Core of Knowledge in Safe Use of Lasers

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Core of Knowledge inSafe Use of Lasers
IPLsin healthcare
Mr John Saunderson, Consultant Medical Physicist
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Why laser core of knowledge?
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Core of Knowledge syllabus

• Understand the characteristics of optical
  radiation emitted from different types of
  equipment.
• Familiar with the intended purpose of the optical
  radiation equipment.
• Aware of the meaning of the warning labels
  associated with optical radiation equipment.
• The effects of exposure and health hazards,
  including eye, skin and tissue, which can arise
  from the use of laser, IPL or other optical
  radiation equipment.
• Equipment related hazards, which can arise from
  the use of laser, IPL or other optical radiation
  devices, including equipment malfunctions.
• Management of equipment and the role of
  personnel, including Controlled Areas and the
  role of the Laser Protection Adviser and
  Supervisor.
• The principles and requirements of equipment
  quality assurance processes and procedures.
• Hazards related to individuals through use of
  optical radiation equipment, including electrical
  hazards, fire risks and smoke plume effects.
• Hazards to patients associated with optical
  radiation treatment procedures and methods of
  minimising risks.
• Hazard control procedures, including the use of
  personal protection.
• Hazards from reflections or absorption of the
  optical radiation beam with respect to
  instruments or surfaces or other equipment.
• General principles of how to deal with a
  suspected accidental exposure to optical
  radiation.
• Aware of the basic principles of the maximum
  permissible exposure levels and the precautions
  required to ensure that exposure of unprotected
  skin and eyes of those present is less than the
  maximum permissible levels.
• Additional precautions that may be necessary when
  undertaking non-routine activities with the
  equipment.
• The safety procedures and policies governing
  optical radiation equipment use, including the
  local rules, Controlled Area, emergency action
  and accident reporting procedures.
• Understand the role of the Laser Protection
  Advisor and Laser Protection Supervisor.
• Be aware of the relevant legislation and
  standards that pertain to lasers and IPLs.
• Principles of risk assessment.
• Be familiar with the basic principles of the
  administration of safety.

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www.hullrad.org.uk
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Nature of Laser Radiation
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• Light
• Amplification by the
• Stimulated
• Emission of
• Radiation

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Electromagnetic Spectrum
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740-620 nm - red 620-585 nm - orange 585-575 nm -
yellow 575-500 nm - green 500-445 nm -
blue 445-425 nm - indigo 425-390 nm - violet
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Light Sources Lasers

• Spontaneous emission
• filament lamp
• fluorescent lamp
• neon lights
• most LEDs
• fire
• fluorescence
• IPL (intense pulsed light source)
• Stimulated emission
• laser

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Spontaneous emission
Atom
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Energy (e.g. electrical current through filament,
or electrical discharge through a fluorescent
tube, or UV light on a fluorescent material)
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Excited atom
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Spontaneous emission
Atom
Photon emitted
Any direction.
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Spontaneous emission
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Stimulated emission
Atom
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Energy (e.g. electrical discharge, flash lamp,
electrical current)
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Excited atom
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Stimulated emission
Incoming photon (correct wavelength)
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Stimulated emission
Two photons emitted
IF correct wavelength then ? STIMULATED
EMISSION Same wavelength and same direction
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Incoming photon (wrong wavelength)
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Scattered photon
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LASER
Tube filled with laser medium (e.g. helium-neon
gas for HeNe laser)
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LASER
Energy (e.g. electrical discharge, flash lamp,
electrical current)
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LASERPopulation Inversion or pumping
Energy (e.g. electrical discharge, flash lamp,
electrical current)
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LASER
Spontaneous emission takes place
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LASER
Some photons will cause stimulated emission
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LASER
Mirrors at either end reflect those photons
travelling along tube
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LASER
More simulated emission in same direction along
the tube
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LASER
Amplification
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One mirror (output coupler) leaky allowing
laser beam to emerge

• All photons same wavelength (colour)
• All photons travelling in same direction
• Can produced extremely short pulses of high
  energy

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Non-coherent vs laser light sourceExtended vs
point source

• 40 Watt incandescent bulb
• 2 efficient
• ? 0.8 W 800 mW light energy

• 1 mW laser pointer
• 800 x less light energy emitted than 40 W bulb

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Extended vs point source

• 800 mW _at_ 100 cm
• Irradiance, E 800 (4? x 1002)
• E 0.006 mW/cm2
• Similar in all directions

• 1 mW pointer, 0.15cm beam diameter
• In most direction, E 0 all distances
• In beam, E 1 mW (? x 0.152)
• E 14 mW/cm2
• i.e. 2,300 x more than 40 W bulb

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Compared to 40 W bulb _at_ 1 m(assuming 1.5 mm dia
beam)

• 1 mW Laser pointer
• x 2,300 _at_ 1 m
• 2W Pascal - 2 W
• x 4,600,000 _at_ 1 m
• 40 W CO2 laser
• x 91,000,000 _at_ 1 m

(Note, other effects make this even higher on
retina)
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Non-coherent vs laser light sourceChromatic
Aberration
Lasers are monochromatic (single wavelength)
so minimal chromatic aberration
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Non-coherent vs laser light sourceExtended vs
Point Sources
Image
Object / Source
Lens
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Image
Object / Source
Lens
1
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Extended source
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Image
Object / Source
Lens
2
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Distance object
Image
? Object / Source
Lens
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Distance object
Image
????????Object / Source
Parallel rays, non divergence, collimated
virtual point source
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All parallel beams will focus to about 20 microns
(0.02 mm)
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e.g. for 1 mW laser pointer

• E(skin) 14 mW/cm2 (from earlier)
• 1.5 mm beam focussed to 20 microns
• ? (1.5/0.020)2 ? 5,600 power density
• E(retina) 70,000 mW/cm2 (assuming 10
  absorption in eye)
• So EYE is at much greater hazard than SKIN for
  wavelengths focussed by cornea lens
• Eye is at greater hazard from LASERS than from
  other light sources
• (Lasers also more useful for creating a
  concentrated point source)

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Intrabeam, specular reflections, diffuse
reflections

• Intrabeam
• directly shone into eye
• if focussed by eye, 20 ?m spot on retina

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Intrabeam Viewing

• If beam larger than pupil only proportion of beam
  will be focussed on retina

• If magnifying glass etc used a greater proportion
  will be focused on retina

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Intrabeam Viewing

• If beam smaller than pupil diameter, magnifying
  glass make no difference to retina (would to
  skin)

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Specular reflection mirror-like reflection

• Potentially same hazard as direct intrabeam
  viewing

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Diffuse Reflection

• e.g. seeing laser spot on wall
• Not a point source,
• so not focussed to 20 ?m
• May still be hazardous

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Lenses, mirrors fibres

• All produce a divergent laser beam

Optical fibre
Mirror
Lens
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Lenses, mirrors fibres

• Concave mirrors and convex lenses
• focal spot - high irradiance
• beam then gets broader
• if bigger than pupil then hazard reduces with
  distance
• Optical fibre
• diverges from exiting fibre
• if bigger than pupil then hazard reduces with
  distance

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Video 1
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Types of Medical Laser
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UV lt 390 390 gt visible gt 740 740 lt
infrared
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Taken from A Non-Binding Guide to the Artificial
Optical Radiation Directive 2006/25/EC, Radiation
Protection Division, Health Protection
Agency http//www.hse.gov.uk/radiation/nonionising
/aor-guide.pdf
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• CO2 laser

NdYAG laser ?
IRA
IRB
IRC
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• CO2 laser

NdYAG laser ?
Argon laser ?
VIBGYOR
KTP-NdYAG - frequency doubling to 532 nm (green)
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UV lt 390 390 gt visible gt 740 740 lt
infrared
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Absorption of electromagnetic radiation in the
eye (Sliney Wolbarsht 1980)
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• __________________________
• Continuous beam
• __
• Single pulse
• __ __ __ __ __ __ __
• Interrupted pulses

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Laser Safety Classes
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Video 2
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Laser Device Classes Hazards

• Class 1
• Class 1M
• Class 2
• Class 2M
• Class 3R
• Class 3B
• Class 4
• Applies to device as a whole.

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MPE Maximum permissible exposure
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• Class 1
• no risk to eyes (including using optical viewing
  instruments)
• no risk to skin
• (either low power device or totally encased)

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• Class 1M
• no risk to the naked eye
• no risk to skin

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• Class 2
• no risk to eyes for short term exposure
  (including using optical viewing instruments)
• no risk to skin
• (visible, so blink response protects)
• (may cause dazzle or flash blindness)

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• Class 2M
• no risk to naked eye for short time exposure
• no risk to skin

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• Class 3R
• low risk to eyes
• no risk to skin
• (risk for intentional intrabeam viewing only)
• (may be a dazzle hazard)

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• Class 3B
• medium to high risk to eyes
• low risk to skin
• (aversion response protects skin, or must be
  focussed to such a small spot that pin-prick
  effect only)

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• Class 4
• high risk to eyes and skin
• diffuse reflection may be hazardous
• (possible fire hazard)

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HEYH Trust CP137Health Safety at Work Policy-
Lasers -

• Includes safety of class 3B and class 4 lasers

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Safety Principles

• Engineering
• e.g. doors, blinds
• Systems of work
• e.g. Local Rules, warning signs, etc
• Personal protective equipment (PPE)
• e.g. Laser safety eyewear

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Risk Assessments
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Risk Assessments
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Laser Safety Structure

• Risk assessment
• Controlled Area
• Local Rules
• Laser Protection Supervisor
• Laser Protection Adviser
• Authorised Operators and Assistants

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Controlled Area

• Must contain the risk
• Need to know nominal ocular hazard distance/zone
  (NOHD, or NOHZ)
• i.e. distance where exposure level lt MPE
• e.g. Lithotripsy laser - 80 centimetres
• e.g. Surgical CO2 - 40 metres
• Walls, blinds, doors (without gaps), etc.
• Lock doors unless can justify not
• Warning signs at every entrance

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Local Rules (How to work safely in the
Controlled Area)

• Specific to each laser
• What are hazards?
• Controlled area - limit area of hazard - signs
• Users Laser Protection Supervisor
• Safety precautions (e.g. eyewear, blinds)
• Methods of safe working, etc.
• Adverse incident procedure, LPA, etc.

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Warning Signs
LASER
IONISING RADIATION (e.g. X-rays)
Hazardous magnetic field
Ultraviolet
RF radiation
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Example
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Laser Protection Supervisor
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Laser Protection Adviser
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Authorised Users
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Authorised Users
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Incidents
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MDA One Liners - Eye risk? August 2002 (Issue
17)

• MDA has become aware of the use of inappropriate
  filters for lasers used in ophthalmic surgery.
  This can lead to permanent eye damage for the
  operator.
• When connecting a laser to a protective system
  with filters, ensure that the wavelengths of
  laser radiation for which the filter offer
  protection match the output wavelength of the
  laser. If a fault is suspected with the filters,
  the procedure should be discontinued and the
  filters examined by a trained engineer.

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Example

• Laser
• 520-575 nm Green, 2 W
• 568-575 nm Yellow, ?1 W
• 670 nm Red (aim), lt 5 mW
• Goggles labelled
• 560-570 nm ODgt4
• 570-580 nm ODgt5
• 580-650 nm ODgt6

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Example

• Laser
• 520-575 nm Green, 2 W
• 568-575 nm Yellow, ?1 W
• 670 nm Red (aim), lt 5 mW
• Goggles labelled
• 560-570 nm ODgt4
• 570-580 nm ODgt5
• 580-650 nm ODgt6

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MDA One Liners - Hind Sight? March 2000 (Issue
8)

• Two separate incidents reported to MDA involving
  faulty laser equipment resulted in permanent
  retinal damage (one to a patient and one to the
  operator). In both cases, the operator had
  noticed that the equipment was behaving unusually
  but carried on with the procedure.
• Abnormal performance of any equipment should be
  questioned immediately.

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Laser Safety Eyewear
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Laser Eyewear Labelling

• DI 1060 L7 X Z
• 620 TO 700 nm OD 2
• CARBON DIOXIDE, O.D. 10 _at_ 10600 NM
• DIR 690 - 1290 L4
• D 1064 L7, IR 1064 L8, DIR 1350 - 1400 L7, DIR gt
  1400 - 1580 L5, DI 2090 - 2100 L5, DI 2900 - 2940
  L5

D continuous wave laser, I pulsed laser (0.1
ms - 100 ms) R giant pulsed laser (1 ns - 10
?s), M mode-coupled pulse laser (lt 1 ns)
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Wavelength

• Number before the L in nanometres
• Colour of beam
• May be single number (e.g. 10600) or a range
  (e.g. 2090 2100)
• Wavelength on laser should fall within range on
  eyewear

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Optical Density

• Number after the L
• Strength of filter
• OD 1 only 1/10th of laser light transmitted
• OD2 - 1/100th,
• OD3 - 1/1000th, etc.
• Local rules should say strength required.
• Note higher ODs may be very dark

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Laser Safety Eyewear

• Must match the laser in use (whether specs or
  filter)
• Must be cleaned in accordance with manufacturers
  instructions
• If damaged, take out of service
• Consider protection of patients eyes

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Other Hazards

• Fire
• Anaesthetic gas ignition
• Plumes
• Electrical hazard

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Can be fatal
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Electrical Hazard

• Big capacitor used to drive laser, so dangerous
  even when unplugged
• Several fatalities from lasers

• DONT OPEN OR DISMANTLE LASER
• Dont let anyone else do so unless they are
  suitably qualified and trained.

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Plume

• Mostly steam, carbon particles, cellular products
  - average 0.3 ?m particles
• May contain formaldehyde, hydrogen cyanide,
  hydrocarbons, mutagens
• Human papilloma DNA identified in plume from
  surgery to remove of papillomas
• Use smoke extraction with filter (lt0.1?m) (not
  hospital vacuum)
• Staff and patients should wear well-fitting high
  filtration face masks where plume hazard
  identified.

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Odds and ends

• Maintenance
• Reflections of polished instruments
• Check fibre. Fibre breaks.
• Oxygen hazard.

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And finally ....Example of laser accident

• Dr. C. David Decker
• NdYAG, 6mJ, 10 ns pulse
• Goggles available, but
• Tunnel vision
• Clouded up
• Uncomfortable
• So not worn
• Reflection beam hit eye
• Pop!

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Goldman-Fields Scan of Dr Deckers damaged eye 4
months after accident

• Damage under high-intensity illumination (red)
• Damage under low-intensity illumination (blue)
• Laser induced blind spots (pink)
• Optic nerve blind spot (orange)

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