during
alignment

• The lowest possible/practical power must be used
  during alignments.
• Have beam paths that differ from the eye level
  when standing or sitting. Do not use paths that
  tempts one to bend down and look into the beam.
• All laser users must receive an introduction to
  the laser area by an authorised laser user of
  that area

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Responsibilities

• The department is responsible for the safety of
  its employees and exercises its responsibility by
  providing guidelines and periodic control by
  designated safety personnel.
• We all have a personal responsibility to make
  sure that our working conditions and working
  habits are safe and in accordance with the
  guidelines.

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Acknowledgement / References

• This presentation is inspired by a similar
  presentation on Laser Safety by the Molecular
  Laser Physics Group of the Radboud University,
  Nijmegen NL.
• Laser incidents taken from laser accident
  database of Rockwell Laser Industries, Inc.
• (http//www.rli.com/resources/accident.asp)
• Certain descriptions and numbers are taken from
  the international standard IEC 60825-1 Edition
  1.2.
• The model of the eye is provided by the National
  Eye Institute, USA.

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• Aqueous flare the presence of floating
  particles in the fluid of the anterior chamber of
  the eye
• Cataract opacity or reduction in clarity of the
  lens of the eye
• Erythema redness of the skin caused by
  dilatation and congestion of the capillaries,
  often a sign of inflammation or infection
• Fovea centralis a small depression near the
  center of the retina, constituting the area of
  most acute vision
• Inflammation A localized protective reaction of
  tissue to irritation, injury, or infection,
  characterized by pain, redness, swelling, and
  sometimes loss of function
• Lesion a localized pathological change in a
  bodily organ or tissue
• Macula letua (yellow spot) A minute yellowish
  area containing the forea centralis located near
  the center of the retina of the eye at which
  visual perception is most acute.
• Macular lesion Loss of central vision
• Photokeratitis Inflammation of the cornea
  produced by ultraviolet radiation
• Photophpobia an abnormal sensitivity to or
  intolerance of light, especially by the eyes, as
  may be caused by eye inflammation, lack of
  pigmentation in the iris, or various diseases
• Schlera outer hard white coat (cover) of the
  eyeball