Copyright © Pro Laser 2005
Module 1Establishing safety in the workplace
Laser safety for safety supervisorsMike Green
Copyright © Pro Laser 2005
Directives
Product Directives
ProductRegulations
User Guidelines Product Standards
Workplace Directives
WorkplaceRegulations
(legal)
The New ApproachDirectives
Workplacesafety
EN 60825-1: 1994Safety of laser productsPart 1 - Equipmentclassification,requirements and user’sguide
TR 60825-14: 2004Safety of laser productsPart 14 - A user’s guide
LEGAL
National implementation
Copyright © Pro Laser 2005
Directives
Product Directives
ProductRegulations
User Guidelines Product Standards
Workplace Directives
WorkplaceRegulations
(legal)
The New ApproachDirectivesLEGAL
National implementation
Lase
r haz
ard
and
com
plex
ityDegree of control
Specificworking
code“shall”
Generaluserguidance“should”
Workplacesafety
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Administration of safetyTR 60825-14
Safety responsibilities of employers and employees
• All users and supervisors have a role to play
• Employers responsible for assessing risksand reducing them to an acceptably low level
• Employer should establish a laser safetypolicy
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Administration of safetyTR 60825-14
Safety responsibilities of employers and employees
• All users and supervisors have a role to play
• Employers responsible for assessing risksand reducing them to an acceptably low level
• Employer should establish a laser safetypolicy
Laser Safety Officer
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Administration of safetyDelegationSafety responsibilities of
employers and employees
Laser Safety Officer• Employers must ensure LSO is competent
• Responsible for:• Day-to-day management
• Monitoring compliance
• Taking action where there isnon-compliance
• Approving procedures
• Maintaining recordsResponsibilities andauthority, in writing
Director
Division head
LSO
Laser User
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Administration of safetyLSO
Documentation• Records of location and applications of all class3B and 4 lasers and control measures in place
• Written procedures
• Risk assessments and audit reports
• Laser safety training records (and plan forrefresher training)
• Copies of standards and guidance documents
• General site safety policy statement
• Laser safety policy statement
LSO Documents to hand
All records kept up todate and reviewedregularly
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Maintenance of a safeworking environment
Inspection oflaser areas
Regular inspection oflaser facilities
Check list
Testing of controls
Key points to look for:
a) modifications, relocation or replacement of laserequipment;
b) changed conditions of use;
c) changes to the environment in which the laserequipment is used;
d) changes of personnel;
e) indications of any reduction in compliance withsafety procedures.
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Incidents and accidentsKey information
Location of medicalcentre
Information on laserwavelength (“grab bag”)
Treat for shock
Laser users:• in the event of an accident or incident terminate
laser emission and report to management;
• Seek medical attention in the event of a real orsuspected laser injury.
LSO:• Possible eye-injured persons must be seen by a
qualified ophthalmologist within 24 hours of thepotential exposure;
• Investigate the circumstances and assess likelyexposure, document the conclusions of theinvestigation and review system of control beforelaser is permitted to be used.
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Screening of laser workersEye tests
T
A S B T V S P F T L C K C
g f e v b p m k l m n o p o
Registered Class 3B and 4laser users should have:
• Effective use of botheyes.
• No visual defects thatcannot be correctedwith spectacles
• No untreated glaucoma.
“… routine ophthalmic examinations ofemployees… have no value as part of a health
surveillance programme”
Eye tests only make sensefor persons at risk ofexposure to Class 3B andClass 4 laser beams atwavelengths within theretinal hazard range.
Such persons wouldnormally be issued withlaser protective eyewear.
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Procedures for laser use inthe research environment
StructureElements of procedures:
1. Essential generalinformation
2. Procedures foremergencies
3. Procedures fornormal operation
4. Procedures foralignment
5. Procedures forexternal contractors
Procedures should be written by the laser supervisorand approved by the LSO.
Copies may be issued to laser users, who should signto acknowledge receipt and that the procedures areunderstood.
Procedures should be reviewed regularly to ensuretheir continued relevance to requirements
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Procedures for laser use inthe research environment
StructureElements of procedures:
1. Essential generalinformation
2. Procedures foremergencies
3. Procedures fornormal operation
4. Procedures foralignment
5. Procedures forexternal contractors
Description and purpose of the equipment/process.
Type, approximate power and classification of lasers.
Drawing identifying the laser hazard area(s).
Listing of other hazards present with references tosafety codes.
Basic engineering and administrative controls.
PPE provided and storage point(s).
Contact details of LSO and responsible person.
Names of authorised laser users.
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Procedures for laser use inthe research environment
StructureElements of procedures:
1. Essential generalinformation
2. Procedures foremergencies
3. Procedures fornormal operation
4. Procedures foralignment
5. Procedures forexternal contractors
Action to be taken in the event of specified equipmentfailure or other emergencies
Incident reporting procedure and the action to be takenin the event of a suspected accident
A plan drawing of the laser area indicating the positionsof electrical isolation switches, fire extinguishers etc.
A list of hazards (especially for emergency services)
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Procedures for laser use inthe research environment
StructureElements of procedures:
1. Essential generalinformation
2. Procedures foremergencies
3. Procedures fornormal operation
4. Procedures foralignment
5. Procedures forexternal contractors
Point out basic good practice (e.g. terminating beams,secure fixing of turning mirrors)
Identify administrative controls and use of PPE.
Highlight any deviations from best practice.
The normal shut-down procedure should be described.
Include requirements for safety checks (interlocks etc.).
Servicing procedures should address the establishmentof temporary hazard areas, administrative controls,PPE and who should carry out the work. It shouldinclude procedures for controlling the work of outsideservice engineers e.g. permits to work.
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Procedures for laser use inthe research environment
Structure
Best practice
Elements of procedures:
1. Essential generalinformation
2. Procedures foremergencies
3. Procedures fornormal operation
4. Procedures foralignment
5. Procedures forexternal contractors
Risk assessment
Procedures
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Best practice in the researchenvironment
General userguidanceEngineering
controls
Administrativecontrols
Personalprotectiveequipment
Installed Engineering Controls
• Install interlocks on access points to(3B or 4) laser areas and connect to laser
• Enclose the beam path (and terminate)
• Make the laser beam path stable
• Minimise exposed shiny surfaces
• Beam at waist height and no chairs
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Best practice in the researchenvironment
General userguidanceEngineering
controls
Administrativecontrols
Personalprotectiveequipment
Installed aids to Administrative Control
• Check for appropriate knowledge andattitude of personnel and provide training
• Develop and document proceduresaddressing normal operation,maintenance and service activities
• Install warning lights and labels
• Provide beam visualisation equipment foruse with safety eyewear
• Control use of laser key switch
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Best practice in the researchenvironment
General userguidanceEngineering
controls
Administrativecontrols
Personalprotectiveequipment
Installed aids to PPE use
• Strict enforcement
• Suitable style(s) of eyewear
• Proper storage and labelling
• Regular inspection and maintenance
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Risk AssessmentAll hazardsHazard
Risk
Injury
= S x A x E where :
S Severity of harm
A Probability of human access tothe hazard
E Probability of exposure whenhazard is accessible
potential to cause harm
likelihood of harm
LEGAL
Laser radiation
Electricity
Fire
Fume
High pressure gases
Mechanical
Solvents
Etc.
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Risk AssessmentAll hazardsHazard
Risk
Injury
= S x A x E where :
S Severity of harm
A Probability of human access tothe hazard
E Probability of exposure whenhazard is accessible
potential to cause harm
likelihood of harm
LEGAL
Laser radiation
Electricity
Fire
Fume
High pressure gases
Mechanical
Solvents
Etc.
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Risk AssessmentLaser radiationHazard
Risk
Injury
potential to cause harm
likelihood of harm
LEGAL
Output
Wavelength
Access to beam
Application
Environment
Personnel at risk
Etc.
= S x A x E where :
S Severity of harm
A Probability of human access tothe hazard
E Probability of exposure whenhazard is accessible
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Laser Radiation RiskAssessment: Wavelength
Laser radiation
Output
Wavelength
Access to beam
Application
Environment
Personnel at risk
Etc.
CO2 laser
Nd:YAG laser
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Laser Radiation RiskAssessment: Wavelength
1Near -IR
High
Noindication
Largehazardrange
(low MPE)
S
E
A
3UV
Low tomoderate
Noindication
Integratedexposure- scatter
plusbeam
2Visible
High
Visibleradiation
Largehazardrange
(low MPE)
4Mid/far-IR
Low tomoderate
Heatsensation
Smallhazardrange
Laser radiation
Output
Wavelength
Access to beam
Application
Environment
Personnel at risk
Etc.
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Step-by-step
Risk Assessment
Identify potentially injurious situations(all operations, all hazards)
BenefitsInvolving users inidentifying hazardousactivities encouragesparticipation andownership of safety
RISKASSESS
Step 1
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Step-by-step
Risk Assessment
Identify potentially injurious situations(all operations, all hazards)
Benefits
RISKASSESS
Step 1
Assess the risk for each situation(severity of injury, likelihood of exposure; then refer torisk tables)
Step 2
Involving users inidentifying hazardousactivities encouragesparticipation andownership of safety
Highlights the keyproblem areas
Copyright © Pro Laser 2005
Step-by-step
Risk Assessment
Identify potentially injurious situations(all operations, all hazards)
Benefits
RISKASSESS
Step 1
Assess the risk for each situation(severity of injury, likelihood of exposure; then refer torisk tables)
Step 2
Review controls for each situations where the riskis intolerable(compare with current best practice and state whetheror not you consider existing controls to be satisfactory)
Step 3
Involving users inidentifying hazardousactivities encouragesparticipation andownership of safety
Highlights the keyproblem areas
Documents deviationsfrom Laboratory Code
Copyright © Pro Laser 2005
Step-by-step
Risk Assessment
Identify potentially injurious situations(all operations, all hazards)
Benefits
RISKASSESS
Step 1
Assess the risk for each situation(severity of injury, likelihood of exposure; then refer torisk tables)
Step 2
Review controls for each situations where the riskis intolerable(compare with current best practice and state whetheror not you consider existing controls to be satisfactory)
Step 3
Review the new situation (repeat steps 2 and 3)Step 4
Review the riskassessmentperiodically
Involving users inidentifying hazardousactivities encouragesparticipation andownership of safety
Highlights the keyproblem areas
Documents deviationsfrom Laboratory Code
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Tick list for open beams(Class 3B and 4)
Beam pathcontrol
Are:• All beam paths are enclosed as much as isreasonably practicable?
• All beam path components that generate errantbeams locally enclosed?
• All beam paths properly terminated?• All upwardly directed beams shielded to preventhuman exposure?
• All unprotected open horizontal laser beams lyingabove or below normal eye level?
• All lasers and optical components on the beam linesecurely mounted?
• Shiny surfaces (including jewellery) prohibitedaround laser beam paths?
• Laser sources and beam paths are kept under thecontrol of competent persons?
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Tick list for open beams(Class 3B and 4)
Beam pathcontrol
Is:• Information of the current laser hazard clearlydisplayed at point of access to the laser area?
• Low level lighting used for ‘lights-out’ operation?• A safe method of beam alignment provided?• A visible or audible warning of the potential laserhazard provided?
• Laser safety eyewear provided?Are:• Persons at risk of exposure to the laser radiationadequately trained and instructed?
• Precautions in place to safeguard visitors enteringthe laser area?
• Unauthorised persons prevented from gainingaccess to the laser area?
• Multiple exposed wavelengths present?
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Learning lessons fromaccidents
Laser accidents in French research laboratories
56% visible lasers
35% Nd:YAG (IR-A)
7% CO2
Of 55 accident reports in11 years, 27 resulted inpermanent eye injury
EU643 Report 'Clininal and epidemiologicalresearch'Commissariat Energie Atomique 1990
Accidentstatistics
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Learning lessons fromaccidents
Lessonslearned
Arrange for a fireassessment whereverClass 4 lasers are used
Carry a fire extinguisherand fit a smoke detector__________________
A Class 4 dye laser ignited the methanol solventused in the laser.
A small explosion and fire occurred in a laser dye(dioxane) mixture pump. Arcing in the pump motor,which ignited the flammable air/dioxane mixture,apparently caused the fire.
A Class 4 CO2 laser beam was reflected upwardsand ignited ceiling tiles in a laser laboratory. Theresearcher had left the room to examine samplesand returned a few minutes later when a smokedetector sounded.
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Learning lessons fromaccidents
Lessonslearned
A technician was replacing a flashlamp on a Nd:YAGlaser. The unit was electrically isolated, shut downand locked out. After 5 minutes wait for thecapacitor to discharge the worker touched thenegative terminal and was shocked. This wasidentified as a bleed circuit malfunction. No seriousharm.
A service engineer was electrocuted while installinga copper vapour laser. An interlocked protectivepanel had been manually bypassed during theinstallation to make adjustments. Despite CPR theserviceman expired.
Electrical hazards inlasers can be lethal
Proper HV training isessential
Provide earthing sticks
Consider secondaryscreening of internal HV__________________
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Learning lessons fromaccidents
Lessonslearned
An untrained summer research assistant wascarrying out alignment on his first day at work usinga 150 mW argon/dye laser. The laser was “slung” ina laser holder located under optical bench and thebeam was directed upwards through a beamchannel in the optical bench. The student chose tostand on top of the table and look downward whileattempting to align a turning mirror. No protectiveeyewear was used. The turning mirror slipped andthe beam was directed into his eye causing animmediate retinal burn on the edge of the macula.
During an experiment, a student climbed onto astool to adjust a periscope with a visible laser. Thestudent noticed a bright flash in her right eye. Noeyewear was worn ‘since she needed to observe thespot on a card’. No pain or bleeding, but anexamination the next day revealed a parafoveallesion.
Fully guard upward-travelling beams
Provide alignmentprocedures that facilitatethe use of protectiveeyewear
Provide proper training__________________
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Learning lessons fromaccidents
Lessonslearned
A student received a reflected Ti-Sapphire laserbeam from the plastic lid of a toolbox while he wasinstalling a laser beam safety tube. No eyeprotection was worn. The student had not receivedlaser safety training.
During optics alignment involving a 30 mJ pulsedNd:YAG laser (10 Hz) on a target using a prism, thebeam exceeded the prism’s critical angle and struckthe scientist in the eye resulting in a permanentretinal burn. No protective eyewear was worn.
A scientist bumped a mirror mount in a complexoptical array, causing a stray beam to move out ofthe horizontal plane. When leaning over the table, hewas struck in his left eye. An examination confirmeda macular lesion. No eyewear worn and safetyknowledge was limited.
Require the use of safetyeyewear wherever thereare exposed Class 3Band 4 laser beams
Control the use ofreflecting objects nearopen beam paths
Locally enclose prismsand other sources ofsecondary beams
Protect optics fromknocks__________________
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Learning lessons fromaccidents
Lessonslearned
A field service engineer was working on an argonlaser photocoagulator. During the inspection, theengineer was looking down the tube bore when thelaser spontaneously fired. He received an intrabeamocular exposure causing a permanent retinal lesion.
A Ti-sapphire accidentally discharged during beamalignment. The graduate student undertaking thealignment sustained a left eye injury. At 4 days, a300 µm hole and sub- retinal haemorrhage wasobserved.He suffers central vision loss and floaters.
A new frequency doubler didn't have A/R coatingsas requested. As the student left the room, beam hithim in the corner of his eye and caused inter-ocularbleeding. He still complains at 8 yrs of floaters andvision that looks "like looking through a dirtywindow".
Do not rely solely oncontrol circuits: add abeam stop or power down
Do not rely on coatingspecification for safety__________________
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Learning lessons fromaccidents
Lessonslearned
A technician received a 60 mW exposure from theBrewster window of an argon laser. Laser protectiveeyewear was available, but was not used theyapparently fogged easily and were annoying to use.A blind spot has persisted in the area of the lesion.
A frequency doubled Nd:YAG laser beam (532 nm)was Raman shifted to 770 nm in a methane cell. Thelaser protective eyewear provided protection at 532nm but did not protect for 770 nm and the techniciansuffered a retinal burn from a 0.8 µJ, 770 nm pulse.
During an alignment of a Nd:YAG laser, a productionworker looked through an opening in the top of achamber and his eyewear slid up as he leaned over.The beam reflection from a target paper went intohis eye causing a bright afterimage lasting 20minutes, which led to a permanent central retinalburn.
Nd:YAG reflectionfrom a surface coatedfilter. Safety gogglesmisted so he took themoff to get a better view ofthe display ….
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Learning lessons fromaccidents
Lessonslearned
A technician received a 60 mW exposure from theBrewster window of an argon laser. Laser protectiveeyewear was available, but was not used theyapparently fogged easily and were annoying to use.A blind spot has persisted in the area of the lesion.
A frequency doubled Nd:YAG laser beam (532 nm)was Raman shifted to 770 nm in a methane cell. Thelaser protective eyewear provided protection at 532nm but did not protect for 770 nm and the techniciansuffered a retinal burn from a 0.8 µJ, 770 nm pulse.
During an alignment of a Nd:YAG laser, a productionworker looked through an opening in the top of achamber and his eyewear slid up as he leaned over.The beam reflection from a target paper went intohis eye causing a bright afterimage lasting 20minutes, which led to a permanent central retinalburn.
Select eyewear that iscomfortable to wear,secure and does not fogup
Isolate wavelengths if theeyewear can’t provideadequate protection at all__________________
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Module 2Laser safety assessment
Laser safety for safety supervisorsMike Green
Copyright © Pro Laser 2005
Guarding
Standards forprotective equipmentLEGAL
Continuous inspection
How Long?
Regular inspection
Suggested times
Continuous operatorobservation
10 s
Short cycle operationwith intermittent
inspection100 s
Automated machineusage
30000 s
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EN 12254 Screens for laser workingplaces - Safety requirements and testing
Standards forprotective equipment
Assessmentand testing
LEGAL
Applies up supervisedscreens to Maximumpower of 100 W and pulseenergy 30 J.
100 s testing for stability tolaser radiation
≥ 1 mm2 test area
Tests for mechanicalstrength and resistance toignition
Marking code (similar toeyewear)
Not a requirement:painted metal or
other non-flammableopaque materials can
be used
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Use of PPEBESTPRACTICE
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Hazard mitigation
Lasertype *
Laserwavelength
Filterscale number
ManufacturerID mark Mechanical
strength
EN207 marking code
D CWI 10-4 - 10-1
R 10-9 - 10-7
M < 10-9
Laser safetyeyewear
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MaximumPermissibleExposure
that level of radiationto which,under normalcircumstances,persons may beexposed withoutsuffering adverseeffects.
MPEs andNOHDs
Definition
Maximum PermissibleExposure
The factors effecting the MPE are
Wavelength (must be within 180nm - 1mm)
Exposure duration (pluspulse width and PRF forpulsed lasers)
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Exposure duration
MPEs andNOHDs
Direct cornealexposure
Maximum PermissibleExposure
Values correspond to:• a single exposures ofthe eye
• a single wavelength
• a value averaged overa specific aperturediameter
0.1ps 1 ns 10s 3.104s
Wav
elen
gth
Mid
& F
ar
Visi
ble
&
UV
I
R
nea
r IR
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Exposure duration
Wav
elen
gth
Laserpulses
Humanresponse
times
Prolongedexposure
<1ns to 0.1s 10s to 30,000s
Mid
& F
ar
Visi
ble
&
UV
I
R
nea
r IR
MPEs andNOHDs
Maximum PermissibleExposure
Non
-line
ar e
ffect
s
retinal thermal
corneal thermal
corneal photochemical
Direct cornealexposure
Values correspond to:• a single exposures ofthe eye
• a single wavelength
• a value averaged overa specific aperturediameter
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Exposure duration
Wav
elen
gth
Laserpulses
Humanresponse
times
Prolongedexposure
<1ns to 0.1s 10s to 30,000s
Mid
& F
ar
Visi
ble
&
UV
I
R
nea
r IR
MPEs andNOHDs
Maximum PermissibleExposure
Non
-line
ar e
ffect
s
retinal thermal
corneal thermal
corneal photochemical
Limitingaperture
The diameter of the circleover which the MPE value
is to be averaged
Total power (or energy)through limiting aperturedivided by the area ofaperture
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LASERHAZARD
Extendedsources
Maximum PermissibleExposure
exposure duration
Mid
& F
ar
V
isib
le &
U
V
IR
ne
ar IR
Thermal retinal injury only
‘Small’ sources [α ≤ 1.5 mrad (αmin)]MPE applies
‘Medium’ sources [100 mrad ≥ α > αmin]MPE x α /αmin
‘Large’ sources [α > 100 mrad (αmax)]MPE x αmax/αmin (=66.7)
17 mm
αα
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Maximum PermissibleExposure
WavelengthGraph(s) of MPE vs. wavelength
MPE
(Wm
-2)
1000 Wm-2
10 Wm-2
3 Wm-2
Wavelength (nm)
10s exposure
400 700 1400180
Thermal corneal
Focusing + absorption depth effects
Photochemical activity
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Maximum PermissibleExposure
DurationGraph(s) of MPE vs. exposure duration
MPE
(Wm
-2)
time (s)
600 nm
10ps 1ns 18µs 10s
10 Wm-2
280 Wm-2
25 Wm-2 @ 0.25s
5 MWm-2
Equilibrium temperature
Diffusion limited temperature
Thermo-mechanical
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Maximum PermissibleExposure
DurationGraph(s) of MPE vs. exposure duration
MPE
(Wm
-2)
time (s)
600 nm
10ps 1ns 18µs 10s
5 mJm-2
0,15 mJm-2
MPE
(Jm
-2)
100 Jm-2
Equilibrium temperature
Diffusion limited temperature
Thermo-mechanical
Joule = Watt x time
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Exposure durationMPE value range10-13 s
30,000 s
Exposure to single laser pulses
Duration of laser work
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Exposure durationVisible Radiation
“light”
Aversion responseto bright light
≤ 0.25s
10-13 s
30,000 s
Exposure to single laser pulses
0.25 s Accidental viewingof visible laser radiation
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Exposure durationSaccadic eye
movement10-13 s
30,000 s
Exposure to single laser pulses
0.25 s Accidental viewingof visible laser radiation
10 s Accidental viewingof invisible laser radiation
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Exposure durationBehaviouralmovement
10-13 s
30,000 s
Exposure to single laser pulses
0.25 s Accidental viewingof visible laser radiation
10 s Accidental viewingof invisible laser radiation
100 s fixation on laserpoint source
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Exposure durationUV radiation10-13 s
30,000 s
Exposure to single laser pulses
0.25 s Accidental viewingof visible laser radiation
10 s Accidental viewingof invisible laser radiation
100 s fixation on laserpoint source
30,000 s intentional viewing ofextended sourceUV radiation.
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Excimer (KrF) 0.25 1 10-8 30 Rhodamine Dye 0.55 1 10-7 5 10-3
Ruby (normal mode) 0.69 1 10-9 5 10-3
Ruby (Q-switched) 0.69 2 10-8 5 10-3
Nd:YAG (normal mode) 1.06 1 10-9 5 10-2
Nd:YAG (Q-Switched) 1.06 1 10-7 5 10-2
Carbon Dioxide 10.6 1 10-5 300
Typical Values of MPEsfor single pulse lasers
Laser Type λ Pulse MPE (µm) (s) (Jm-2)
MPEs andNOHDs
Single pulses
Exposure duration=
pulse duration
Maximum PermissibleExposure
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MPEs for intrabeam viewing of CW lasers
Laser Type λ MPE (Wm-2) (µm) 0.25s 100s 30000s
Helium 0.32 N/A 100 10-Cadmium 0.44 25 1.0 1.0
Argon Ion 0.49 25 6.3 6.30.51 25 10 10
He-Ne 0.63 25 10 10
Nd -YAG 1.06 N/A 50 50
CO2 10.6 N/A 1000 1000
MPEs andNOHDs
CW lasers
Choice of MPE depends onconditions of exposure.
Quoted values are for pointsources.
Maximum PermissibleExposure
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Assessed duration of exposure
MPEs andNOHDs
Multiple pulsesMPE is the smallest of:
Assessing multiple pulses
Condition 1Single pulse MPE for thelargest pulse
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Assessed duration of exposure
AveragePower
MPEs andNOHDs
Multiple pulsesMPE is the smallest of:
Assessing multiple pulses
Condition 2MPE for equivalent CW laser
Condition 1Single pulse MPE for thelargest pulse
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MPEs andNOHDs
Multiple pulses
Condition 3 (excluding UV)Reduced single pulse(MPErsp)For a regular pulse train:MPErsp = MPEsp x N-1/4
Assessing multiple pulses
Total-on-time-pulseTOTP
Sum of pulse energyand duration
MPE is the smallest of:
Condition 2MPE for equivalent CW laser(MPEcw)
Condition 1Single pulse MPE for thelargest pulse (MPEsp)
Summed over specified period (Generally 10s)
Assigned MPE is the smallest ofMPEsp, MPEcw, MPErsp
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MPE values for repetitively pulsed lasersExcimer(0.25 µm, 10ns, 10 Hz)(0.25 µm, 10ns, 100 Hz)
Dye(0.55 µm, 100ns, 10 Hz)(0.55 µm, 100ns, 100 Hz)
Nd:YAG(1.06 µm, 100ns, 100 Hz)(1.06 µm, 100ns, 100 kHz)
CO2(10.6 µm, 10µm, 1 Hz)(10.6 µm, 10µm, 1 kHz)
Exp s3 104
0.25
3 104
10
MPE Jm-2
1 10-4
1 10-5
4 10-3
1.3 10-3
8.9 10-3
5.0 10-4
1701
MPEs andNOHDs
Repetitivelypulsed lasers
Average power MPE is thesmaller
Reduced single pulseMPE is the smaller
Maximum PermissibleExposure
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MPE
NOHD
MPEs andNOHDs
NOHD
NOHD Nominal Ocular Hazard Distance
is that distance at which the beamirradiance equals the appropriateocular MPE.
Calculation assumes:• conical expansion• simple power
distribution:
Maximum PermissibleExposure
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Class 1
ENOHD
MPEs andNOHDs
ENOHD Extended Nominal Ocular Hazard Distance
is that distance at which the beamirradiance equals the Class 1 AEL.
Maximum PermissibleExposure
ENOHD
Calculation assumes:• conical expansion• simple power
distribution:
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A laser beam has adiffuse edge
The beam diameter iscommonly defined as thatwhich encloses 86% of the
beam energy
Hazard distanceBASICS
Beam crosssection
Lase
r
radius
Powerdensity
100%
beam “diameter”
‘1/e2’ beam diameter
‘1/e’ beam diameter
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High divergence/long range
Class 4CW visible
Higheyeandskin
injury
Fire
Mideye
injury
(>5xMPE)
Loweye
injury
(≤5xMPE)
Safeacci-
dentalif NO
viewingaids
(0.25s)
Safeacci-
dental
(0.25s)
No
risk
Question
Where does theNOHD and theENOHD lie in
this figure
Variation of hazardwith distance
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