Laser Safety Training

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Laser Safety Training Prof Tony Kent University
Of Nottingham 4th. October 2007.
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Management of health and safety is based on
principles of risk assessment Hazard the
potential of a process, material, device etc. to
do harm. The hazard is often quantified with
regard to the severity of the damage/harm that
could occur in a worst-case situation. Risk the
likelihood that the potential harm would be
realized in practice. The aim is to develop a
safe system of work that minimises risk. This
general approach to health and safety is no
different for lasers.
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Laser hazards Compare with looking directly at
the sun Solar radiation flux density at the
surface of the earth 1 kW/m2. If one were silly
enough to stare at the sun, the pupil would
contract to about 1 mm2. Therefore 1 mW of
sunlight would enter the eye. For flux density at
retina, use geometrical optics
o
r1
r2
i
i (r2/r1)o 200 µm
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Therefore at retina we have 25 kW/m2. Now
consider a weak laser, 1 mW laser pointer with
1 mm2 beam. Again 1 mW of light enters the
eye. However, unlike the sun, laser light is
highly spatially coherent (as if from a point
source) and so is focussed to the theoretical
minimum spot size d ff, where f is the focal
length ( about 2 cm) and f the beam angular
divergence, typically 1 mrad. This gives d 20
µm or 2.5 MW/m2 at the retina. 100 times stronger
than staring at the sun!
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Based on published guidance, the University has
adopted administrative procedures to ensure that
risks associated with laser work are minimised.
Details of these administrative procedures are
contained within the handout. However, it
should be remembered that lasers are being used
in lots of different ways across the campuses and
there is no one size fits all approach to laser
safety local risk assessment is essential. In
this talk I will concentrate on some of the
practical aspects of laser safety at the
University of Nottingham.
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Laser Classification

• It is a legal requirement for suppliers to
  classify the lasers they sell.
• Classes 1(1M) 2(2M) 3R/3A 3B 4 (in
  increasing order of ability to do harm)
• However, some older systems may not have
  appropriate labels.
• The class can be worked out using the yellow
  book and knowing the wavelength, power and pulse
  width (if pulsed) of the laser. Example
  (calculation on the board)

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Laser Classification
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Laser Classification

• Class 1
• The most limiting MPE values cannot be exceeded
  and no specific safety controls are required.
• For CW visible lasers, the maximum limit is 70
  microwatts.
• Class 1 operation cannot be claimed for a product
  containing an embedded laser of a higher class
  unless full-interlocked high-integrity enclosures
  using fail-safe interlocks are incorporated.
• Class 1M is a large diameter or widely divergent
  beam (302.5 4000 nm).
• Class 2
• Visible lasers only, for which the MPE cannot be
  exceeded in less than 0.25 seconds.
• For CW laser the limit is 1 mW.
• Class 2M is a large diameter or widely divergent
  beam.

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Laser Classification

• Class 3R
• 302.5 106 nm
• Lower risk than 3B, but direct viewing of beam
  potentially hazardous
• Visible lasers up to five times the Class 2
  limits and invisible lasers up to five times the
  Class 1 limits, for which specific H (Jm-2) or
  E(Wm-2) values are not exceeded.
• Class 3B
• Visible and invisible lasers not exceeding
  specified limits, which are 0.5W for CW lasers
  and 105 Jm-2 for pulsed lasers (less for
  ultraviolet wavelengths).
• Direct beam viewing not safe to the eye,
  specularly reflected beams may also be harmful to
  the eye, diffusely reflected beam usually safe to
  the eye, assumed to be safe to the skin.
• Class 4
• Those that exceed the limits of Class 3B!
• Viewing a direct beam or a reflected beam is
  always harmful to the eye and skin, diffusely
  reflected beams should be assumed harmful to the
  eye or skin unless proven otherwise, both
  scattered and reflected beams can present a fire
  hazard.

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Notes on Practical Laser Safety

• The general safety precautions fall under very
  simple headings.
• a) Use of a remote interlock connector
• b) Key control
• c) Beam stop or attenuator
• d) Warning signs
• e) Beam paths
• f) Specular reflections
• g) Eye protection

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Laser Eyewear

• Eyewear is the most common and certainly the most
  important aspect of personal laser protection,
  wherever there is some risk of laser exposure
  above the specified MPEs. Protective eyewear
  does not, however, preclude a full safety
  evaluation and consideration of all alternative
  means of affording protections - such as total
  enclosure of the beam, interlocks, beam dumps
  etc. Laser safety glasses are the last line of
  defence and not a convenient alternative to
  avoiding any engineering controls that it may be
  possible to implement.

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Procedure for Selection of Eye Protection

• Step 1
• Determine wavelength of laser (l)
• Determine maximum exposure duration (t)
  anticipated for the use of eye protection
• unintentional, accidental exposure to a visible
  beam where the maximum exposure may be of the
  order of 0.25 sec (aversion response).
• unintentional, accidental viewing of near IR
  laser beams for up to 10 sec.
• situations where occasional viewing of diffuse
  visible reflections for up to 600 sec is
  anticipated.
• 4 to 8 hour occupational viewing of a diffuse
  reflection (generally from an invisible beam).

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Procedure for Selection of Eye Protection

• Step 2
• Determine Maximum Permissible Exposure (MPE) for
  desired laser
• Determine MPE from l, maximum exposure duration
  (t), and viewing conditions determined in Step 1.
  MPE will be in units of J/cm2 for pulsed lasers
  and W/cm2 for CW lasers. Example (calculation
  on the board)

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Procedure for Selection of Eye Protection
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Procedure for Selection of Eye Protection

• Step 3
• Determine the desired optical density
• REMEMBER MPE was determined in Step 2!
• Calculate Optical Density for a CW laser
• Dl Optical Density for CW laser
• log10(H/MPE)
• Calculate Optical Density for a pulsed laser
• Dl Optical Density for pulsed laser
• log10(E/MPE)

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Procedure for Selection of Eye Protection

• Step 4
• Choose laser eye protection that meets the
  Optical Density requirements for the laser
• Compare the calculated requirements with
  manufacturer's specifications and find eyewear
  with an optical density value equal to or greater
  than the calculated value.
• Additional factors in choosing laser eyewear
• side-shield protection
• peripheral vision requirement
• need for prescription glasses
• comfort and fit
• degradation of absorbing media (photo bleaching)
• strength of materials
• anti-fog
• impact requirements

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• Limitations of Eye Protection
• General
• In general, eye protection will afford adequate
  protection against medium power, Class 3 lasers
  but will seldom provide sufficient protection
  against direct beam viewing of CW lasers
  exceeding 10 W in power or pulsed lasers
  exceeding 10 to 100 J in output energy.
  Obviously, for the higher power lasers, if a
  plastic frame or lens bursts into flames the
  wearer is going to move out of the beam path very
  rapidly. In these situations, the laser user
  should attempt to eliminate the need for eye
  protection when using such high power lasers by
  using engineering controls.
• Multiple Wavelengths
• One pair of laser eyewear may not provide
  adequate protection from all multiple or tunable
  wavelengths produced by the laser. The laser user
  must be very conscious of which type of eye
  protection is appropriate for each different
  wavelength which may be used in the operation of
  the laser. It is the responsibility of the laser
  equipment supervisor to assure that the
  appropriate eyewear (for each wavelength) is
  provided for all users of the laser.

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Whos who in laser safety
University laser safety adviser
University safety officer
School/Dept. laser safety officer
Laser lab/project supervisor
Laser workers
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Breakdown of Responsibilities

• University
• Safety Office
• To keep a register of all laser users and all
  lasers.
• To carry out periodic checks on designated laser
  areas in departments and the records kept..
• To provide DLSOs with adequate support in their
  roles.
• To provide yearly a training course for all new
  laser users
• DLSO
• To register new users
• To provide users with the CVCP Yellow Book
• To carry out yearly audits of designated laser
  areas
• To follow up on any problem areas identified in
  the audits
• To give advice on appropriate training for users
  where requested by either the user or a supervisor

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Breakdown of Responsibilities

• Supervisors
• To write a protocol for work to be carried out in
  any area where Class IIIR, Class IIIb and Class
  IV lasers are used.
• To provide adequate personal safety equipment for
  users
• To act promptly on the advice of the DLSO
  following an audit of the DLA
• (Undergraduates only) To have provide a copy of
  the Approved Scheme of Work for a project
• (Postgraduate/post doctoral only) To have ensured
  that the Project Supervisory Requirements Form
  has been updated and carried entries of risk
  assessments associated with the use of lasers.

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Breakdown of Responsibilities - Individuals

• To complete the medical eye survey form if
  required.
• To view the laser safety video
• To read and have a working knowledge of the CVCP
  yellow book and to know the location of the
  laboratory copy
• To understand access restrictions in designated
  laser areas and the operation of any laboratory
  door interlocks
• To know the location and capabilities of laser
  safety equipment
• To calculate representative MPE figures for the
  system(s) being used
• (Undergraduates only) To have read, signed, and
  approved a copy of an Approved Scheme of Work
  written by the supervisor for the project
• (Postgraduate/post doctoral only) To have ensured
  that the Project Supervisory Requirements Form
  has been updated and carried entries of risk
  assessments associated with the use of lasers.

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Requirements for all new research workers who
will be registered laser users

• If the research worker arrives after the start of
  the academic year they must obtain the Laser
  Safety Video from DLSO and, as above, sign a
  statement indicating if they did understand the
  video and the documentation given to them.
• If at any time a research worker feels that they
  have not understood the laser safety protocol and
  the general recommendations outlined, or that
  they are unsure about these recommendations as
  they pertain to the designated laser area in
  which they work, they should approach their
  supervisor who will discuss with the DLSO what
  further training is appropriate for the
  situation.

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