Download - 11)Laser Safety
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Laser Safety
Sharon McQuillan, MD
Laser Safety
Sharon McQuillan, MD
Basics of Laser & Laser Light
Light AmplificaAon by
SAmulated
Emission of
RadiaAon
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Laser Light
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Laser Light
• Coherent – All waves of light generated in phase with each other
– MonochromaAc – DirecAonal
• Non-‐coherent – PolychromaAc – Non-‐direcAonal
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Laser Light
• DirecAonal – Laser beam does not expand (diverge) as quickly as other light
• Beam divergence – Natural diffracAon occurrence – Measured in radans
How Lasers Work
• ProducAon of normal light – Electrons in atoms move from larger orbits to smaller orbits
– Vast number of electrons are excited – Light emiWed at random Ames, random direcAons, different wavelengths
ProducAon of Laser Light
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ProducAon of Laser Light
ProducAon of Laser Light
Laser Components • AcAve Medium
– Solid (crystal) – Gas – Semiconductor (diode) – Liquid (dye)
• ExcitaAon Mechanism – OpAcal – Electrical – Chemical
• OpAcal Resonator – HR mirror and output coupler
High Reflectance Mirror (HR)
Output Coupler Mirror (OC)
Ac8ve Medium
Output Beam
Excita8on Mechanism
Op8cal Resonator
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Laser Components • AcAve Medium
– Contains atoms which can emit light by sAmulated radiaAon
• ExcitaAon Mechanism – Source of energy to excite the atoms to the proper energy state
• OpAcal Resonator – Reflects laser beam through acAve medium for amplificaAon
High Reflectance Mirror (HR)
Output Coupler Mirror (OC)
Ac8ve Medium
Output Beam
Excita8on Mechanism
Op8cal Resonator
Types of Lasers
• Lasers can be described by : – Which part of the electromagneAc spectrum is represented • Infrared • Visible spectrum • Ultraviolet
– Length of Ame beam is acAve • ConAnuous Wave (CW) • Pulsed • Ultra-‐short Pulsed
Solid State Lasers
• Group of opAcally clear materials • Composed of a “host” crystal with an “impurity” dopant – Operate in either pulsed or CW mode – Energy input in form of bright light – Light absorbed by dopant – Lasing occurs when atoms or ions return to normal energy states
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Gas Lasers
• Generally operated as ConAnuous Wave (CW) • Most common gas lasers – CO2 – Argon – HeNe – Excimer
Semiconductor
• Diode • Most common – Gallium/Aluminum/Arsenide • 750-‐950 nm range
– Indium/Phosphorous • 1100-‐1650 nm range
Liquid
• UAlizes a flowing dye • Pumped by a flash-‐lamp of other laser • Operate as CW or pulsed • Have tunable wavelengths
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Radiometric Terms
• Light emiWed by laser is non-‐ionizing electromagneAc radiaAon
• Radiant Energy (Q) – Energy emiWed, transferred, or received in form of radiaAon
– Unit: joule (J)
Radiometric Terms
• Radiant Power (Φ) – Power emiWed, transferred, or received in the form of radiaAon
– Equal to the radiant energy (Q) divided by the corresponding Ame interval
– Also known as radiant flux – Unit: waW (W)
Radiometric Terms
• Radiant exposure (H) – Radiant energy (Q) striking a surface divided by the area of that surface over which the radiant energy is distributed
– Unit: joules per square cenAmeter (Jcm-‐2)
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Radiometric Terms
• Irradiance (E) – Radiant power (φ) striking a surface, divided by the area of that surface over which radiant power is distributed
– Radiant exposure divided by corresponding Ame interval
– Unit: waWs per square cenAmeter (Wcm-‐2)
Characterizing Laser Output
InteracAon of Light & MaWer
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InteracAon of Light and MaWer
Laser Biophysics
Anatomy of the Eye
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Anatomy of the Eye
Effects
Pupil Size
• Determines amount of energy entering the eye
• Typical sizes – 2mm daylight – 3mm indoor – 7mm dark adapted – 8mm dialted (eye exam)
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Laser Thermal Effects
• Rate process • Heat dissipaAon with Ame – Thermal damage is not cumulaAve as long as the reAna cools down between exposures
• Not limited by photon energy
Laser Photochemical Effects
• Wavelength dependent • Individual photon interacts with molecule – Damage is sever at shorter visible wavelengths (violet and blue) and is cumulaAve over Ame
Laser AcousAc Effects
• AcousAc shock – From exposure to high energy pulsed lasers results in physical Assue damage
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White Light Effects
Laser Radiance Effects
ReAnal Hazard Region
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Ocular AbsorpAon Site
• Wavelengths that focus on reAna (400-‐1400 nm), opAcal gain is 100,000 Ames
• Irradiance entering is 1 mW/cm2, at reAna will be 100 W/cm2
ReAnal Hazards
• O.25 seconds: human eye aversion Ame for bright light sAmuli (blink reflex)
• 10 seconds: worst-‐case Ame period for ocular exposures to infrared (mostly near-‐infrared)
• 600 seconds: worst-‐case period for viewing visible diffuse reflecAons
• 28,800 seconds: represents full 1-‐day occupaAonal exposure
Corneal and Lens Hazard Region
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Ocular AbsorpAon Site
Chronic exposure can cause cataract formaAon in the lens of eye just as UV from sun can
Ocular AbsorpAon Site
InflammaAon injury to cornea caused by ultraviolet (UV) wavelengths (200-‐400 nm)
Corneal Injury
• Superficial (Threshold) Injury – Epithelium repairs itself quickly and lesion clears within one or two days
• Deep Burns – PenetraAng burns produce a permanent opacity and may require corneal transplant in order to repair
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Skin effects
Photochemical/Thermal Burns
• Ultraviolet (UV) – UV can cause skin injuries comparable to sun burn • As with damage from the sun, there is increased risk for developing skin cancer from UV laser exposure
• Thermal Injuries – High power (Class 4) lasers, especially infrared and visible range of spectrum, can burn skin and even set clothes on fire
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Photochemical/Thermal Burns
• Thermal Skin Burns – Rare – Normally requires high exposure of several J/cm2 – Most common from CO2 or 10.6 μm laser exposure
– First degree (erythema), second degree (blistering), and third degree (charring) burns are possible dependent upon exposure dose
Laser RegulaAons
Laser Safety RegulaAons
• OccupaAonal Safety & Health AdministraAon (OSHA) – No specific laser safety regulaAons – Will cite safety issues under General Duty clause 29 CFR 1910.132 and 133
– Will enforce ANSI standards for laser safety
• American NaAonal Standards InsAtute (ANSI) – ANSI Z136.1
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ANSI Z136.1 Safe Use of Lasers
• Principal U.S. safety standard for users • Began in 1969 at request of U.S. Department of Labor
• Final document approved 1973 • Revised 1976, 1980, 1986, 1993, 2000 • Provides recommendaAons for safe use of lasers and laser systems between 180 nm and 1mm
Laser Hazard Classes
• ANSI Laser Safety standard defines Laser Hazard Classes
• Based on relaAve dangers associated with the use of these devices
Class I Lasers
• Cannot normally produce hazardous beam because of its extremely low power
• Has been rendered intrinsically safe due to laser being completely enclosed so that no hazardous radiaAon can escape and cause injury
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Class II Lasers
• Visible light (400-‐760 nm) conAnuous wave or pulsed lasers
• Emit energy greater than limit for Class I lasers and radiaAon power not about 1 mW
• Hazardous only if one stares directly into beam for long Ame period, similar to looking directly at the sun
• Eye protecAon is aversion response • CW upper limit 1mW
Class IIIa Lasers
• Class of intermediate power lasers • Includes any wavelength • Hazardous under direct and specular reflecAon viewing
• Diffuse reflecAon usually not hazardous • Normally not fire hazard • CW upper limit 0.5 W
Class IIIb Lasers
• Visible and near-‐IR lasers dangerous to eye • Pulsed lasers may be included • Normally does not cause thermal skin burn or cause fires
• Requires wriWen standard operaAng procedures
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Class IV Lasers
• Most hazardous class • Hazardous to eye and skin from direct viewing and diffuse reflecAon
• Fire hazard • May produce generated air contaminants • May produce hazardous plasma radiaAon • Requires wriWen standard operaAng procedures
Purpose of Control Measures
• Reduce exposure to laser radiaAon to non-‐hazardous levels or below MPE levels
• Minimize other hazards associated with laser devices during operaAon, maintenance, and service
• Control exposure to non-‐beam hazards
Types of Control Measures
• AdministraAve and Procedural • Engineering • Personnel ProtecAve Equipment • Warning Signs and Labels
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Maximum Permissible Exposure (MPE)
• Highest level of radiaAon that a person can be exposed without hazardous effects
• MPE specified in W/cm2 for CW lasers and J/cm2 for pulsed lasers
• Value depends on wavelength, exposure duraAon, and pulse repeAAon frequency
• Exposure to radiaAon levels in excess of MPE results in adverse biological effects
Nominal Hazard Zones (NHZ)
• Space within which level of direct, reflected, or scaWered laser radiaAon during operaAon exceeds applicable MPE
• Exposure levels beyond boundary of NHZ are below applicable MPE
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Nominal Hazard Zones
Nominal Hazard Zones
• Purpose of NHZ evaluaAon is to define where control measures are required
• Factors required in NHZ computaAons – Laser power or energy output – Beam diameter – Beam divergence – Pulse repeAAon frequency – Wavelength – Beam opAcs and beam path – Maximum anAcipated exposure duraAon
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Non-‐Beam Hazards
• Refer to anything other than the laser itself that can create a hazard
• Includes – Electrical hazards – Fire hazards – Laser generated air contaminants (LGAC) – Compressed gases – Chemical hazards – Collateral and plasma radiaAon – Noise
Electric Shock
• Use cauAon when working on or near high voltage power supplies used for Class III and IV lasers
• Sufficient voltage to injure or kill
Fire
• Following laser components may product fire hazards – Electrical circuits – Laser gases – Laser generated airborne contaminants – Laser dyes – Beam enclosures – Beam itself
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Air Contaminants
• Air contaminated due to interacAon of laser beam with target material can result in producAon of toxic chemicals
• Thermal destrucAon of Assue creates smoke byproduct
• Plume can contain live cellular materials including blood fragments or viruses
Chemicals
• Hazardous chemicals used as part of lasing medium can create special problems
• Dyes and solvents used in dye lasers are toxic and open carcinogenic
• Laser operators should be familiar with Material Safety Data Sheets (MSDS) for these chemicals
Engineering Controls
• ProtecAve housings • Service access panels • Key control master switch • Viewing windows, display screens • Beam path enclosures • Remote interlock connectors • Beam stop
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PPE for Skin
• Personnel ProtecAve Equipment (PPE) for skin exposed to Class IIIb or IV lasers
• Ultraviolet lasers may require that Aghtly woven fabrixs be worn to protect arms and hands
• For lasers with wavelengths > 1400 nm, large area exposures to skin can result in dryness and heat stress
PPE for Eyes
• PPE for eyes exposed to Class IIIb or IV lasers is mandatory
• Eyewear with side protecAon is best • PPE is recommended for class II or IIIa lasers when intenAonal direct viewing >0.25 seconds is necessary
PPE for Eyes
• Factors to consider when selecAng eyewear – Wavelength compatability with laser – AWenuaAon at that wavelength or opAcal density – Visual transmiWance – Comfort and fit
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Intrabeam Ocular Density DeterminaAon
• Based upon typical exposure condiAons, opAcal density required can be determined
• OpAcal density (OD) is a logarithmic funcAo defined by – OD= log 10(H0/MPE) – H0 = anAcipated worst-‐case exposure {Power/Area} (J/cm2 or W/cm2)
– MPE = maximum permissible exposure level expressed in same units as H0aser
Laser Safety Signs
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Laser Accident Summary
skin injury11%
electrical6%
malfunction5%
no-harm exp4%
fire2% others
2%
eye injury70%
Leading Causes of Laser Accidents
• Available eye protecAon not used • Equipment malfuncAon • Improper methods of handling high voltage • Inadequate training • Failure to follow SOP • Failure to provide non-‐beam hazard protecAon
• Incorrect eyewear selecAon and/or failure
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EducaAon & Training • ANSI requires that all staff that work with lasers
receive educaAon and training • Currently no standard educaAon program • Recommend combinaAon of lecture and hands-‐on
experience that covers the following: – Laser physics – Laser operaAon – Laser classificaAon – Biological effects – Beam and nonbeam hazards – Control and protecAon measures – IndicaAon and contraindicaAons for treatment
Regulatory Issues Regarding Laser Procedure DelegaAon
• Does your state have laws governing the ownership, registraAon and use of laser devices?
• Under which malpracAce/liability will the treatment provider pracAce?
• Who can perform laser procedures in your state? • What educaAon & training is required? • Are there any supervision or protocols that need to be implemented?
Laser Safety Officer
• Ensures laser safety standards and protocols are followed
• ResponsibiliAes include: – Developing standard operaAng procedures – Maintain wriWen laser safety manual – Maintain service records of devices – Train staff in laser safety – Comply with all regulatory bodies – Know laser hazards and control measures – Maintain records of all laser incidents/accidents