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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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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Chronic exposure can cause cataract formaAon in the lens of eye just as UV from sun can


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

11)Laser Safety

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