Laser safety Introduction

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Laser safety Introduction

• B. Fischer

T-ray group meeting 08/06/06
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Motivation

• It might appear unnecessary
• Our lab is safer than most other T-ray lab in
  the world

source http//www.adrenotex.de/augenklappe.htm
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In older times
Why do pirates wear patches?
intense light damages your eyes!
sources http//en.wikipedia.org/
http//www.stuckiag.ch/shop/de-ch/dept_380.html
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Eye damage 400-1400 nm
Visible and near-infrared light enters the eye
and is focused tightly on the retina (10-25 mm
diam).
even in VIS, only about 5 will be absorbed in
visual pigments
retinal burn (irreparable) damage
cw and long-pulse lasers mainly thermal, 400-600
nm also photochemical
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Eye damage 315-390 nm
Light penetrates to the lens and can cause damage
here (photochemical cataract)
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Eye damage 180-315nm and gt1400nm
light stopped by the cornea
photokeratitis, corneal burns (similar to
sunburns)
(1.5 mm 2.6 mm light penetrates in aqueous
humour, large volume, rather eye-safe)
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Laser safety other hazards

• Skin exposure
• Particularly high power and/or UV lasers
• Fire hazard
• Beams hitting flammable materials
• Electrical shocks
• Gas discharge lasers can operate with high
  voltage (kV) and high currents (50-100 A)
• Chemical hazards
• Toxic laser materials
• Dyes and solvents
• Chemical lasers

there is a general understanding that accidents
of this kind greatly outnumber eye strikes
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Laser safety legislation

• Legal Responsibilities for employer employee
• Occupational Health Safety at Work Act
• Work Equipment Regulations
• Management Regulations risk assessments

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Australian Standards
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European Health Safety Law

• Health Safety at Work Act
• The act places duties on both employers and
  employees
• It is criminal law and can be enforced against
  criminals and organisations
• The act can be summed up as
• Employers duty To safeguard so far as
  reasonably practicable the health, safety and
  welfare of employees and others affected by the
  work.
• Employees duty To take reasonable care for the
  safety of themselves and others to cooperate
  not to be reckless

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Typical Work Equipment Regulations

• All equipment must be suitable
• Maintained in an efficient state
• Maintenance recorded
• Restricted to trained users
• Users must have information and training
• Access prevented to dangerous parts
• Adequate controls and lock-offs
• Suitable environment

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European standards on laser safety

• deals with lasers and laser products, i.e.
  product or assembly of components which contain
  lasers or laser systems
• E.g. compact disc players
• includes also light emitting diodes (LEDs)
  (modern LEDs are high-power, highly directional
  light sources)

• indicates safe working level for laser radiation
• classification of lasers laser products
  according to degree of hazard
• labeling ? warnings
• minimize accessible radiation, control measures
• protection against non-radiation hazards
  associated with lasers

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Reasoning behind classification

• Classification of laser determined by
•  Accessible Emission Limit (AEL)
• Maximum level of laser radiation accessible over
  its full range of capability during operation at
  any time after its manufacture 
• To classify a laser, you need to know
• Laser wavelength
• Exposure duration
• Viewing conditions
• Each laser class has a set of safety control
  measures that manufacturers and users must obey
•  Manufacturers should supply this classification
  (attention slight differences between USA and
  Europe -gt Australia?)

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Laser classification
Class 1 Safe under reasonably foreseeable
operation Class 1M Generally safe some
precautions may be required Class 2
Visible light at low power, blink limits
risk Class 2M Visible light at low power,
generally safe some
precautions may be required Class 3R Low risk
for direct viewing of beam Class 3B Viewing beam
hazardous, diffuse reflections safe Class 4
Hazardous under all conditions, eyes and
skin
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Class 1 (safe)

• Safe under reasonably foreseeable conditions of
  operation, including the use of optical
  instruments for intra-beam viewing
• rather complex calculation, but rule of thumb for
  cw lasersVIS (400-700) 0.39 mWNIR/IR
  (700-1400) slowly increasing, e.g. 1.6 mW for 1
  mmMIR (1.4 4 ?m) 10 mW (eye-safe
  communication)FIR (gt 4 ?m) 1000 W/m2
• measurement area normally iris with diameter 7
  mm
• A product may contain high power laser with
  higher classification, if effective engineering
  controls restrict routine exposure to Class 1 AEL
• CD, laser printers
• possibly machining, etc.
• in lab cleverly set up spectrometer (?)

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Class 1M

• New class, mainly for EN60825-2 regulations to
  deal with fibres (communications) LEDs
• Wavelength range ? 302.5 nm to 4 ?m
• Generally these lasers are as safe as Class 1
• Except for diverging or large area beams when
  collecting optics used
• ? These large beams may be focused
  to a spot of sufficient
• intensity to cause damage
  to the retina

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Class 2 (low power)

• Max output 1 mW
• Visible only 400 nm to 700 nm
• Blink response of eye affords protection (0.25 s)
• E.g
• Supermarket scanner
• many HeNe laser, some laser diodes
• legal laser pointers
• note recent research questions reliability of
  blink reflexconsider also fatigue, alcohol,
  drugs, ...
• Class 2M divergent or broad-aperture sources,
  which meet Class 2 standard without additional
  optics
• OK if collecting optics not used

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Class 3R (low to medium power)

• Direct intrabeam viewing is hazardous, but risk
  is lower than for 3B
• wavelength gt 302 nm
• maximum AEL 400-700 nm 5 times AEL of class 2,
  i.e. 5 mW
• maximum AEL at other l 5 times AEL of class
  1
• E.g
• Surveying equipment
• many laser pointers
• Some HeNe and laser diodes in teaching research
  labs
• there is no class 3A anymore

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Class 3B (medium power)

• Max output - 0.5W (500 mW)
• Includes all visible and non-visible lasers
• Direct intrabeam viewing is always hazardous
• Viewing diffuse reflections is normally safe
  provided
• Eye is not closer than 13 cm from diffusing
  surface
• Exposure duration is less than 10 seconds
• e.g.
• many laser diodes
• small solid-state lasers
• small ion lasers

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Class 4 (high power)

• gt 500 mW
• capable of producing hazardous diffuse
  reflections
• capable of producing also skin burns and fire
  hazards
• e.g.
• most solid-state lasers
• laser diode bars, some single emitters
• most ion lasers

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(Repetitively) Pulsed lasers

• exposure from any single pulse shall not exceed
  AEL for single pulse AEL depends on pulse
  duration, wavelength, ...
• average power of a pulse train of duration T
  shall not exceed the AEL for a single pulse of
  duration T
• for wavelength larger than 400 nm (thermal
  limits) average pulse energy shall not
  exceed single pulse AEL times correction
  factor AE train AELsingle N0.25 N number
  of pulses
• (by the way, there are more details to it)

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Consequences

• appointment of laser protection officer
  (invisible class 3R, 3B, 4)
• labelling
• training (class 1M, 2M, 3R, 3B, 4)
• protective enclosures where applicable, access
  restrictions
• interlocks (class 3B and 4)

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Labelling

• Labels for laser user laser servicer
• Correct labels should be provided by manufacturer
• If size or design of laser makes labeling
  impractical (e.g. laser diode), put it on the
  mount or base.(only in rarest circumstances
  labels should be included only with user
  information or placed on package)
• Laser starburst warning label
• on all laser products of Class 2 and above
• Access panels, Safety interlocked panels
• Should be labeled if access to laser radiation
  in excess of the AEL for Class 1/1M is possible
  on their removal or over-riding

source http//www.lasermet.com/labels/labels-upda
ted.html
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Labelling II

• every laser needs a label with warning level
  increasing with class
• e.g. class 2
• e.g. class 3R
• lasers of class 3R, 3B, 4 need labelling of
  aperture
• if radiation is outside the 400-700 nm range,
  laser radiation needs to be replaced by
  invisible laser radiation or visible and
  invisible laser radiation

source http//www.lasermet.com/labels/labels-upda
ted.html
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MaiTai -gt Class 4 laser
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Laser safety University policy

• Appointed Laser Safety Officer (LSO)
• All lasers (3R, 3B, 4) must be registered(?)
• All lasers and users conform to Australian
  Regulations
• Risk assessment safe method of work completed
  at workplace
• All laser users must attend risk assessment
  safe method of work briefing
• The supervisor (Bernd or Tamath) overseeing the
  laser project must ensure safe working practices
  as followed

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Practical laser safety

• There is a hierarchy of controls to ensure the
  safe use of lasers
• Risk Assessment and Safe Method of Work
• (1) Engineering controls
• (2) Administrative controls
• (3) Personal protective equipment (PPE)

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Engineering controls

• To Restrict exposure to laser radiation use 
• Housings ? Put the laser in a box if
  applicable
• Enclosures ? Use tubing on (long) laser
  runs
• Beam stops ? Block beams as soon as is
  possible
• Interlocks ? Prevent unauthorised
  access to danger
• Warning lights ? Informs others of the
  possible danger

Advantage improves stability and reduces
contamination Disavantage Not applicable in
laminar flow conditions

• remote sensing ? align beams without danger

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Engineering controls II
Controls should not be over restrictive and
hamper ease of working
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Administrative controls

• But Engineering controls may not provide
  adequate protection in cases such as 
• Phases of research when laser system is being
  commissioned
• Servicing of laser equipment
• Manufacture or research into laser design
• Laser alignment
• Special projects waveguides, near-field, dynamis
• In these situations
• Use Administrative
  controls to minimise risk

so essentially in many, but not all situations we
are working in
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T-ray labs around the world
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Its also about communication
Clear instructions? Clearly understood?!
Actually, your colleagues in the lab are often
more at risk, if you do something dodgy, than you
are, because they do not know that you are going
to do it.
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Examples for administrative controls

• Warning Signs Notices Prominently displayed
  clear and unambiguous
• Labels at entrances to lab or workshop
  containing Class 3B or 4 laser
• Laser Controlled Area (Class 3B or 4 laser)
• Restricted to authorized persons
• By physical means walls doors, Locks or number
  pads
• Key Control  
• Class 3B 4 laser keys removed when not in use
• Kept secure in key cabinet to which authorized
  users only have access
• Training
• Only trained persons allowed to use 1M, 2M, 3R
  and the more 3B and 4 lasers
• Maintenance Service Manuals 
• Must be available and easily accessible to laser
  users

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Personal protective equipment (PPE)

• Used only when
• Risk of injury or harm can not be suitably
  minimised by engineering controls etc

• Laser safety goggles
• required for Class 3R outside of 400-700 nm
  window, 3B and 4
• saves us in teaching labs, if everything else is
  ok, i.e. direct beam viewing is not possible due
  to engineering controls
• Fire resistant clothing, gloves, overalls
• against hazards associated with lasers (noise,
  chemical etc)
• Protective clothing when exposure to radiation
  exceeding maximum permissible exposure for skin
  (MPE), i.e. possibly strong class 4 lasers
• use during
• alignment or open beam experiments
• maintenance and servicing

Employers are obliged to provide employees with
PPE!
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Goggles

• Purpose to reduce level of incident laser
  radiation upon cornea to below MPE maximum
  permissible exposure, essentially make it a
  class 1 laser!
• Filter Sufficient optical density (OD) to
  attenuate incident radiation to MPE rule of
  thumb 0.4 mW some mWs, but check your
  wavelength and conditions(OD of 5 means that a
  filter transmits less than a part in 105 at that
  wavelength)
• Legal requirement to comply with
• Personal Protective Equipment Product Directive
  (89/686/EEC) July 1995
• European Standards
• EN2071998 Filters equipment used for personal
  eye protection against laser radiation 
• EN208 1999 Personal eye-protectors used for
  adjustment work on lasers and laser systems

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Markings on goggles
In order to meet legal requirements, the goggles
need to be marked with

• Wavelength or wavelength range in nm against
  which protection is afforded
• Scale No or lowest scale No if protection against
  a spectral range is afforded
• The manufacturers identification mark
• Test mark of the inspection body (CE or possibly
  DIN for rather old goggles)

Marking with OD alone is NOT sufficient ! The
scale number confirms that the filter withstands
at least 10 s and that also the frame does not
disintegrate
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Frames of goggles
high safety (TOPS)
possibly weak points at side
ok
balance between optimal safety and acceptance by
the user (what happens with prescription
glasses?)
sources Lasermet, Laservison
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Practical laser safety again
If you do not find at least eight safety flaws in
here contact me (discreetly)