IEC 60825-4:2006+AMD1:2008+AMD2:2011 CSV

IEC 60825-4 ®
Edition 2.2 2011-06
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Safety of laser products –
Part 4: Laser guards
Sécurité des appareils à laser –
Partie 4: Protecteurs pour lasers
IEC 60825-4:2006+A1:2008+A2:2011

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IEC 60825-4 ®
Edition 2.2 2011-06
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Safety of laser products –
Part 4: Laser guards
Sécurité des appareils à laser –
Partie 4: Protecteurs pour lasers

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX CS
ICS 31.260 ISBN 978-2-88912-515-9

– 2 – 60825-4  IEC:2006+A1:2008+A2:2011
CONTENTS
FOREWORD . 4
INTRODUCTION . 6

1 Scope . 7
2 Normative references. 7
3 Definitions . 7
4 Laser processing machines . 9
4.1 Design requirements . 9
4.2 Performance requirements . 10
4.3 Validation . 10
4.4 User information . 11
5 Proprietary laser guards . 11
5.1 Design requirements . 11
5.2 Performance requirements . 11
5.3 Specification requirements . 11
5.4 Test requirements. 12
5.5 Labelling requirements. 12
5.6 User information . 13

Annex A (informative) General guidance on the design and selection of laser guards . 14
Annex B (informative) Assessment of foreseeable exposure limit (FEL) . 16
Annex C (informative) Elaboration of defined terms . 23
Annex D (normative) Proprietary laser guard testing . 25
Annex E (informative) Guidelines on the arrangement and installation of laser guards . 30
Annex F (informative) Guideline for assessing the suitability of laser guards . 40
Annex G (normative)  Beam delivery systems . 67

Bibliography . 76

Figure B.1 – Calculation of diffuse reflections . 17
Figure B.2 – Calculation of specular reflections . 17
Figure B.3 – Some examples of a foreseeable fault condition . 18
Figure B.4 – Four examples of errant laser beams that might have to be contained by a
temporary guard under service conditions. 19
Figure B.5 – Illustration of laser guard exposure during repetitive machine operation . 20
Figure B.6 – Two examples of assessed duration of exposure . 21
Figure B.7 – Assessed duration of exposure for a machine with no safety monitoring . 22
Figure C.1 – Illustration of guarding around a laser processing machine . 23
Figure C.2 – Illustration of active laser guard parameters . 24
Figure D.1 – Simplified diagram of the test arrangement . 27
Figure D.2 – Simplified diagram of the ventilation for the guard under test . 27

60825-4  IEC:2006+A1:2008+A2:2011 – 3 –
Figure F.1 – Damage resistance of 1 mm thick zinc coated steel sheet derived from
10 s exposure to a defocused beam during experiments using a CW CO laser . 56
Figure F.2 – Damage resistance of 1 mm thick zinc coated steel sheet derived from
100 s exposure to a defocused beam during experiments using a CW CO laser . 56
Figure F.3 – Damage resistance of 2 mm thick zinc coated steel sheet derived from 10
s exposure to a defocused beam during experiments using a CW CO laser . 57
Figure F.4 – Damage resistance of 2 mm thick zinc coated steel sheet derived from
100 s exposure to a defocused beam during experiments using a CW CO laser . 57
Figure F.5 – Damage resistance of 3 mm thick zinc coated steel sheet derived from 10
s exposure to a defocused beam during experiments using a CW CO laser . 58
Figure F.6 – Damage resistance of 3 mm thick zinc coated steel sheet derived from
100 s exposure to a defocused beam during experiments using a CW CO laser . 58
Figure F.7 – Damage resistance of 2 mm thick aluminium sheet derived from 10 s
exposure to a defocused beam during experiments using a CW CO laser . 59
Figure F.8 – Damage resistance of 2 mm thick aluminium sheet derived from 100 s
exposure to a defocused beam during experiments using a CW CO laser . 59
Figure F.9 – Damage resistance of 1 mm thick stainless steel sheet derived from 10 s
exposure to a defocused beam during experiments using a CW CO laser . 60
Figure F.10 – Damage resistance of 1 mm thick stainless steel sheet derived from 100
s exposure to a defocused beam during experiments using a CW CO laser . 60
Figure F.11 – Damage resistance of 6 mm thick polycarbonate sheet derived from 10 s
exposure to a defocused beam during experiments using a CW CO laser . 61
Figure F.12 – Damage resistance of 6 mm thick polycarbonate sheet derived from 100
s exposure to a defocused beam during experiments using a CW CO laser . 61
Figure F.13 – Damage resistance of 1 mm thick zinc coated steel sheet derived from
10 s exposure to a defocused beam during experiments using a CW Nd:YAG laser . 62
Figure F.14 – Damage resistance of 1 mm thick zinc coated steel sheet derived from
100 s exposure to a defocused beam during experiments using a CW Nd:YAG laser . 62
Figure F.15 – Damage resistance of 2 mm thick zinc coated steel sheet derived from
10 s exposure to a defocused beam during experiments using a CW Nd:YAG laser . 63
Figure F.16 – Damage resistance of 2 mm thick zinc coated steel sheet derived from
100 s exposure to a defocused beam during experiments using a CW Nd:YAG laser . 63
Figure F.17 – Damage resistance of 3 mm thick zinc coated steel sheet derived from
10 s exposure to a defocused beam during experiments using a CW Nd:YAG laser . 64
Figure F.18 – Damage resistance of 3 mm thick zinc coated steel sheet derived from
100 s exposure to a defocused beam during experiments using a CW Nd:YAG laser . 64
Figure F.19 – Damage resistance of 2 mm thick aluminium sheet derived from 10 s
exposure to a defocused beam during experiments using a CW Nd:YAG laser . 65
Figure F.20 – Damage resistance of 2 mm thick aluminium sheet derived from 100 s
exposure to a defocused beam during experiments using a CW Nd:YAG laser . 65
Figure F.21 – Damage resistance of 1 mm thick stainless steel sheet derived from 10 s
exposure to a defocused beam during experiments using a CW Nd:YAG laser . 66
Figure F.22 – Damage resistance of 1 mm thick stainless steel sheet derived from
100 s exposure to a defocused beam during experiments using a CW Nd:YAG laser . 66

Table D.1 – Laser guard test classification . 28
Table F.1 – Application of ALARP . 43
Table G.1 – Beam delivery systems using free space beam delivery systems . 72
Table G.2 – Beam delivery systems using fibre optic cables . 74

– 4 – 60825-4  IEC:2006+A1:2008+A2:2011
INTERNATIONAL ELECTROTECHNICAL COMMISSION
___________
SAFETY OF LASER PRODUCTS –
Part 4: Laser guards
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
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9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 60825-4 has been prepared by IEC technical committee 76: Optical
radiation safety and laser equipment.
This consolidated version of IEC 60825-4 consists of the second edition (2006) [documents
76/342/FDIS and 76/351/RVD], its amendment 1 (2008) [documents 76/383/FDIS and
76/385/RVD] and its amendment 2 (2011) [documents 76/428/CDV and 76/442/RVC.
The technical content is therefore identical to the base edition and its amendments and has
been prepared for user convenience.
It bears the edition number 2.2.
A vertical line in the margin shows where the base publication has been modified by
amendments 1 and 2.
60825-4  IEC:2006+A1:2008+A2:2011 – 5 –
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
The committee has decided that the contents of the base publication and its amendments will
remain unchanged until the maintenance result date indicated on the IEC web site under
"http://webstore.iec.ch" in the data related to the specific publication. At this date,
the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct understanding
of its contents. Users should therefore print this document using a colour printer.

– 6 – 60825-4  IEC:2006+A1:2008+A2:2011
INTRODUCTION
At low levels of irradiance or radiant exposure, the selection of material and thickness for
shielding against laser radiation is determined primarily by a need to provide sufficient optical
attenuation. However, at higher levels, an additional consideration is the ability of the laser
radiation to remove guard material – typically by melting, oxidation or ablation; processes that
could lead to laser radiation penetrating a normally opaque material.
IEC 60825-1 deals with basic issues concerning laser guards, including human access,
interlocking and labelling, and gives general guidance on the design of protective housings and
enclosures for high-power lasers.
This part of IEC 60825 deals with protection against laser radiation only. Hazards from
secondary radiation that may arise during material processing are not addressed.
Laser guards may also comply with standards for laser protective eyewear, but such
compliance is not necessarily sufficient to satisfy the requirements of this standard.
Where the term “irradiance” is used, the expression “irradiance or radiant exposure, as
appropriate” is implied.
60825-4  IEC:2006+A1:2008+A2:2011 – 7 –
SAFETY OF LASER PRODUCTS –
Part 4: Laser guards
1 Scope
This part of IEC 60825 specifies the requirements for laser guards, permanent and temporary
(for example for service), that enclose the process zone of a laser processing machine, and
specifications for proprietary laser guards.
This standard applies to all component parts of a guard including clear (visibly transmitting)
screens and viewing windows, panels, laser curtains and walls. Requirements for beam path
components, beam stops and those other parts of a protective housing of a laser product which
do not enclose the process zone are contained in IEC 60825-1.
In addition this part of IEC 60825 indicates:
a) how to assess and specify the protective properties of a laser guard; and
b) how to select a laser guard.
2 Normative references
The following referenced documents are indispensable for the application of this document. For
dated references, only the edition cited applies. For undated references, the latest edition of
the referenced document (including any amendments) applies.
IEC 60825-1:2007, Safety of laser products – Part 1: Equipment classification and
requirements
ISO 11553-1:2005, Safety of machinery – Laser processing machines – Safety requirements
ISO 12100-1:2003, Safety of machinery – Basic concepts, general principles for design –
Part 1: Basic terminology, methodology
ISO 12100-2:2003, Safety of machinery – Basic concepts, general principles for design – Part 2:
Technical principles and specifications
ISO 13849-1:2006, Safety of machinery – Safety-related parts of control systems – Part 1:
General principles for design
ISO 14121-1:2007, Safety of machinery – Risk assessment – Part 1: Principles
3 Definitions
For the purpose of this part of IEC 60825, the following definitions apply in addition to the
definitions given in IEC 60825-1.

– 8 – 60825-4  IEC:2006+A1:2008+A2:2011
3.1
active guard protection time
for a given laser exposure of the front surface of an active laser guard, the minimum time,
measured from the issue of an active guard termination signal, for which the active laser guard can
safely prevent laser radiation accessible at its rear surface from exceeding the class 1 AEL
3.2
active guard termination signal
in response to an excess exposure of its front surface to
the signal issued by an active guard
laser radiation and which is intended to lead to automatic termination of the laser radiation
NOTE The action of a safety interlock becoming open circuit is considered a "signal" in this context.
3.3
active laser guard
a laser guard which is part of a safety-related control system. The control system generates an
active guard termination signal in response to the effect of laser radiation on the front surface
of the laser guard
3.4
foreseeable exposure limit
FEL
the maximum laser exposure on the front surface of the laser guard, within the maintenance
inspection interval, assessed under normal and reasonably foreseeable fault conditions
3.5
front surface
the face of the laser guard intended for exposure to laser radiation
3.6
laser guard
a physical barrier which limits the extent of a danger zone by preventing laser radiation
accessible at its rear surface from exceeding the class 1 AEL
3.7
laser processing machine
a machine which uses a laser to process materials and is within the scope of ISO 11553-1
3.8
laser termination time
the maximum time taken, from generation of an active guard termination signal, for the laser
radiation to be terminated
NOTE Laser termination time does not refer to the response of an active laser guard but to the response of the
laser processing machine, in particular the laser safety shutter.
3.9
maintenance inspection interval
the time between successive safety maintenance inspections of a laser guard
3.10
passive laser guard
a laser guard which relies for its operation on its physical properties only

60825-4  IEC:2006+A1:2008+A2:2011 – 9 –
3.11
process zone
the zone where the laser beam interacts with the material to be processed
3.12
proprietary laser guard
a passive or active laser guard, offered by its manufacturer as a guard with a specified
protective exposure limit
3.13
protective exposure limit
PEL
the maximum laser exposure of the front surface of a laser guard which is specified to prevent
laser radiation accessible at its rear surface from exceeding the class 1 AEL
NOTE 1 In practice, there may be more than one maximum exposure.
NOTE 2 Different PELs may be assigned to different regions of a laser guard if these regions are clearly
identifiable (for example a viewing window forming an integral part of a laser guard).
3.14
rear surface
any surface of a laser guard that is remote from the associated laser radiation and usually
accessible to the user
3.15
reasonably foreseeable
an event (or condition) when it is credible and its likelihood of occurrence (or existence) cannot
be disregarded
3.16
safety maintenance inspection
documented inspection performed in accordance with manufacturer’s instructions
3.17
temporary laser guard
a substitute or supplementary active or passive laser guard intended to limit the extent of the
danger zone during some service operations of the laser processing machine
4 Laser processing machines
This clause specifies the requirements for laser guards that enclose the process zone and are
supplied by the laser processing machine manufacturer.
4.1 Design requirements
A laser guard shall satisfy ISO 12100-2 with respect to the general requirements for guards
and also the more specific requirements with regard to its location and method of fixture. In
addition, the following specific laser requirements shall be met.
4.1.1 General requirements
A laser guard, in its intended location, shall not give rise to any associated hazard at or beyond
its rear surface when exposed to laser radiation up to the foreseeable exposure limit.

– 10 – 60825-4  IEC:2006+A1:2008+A2:2011
NOTE 1 Examples of associated hazards include: high temperature, the release of toxic materials, fire, explosion,
electricity.
NOTE 2 See Annex B for assessment of foreseeable exposure limit.
4.1.2 Consumable parts of laser guards
Provision shall be made for the replacement of parts of a laser guard prone to damage by laser
radiation.
NOTE An example of such a part would be a sacrificial or interchangeable screen.
4.2 Performance requirements
4.2.1 General
When the front surface of a laser guard is subjected to exposure to laser radiation at the
foreseeable exposure limit, the laser guard shall prevent laser radiation accessible at its rear
surface from exceeding the class 1 AEL at any time over the period of the maintenance
inspection interval. For automated laser processing machines, the minimum value of the
maintenance inspection interval shall be 8 h.
This requirement shall be satisfied over the intended lifetime of the laser guard under expected
conditions of operation.
NOTE 1 This requirement implies both low transmission of laser radiation and resistance to laser-induced
damage.
NOTE 2 Some materials may lose their protective properties due to ageing, exposure to ultraviolet radiation,
certain gases, temperature, humidity and other environmental conditions. Additionally, some materials will transmit
laser radiation under high-intensity laser exposure, even though there may be no visible damage (i.e. reversible
bleaching).
4.2.2 Active laser guards
a) The active guard protection time shall exceed the laser termination time up to the
foreseeable exposure limits.
b) The generation of an active guard termination signal shall give rise to a visible or audible
warning. A manual reset is required before laser emission can recommence.
NOTE See Annex C.2 for an elaboration of terms.
4.3 Validation
If the laser processing machine manufacturer chooses to make a laser guard, the manufacturer
shall confirm that the guard complies with the design requirements of 4.1 and can satisfy the
performance requirements set out in 4.2.
NOTE See Annex A for guidance on the design and selection of laser guards.
4.3.1 Validation of performance
4.3.1.1 The complete laser guard, or an appropriate sample of the material of construction of
the laser guard, shall be tested at each FEL identified.
NOTE 1 A table of predetermined PELs for common combinations of lasers and guarding materials, together with
suitable testing procedures shall be issued as an informative annex in a future amendment to this standard. This
could provide a simple alternative to direct testing for the majority of cases.
NOTE 2 See Annex B for the assessment of FEL.

60825-4  IEC:2006+A1:2008+A2:2011 – 11 –
4.3.1.2 For testing purposes, the FEL exposure shall be achieved either:
a) by calculating or measuring the exposure and reproducing the conditions; or
b) without quantifying the FEL, by creating the machine conditions under which the FEL is
produced.
The condition of the laser guard or sample shall be such as to replicate those physical
conditions of the front surface permitted within the scope of the routine inspection instructions
and within the service life of the guard, which minimize the laser radiation protective properties
of the laser guard (for example wear and tear and surface contamination) (see 4.4.2).
4.4 User information
4.4.1 The manufacturer shall document and provide to the user the maintenance inspection
interval for the laser guard, and details of inspection and test procedures, cleaning,
replacement or repair of damaged parts, together with any restrictions of use.
4.4.2 The manufacturer shall document and provide to the user instructions that after any
actuation of the safety control system of an active guard, the cause shall be investigated,
checks shall be made for damage, and the necessary remedial action to be taken before
resetting the control system.
5 Proprietary laser guards
This clause specifies the requirements to be satisfied by suppliers of proprietary laser guards.
5.1 Design requirements
A proprietary laser guard shall not create any associated hazard at or beyond its rear surface
when exposed to laser radiation up to the specified PEL when used as specified in the user
information (see 5.6).
5.2 Performance requirements
The accessible laser radiation at the rear surface of the laser guard shall not exceed the
class 1 AEL when its front surface is subjected to laser radiation at the specified PEL. For an
active laser guard, this requirement shall apply to laser radiation accessible over the period of
the active guard protection time, measured from the moment an active guard termination signal
is issued.
This requirement shall be satisfied over the intended lifetime of the guard under expected
service conditions.
5.3 Specification requirements
The full specification of a PEL shall include the following information:
a) the magnitude and variation with time of irradiance or radiant exposure at the front surface
–2 –2
of the laser guard (in units of Wm or Jm respectively), specifying any upper limit to the
area of exposure;
b) the overall duration of exposure under these conditions;
c) the wavelength for which this PEL applies;
d) the angle of incidence and (if relevant) the polarization of the incident laser radiation;

– 12 – 60825-4  IEC:2006+A1:2008+A2:2011
e) any minimum dimensions to the irradiated area (for example as might apply to an active
laser guard with discrete sensor elements so that a small diameter laser beam could pass
through the guard undetected);
f) for an active laser guard, the active guard protection time.
NOTE 1 See Clause B.1 for an elaboration of terms.
NOTE 2 In all cases, a range or set of values can be stated rather than a single value.
NOTE 3 A graphical form of presentation is acceptable (for example irradiance vs. duration with all other
parameters constant).
5.4 Test requirements
5.4.1 General
Testing shall be performed using the complete laser guard or an appropriate sample of the
material used to construct the guard. In either case, the condition of the guard or sample shall
be such as to replicate or exceed the worst permissible physical condition of the front surface,
including reduced surface reflection and damage permitted within the scope of the routine
maintenance instructions (see 5.6).
The front surface irradiation shall be either as specified by the PEL or, in the case of sample
testing, as specified in 5.4.2 below.
When the front surface is subjected to the PEL exposure conditions, the accessible laser
radiation measured at the rear surface of the laser guard shall not exceed the class 1 AEL
(tests as prescribed in Clause 8 of 60825-1). This requirement applies over the exposure
duration specified in the PEL or, in the case of an active guard, over the specified active guard
protection time measured from the moment an active guard termination signal is issued.
NOTE In cases where materials opaque at the laser wavelength(s) are used (for example metals), the transmitted
radiation will only rise to the class 1 AEL when complete (or almost complete) physical removal of material along a
path through to the rear surface has been achieved. In such cases, the rise from zero transmission to a value
greatly in excess of the class 1 AEL will therefore be rapid, and sensitive radiation detectors will not be required.
5.4.2 Sample testing
Sample guard testing shall be performed by irradiating the front surface of the guard material
using the procedure and methodology as specified in Annex D.
5.5 Labelling requirements
5.5.1 All labelling shall be placed on the rear surface of the guard.
5.5.2 The rear surface of the guard shall be clearly identified if the orientation of the guard is
important.
5.5.3 If only part of the front surface of the guard is a laser guard, this area shall be clearly
identified by a bold coloured outline and words to indicate the outer boundary of the laser
guard.
5.5.4 The labelling shall state the full PEL specification.
5.5.5 The manufacturer’s name, the date and place of manufacture according to
ISO 11553-1, and a statement of compliance with this standard shall be provided.

60825-4  IEC:2006+A1:2008+A2:2011 – 13 –
5.6 User information
In addition to the specifications listed in 5.3, the following information shall be supplied to the
user by the manufacturer of a proprietary laser guard:
a) a description of the permitted uses of the laser guard;
b) a description of the form of mounting and connection of the laser guard;
c) information on the installation of the laser guard – for active laser guards this shall include
interface and supply requirements for the guard;
d) maintenance requirements, including for example details of inspection and test procedures,
cleaning, replacement or repair of damaged parts;
e) instructions, that after any actuation of the safety control system of an active guard, the
cause shall be investigated, checks shall be made for damage, and the necessary remedial
action to be taken before resetting the control system;
f) the labels in 5.5 and their locations. If only part of the front surface of the guard is a laser
guard, this area shall be identified;
g) a statement of compliance with this standard.

– 14 – 60825-4  IEC:2006+A1:2008+A2:2011
Annex A
(informative)
General guidance on the design and selection of laser guards

A.1 Design of laser guards
A.1.1 Passive laser guards
Examples of a passive laser guard include the following.
a) A metal panel relying on thermal conduction, if necessary enhanced by forced air or water
cooling, to maintain the surface temperature below its melting point under normal and
reasonably foreseeable fault conditions.
b) A transparent sheet, opaque at the laser wavelength, which is unaffected by low value of
laser exposure under normal operation of the laser processing machine.

A.1.2 Active laser guards
Examples of an active laser guard include the following.
a) A guard, with discrete embedded thermal sensors, which detects overheating.
NOTE The spacing between sensors should be considered in relation to the minimum dimensions of an errant
laser beam.
b) A laser guard comprising two panels between which is contained a pressurized liquid or
gaseous medium in combination with a pressure-sensing device capable of detecting the
pressure drop following perforation of the front surface.

A.1.3 Hazard indication (passive guards)
Visible indication of exposure of the laser guard to hazardous amounts of laser radiation should
be provided where feasible (for example by adding a layer of an appropriate paint on both sides
of the laser guard).
A.1.4 Power supply (active guards)
If power is required for the proper functioning of an active guard, its supply should be arranged
so that laser operation is not possible in the absence of such power.
A.2 Selection of laser guards
A simple selection process is as follows:
a) identify the preferred position for the laser guard and estimate the FEL at this position.
Annex B gives guidance on the estimation of FEL values;

60825-4  IEC:2006+A1:2008+A2:2011 – 15 –
b) if necessary, minimize the FEL under fault conditions, preferably by including automatic
monitoring in the machine which will detect the fault conditions and limit the exposure time.
Examples of alternatives include the following:
– ensure that the laser guard is sufficiently far away from beam focus produced by
focusing optics;
– install vulnerable parts of laser guard (such as viewing windows) away from regions that
could be exposed to high irradiance;
– move the laser guard farther away from the laser process zone;
– require in the essential servicing documentation for temporary laser guards, additions
such as:
• one or more persons to be present to supervise the condition of the front surface of
the laser guard, to reduce the assessed exposure duration of a passive guard;
• a hold-to-operate controller to be used by the person(s) supervising the condition of
the front surface of the laser guard, to reduce the assessed exposure duration of a
passive guard;
• additional local temporary guarding, apertures and beam dumps to be employed, to
absorb any powerful errant laser beams;
• the danger zone to be bounded by errant beam warning devices and the guard
placed beyond this zone to reduce the assessed exposure duration;
– incorporate in the design of the machine, when using temporary laser guards, beam
control features to facilitate improved laser beam control during servicing operations,
such as:
• holders for precise location of additional beam forming components (for example
turning mirrors) required during servicing;
• mounts which allow only limited scope for beam steering.
Three options then follow. The order below does not indicate a preference.
A.2.1 Option 1: passive laser guard
This is the simplest option.
NOTE Design and quality control are particularly important considerations where the absorption at the laser
wavelength is dominated by a minority additive, such as a dye in a plastic. In such cases, where the manufacturer
of the material does not specify the concentration of the absorber or the material optical attenuation at the laser
wavelength, samples from the same batch of the material should first be tested as described in 4.3.1.

A.2.2 Option 2: active laser guard
If the FEL cannot be reduced to a value where common guarding materials provide adequate
protection in the form of a passive laser guard, an active laser guard can always be used.
A.2.3 Option 3: proprietary laser guard
A proprietary laser guard can be used if the assessed FEL values are less than the PEL values
quoted by the laser guard manufacturer.

– 16 – 60825-4  IEC:2006+A1:2008+A2:2011
Annex B
(informative)
Assessment of foreseeable exposure limit (FEL)

B.1 General
FEL values may be assessed either by measurement or by calculation (see below).
The standard ISO 14121 provides a general methodology for risk assessment. The assessment
should include consideration of cumulative exposure in normal operation (for example during
each part processing cycle of the machine) over the maintenance inspection interval.
From this assessment, the most demanding combinations of irradiation, area of exposure and
exposure duration should be identified. It is quite likely that several FELs will be identified;
for example one condition may maximize the duration of exposure at a relatively low irradiance,
while another may maximize the irradiance over a shorter duration of exposure.
The full specification of an FEL comprises the following information.
a) The maximum irradiance at the front surface of the laser guard.
NOTE Irradiance is expressed as the total power or energy divided by the area of the front surface of the guard, or
specified limited area, as appropriate.
b) Any upper limit to the area of exposure of the front surface at this level of irradiance.
NOTE No limit to the area would be appropriate for protection against scattered laser radiation while an upper limit
to the exposed area would be appropriate for direct exposure to laser beams.
c) The temporal characteristics of the exposure, i.e. whether continuous wave or pulsed laser
radiation, and if the latter, then the pulse duration and pulse repetition frequency.
d) The full duration of exposure.
NOTE See Clause B.4 for an elaboration of this term.
e) The wavelength of the radiation.
f) The angle of incidence and (if relevant) the polarization of the radiation.
NOTE 1 Stipulation of angle of incidence is particularly important for laser guards exploiting interference layers to
reflect impinging laser radiation.
NOTE 2 CAUTION: At Brewster's angle of incidence "p" polarized radiation is strongly coupled into the surface of
the guard.
g) Any minimum dimensions to the irradiated area (for example as might apply to an active
laser guard with discrete sensor elements so that a small diameter laser beam could pass
through the laser guard undetected).
h) For an active laser guard, the active guard protection time.

60825-4  IEC:2006+A1:2008+A2:2011 – 17 –
B.2 Reflection of laser radiation
B.2.1 Diffuse reflections
Laser guard
Assuming a Lambertian reflector with 100 %
reflectivity
P Irradiance E
A
o
P
cosθ
o
E = ⋅ ⋅ cosϕ
ϕ
A
π
R
R
θ
IEC  1570/06
Figure B.1 – Calculation of
diffuse reflections
B.2.2 Specular reflections
It is difficult to generalize for the case of specular
reflections.
For a circularly symmetric laser beam with a
A
Gaussian distribution, power P and diameter d
o 63
at the focusing lens, focal length f, the maximum
irradiance (at the centre of the Gaussian P
o
distribution) in a normal plane distance R from the
R
focus is:
A’
4P ρ
 f 
o
E =
 
AA'
θ
 
R
πd
Laser guard
where ρ is the reflectivity of the workpiece
surface.
IEC  1571/06
CAUTION: Certain curved surfaces may increase
the reflection hazard.
Figure B.2 – Calculation of
specular reflections
– 18 – 60825-4  IEC:2006+A1:2008+A2:2011
B.3 Examples of assessment conditions
FELs should be assessed for the worst reasonably foreseeable combination(s) of available
laser parameters, workpiece materials, geometry and processes likely to be encountered
during normal operation (IEC/TR 60
...