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ImperialCollegeSafetyUnit-Intro

ductiontolasersafety-1

Introduction tolaser safety

Ian GillettSafety Director

Imperial College

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What is a laser?

The word laser is an acronym which stands for Light

Amplification by Stimulated Emission of Radiation.

Light energy is amplified to extremely high intensity by aprocess called stimulated emission.

The energy generated by the laser is in or near theoptical portion of the electromagnetic spectrum.

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How does a laser work?

Electrons surrounding atoms are excited into higherenergy states to create a population inversion.

The excited electrons release their energy in the form ofphotons which can, in turn, collide with other excitedelectrons and cause them to release an identical photon- this is called stimulated emission.

As more energy is put in so more photons are released.

By reflected the photons back and forth in a mirroredsystem the amount of energy can be increased.

Some of the energy is allowed to escape through apartially coated mirror to create a laser beam.

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Types of laser

Gas lasers

including He-Ne and carbon dioxide lasers

Dye lasers

Solid state lasers including neodymium-YAG (Nd:YAG) lasers

Semiconductor lasers

diode lasers

Chemical lasers

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Laser light

Laser light has the following properties:

it is monochromatic

it is very intense

it has low divergence

it is coherent.

Lasers can have different types of beam output

continuous wave (CW), or

pulsed.

Laser speckle is caused by scattered laser radiationinterfering with incident laser radiation.

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Beam hazards

The laser produces an intense, highly directional beamof light. This light will be absorbed by surfaces it isdirected at, raising the temperature of that surface.

The eyes and skin of the body are vulnerable to thisenergy.

Of greatest concern is laser exposure in the retinalhazard region, but ultraviolet and infra-red light also havean effect.

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The Retinal Hazard Region

400-1400nmAffects the retina

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UV-C (100-280nm)Cornea surface

UV-A (315-400nm)Affects the lens

UV-B (280-315nm)Absorbed by the cornea

Ultraviolet light

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Far IRAffects cornea and aqueous humor

Near IR (< 1400nm)Affects the retina

Infra-red Region

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Reflections

There are two principle types of laser reflection:

specular reflection - which occurs from mirror-like surfaces. Theincident beam striking a specularly reflecting surface will leave itessentially unchanged.

diffuse reflections - which occur from rough surfaces such aspaper or matt-painted walls. These reflections bear no relationto the direction of the incident radiation.

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ImperialCollegeSafetyUnit-Introductiontolasersafety-12

Non-beam hazards

Non-beam hazards include:

electrical hazards - especially from trailing cables and risk ofwater spillages

fumes - from vaporised target material

laser dyes - many of these are carcinogenic optical hazards - arising from the flash lamps used to pump the

lasers.

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Safety Standards

There are two principle international laser safetystandards:

International Electrotechnical Commission (IEC) 60825 - this hasbeen adopted in the UK as British Standard BS EN 60825-

1:1994 Safety of laser products. Part 1. Equipmentclassification, requirements and users guide.

American National Standards Institute (ANSI) Z136

Both standards share a common classification systemfor lasers based on their power output, wavelength andpulse duration.

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British Standard

BS EN 60825-1:1994 is dividedinto three sections (General;Manufacturing Requirements;and Users Guide)

The objectives of the Standardare to:

protect persons from laser radiation

lay down requirements for user and

manufacturer to establishprocedures

ensure adequate warning of hazards

reduce possibility of injury, and

protect persons from other hazards.

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Laser Hazard Classification

Exposure limits have been set for nearly all types oflaser radiation.

These limits are referred to as Maximum PermissibleExposures (MPEs).

MPEs are those levels of radiation to which persons maybe exposed without suffering adverse effects.

MPEs depend upon the wavelength of the laser and theduration of the exposure.

Detailed tables are found in the British Standard.

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Class 1

MPE less than 7 microwatts of visible radiation.

A Class 1 laser is considered safe under reasonably

foreseeable conditions of operation and they present nohazard to the eye or skin.

This Class also includes laser systems which cannotemit hazardous levels of laser radiation because of theinherent design of the product.

Note that there may be a more hazardous laser systemembedded in the product and additional precautionswould be necessary if the system is opened up.

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Exceed accessible emission limits for Class 1 but,because of the geometrical spread of the emittedradiation, the laser does not cause harmful levels of

exposure to the unaided eye. Safe limit can be exceeded, and injury can occur, if

magnifying viewing instruments are used, eg binoculars,telescopes, magnifying glasses, microscopes.

Class 1M

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Class 2

MPE less than 1 mW of visible radiation.

A Class 2 laser or laser system must only emit a visiblelaser beam.

Momentary viewing of a Class 2 laser beam is notconsidered hazardous since the upper limit for this typeof device is less than the MPE for momentary exposuresof 0.25 second or less - the so-called blink reflex.

Intentional extended viewing is considered hazardous.

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Class 2M

Laser products which exceed the permitted accessiblelimits for Class 2 but, because of the geometric spread ofthe emitted radiation, protection of the unaided eye is

normally afforded by natural aversion responses to brightlight.

The use of magnifying viewing instruments can give riseto higher levels of exposure and injury can occur. These

instruments include: binoculars; telescopes; magnifyinglenses; and microscopes.

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Class 3R

Laser products having a level of accessible emission upto five times the limits for Class 1 (if invisible) or Class 2(if visible).

The maximum permissible exposure may be exceededbut the risk of injury is low.

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Class 3B

Less than 500 mW of visible radiation

note that Class 3B also covers pulsed lasers and invisibleradiation. Reference should be made to the MPE limitscontained in the British Standard in order to verify classification.

Direct intra-beam viewing is always hazardous. Viewing diffuse reflections from a distance is normally

safe provided the exposure duration is less than 10seconds.

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Class 4

Over 500 mW visible radiation

note that Class 4 also covers pulsed lasers and invisibleradiation. Reference should be made to the MPE limitscontained in the British Standard in order to verify classification.

These lasers are very powerful and may also be a firehazard.

Exposure of the skin to the beam may cause injury.

Even diffuse reflections are hazardous.

Very stringent control measures are required.

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ImperialCollegeSafetyUnit-Intr

oductiontolasersafety-23

Engineering controls

Engineering controls remove the dependence to followrigorous procedures and the possibility of failure ofpersonal protective equipment.

Engineering controls all the safety features built into thedesign of the laser and its associated equipment.

Examples of Engineering Controls include:

key control;

remote interlock;

beam enclosures;

protective filter installations.

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Administrative controls

Administrative and Procedural Controls are intended tosupplement Engineering Controls to ensure that laserpersonnel are fully protected from laser hazards.

Administrative/Procedural Controls include:

information, instruction and training;

signage;

protocols

arrangements for maintenance;

arrangements for servicing.

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Signage

Class 1

CLASS 1 LASER PRODUCT

Class 2 LASER RADIATION

DO NOT STARE INTO BEAM


Class 2M LASER RADIATION

DO NOT STARE INTO BEAM OR VIEW

DIRECTLY WITH OPTICAL INSTRUMENTS

CLASS 2M LASER PRODUCT

Class 3B LASER RADIATION

AVOID EXPOSURE TO BEAM

CLASS 3B LASER PRODUCT

Class 4 LASER RADIATION

AVOID EYE OR SKIN EXPOSURE TO

DIRECT OR SCATTERED RADIATION


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Personal Protective Equipment

Personal protective equipment should only be usedwhen the above measures do not provide sufficientcontrol.

Personal protective equipment includes:

protective eyewear; and

protective clothing.

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Laser eye protection

Selection of eyewear shouldbe based on:

wavelength(s) being used

radiant exposure;

maximum permissible exposure(MPE);

optical density of eyewear;

visible light transmissionrequirements;

adequate peripheral vision;prescription lenses; and,

comfort.

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College Procedures

The Colleges High Power Laser Safety Policy requires

all work with Class 3B and Class 4 lasers to be subjectto protocols approved by Heads of Department and tocomply with British Standard BS EN 60825.

There is a supporting Code of Practice which describesthe Colleges requirements for:

preparation and approval of protocols;

registration of Designated Areas, users and equipment; and,

the need for the lowest class of laser to be used.

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Protocols

Protocols should be developed and implemented beforeany use of Class 3B and Class 4 lasers.

Protocols should describe:

the use of the laser;

the Designated Area being used

the laser(s) being used;

the training and competence of the user(s)

the use of personal protective equipment;

any departure from standard conditions.

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Designated Areas

Areas where Class 3B andClass 4 lasers are used mustbe registered with theCollege Safety Unit.

A sign must be affixed nearto the entrance of eachDesignated Area and containthe details of the person

responsible for the area,emergency contacts and thename of the DepartmentalLaser Safety Officer.

DESIGNATED AREACLASS 4 LASER HAZARDNO ENTRY WHEN WARNING LIGHT IS ON

Departmental Laser Safety Officer:

Emergency contact numbers:1)

2)

PERMIT-TO-WORK REQUIRED

Person Responsible for this area:

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Laser equipment registration

All lasers must be registeredwith the Departmental LaserSafety Officer and the CollegeLaser Safety Officer.

The form includes a checklistof the precautions required foreach class of laser.

IMPERIAL COLLEGE OF SCIENCE, TECHNOLOGY & MEDICINE

REGISTRATION OF LASER EQUIPMENT

All lasers, except Class 1, must be registered with the Departmental Laser Supervisor and the College Laser Safety Officer.

Supervisor - it is your responsibility to complete this form, keep a copy for your records and return copies to:

(1) Safety Director, 14 Prince's Gardens (2) Departmental Laser Supervisor (3) Technician Head of Section.

Supervisor Name (Block Capitals): ________________________________________________________________ Phone No: ________________________________

Laser Details(tick or complete entries, asappropriate):

Department: Laser identification number (issued by the Department):

Precise Location (building, roomnumber, location):

Equipment Make: Model: Specification:

Class 2 up to 1mW continuous (visible) Visible or UV or IR

Class3A up to 5mWcontinuous(visible)and 25Wm-2

Portable or Fixed

Class 3B* up to 5mW (visible) Continuous or Pulsed

Class 3B** up to 500mW Name of key holder - Classes 3B**, 4 and 1E

Class4 above 500mW

Class1E fully enclosed

Briefdescription ofwork:

The table belowin dicatesthe precautions required for each classo f laser and istaken fromCVCP Notes of Guidance Part 2:1 Lasers(1992 ). It will be used by the Departmental

Laser Supervisor to monitor laser safety. An unshaded block denotesthat action isreq uired.

Precautions Class 2 Class 3A Class 3B* Class 3B** Class 4 Class 1 (E)

Remote Interlock

Key Control

Emission Indicator

BeamShutter

BeamStop

BeamLevel

BeamEnclosure

Eye Protection

Protective Clothing

Eye Examinations

Training

Laser Labels

Door Signs

Signature of Supervisor: _______________________________________________________________________________ Date: ____/____/_____

Signature of Departmental Laser Supervisor: _____________________________________________________________ Date: ____/____/_____

May 94

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Laser user registration

All laser users must beauthorised and must beregistered with the CollegeLaser Safety Officer.

Before a user is registered theyshould have had an eye testand attended the Introduction

to Laser Safety course.

IMPERIAL COLLEGE OF SCIENCE, TECHNOLOGY AND MEDICINE

REGISTRATION OF LASER USER

All laser users must be authorised by the Head of Department or the Departmental Laser Supervisor.

Supervisor - it is your responsibility to ensure completion of this form, keep a copy for your records and return copies to:

(1) Safety Director, 14 Prince's Gardens (2) Depa rtmentalLaser Supervisor (3) Technician Head of Section.

Name of Laser User (Block Capitals): _________________________________________ Phone No: ____________________

Department: ______________________________________________________________________________________________

Supervisor Name (Block Capitals): _________________ _________________ _________________ _____________Phon e No:

________________________________

Us er is (pl ea se cir cl e) : A. U nde rg ra du ate C . R es ea rc h Assis ta nt E. Aca de mi c

B. Pos tg raduate D. Techn ician

Details of laser(s) User is authorised to use:

Laser Number Class and Type Laser Number Class and Type

To be completed by the User

Have you attended the College Laser Safety Officer's lecture on laser safety (see Note 2 below)? YES / NO

I f " No ", ha ve you spoke n to the Dep ar tm en ta l Las er Supe rvis or abo ut la se r sa fet y? YES / NO

Have you had an eye test - Users of Clas s 3B** and Clas s 4 lasers on ly (see Note 3 below)? YES / NO

H av e y ou re ad th e C ol le ge La se r S af et y P ol ic y a nd Co de of Pr ac ti ce (s ee No te 4 b el ow )? Y ES / N O

Notes:

1. Specify Laser Identification Number (issued by the Department), Class and Type (e.g. He - Ne).

2. All new laser users should attend the lecture given by the College Laser Safety Officer. This takes place annually inNovember. If you wish to start using a laser before that date, or miss the lecture, then you must talk to the Departmental

Laser Supervisor about laser safety training before starting work with lasers.

3. All users of lasers classified as 3B** or 4 must have an eye test before starting work with the lasers and on its

completion. Long term users should have an eye test every three years. Eye tests must be carried out by an Appointed

Optician arranged through the College Health Centre.

4. Copies of the Policy and Code of Practice have been sent to all supervisors of laser work.

Signature of User: ________________ _________________ _________________ ________________ _ Date: ____/____/ ____

Signature of Supervisor: _______________ ________________ _________________ ______________ Date: ____/____/ ____

Signature of Departmental Laser Supervisor: _________________ ________________ ___________ Date: ____/____/ ____

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Eye test

Current arrangements at the Collegerequire all users of Class 3B andClass 4 lasers to have a laser eye

test before starting work with lasers.

A medical examination by a qualifiedspecialist should be carried outimmediately after an apparent orsuspected injurious ocular exposure.

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College Laser Safety Officer

The College Laser Safety Officer monitors departmentalarrangements and assists departments by:

providing expert advice;

reviewing protocols

maintaining central registers of Designated Areas, users andlaser equipment;

providing training; and,

investigating accidents.

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Accident Reporting Procedures

All incidents or accidents involving the use of lasers mustbe reported to the Safety Unit as soon as possible.

Any individual who may have been exposed to damaginglaser radiation must be referred for assessment of any

damage, preferably within 24 hours of the incident.

Certain accidents may be reportable to the Health andSafety Executive, including:

an accident involving a student which results in them being taken

to hospital for treatment; an accident which causes a specified major injury, which

includes temporary or permanent loss of sight.

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Legislation

There is no specific legislation in the UK regarding theuse of lasers.

However, the following regulations do have to becomplied with:

Management of Health and Safety at Work Regulations 1999

Provision and Use of Work Equipment Regulations 1998

Personal Protective Equipment Regulations 1992

Control of Substances Hazardous to Health Regulations 2002

Electricity at Work Regulations 1989 Reporting of Injuries, Diseases and Dangerous Occurrences

Regulations 1995

Health and Safety (Safety Signs and Signals) Regulations 1996

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Further training and supervision

Please remember this course has only been anIntroduction to Laser Safety.

Further information, instruction, training and supervision

needs to be given by your supervisor.

Documents

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