Department of Physics

Safe use of Class 3B and 4 Lasers

2012

Duncan McCallumHealth and Safety Coordinator

Introduction

Introduction to Safe use of Class 3B

and 4 Lasers In Physics

• Departmental Laser safety officer

Prof A.P. Monkman

• Health and safety co-ordinator

Duncan McCallum

Class 3B and 4 Laser

• Class 3B and 4 Laser use in Physics

• These lasers present a HIGH level of HAZARD

• Potential of injury to eyes and skin

• Eye Damage is usually irreversible

Health and Safety

• Failure to follow the Universities policies can result in serious consequences in terms of :-

• Personal injury to oneself and others• Legal liability for individuals and for the

university• In serious cases prosecution by the HSE

LASER

LASER stands for:• Light• Amplification by the• Stimulated• Emission of• Radiation

Laser Light

Laser light presents a particular hazard as it– is monochromatic, unlike ordinary light which is made of a

spectrum of many wavelengths. Because the light is all of the same wavelength, the light waves are said to be synchronous.

– is directional and focused so that it does not spread out from the point of origin.

Synchronous,monochromatic, directional

light waves

Asynchronous, multi-directional light.

Lasers Description

• Lasers can be described by:• which part of the electromagnetic spectrum is

represented:– Infrared– Visible Spectrum– Ultraviolet

• the length of time the beam is active:– Continuous Wave– Pulsed– Ultra-short Pulsed

Laser types

• Continuous wave operation

A beam whose output power is constant over time. Such a laser is known as continuous wave (CW). • Pulsed operation

Pulsed operation of lasers refers to any laser not classified as continuous

wave, so that the optical power appears in pulses of some duration at some repetition rate.

Laser labels

• Lasers must be labelled with the following• All types must display this label close to where the

beam is emitted

• Plus Class 3B Class 4

Laser Labels

All laser products, except for low power Class 1 devices, must describe the following details on an explanatory label :-

• maximum output • emitted wavelength • whether laser beam is visible, invisible or both • pulse duration (if appropriate) • name and publication date of classification

standard

Laser Labels

Some lasers will have US classification The classes do not directly correspond with EEC Classification

Check name and publication date of classification standard

Common Causes of Laser Accidents

Alignment

• Alignment

High voltag

e

• High voltage

Eyewear

failure

• Eyewear failure

Nonbeam

Hazards

• Nonbeam Hazards

No Eyewe

ar

• No Eyewear

Malfunction

• Malfunction

Accidental

exposure

• Accidental exposureImprop

er restoration of laser after

servicing

• Improper restoration of laser after servicing

BEAM HAZARDS- EYE DAMAGE

Eye damage caused by a class 3B/4 laser beam is usually PERMANENT Injury can result from exposure to:

- direct beam- specular reflection- diffuse reflection or beam

- Damage dependent on:- Intensity - lens of eye can focus beam onto the retina - Wavelength - absorbed by different parts of the eye

- Duration - can occur in a fraction of a second

Specular Reflection

Specular reflection is a reflection from a mirror-like surface. A laser beam will retain all of its original power when reflected in this manner.

Note that surfaces which appear dull to the eye may be specular reflectors of IR wavelengths.

Types of Reflection :- Specular Reflection

Diffuse reflection is a reflection from a dull surface.

Note that surfaces that appear shiny to the eye may be diffuse reflectors of UV wavelengths.

Diffuse Reflection

Types of Reflection :- Diffuse Reflection

Laser Wavelength Region

IR-C = 1 mm to 1400 nm

IR-B = 3000 nm to 1400 nm

IR-A = 1400 nm to 700 nm

Visible light = 700 nm to 400 nm

UV-A = 400 nm to 315 nm

UV-B = 315 nm to 280 nm

UV-C = 280 nm to 100 nm

Absorption of Light by the Eye

Lens

Cornea

Retina

Mid and Far IR(1400 nm-1 mm)

Mid UV (180 nm-315 nm)

Near UV(315 nm-400 nm)

Visible and Near IR(400 nm-1400 nm)

Retinal Hazard RegionThe wavelength range of light we can see is only 400 – 760 nm but light in the range 400 to 1400 nmcan enter the eye

The eye can focus a collimated beam of lightto a spot 20 microns in diameter on the retina(called the focal point).

This focusing ability places the retina at risk when exposed to laser light in the wavelength range 400 to 1400 nm because even low wattage laser light can impact the retina with 100,000 times the radiant power that entered the eye. Because of this optical gain, laser light in the 400 – 1400 nm is referred to as the Retinal Hazard Region.

This is important to remember when working with infrared lasers, because the retina can be injured even though the laser is invisible.

Biological Hazards - Retina

• Thermal damage (a thermal burn) to the retina occurs in the Retinal Hazard Region (from 400 nm – 1400 nm).

• Photochemical damage is severe at shorter visible wavelengths (violet & blue) and is cumulative over a working day.

• Acoustic shock from exposure to high energy pulsed lasers induce shock waves that cause tissue rupture and results in physical tissue damage.

Biological Hazards – Cornea & Lens

• Ultraviolet and far-infrared laser radiation is absorbed at the cornea or lens

• Inflammation injury to the cornea is caused by ultraviolet (UV) wavelengths (200-400 nm). This is the same type of injury that is caused by snow blindness.

• Chronic exposure can cause cataract formation in the lens of the eye. At high intensities, immediate thermal burns occur, while lower exposures may lead to the development of cataracts over a period of years.

Cornea

Lens

Corneal injury from CO2 laser

Retinal injury from a dye laser

Examples of EYE Damage

Protect Your Eyes!

In a fraction of a second, your vision can go dark.

Biological Hazards - Skin

• Ultraviolet (UV)– UV can cause skin injuries comparable to sun burn.

– As with damage from the sun, there is an increased risk for developing skin cancer from UV laser exposure.

• Thermal Injuries– High powered (Class 4) lasers, especially from the

infrared (IR) and visible range of the spectrum, can burn the skin and even set clothes on fire.

Non-Beam HazardsNon-beam hazards refer to anything other than the laser itself that can create a hazard. This type of hazard includes:• Electrical Hazards

Use caution when working on or near the high-voltage power supplies used for high-power Class 3 and 4 lasers; there is sufficient voltage in these power supplies to injure or kill.

• Fire HazardsHigh powered Class 4 lasers will easily ignite flammable materials (such as paper or flammable liquids

• Laser Generated Air Contaminants (LGAC)interaction of laser beam with target material can result in the production of toxic

chemicals

• Compressed Gases• Chemical Hazards• Collateral and Plasma Radiation• Noise

Laser User Responsibilities

• To undertake risk assessments and complete all safety documentation

• To follow laboratory administrative, alignment and standard operating procedures while operating lasers.

• Keep the Principal Investigator/Supervisor fully informed of any departure from established safety procedures. This includes notification of an exposure incident.

• To attend the Departments Laser Safety Training program or view the on-line Laser Safety power point training

Laser Tables• The experiment layout must be designed to keep

the beam parallel to and within the confines of the optical bench as far as is reasonably practicable

• All periscopes, or other features where the beam leaves the plane of the bench, have to be fitted with fixed covers to prevent accidental viewing of the beam and mirrors being rotated out of alignment

• A barrier must be fitted around the edge of the table to contain the beam

Laser Tables • Be aware of the need for good housekeeping both

on the optical bench and the surrounding floor area.

• There should be NO tools or loose optics on the table, use a tool trolley or tray.

• There should be no visual displays on the table laptops ,monitors etc.

• Be aware of the risks of reflections from tools, rings, watches, etc.

Take them off or cover them

PPE for Eyes

Personnel Protective Equipment (PPE) for eyes exposed to Class 3B or 4 lasers is mandatory. Consider these factors when selecting eyewear:

– Optical Density (OD) of the eyewear– Laser Power and/or pulse energy– Laser Wavelength(s)– Exposure time criteria– Maximum Permissible Exposure (MPE)– Filter characteristics, such as transient bleaching

EN207 L Number

• EN207 L Number• These numbers are used by laser safety goggle

manufactures to specify the level of protection they afford.

• The numbers define the minimum optical density and the maximum energy or power density that the goggle can withstand

• On log scale so L2 10x L1 • Can also have a prefix specific to type of laser output

referring to pulse lengths

MPE

Maximum Permissible exposure • This is the level of laser radiation that a

persons eye or skin may be exposed to without suffering adverse effects.

• The level is determined by the wavelength, duration of exposure ,the size and divergence of the source

N.O.H.D.

The Nominal Ocular Hazard Distance

(NOHD), is the minimum distance from the laser emitter along its optical axis at which no hazard exists to the human eye. An observer at this point or further away would have no adverse eye effects.

Accessible Emission

Accessible Emission • This is the level of laser radiation that a

person will be exposed to at the closest accessible point of the laser beam

Laser classification

Divided into the following class

es

• Class 1• Class 1M• Class 2• Class 2M• Class 3R• Class 3B• Class 4

• Class 1• A Class 1 laser is safe for use under all

reasonably-anticipated conditions of use; in other words, it is not expected that the MPE can be exceeded. [Comment: This class may include lasers of a higher class whose beams are confined within a suitable enclosure so that access to laser radiation is physically prevented.]

Class 1M

• Class 1M• Class 1M lasers produce large-diameter

beams, or beams that are divergent. The MPE for a Class 1M laser cannot normally be exceeded unless focusing or imaging optics are used to narrow down the beam. If the beam is refocused, the hazard of Class 1M lasers may be increased and the product class may be changed.

Class 2

• Class 2• A Class 2 laser emits in the visible region.

It is presumed that the human blink reflex will be sufficient to prevent damaging exposure, although prolonged viewing may be dangerous.

Class 2M

• Class 2M• A Class 2M laser emits in the visible

region in the form of a large diameter or divergent beam. It is presumed that the human blink reflex will be sufficient to prevent damaging exposure, but if the beam is focused down, damaging levels of radiation may be reached and may lead to a reclassification of the laser.

Class 3R

• Class 3R• A Class 3R laser is a continuous wave

laser which may produce up to five times the emission limit for Class 1 or Class 2 lasers. Although the MPE can be exceeded, the risk of injury is low. The laser can produce no more than 5 mW in the visible region.

Class 3B

• A Class 3B laser produces light of an intensity such that the MPE for eye exposure may be exceeded and direct viewing of the beam is potentially serious.

• CW emission from such lasers at wavelengths above 315nm must not exceed 0.5 watts.

Class 4• Class 4 lasers are of high power (typically up to

500 mW or more if CW, or 10 J cm-2 if pulsed). • These are hazardous to view at all times, may

cause devastating and permanent eye damage, may have sufficient energy to ignite materials, and may cause significant skin damage.

• Exposure of the eye or skin to both the direct laser beam and to scattered beams, even those produced by reflection from diffusing surfaces, must be avoided at all times. In addition, they may pose a fire risk and may generate hazardous fumes.

Laser Safety

Department has strict policy which must be compiled with

Usage of class 3B and class 4 lasers will be monitored by the Laser Safety Subcommittee via periodic inspections.

An internal prohibition notice will be served on any person or Group found to be using lasers in an unsafe manner.

The prohibition notice will only be lifted once the control measures described in this document have been fully implemented

Signage

• Warning sign on the door of the laser laboratory

• Should have emergency contacts• All laser users should be named• Laboratory should have door interlocked

illuminated sign • First aid advice specific to laser accidents

should be displayed in the Laboratory

Departmental Laser Sign

Engineering Controls• Engineering controls are measures that are incorporated into

the laser system and are designed to prevent injury to personnel. Engineered safety controls are preferable to PPE or Administrative controls.

• Examples include– Protective housings– Interlocks on Removable protective housings– Service access panels– Key control master switch (Class 3B & 4)– Viewing Windows, Display Screens, Collecting Optics– Beam path enclosures– Remote interlock connectors (Class 3B & 4)– Beam Stop or attenuator (Class 3B & 4)

Physics Laser safety policyLaser safety policy This document contains• 1. Laser worker registration form,

This should be completed by any person whose work involves a class 3b or 4 laser.

• 2. Laser registration form,

A separate laser registration form is required for each class 3B or class 4 laser.

• 3. Laser controlled area registration form,

Only one laser controlled area registration form is required for each area but the form should be reviewed and updated if necessary whenever a new laser is put into use.

• 4. Pro-forma risk assessment,

A risk assessment is required for each experiment making use of class 3B or class 4 lasers it is recommended that separate assessments are carried out for the alignment and normal use stages of the experiment. Unmodified copies of the generic risk assessment are not acceptable

• 5. Pro-forma safe method of work.

Each authorised user should sign a copy of the safe method of work

Laser Worker Registration Form,

All persons who intend to work with lasers of Class 3B or above must register as laser workers and sign the declaration that they have read and understood the Local Rules and the University Health and Safety Manual Section L1

Laser Safety Policy Statement

• Outline of safety policy• Requires that ULSO is notified of all class

3b and 4 lasers• Laser supervisors should be familiar with

CVCP code of practice and Pd IEC TR 60825-14 :2004

• AURPO Guidance Note No. 7 “Guidance on the Safe Use of Lasers in Education & Research”.

Laser Controlled Area Registration form

• Filled in by laser supervisor • Copy available to all laser users• Submitted to ULSO • Must be regularly reviewed

General risk assessment

• University risk assessment form• Completed by every laser user with

assistance of supervisor• Form plus guidance on completion on

University H&S website

Class 3B and 4 Laser Registration Form

• Filled in by laser supervisor • Copy available to all laser users• Mpe calculation

Safety Co-ordinator has copy of a software package to produce the calculations

• Submitted to LSO

Safe method of working

• Provides guidance on safe working with lasers

• Requires knowledge of AURPO Guidance Note No. 7 “Guidance on the Safe Use of Lasers in Education & Research”.

• Requires viewing of NPL Laser Safety training DVD

• requires signature of laser user

What do with the forms

• One copy of forms to be retained by laser user

• One copy to be displayed in relevant laser area

• One copy to be forwarded to Safety Co-ordinator