08/06/2006 Laser safety 1

Laser safety Introduction

B. Fischer

T-ray group meeting 08/06/06

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Motivation

It might appear unnecessary Our lab is safer than most other T-ray lab in the world

but:

Regular training is required by law Initial laser training for new staff Gives you the opportunity to become aware again of some issue Possibility to reflect on your practice

finally: You have only two eyes !

source: http://www.adrenotex.de/augenklappe.htm

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In older times

Why do pirates

wear patches?

sources: http://en.wikipedia.org/; http://www.stuckiag.ch/shop/de-ch/dept_380.html

navigators had to stare into

the sun if using a sextant

intense light damages your eyes!

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Eye damage – 400-1400 nm

retinal burn: (irreparable) damage

Visible and near-infrared light enters

the eye and is focused tightly on the

retina (10-25 m diam).

cw and long-pulse lasers: mainly thermal, 400-600 nm also photochemical

even in VIS, only about

5% will be absorbed in

visual pigments

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Eye damage – 315-390 nm

Light penetrates to the lens and can cause damage here

(photochemical cataract)

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Eye damage – 180-315nm and >1400nm

photokeratitis, corneal burns (similar to sunburns)

light stopped by the cornea

(1.5 mm – 2.6 mm light penetrates in aqueous humour, large volume, rather eye-safe)

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Laser safety – other hazards

• Skin exposure

– Particularly high power and/or UV lasers

• Fire hazard

– Beams hitting flammable materials

• Electrical shocks

– Gas discharge lasers can operate with high voltage (kV) and high currents

(50-100 A)

• Chemical hazards

– Toxic laser materials

• Dyes and solvents

• Chemical lasers

there is a general understanding that

accidents of this kind greatly

outnumber eye strikes

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Laser safety legislation

• Legal Responsibilities – for employer & employee

Occupational Health & Safety at Work Act

Work Equipment Regulations

Management Regulations – risk assessments

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Australian Standards

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European Health & Safety Law

• Health & Safety at Work Act

The act places duties on both employers and employees It is criminal law and can be enforced against criminals and

organisations The act can be summed up as;

Employers duty: ‘To safeguard so far as reasonably practicable the health, safety and welfare of employees and others affected by the work’.

Employees duty: ‘To take reasonable care for the safety of themselves and others; to cooperate; not to be reckless’

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Typical Work Equipment Regulations

All equipment must be suitable

Maintained in an efficient state

Maintenance recorded

Restricted to trained users

Users must have information and training

Access prevented to dangerous parts

Adequate controls and lock-offs

Suitable environment

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European standards on laser safety

indicates safe working level for laser radiation

classification of lasers & laser products according to degree of hazard

labeling warnings

minimize accessible radiation, control measures

protection against non-radiation hazards associated with lasers

deals with lasers and laser products,

i.e. product or assembly of components which contain lasers or laser systems

E.g. compact disc players

includes also light emitting diodes (LEDs)

(modern LEDs are high-power, highly directional light sources)

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Reasoning behind classification

• Classification of laser determined by:

 Accessible Emission Limit (AEL)

Maximum level of laser radiation accessible over its full range of capability during operation at any time after its manufacture 

• To classify a laser, you need to know:

Laser wavelength

Exposure duration

Viewing conditions

• Each laser class has a set of safety control measures that manufacturers and users must obey

• Manufacturers should supply this classification (attention: slight differences between USA and Europe -> Australia?)

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Laser classification

Class 1 Safe under reasonably foreseeable operation

Class 1M Generally safe – some precautions may be required

Class 2 Visible light at low power, blink limits risk

Class 2M Visible light at low power, generally safe – some

precautions may be required

Class 3R “Low” risk for direct viewing of beam

Class 3B Viewing beam hazardous, diffuse reflections safe

Class 4 Hazardous under all conditions, eyes and skin

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Class 1 (safe) Safe under reasonably foreseeable conditions of operation, including the use

of optical instruments for intra-beam viewing

rather complex calculation, but rule of thumb for cw lasers

VIS (400-700): 0.39 mW

NIR/IR (700-1400): slowly increasing, e.g. 1.6 mW for 1 m

MIR (1.4 –4 m) 10 mW (“eye-safe” communication)

FIR (> 4 m) 1000 W/m2 measurement area: normally iris with diameter 7 mm

A product may contain high power laser with higher classification, if

effective engineering controls restrict routine exposure to Class 1 AEL• CD, laser printers• possibly machining, etc.• in lab: cleverly set up spectrometer (?)

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Class 1M

New class, mainly for EN60825-2 regulations to deal with

fibres (communications) & LEDs

Wavelength range 302.5 nm to 4 m

Generally these lasers are as “safe” as Class 1

Except for diverging or large area beams when collecting optics

used

These large beams may be focused to a spot of sufficient

intensity to cause damage to the retina

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Class 2 (low power)

Max output – 1 mW

Visible only: 400 nm to 700 nm

Blink response of eye affords protection (0.25 s)

E.g:

Supermarket scanner

many HeNe laser, some laser diodes

legal laser pointers

note: recent research questions reliability of blink reflex

consider also fatigue, alcohol, drugs, ...

Class 2M divergent or broad-aperture sources, which meet Class 2

standard without additional optics

OK if collecting optics not used

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Class 3R (low to medium power)

Direct intrabeam viewing is hazardous, but risk is lower than for 3B

wavelength > 302 nm

maximum AEL 400-700 nm = 5 times AEL of class 2, i.e. 5 mW

maximum AEL at other = 5 times AEL of class 1

E.g:

Surveying equipment

many laser pointers

Some HeNe and laser diodes in teaching & research labs

there is no class 3A anymore

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Class 3B (medium power)

Max output - 0.5W (500 mW)

Includes all visible and non-visible lasers

Direct intrabeam viewing is always hazardous

Viewing diffuse reflections is normally safe provided: Eye is not closer than 13 cm from diffusing surface Exposure duration is less than 10 seconds

e.g. • many laser diodes• small solid-state lasers• small ion lasers

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Class 4 (high power)

> 500 mW

capable of producing hazardous diffuse reflections

capable of producing also skin burns and fire hazards

e.g.• most solid-state lasers• laser diode bars, some single emitters• most ion lasers

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(Repetitively) Pulsed lasers

exposure from any single pulse shall not exceed AEL for single pulse

AEL depends on pulse duration, wavelength, ...

average power of a pulse train of duration T shall not exceed the AEL for a

single pulse of duration T

for wavelength larger than 400 nm (thermal limits):

average pulse energy shall not exceed single pulse AEL times correction factor

AE train = AELsingle N–0.25 N number of pulses

(by the way, there are more details to it)

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Consequences

• appointment of laser protection officer (invisible class 3R, 3B, 4)

• labelling

• training (class 1M, 2M, 3R, 3B, 4)

• protective enclosures where applicable, access restrictions

•interlocks (class 3B and 4)

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Labelling

Labels for laser user & laser servicer

Correct labels should be provided by manufacturer

If size or design of laser makes labeling impractical (e.g. laser diode),

put it on the mount or base.

(only in rarest circumstances labels should be included only with user

information or placed on package)

Laser starburst warning label

on all laser products of Class 2 and above

Access panels, Safety interlocked panels

Should be labeled if access to laser radiation in excess of the AEL for Class 1/1M is possible on their removal or over-riding

source: http://www.lasermet.com/labels/labels-updated.html

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Labelling II

source: http://www.lasermet.com/labels/labels-updated.html

every laser needs a label with warning level increasing with class

e.g. class 2

e.g. class 3R

lasers of class 3R, 3B, 4 need labelling of aperture

if radiation is outside the 400-700 nm range, “laser radiation” needs to be

replaced by “invisible laser radiation” or “visible and invisible laser radiation”

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MaiTai -> Class 4 laser

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Laser safety – University policy

Appointed Laser Safety Officer (LSO)

All lasers (3R, 3B, 4) must be registered(?)

All lasers and users conform to Australian Regulations

Risk assessment & safe method of work completed at workplace

All laser users must attend risk assessment & safe method of work

briefing

The supervisor (Bernd or Tamath) overseeing the laser project must

ensure safe working practices as followed

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Practical laser safety

There is a hierarchy of controls to ensure the safe use of lasers:

• Risk Assessment and Safe Method of Work (1) Engineering controls (2) Administrative controls (3) Personal protective equipment (PPE)

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Engineering controls

To Restrict exposure to laser radiation use: 

Housings Put the laser in a box if applicable Enclosures Use tubing on (long) laser runs

Beam stops Block beams as soon as is possible Interlocks Prevent unauthorised access to danger Warning lights Informs others of the possible danger

remote sensing align beams without danger

Advantage: improves stability and reduces contamination

Disavantage: Not applicable in laminar flow conditions

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Engineering controls II

Controls should not be over restrictive and hamper ease of working

Never bodge and no temporary fixes

It compromises safety

but also:

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Administrative controlsBut: Engineering controls may not provide adequate protection in

cases such as: 

Phases of research when laser system is being commissioned

Servicing of laser equipment

Manufacture or research into laser design

Laser alignment

Special projects: waveguides, near-field, dynamis

In these situations:

Use Administrative controls to minimise risk

so essentially in

many, but not all

situations we are

working in

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T-ray labs around the world

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It’s also about communication

Clear instructions?Clear instructions?

Clearly understood?!Clearly understood?!

Actually, your colleagues in the lab are

often more at risk, if you do something

dodgy, than you are, because they do

not know that you are going to do it.

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Examples for administrative controls

Warning Signs & Notices Prominently displayed – clear and unambiguous Labels at entrances to lab or workshop containing Class 3B or 4 laser

Laser Controlled Area (Class 3B or 4 laser)Restricted to authorized personsBy physical means: walls & doors, Locks or number pads

Key Control  Class 3B & 4 laser keys removed when not in useKept secure in key cabinet to which authorized users only have access

Training Only trained persons allowed to use 1M, 2M, 3R and the more 3B and 4 lasers

Maintenance & Service Manuals  Must be available and easily accessible to laser users

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Personal protective equipment (PPE)

Laser safety goggles

• required for Class 3R outside of 400-700 nm window, 3B and 4

• saves us in teaching labs, if everything else is ok, i.e. direct beam

viewing is not possible due to engineering controls

Fire resistant clothing, gloves, overalls

• against hazards associated with lasers (noise, chemical etc)

• Protective clothing when exposure to radiation exceeding maximum

permissible exposure for skin (MPE), i.e. possibly strong class 4 lasers

use during

• alignment or open beam experiments

• maintenance and servicing

Used only when: Risk of injury or harm can not be suitably minimised by engineering controls etc

Employers are obliged to

provide employees with PPE!

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Goggles Purpose: to reduce level of incident laser radiation upon cornea to below MPE

maximum permissible exposure,

essentially: make it a class 1 laser!

Filter: Sufficient optical density (OD) to attenuate incident radiation to MPE

rule of thumb 0.4 mW – some mWs, but check your wavelength and conditions

(OD of 5 means that a filter transmits less than a part in 105 at that wavelength)

Legal requirement to comply with:

Personal Protective Equipment Product Directive (89/686/EEC) July 1995

European Standards;

EN207:1998 Filters & equipment used for personal eye protection against

laser radiation 

EN208: 1999 Personal eye-protectors used for adjustment work on lasers

and laser systems VIS, 400 – 700 nm, attenuation to < 1 mW

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Markings on goggles

Wavelength or wavelength range in nm against which protection is afforded

Scale No or lowest scale No if protection against a spectral range is afforded

The manufacturers identification mark

Test mark of the inspection body (CE or possibly DIN for rather old goggles)

In order to meet legal requirements, the goggles need to be marked with

scale number

corresponds to

optical density

Marking with OD alone is NOT sufficient ! The scale number confirms that the

filter withstands at least 10 s and that also the frame does not disintegrate

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Frames of goggles

sources: Lasermet, Laservison

balance between optimal safety and acceptance by the user

(what happens with prescription glasses?)

high safety

(TOPS)

possibly weak

points at sideok

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Practical laser safety again

If you do not find

at least eight

safety flaws in

here contact me

(discreetly)

wrong

brand?