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Laser Safety Training

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Laser Safety Training Prof Tony Kent University Of Nottingham 4th. October 2007. Laser Classification It is a legal requirement for suppliers to classify the lasers ... – PowerPoint PPT presentation

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Title: Laser Safety Training


1
Laser Safety Training Prof Tony Kent University
Of Nottingham 4th. October 2007.
2
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.
3
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
4
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!
5
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.
6
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)

7
Laser Classification
8
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.

9
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.

10
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

11
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.

12
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).

13
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)

14
Procedure for Selection of Eye Protection
15
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)

16
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

17
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18
  • 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.

19
Whos who in laser safety
University laser safety adviser
University safety officer
School/Dept. laser safety officer
Laser lab/project supervisor
Laser workers
20
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

21
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.

22
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.

23
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24
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.

25
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