Laser Safety Training
Dr Katy Voisey
Faculty of Engineering
University Of Nottingham
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.
• 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 at
http://www.nottingham.ac.uk/safety/laserindex.htm
• 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.
Laser Classification
• The hazard presented by a particular laser is
reflected in its class. It is a legal requirement for
suppliers to classify the lasers they sell.
• Classes 1(1M) – 2(2M) – 3R (formerly 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.
• http://www.aurpo.org/images/documents/guidea
nce/aurpogn7.pdf
Laser Classification
Safety of Laser Products – Part 14:
A user’s guide, PD IEC/TR 60825‐14
Laser Classification
• Class 1: Safe – very low power or enclosed
system
• Class 2: Low power (<= 1mW) visible lasers
– protection afforded by natural aversion
(blink response)
• Class 3R: Medium power (<= 5mW) visible
lasers – as class 2, but intrabeam viewing via
optical instruments may damage sight.
• Class 3B: Hazard from direct beam viewing
and specular reflections.
• Class 4: Hazard from direct beam viewing and
viewing of specular and diffuse reflections.
Hazard to skin and fire hazard.
Who’s who in laser safety:
University
safety officer
University
laser safety
adviser
School/Dept.
laser safety
officer
Laser
lab/project
supervisor
Laser workers
Breakdown of Responsibilities
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University
Safety Office
To keep a register of all lasers.
To carry out periodic checks on designated laser areas in departments and the
records kept..
To provide DLSO’s 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/AURPO Guidelines
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
Breakdown of Responsibilities
• Supervisors
• To write a protocol for work to be carried out in any area where Class
3R, Class 3b and Class 4 lasers are used.
• To provide adequate personal safety equipment for users
• To act promptly on the advice of the DLSO following an audit
• (Undergraduates only) To 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.
Breakdown of Responsibilities - Users
• 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/AURPO Guidelines 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 be aware of the 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.
Laser User Registration
Academic supervisor to inform user to
Register as a laser user
User completes registration
form, supervisor signs and copies
User completer medical
eye survey form if using
3B/4 lasers and sends to OH
SLS* authorises form and maintains
A record of users for the School
OH sends letter
confirming “safe to work with
lasers” to SLS & user
User must be provided
With suitable training
(- university intro course
- School course
- Laser system training)
Training recorded
(PRSF, course registers)
Laser User may commence laser work
With suitable supervision.
(If Student, PSRF reviewed until user is competent)
*SLS - School Laser Supervisor
#OH - Occupational Health
• laser film
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
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.
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).
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.
Procedure for Selection of Eye
Protection
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)
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
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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
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.
Summary of Laser Administration Process
Laser Registrations
New laser to be put into use
(or change of status for existing laser)
Principle investigator
(laser "owner") to register laser
on university form (all 3R & above)
Registration form sent to
SLS* and Safety Office
Safety Office maintain inventory
of lasers and check laser
installation if necessary
SLS to authorise &
Ensure laser survey
& risk assessment
completed
Laser may be put into use
annual laser survey
list of users
risk assessment
written protocol
-
Annual update of laser inventory confirmed with School
Annual inspection by Safety Office (since 2003/4)
Change of laser or taking laser out of use:
School to notify Safety Office via registration form
* SLS School Laser Supervisor
Laser hazards in context
Compare with looking directly at the sun:
Solar radiation flux density at the surface of the
earth ~ 1 kW/m2.
If you stare at the sun (don’t do this), 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
o=7x108m
r1= 1.5x1011m
r2= 2.5x10-2m
r1
r2
i
i = (r2/r1)o ≈ 200 μm
Laser hazards in context
Compare with looking directly at the sun:
Solar radiation flux density at the surface of the
earth ~ 1 kW/m2.
If you stare at the sun (don’t do this), 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
i = (r2/r1)o ≈ 200 μm
r2
i
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 ~ fφ, where f is the focal length ( about 2 cm)
and φ 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!