Laser Classification, Hazards & Controls
Contents:
 Laser Classification
 Eye And Skin Damage From Lasers
 Laser Signage
 Non-Beam Hazards
 Control Of Hazards: Engineering Controls
 Control Of Hazards: Administrative Arrangements
 Control Of Hazards: Personal Protection Equipment
LASER CLASSIFICATION
Class 1: Safe, max power 0.4 mW CW e.g CD players, printers
These lasers cause no damage to both the eyes and skin under reasonably
foreseeable circumstances and therefore can be treated as totally safe.
Class 2: Low hazard, max power 1 mW CW e.g. supermarket scanner
Only emit radiation in the visible region (400-700 nm). These lasers are safe to the
skin and cause no damage to the eye as long as the exposure time is less than 0.25
seconds i.e. the aversion response (time it takes to look away).
Class 1M & 2M: Both considered low hazard, but contain magnifying optics, class
takes into account amount of beam that can enter the eye.
Class 3R: Low-medium hazard, max power 5 mW CW e.g. surveying equipment
Direct exposure to the beam of a Class 3R laser is potentially hazardous so must be
treated with respect, however the risk is lower than that for the Class 3B products.
Class 3B: Medium-high hazard, max power 500 mW CW e.g. HeNe
These lasers have sufficient intensities to cause eye damage through the direct
beam but diffuse specular reflections (see below) are safe, as long as exposure time
is less than 10 seconds and the eye is no closer than 13 cm from the diffusing
surface. Systems containing Class 3B lasers should be sufficiently interlocked to
eradicate any open beam exposure. If it is necessary to override the interlock for
alignment purposes, the amount of open beam exposure should be minimized as
much as possible and the relevant eye protection must be worn (check that the
wavelength range if the eye protection is correct for that laser).
Class 4: High hazard, power > 500 mW CW or pulsed (no upper limit) e.g. Nd-Yag
These lasers have sufficient intensities to cause eye damage both through the direct
beam and specular reflections (see below). These lasers also have an associated fire
hazard. Extreme caution must be used when using these lasers. Systems containing
Class 4 lasers should be sufficiently interlocked to eradicate any open beam
exposure. If it is necessary to override the interlock for alignment purposes, the
amount of open beam exposure should be minimized (as described fro Class 3B).
Reflections. There are two principle types of laser reflection:
•
specular reflection - these occur from mirror-like surfaces. The incident beam
striking a specularly reflecting surface will leave it essentially unchanged.
•
diffuse reflections - these occur from rough surfaces such as paper or mattpainted walls. These reflections bear no relation to the direction of the incident
radiation.
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EYE AND SKIN DAMAGE FROM LASERS
The damage caused to the eye and skin by a laser varies with wavelength. Users of
lasers should be aware of the damage that can be caused by the wavelength region
they are working in. The most serious damage to the eye is caused by wavelengths
of 400-1400 nm, which affects the retina (known as the Retinal Hazard Region). The
skin can be burnt by wavelengths above 315 nm (far UV to IR). The tables below
summarise the regions of the eye affected by UV/Vis/IR (Table 1) and the effects that
radiation will have on the eye and skin (Table 2).
Table 1 – Summary of areas of the eye affected by radiation
Spectral region
UV-C
UV-B
UV-A
Visible
IR-A
IR-B
Wavelength range
100-280 nm
280-315 nm
315-400 nm
400-700 nm
700-1400 nm
1400-3000 nm
IR-C
3000 nm -1 mm
Area of eye affected
Surface of cornea
Absorbed by cornea
Lens
Retina
Retina
Absorbed by cornea & penetrates
aqueous humor
Absorbed by cornea
Table 2 – Summary of laser beam hazards to the eye and skin
Spectral region
UV-C
UV-B
Effects on the eye
Photokeratitis (milky
white cornea)
UV-A
Visible
Photochemical cataracts
Photochemical and
thermal injury to retina
Cataract, retinal burns
Aqueous flare, cataract,
corneal burns
Corneal burns
IR-A
IR-B
IR-C
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Effects on the skin
Erythema (sunburn)
Accelerated skin ageing
Increased skin pigmentation
Skin darkening
Photosensitive
reactions
Skin burns
LASER SIGNAGE
Every laser product higher than Class 1 should be clearly marked with the laser
hazard sign and a label indicating the class, power and wavelength (Table 3)
Table 3: Signage required for laser products.
Class 1
CLASS 1 LASER PRODUCT
Class 1M
LASER RADIATION
DO NOT VIEW DIRECTLY WITH
OPTICAL INSTRUMENTS
CLASS 1M LASER PRODUCT
Class 2
LASER RADIATION
DO NOT STARE INTO BEAM
CLASS 2 LASER PRODUCT
Class 2M
LASER RADIATION
DO NOT STARE INTO THE BEAM
OR NOT VIEW DIRECTLY WITH
OPTICAL INSTRUMENTS
CLASS 2M LASER PRODUCT
Class 3R
LASER RADIATION
AVOID DRIECT EYE EXPOSURE
CLASS 3R 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
CLASS 4 LASER PRODUCT
Designated Laser Areas: The points of access to areas in which Class 3B or 4 laser
products are used must be marked with warning signs complying with BS 5378 and
the Health & Safety (Safety Signs and Signals) Regulations 1996. The signs shall
incorporate the following information:
1) hazard warning symbol
2) highest class of laser in the area
3) responsible person with contact details
N.B. Warning lights must always be on when lasers are in use
.
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NON-BEAM HAZARDS
Many regard laser radiation to be the main hazard of lasers but this is often not the
case. The main cause of accidents from lasers is electrocution from exposed
electrical parts during repair or adjustment. These associated hazards should not be
overlooked and details should be included in all risk assessments for laser based
work. A summary of non-beam hazards are summarized in Table 4.
Table 4: Summary of non-beam hazards
Type of
Hazard
Electrical
Source of Hazard
Comments
High voltage power supplies
Laser cavities
Chemical
Laser gases
Laser generated fume &
particulate matter
Cleaning fluids
Mechanical
Installation of gas cylinders
Moving tables
Cables and wiring
Noise hazard
Hot work pieces
Optical
Beam delivery system
Secondary emissions from
radiation-material interactions
Fire
Class 4 laser radiation
Combustion of work piece
Cleaning solvents
X Ray/EMI
Thyratron valves > 5 kV
Radiation/material
interactions
Laser cavities
A 2kW CO2 laser typically requires 100
A, 3 phase supply at 40 kW
No electrical work should be undertaken
by unqualified staff
Electricity at Work Regulations apply
Suitable extraction and filtration should
be in place
MSDS and COSHH assessments must
be available and complete
COSHH Regulations apply
Covered by Manual Handling Operations
Regulations
Fitting and location of services should be
considered
Appropriate guarding of machines
required
Appropriate protective clothing
Flight tubes, beam stops and fibre
delivery systems must be appropriate
materials, correctly mounted and
installed. Optical components should be
clean and securely mounted.
Ozone produced as part of plasma
production – usually extracted by fume
systems
Direct and diffuse laser beams from
Class 4 lasers can combust materials,
especially in oxygen rich environment.
Errant beams should be eliminated.
Enclosures should prevent stray
reflections causing damage
Safe use of chemicals & solvents
covered by COSHH Regulations
CO2 laser power supplies. Covers should
not be removed – trained service
personnel only.
High energy radiation interaction with
heavy metal targets can generate X-ray.
Electromagnetic Interference (EMI)
generated in radio frequency excited
lasers. Metallic casements and Faraday
cages.
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CONTROL OF HAZARDS
The control of hazards associated with lasers is described by a hierarchy of control,
the first level of which being the most important in avoiding accidents:
- Engineering controls
- Administrative controls
- PPE
Each will be described with details of procedures that must be followed for any
experiments involving lasers.
ENGINEERING CONTROLS
Laboratory design
The following considerations relate mainly to the use of Class 4 lasers but some may
be appropriate for Class 3B devices as well, or, as general specifications for a laser
laboratory.
1) If practicable the laser laboratory should have a high level of illumination that will
minimise pupil size and reduce the risk of stray laser light reaching the retina.
Windows may need to be covered or protected by blinds. These should be nonreflective and may need to be fireproof where higher-powered lasers are used.
2) Ventilation is important especially with higher-powered lasers if cryogens are used,
or if toxic fumes are produced that need to be extracted and in this case it is
important that the extraction is very close to the source. Facilities may also be
needed for the handling of toxic chemicals that are associated with some dye lasers.
3) The laboratory should be equipped with appropriate fire fighting equipment.
4) Electrical supplies, switch and control gear should be sited in order to: enable the laser to be shut down by a person standing next to the laser
 enable the laser to be made safe in an emergency from outside the laser area
if reasonably practicable
 prevent accidental firing of a laser
 provide an indication of the state of readiness of the laser
 enable personnel to stand in a safe place
 provide sufficient and adequate power supplies for all ancillary equipment and
apparatus so that the use of trailing leads is minimised.
Experimental set-up – key control
Before starting to use your laser there are a number of basic risk reduction measures
that should be considered.
1) If a lower powered laser can be used then it should. The experiment may lend
itself to lowering the output power of a laser if full power is not needed. Lasers should
be operated so that individuals are not exposed to levels in excess of the Maximum
Permissible Exposure (MPE) levels given in the current BS EN document. These are
the maximum amounts of laser radiation that are unlikely to cause harm to the eyes
or skin and can be established by calculation. In some cases appropriate
measurements using specific detectors/instrumentation may be necessary; if this is
the case then a suitably qualified person will be required to undertake the
measurements.
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2) Intra-beam viewing must be minimized by engineering design. This design should
include a fully interlocked casing around the laser (see below). EU legislation coming
into force in 2010 will mean that any open beam work on Class 3B lasers or above
will be illegal, thus the systems with these lasers should be totally enclosed.
3) Beam paths should be as short as possible, optical reflections should be
minimised and the beam terminated with an energy absorbing non-reflective beam
stop. This includes casing the laser with lead/lamented Perspex. These surfaces will
stop any beam escape for a short period of time, after which the laser will start to
burn the surface, which can be detected by the user and the laser shut down
4) Lasers should be securely fixed to avoid displacement and unintended beam
paths.
5) Powerful lasers should be aligned with low-power devices that are safe for
accidental viewing or with reduced power of the laser (by turning it down or
introducing neutral density filters). The aim should be to get the output power <1mW,
NB some kW lasers will only be able to be turned down to a few watts. If higher
power is needed then remote viewing techniques e.g webcam should be used.
6) Eliminate the chance of stray reflections - use coated optical components or
shroud them so that only the intended beam can be refracted or reflected. Keep the
optical bench free from clutter and remove jewellery, wristwatches etc.
7) Have the laser pointing away from the laboratory entrance.
PLEASE NOTE: Eye protection should be a last line of defense in protecting against
a direct eye strike. A properly interlocked system should negate the need to wear any
eye protection.
ADMINISTRATIVE ARRANGEMENTS
This section summarises the administrative arrangements that should be in force for
the control of laser safety. These arrangements are based on guidance from the
Users Guide associated with the BS EN 60825-1 standards (published as PD IEC TR
60825-14). This Users Guide suggests three aspects of the use of lasers that need to
be taken into account in the evaluation of a possible hazard and the application of
control measures:
i.
Capability of the laser or laser system to injure personnel
ii.
Environment in which the laser is used
iii.
Level of training received by personnel using the laser or who may be
exposed to its radiation.
Risk Assessments (RA’s): These are required for all laser related work and must
cover all details & hazards associated with the laser & experiment, considering the
points listed above. Before carrying out any laser-related work, details of the laser
(see “Inventory” below) and RA’s must be passed to the DLSO (see “Administrative
responsibilities” below). Anyone using the laser must have read & signed a hard copy
of the associated RA, which must be kept in the same lab as the laser.
Scheme of work: These must be written for all work with Class 2 lasers and above.
They must contain as much detail as possible about the protocol of the experiment
itself, including:
 descriptions of the activity
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


details of the laser(s) being used
authorized users
experimental set-up (with engineering controls in place to prevent an
accident)
 alignment procedures
 day-to-day safety checks
 maintenance
 adding new equipment to the set-up
Signed hard copies of the Scheme of Work must be kept in the lab relating to that
laser(s) and must also be passed to the DLSO.
Inventory: Details of every laser, including type, power and wavelength, must be
recorded in an inventory before any work using that laser can be carried out. This
must be updated whenever modifications are made or new laser equipment is added
to a set-up.
User Registration: Every laser user must be registered with the University and
Department. New users must be authorised to use lasers by completing the criteria
set out in the Training Record Form. This must be done to make people aware of the
hazards of lasers and to ensure that safe systems of work are being practiced. RA’s
and Schemes of Work should also identify users of lasers and a list/record must be
kept up. All people intending to work with any class of laser, except for inherently
safe Class 1 or 2 devices or embedded laser products such as those in laser printers
or CD players, should be identified. Persons who could or are going to modify Class
1M or 2M devices should also be identified, as they will require instruction/training.
Emergency sheet: A sheet containing details of the laser type, associated hazards
and emergency contacts MUST be kept by every laser. In the case of a direct eye
strike or burn, this sheet then provides the information on the correct course of
action. Emergency procedures must include details of a local Ophthalmic Hospital.
Any eye damage must be attended to within 24 hours and must be reported to the
HSE if the injury is serious or causes more than a 3 day absence from work.
Administrative responsibilities
Laser Safety Adviser (LSA)
The role of the Laser Safety Adviser is to provide advice and assistance to implement
the requirements of BS EN 60825 when Class 3 and 4 lasers are being used. The
LSA will liaise with the DLSO (see below) and may be consulted during the planning
and specification for the laser application and any related safety issues.
Departmental Laser Safety Officer (DLSO)
The Departmental Laser Safety Officer (DLSO) is responsible for ensuring that all
lasers used in the department are identified and used in compliance with the
University policy. The DLSO will ensure that:


all lasers except for low power Class 1 devices (excluding laser printers,
DVDs, Class 2 laser pointers etc) are identified
all lasers are labelled in accordance with Table 3 and laser designated areas
clearly identified
all hazards are identified and RA’s of laser work areas are appropriately and
accurately completed.
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



personnel intending to work with Class 3R, 3B and 4 lasers, and others who
may be working with modified Class 1M or 2M devices, are identified and
receive training in the safe use of lasers
laser safety eyewear are provided and worn (when appropriate) by all people
working with Class 3B and 4 lasers when the beam is not totally enclosed and
that training is given in the use and maintenance of this eyewear
all lasers in the department are used in accordance with the University policy
routine surveys are undertaken to ensure compliance with this policy.
If a survey reveals non-compliance with the standards and a potentially dangerous
situation, the laser should not be used until the situation has been remedied by the
adoption of additional control measures.
Responsibilities of Research Supervisor/Principal Investigator
The day-to-day Health and Safety Management of individual research projects is the
responsibility of the Principal Investigator (PI). All work involving hazardous lasers
MUST be covered by RA’s and where appropriate by written schemes of work and
protocols. There should also be procedures to ensure that lasers are made safe prior
to disposal and dealt with appropriately if they contain hazardous materials. The PI
should also ensure that their laser workers are effectively trained in the operating
techniques required and that inexperienced staff are adequately supervised.
Responsibilities of Laser Users
All users of lasers must have a full eye examination before starting to use any laser
application. This is to ensure the eye is in healthy state and allows the assessment of
any subsequent damage caused by a laser strike.
Laser users have a responsibility:




to observe the Local Arrangements and Schemes of Work applicable to the
lasers that will be used and to follow the guidance of supervisors and the
DLSO
not to leave a laser experiment running unattended unless a RA has
established that it is safe to do so
for their own safety and that of others who may be affected by their acts or
omissions
inform RS/PI of any medical condition that could be affected by lasers e.g.
epileptic fits which could be triggered by pulsed lasers
when working with Class 3B or 4 lasers and there is the possibility of stray
laser beams that could damage the eyesight, the appropriate laser eyewear
MUST BE WORN.
PERSONAL PROTECTIVE EQUIPMENT (PPE)
Personal protective equipment (PPE) may be necessary when performing work with
a laser or associated equipment. However, PPE must always be regarded as a last
resort to protect against risks to health and safety. Situations where protective
goggles or gloves are necessary do arise, and if these are planned and accounted
for, after all other methods of engineering and administrative control have been
employed, laser users are not putting themselves at unnecessary risk.
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Choosing the correct PPE is crucial to ensuring safety. A laser user should be kept
informed of changes in standards or designs of PPE by the DLSO and be offered
suitable materials for them to undertake tasks safely. A summary of PPE is given in
Table 5.
Table 5: Summary of Personal Protective Equipment.
PPE
Protective eyewear
Protective clothing
and gloves
Function
Eyewear should allow you to see everything in the work area but
restrict the laser beam or reflections to acceptable ‘safe’ levels.
The choice of appropriate eyewear depends upon many factors,
including: wavelength, laser power/energy, optical density, need
for prescription lenses, comfort etc.
Class 4 lasers present a fire hazard and protective clothing may
be necessary.
Lasers that produce UV radiation present a skin hazard and skin
should be covered using suitable protective clothing.
Gloves should be worn when preparing chemicals for dye lasers,
using optics cleaning chemicals, handling cryogenic coolant
materials and when handling filters from extraction systems used
for material processing.
Respiratory
equipment
Respiratory equipment may be necessary for emergency use such
as toxic gas escape from excimer lasers.
Ear defenders
Noise can be hazard from some laser applications e.g. capacitor
banks from pulsed lasers can present a noise hazard if
experienced over long working hours.
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