LASER SAFETY TRAINING

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LASER SAFETY TRAINING

• For more information refer to the department
  Laser Safety Procedure
• http//www.chem.ubc.ca/safety/safety_manual/laser.
  shtm
• l

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Definition Properties of Laser Light

• Acronym For

LIGHT AMPLIFICATION BY STIMULATED EMISSION OF
RADIATION
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Properties Of Laser Light

• Laser light is monochromatic, directional and
  coherent
• These three properties make it more of a hazard
  than ordinary light. 
• Laser light can deposit a great deal of energy
  within a very small area

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Properties Of Laser Light

• Monochromatic
• The light emitted from a laser is monochromatic,
  it is of one wavelength (color). 
• In contrast, ordinary white light is a
  combination of many different wavelengths
  (colors).
•  
•  

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Properties Of Laser Light

• Directional
• Lasers emit light that is highly directional. 
• It is emitted as a narrow beam in a specific
  direction.
• Ordinary light (sun, light bulb, a candle), is
  emitted in many directions away from the source

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Properties Of Laser Light

• Coherent
• The light from a laser is coherent
• The wavelengths of the laser light are in phase
  in space and time

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The Electromagnetic Spectrum

• The electromagnetic spectrum consists of the
  complete range of frequencies from radio waves to
  gamma rays 
• All electromagnetic radiation consists of
  photons - individual quantum packets of energy 
• Light consists of photons, each with discrete
  quantum of energy proportional to their
  wavelength
•  
• Light with a shorter wavelength is consisted of
  higher energy photons

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The Electromagnetic Spectrum
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The Electromagnetic Spectrum

• The portion of the electromagnetic spectrum where
  lasers operate
• Infrared near infrared 750 nm - 3000 nm far
  infrared 3000 nm - 1 mm
• Visible 400 nm - 750 nm
• Ultraviolet 100 nm - 400 nm.

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How Does Laser Work?

• The Lasing Medium
• A substance that when excited by energy emits
  light in all directions. Can be a gas, liquid, or
  semi-conducting material.
•  
• The Excitation Mechanism or Energy Pump
• The excitation mechanism of a laser is the source
  of energy used to excite the lasing medium. 
• Excitation mechanisms typically used are
  electricity, flash tubes, lamps, or the energy
  from another laser.
•  

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How Does Laser Work?

• The Optical Cavity
• The optical cavity is used to reflect light from
  the lasing medium back into itself.  It typically
  consists of two mirrors, one at each end of the
  lasing medium.  As the light is bounced between
  the two mirrors, it increases in strength,
  resulting in amplification of the energy in the
  form of light. 
• The output coupler of a laser is usually a
  partially transparent mirror on one end of the
  lasing medium that allows some of the light to
  leave the optical cavity to be used for the
  production of the laser beam.

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How it Works?

• The lasing medium emits photons in specific
  spectral lines when excited by an energy source. 
• The wavelength is determined by the different
  energy states of the material.  Most atoms in a
  medium are in the ground state. Small percentage
  will exist at higher energies. These higher
  energy states are unstable and the electrons will
  release the excess energy as photons and will
  return to the ground state.
• The energy is supplied to the laser medium by the
  energy pumping system is stored in the form of
  electrons trapped in the metastable energy
  levels. Pumping must produce more atoms in the
  metastable state than the ground state before
  laser action can take place.

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How it Works?

• When this is achieved, the spontaneous decay of a
  few electrons from the metastable energy level to
  a lower energy level, starts a chain
  reaction. The photons emitted spontaneously will
  hit other atoms and stimulate their electrons to
  make the transition from the metastable energy
  level to lower energy levels - emitting photons
  of precisely the same wavelength, phase, and
  direction.
• This action occurs in the optical cavity.  When
  the photons that decay in the direction of the
  mirrors reach the end of the laser material, they
  are reflected back into the material where the
  chain reaction continues and the number of
  photons increase.  When the photons arrive at the
  partially-reflecting mirror, only a portion will
  be reflected back into the cavity and the rest
  will emerge as a laser beam.

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Laser Components
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Types of Lasers by kind of Lasing Media

• Lasers are often described by the kind of lasing
  medium they use - solid state, gas, excimer, dye,
  or semiconductor.
•  
• Solid state lasers have lasing material
  distributed in a solid matrix, e.g., the ruby or
  neodymium-YAG (yttrium aluminum garnet) lasers.
  The neodymium-YAG laser emits infrared light at
  1.064 micrometers.
•  
• Gas lasers (helium and helium-neon, HeNe, are
  the most common gas lasers) have a primary output
  of a visible red light. CO2 lasers emit energy in
  the far-infrared, 10.6 micrometers, and are used
  for cutting hard materials.
•  
• Excimer lasers (the name is derived from the
  terms excited and dimers) use reactive gases such
  as chlorine and fluorine mixed with inert gases
  such as argon, krypton, or xenon. When
  electrically stimulated, a pseudomolecule or
  dimer is produced and when lased, produces light
  in the ultraviolet range.
•  

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Types of Lasers by kind of Lasing Media

• Dye lasers use complex organic dyes like
  rhodamine 6G in liquid solution or suspension as
  lasing media. They are tunable over a broad range
  of wavelengths.
•  
• Semiconductor lasers sometimes called diode
  lasers, are not solid-state lasers. These
  electronic devices are generally very small and
  use low power. They may be built into larger
  arrays, e.g., the writing source in some laser
  printers or compact disk players.

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Types of Lasers by Duration of LASER Emission

• Lasers are also characterized by the duration of
  laser emission, continuous wave or pulsed laser. 
• Q-Switched laser is a pulsed laser which contains
  a shutter-like device that does not allow
  emission of laser light until opened.   Energy is
  built-up in a Q-Switched laser and released by
  opening the device to produce a single, intense
  laser pulse.
• Continuous Wave (CW) lasers operate with a stable
  average beam power. In most higher power systems,
  one is able to adjust the power. In low power gas
  lasers, such as HeNe, the power level is fixed by
  design and performance usually degrades with long
  term use.
•  

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Types of Lasers by Duration of LASER Emission

• Single Pulsed (normal mode) lasers generally have
  pulse durations of a few hundred microseconds to
  a few milliseconds. This mode of operation is
  sometimes referred to as long pulse or normal
  mode.
•  
• Single Pulsed Q-Switched lasers are the result
  of an intracavity delay (Q-switch cell) which
  allows the laser media to store a maximum of
  potential energy. Then, under optimum gain
  conditions, emission occurs in single pulses
  typically of 10(-8) second time domain. These
  pulses will have high peak powers often in the
  range from 10(6) to 10(9) Watts peak.
•  
• Repetitively Pulsed or scanning lasers generally
  involve the operation of pulsed laser performance
  operating at a fixed (or variable) pulse rates
  which may range from a few pulses per second to
  as high as 20,000 pulses per second. The
  direction of a CW laser can be scanned rapidly
  using optical scanning systems to produce the
  equivalent of a repetitively pulsed output at a
  given location.
•  
• .

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Types of Lasers by Duration of LASER Emission

• Mode Locked lasers operate as a result of the
  resonant modes of the optical cavity which can
  effect the characteristics of the output beam.
  When the phases of different frequency modes are
  synchronized, i.e., "locked together," the
  different modes will interfere with one another
• The result is a laser output which is observed
  as regularly spaced pulsations. Lasers operating
  in this mode-locked fashion, usually produce
  spaced pulses, each having a duration of 10(-15)
  (femto) to 10(-12) (pico) sec. A mode-locked
  laser can deliver extremely high peak powers
  often in the range from 10(12) Watts peak

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Classifications of Lasers

• Lasers are classified with respect to their
  hazards based on power, wavelength, and pulse
  duration. 
•  
• A classification label will be found on the laser
  housing.  This label provides important
  information on the hazard of the laser. 
• Classes of Lasers adopted from ANSI Z-136.1-2000
•  

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Classifications of Lasers- Class 1

• Not capable of emitting in excess of the Class 1
  Accessible Emission Limit (AEL) (Note AEL's vary
  by laser wavelength and pulse duration)
• Most lasers in this class are lasers which are in
  an enclosure which prohibits or limits access to
  the laser radiation.
• Not capable of producing damage to the eye
  (unless disassembled).

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Classifications of Lasers- Class 2

• Continues wave and repetitive-pulse lasers in the
  visible region of the spectrum (0.4 to 0.7 mm)
  which can emit accessible radiant energy
  exceeding the Class 1 AEL for the maximum
  duration inherent in the laser, but not exceeding
  the Class 1 AEL for any pulse duration lt 0.25s
  (the time estimated to blink or look away) and
  not exceeding an average radiant power of 1 mW.
• The output of the laser is not intended to be
  viewed.
• An example of a Class 2a laser is a supermarket
  point-of-sale scanner.
•  

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Classifications of Lasers- Class 3a

• Have output between 1 and 5 times the Class 1 AEL
  for wavelengths shorter than 0.4 mm or longer
  than 0.7 mm, or less than 5 times the Class 2 AEL
  for wavelengths between 0.4 mm and 0.7 mm.
• Is only a hazard if collected and focused in the
  eye. 
•  
• Most laser pointers are 3a lasers.

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Classifications of Lasers- Class 3b

• Ultraviolet and infrared lasers and laser systems
  that can emit accessible radiant power in excess
  of the Class 3a AEL during any emission duration
  within the maximum duration inherent in design of
  the laser or system, but that - cannot emit an
  average radiant power in excess of 0.5 W for
  greater than or equal to 0.25 s or cannot produce
  a radiant energy greater than 0.125 J within an
  exposure time gt 0.25 s.
• Visible or near-infrared lasers or systems that
  emit in excess of the 3a AEL but that cannot emit
  an average radiant power in excess of 0.5 W for
  greater than or equal to 0.25 s and cannot
  produce a radiant energy greater than 0.03 Ca J
  per pulse. (Ca is a correction factor that
  increases the maximum permissible exposure values
  in the near infrared spectral band based upon
  reduced absorption propertied of melanin pigment
  granules found in skin and in the retinal pigment
  epithelium).
• Is a hazard if the direct or reflected beam is
  viewed.
•  

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Classifications of Lasers- Class 4

• Limits exceed Class 3b limits.
• Direct and reflected exposure can cause both eye
  and skin injury.
• Class 4 lasers are also a fire hazard.

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Biological Beam Hazard

• The damage is principally due to temperature
  effects, the critical organs are the eye and the
  skin.
• The components of the eye most susceptible to
  laser damage are the cornea, retina, and lens

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Summary of Biological Effects of Light
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Eye Injury

• Light causes biological damage through
  temperature effects due to absorbed energy and
  through photochemical reactions.  The chief mode
  of damage depends on the wavelength of the light
  and on the tissue being exposed
• A laser beam of sufficient power can produce
  retinal intensities at magnitudes that are
  greater than conventional light sources, and even
  larger than those produced when directly viewing
  the sun. Permanent blindness can be the result
• Laser irradiation of the eye may cause damage to
  the cornea, lens, or retina, depending on the
  wavelength of the light and the energy absorption
  characteristics of the ocular tissues.

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Light Induced Biological Damage

• The potential location of injury in the eye is
  directly related to the wavelength of the laser
  radiation entering the eye
• Near Ultraviolet Wavelengths (UVA) 315 - 400 nm
• Most of the radiation is absorbed in the lens of
  the eye.
• The effects are delayed and do not occur for many
  years (e.g. cataracts).
• Far Ultraviolet (UVB) 280 - 315 nm, (UVC) 100 -
  280 nm
• Most of the radiation is absorbed in the cornea.
• Keratocojunctivitis (snow blindness/welder's
  flash) will result if sufficiently high doses are
  absorbed.

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Light Induced Biological Damage

• Visible (400 -760 nm) and Near Infrared (760 -
  1400 nm)
• Most of the radiation is transmitted to the
  retina. ()
• Overexposure may cause flash blindness or retinal
  burns and lesions.
• Far Infrared (1400 nm - 1 mm)
• Most of the radiation is transmitted to the
  cornea.
• Overexposure to these wavelengths will cause
  corneal burns.
• () Laser retinal injury can be severe because of
  the focal magnification (optical gain) of the eye
  which is approximately 100,000 times. This means
  that an irradiance of 1 mW/cm2 entering the eye
  will be effectively increased to 100 W/cm2 when
  it reaches the retina.

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Light Induced Biological Damage

• For pulsed lasers, the pulse duration also
  effects the potential for eye injury. Pulses less
  than 1 ms in duration focused on the retina can
  cause an acoustical transient, resulting in
  substantial damage and bleeding in addition to
  the expected thermal injury. Many pulsed lasers
  now have pulse duration less than 1 pico-second.
• The ANSI Z136.1 standard defines the Maximum
  Permissible Exposure (MPE) that the eye can
  receive without expecting an eye injury (under
  specific exposure conditions). If the MPE is
  exceeded, the probability that an eye injury can
  result increases dramatically.
•  

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Light Induced Biological Damage

• Thermal burns (lesions) in the eye are caused
  when the heat loading of the retina can not be
  regulated. Secondary bleeding may occur as a
  result of burns which damage blood vessels. This
  bleeding can obscure vision well beyond the area
  of the lesion.
• Although the retina can repair minor damage,
  major injury to the macular region of the retina
  may result in temporary or permanent loss of
  vision or blindness.
• Photochemical injury to the cornea by ultraviolet
  exposure may result in photokeratoconjunctivitis
  (often called welders flash or snow blindness).
  This painful condition may last for several days
  is long term.
• UV exposure can cause cataract formation in the
  lens.

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Light Induced Biological Damage

• The duration of exposure also plays a role in eye
  injury
• If the laser is a visible wavelength (400 to 700
  nm), the beam power is less than 1.0 mW and the
  exposure time is less than 0.25 second (the human
  aversion response time), no injury to the retina
  would be expected to result from an intrabeam
  exposure. Class 1, 2a and 2 lasers fall into this
  category and do not normally present a retinal
  hazard.
• Intrabeam or specular reflection viewing of Class
  3a, 3b, or 4 lasers and diffuse reflections from
  Class 4 lasers may cause an injury before the
  aversion response can protect the eye.

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Skin Hazard

• The most likely skin surfaces to be exposed to
  the beam are the hands, head, or arms.
• Laser effects on tissue depend on - the power
  density of the incident beam, absorption of
  tissues at the incident wavelength, the time beam
  is held on tissue, and the effects on blood
  circulation and heat conduction in the effected
  area.
•  

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Skin Hazard

• Immediate Effects
• The immediate effect of exposure to laser light
  above the biological damage threshold is normally
  burning of the tissue.  Injury to the skin can
  result either from thermal injury following
  temperature elevation in skin tissues or from a
  photochemical effect (e.g., "sunburn") from
  excessive levels of ultraviolet radiation.
•  
• Delayed Effects
• Only optical radiation in the ultraviolet region
  of the spectrum has been shown to cause
  long-term, delayed effects. These effects are
  accelerated skin aging and skin cancer.  At
  present, laser safety standards for exposure of
  the skin attempt to take these adverse effects
  into account.

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Non-Beam Hazards

•  
• Many of these non-beam related hazards can be
  far more dangerous than the beam itself.
• Electrical Hazard
• The use of large power supplies and repetitively
  pulsed lasers, present a great potential for
  electric shock.  Shocks usually happen when the
  equipment is not properly grounded or has a large
  capacitor bank that was not discharged.
  According to the ANSI Z136.1, the following
  potential problems have frequently been
  identified during laser facility audits
• Uncovered electrical terminals.
• Improperly insulated electrical terminals.
• Hidden "power up" warning lights.
• Lack of training in current cardiopulmonary
  resuscitation practices, or
• lack of refresher training.
• "Buddy system" not being practiced during
  maintenance and service.
• Non-earth-grounded or improperly grounded laser
  equipment.
• Non-adherence to the lock-out procedures
• Excessive wires and cables on floor that create
  fall or slip hazards

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Non-Beam Hazards

• Explosion Hazard
• With the use of high-pressure arc lamps,
  filament lamps, and capacitor banks in laser
  equipment, there is a potential for explosion
  hazards.  These items should be enclosed in
  housings that can withstand the high pressure
  resulting from exploding components.
• Compressed Gasses
• Many lasers are using hazardous gases such as
  chlorine, fluorine, hydrogen chloride, and
  hydrogen fluoride.  Referring to ANSI Z136.1,
  typical safety problems arise in the use of
  compressed gasses
• Inability to protect open cylinders (regulator
  disconnected) from atmosphere and contaminants.
• No remote shutoff valve or provisions for purging
  gas before disconnect or reconnect.
• Hazardous gas cylinders not maintained in
  exhausted enclosures.
• Gases of different hazard (toxics, corrosives,
  flammable, oxidizers, and cryogenics) not stored
  separately.

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Non-Beam Hazards

• Laser Dyes and Solvents
• Dyes are used in some lasers as a lasing
  medium. These dyes are complex organic compounds
  that are mixed in solution with certain
  solvents.  Some dyes are highly toxic or
  carcinogenic, and great care must be taken when
  handling them, preparing solutions, and operating
  lasers that contain these dyes.  A Material
  Safety Data Sheet must be made available to
  anyone working with these dyes.
• Noise
• Some lasers, such as the Excimer, create an
  intensity of noise that may require controls to
  be instituted.  The Health and Safety Office
  should be consulted if there are concerns about
  noise.

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Non-Beam Hazards

• Fire Hazards
• There is a great potential for a fire hazard with
  the use of Class IV lasers.  Fires can occur when
  a Class IV laser is enclosed in a material that
  is exposed to irradiances greater than 10 W/cm2
  or beam powers exceeding 0.5 W.  Fire resistant
  materials should be used in this situation.
• Barriers such as black photographic cloth are
  used in a wide variety of applications for the
  purpose of containing the beam.  These materials
  should not be used as the primary barrier for a
  high-powered Class IV system. Beams of sufficient
  energy will burn this material quickly, causing
  smoke, fire, and breach of the barrier. The use
  of beam blocks and beam stops is highly
  encouraged in this situation.

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Non-Beam Hazards

• X-Ray Radiation Hazards
• X-rays may be generated by electronic components
  of the laser system (e.g., high-voltage vacuum
  tubes and from laser-metal induced plasmas).
• Some lasers contain RF excited components, such
  as plasma tubes and Q-switches. 
• Other Hazards
• Mechanical Hazards Associated with Robotics
• Limited Work Space Dangers
• Ergonomics Considerations

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Protective Measures

• Protective measures are devised to reduce the
  possibility of exposure of the eye and skin to
  hazardous levels of laser radiation. And reduce
  other hazards associated with laser devices
  during operation and maintenance.
• Engineering controls will be the "first line of
  defense" when it comes to protection from laser
  radiation and its ancillary hazards.
• Enclosure of the beam path is the preferred
  method of control since the enclosure will
  isolate or minimize the hazard.
• If engineering controls are impractical or
  inadequate, administrative and procedural
  controls and personal protective equipment will
  be used

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Summary of Engineering Controls
Legend R- Normally required O- Optional
X-No requirements NC- No further controls
required LSO- Laser Safety Officer
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Engineering Controls
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Summary of Administrative Controls
Legend R- Normally required O- Optional
X-No requirements NC- No further controls
required LSO- Laser Safety Officer
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Laser Safety Glasses

•     
• When all other protective measures fail, wearing
  proper laser safety glasses for the wavelength
  and power of the laser will protect your eyes. 
• Wear these glasses whenever there is a
  possibility of exposure to laser light above the
  MPE
• Different protective lenses should be used for
  different wavelengths
• The first thing to take into account when
  choosing safety glasses is WAVELENGTH
•  

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Laser Safety Glasses

• The Optical Density must also be taken into
  account even if the proper protection for a
  certain wavelength was chosen, lenses do not
  filter out all of the light that incident upon
  them, and all lenses are not rated the same. This
  is where (OD) comes into play. The OD is defined
  by the ANSI Z136.1 as the logarithm to the base
  ten of the reciprocal of the transmittance
• Dl - log10 tl (where tl is the transmittance)
• Both the wavelength and the OD must be labeled on
  either the temple for glasses, or on the frame,
  for goggles.

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Laser Safety Glasses

• In certain applications, as in the use of
  powerful Class IV lasers, certain protective
  lenses are not meant as a permanent protective
  shield. For example, in the use of Class IV CO2
  lasers _at_ 10,600 nm, the protective lens only
  provides sufficient protection to allow immediate
  movement away from the beam. If the operator
  remains in the path of the beam, the beam will
  burn through the lens very quickly.

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Laser Safety Glasses

• Other considerations when Selecting Eye
  Protection
• High Visual Transmittance
• Resistance to Fogging
• Good Peripheral Vision
• Side Shield and Vent Ports
• Optical Correction
• Resistance to UV Degradation
• Comfort

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Laser Safety Glasses

• All protective eyewear must be inspected before
  each use to ensure that it will provide adequate
  protection.
• Prior to using laser safety glasses
• Check that the eyewear will provide the proper
  protection for the wavelength of concern
• The lenses must be inspected for any deep
  scratches or grooves. If any are found, the
  eyewear is not to be used
• The frame should also be inspected at this time.
• Check for missing or loose temple screws and
  ensure that the glasses comfortably fit your
  face.

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Responsibilities

• The laser lab Principal Investigator has the
  Laser Safety Officer responsibilities for their
  lab
• The laser worker is one who operates or works in
  proximity to Class 3b or Class 4 lasers. He/she
  has the following responsibilities
• To participate Laser Safety training
• To be familiar with all operational procedures
  and specific safety hazards of the Class 3b or
  Class 4 laser/laser systems that he/she will
  operate
• To operate Class 3b and Class 4 laser/laser
  systems safely and in a manner consistent with
  safe laser practices, requirements and written
  SOPs
• To operate Class 3b and Class 4 laser/laser
  systems only under the conditions authorized by
  the laser principal investigator
• To report all unsafe conditions, known or
  suspected accidents to the principal
  investigator
• To report to the laser principal investigator any
  medical conditions that could cause him/her to be
  at increased risk for chronic exposure