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Introduction to Laser Safety

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Accelerated skin ageing. Photokeratitis. Ultra-violet C (180 nm to 280 nm) 24 ... safety of its employees and exercises its responsibility by providing guidelines ... – PowerPoint PPT presentation

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Title: Introduction to Laser Safety


1
Introduction to Laser Safety
2
Examples of laser accidents
3
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
4
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 

5
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.

6
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

7
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 

8
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

9
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.

10
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

11
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.

12
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.

13
You have to ask yourself can this happen in our
laboratories?
14
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

15
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
16
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
17
Sensitivity to damage eye transmission
18
Effect of laser beam depends strongly on
wavelength
19
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.

20
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.
21
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
22
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.

23
(No Transcript)
24
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.
25
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.

26
Eye Damage Focusing Remember Your Eyes Are
Designed to Focus
With safety rule
Cornea Damage BAD
Retina Damage WORSE
27
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.
28
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.

29
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.

30
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

31
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.
32
Exposure limits, Retinal injury example
  • 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

33
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

34
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

35
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 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.

36
Guidelines to help prevent accidents 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

37
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.

38
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.

39
  • 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
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