IEC 62305-2:2010

IEC 62305-2 ®
Edition 2.0 2010-12
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Protection against lightning –
Part 2: Risk management
Protection contre la foudre –
Partie 2: Evaluation des risques

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IEC 62305-2 ®
Edition 2.0 2010-12
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Protection against lightning –
Part 2: Risk management
Protection contre la foudre –
Partie 2: Evaluation des risques

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX XC
ICS 29.020; 91.120.40 ISBN 978-2-88912-794-8

– 2 – 62305-2  IEC:2010
CONTENTS
FOREWORD . 6
INTRODUCTION . 8
1 Scope . 10
2 Normative references . 10
3 Terms, definitions, symbols and abbreviations . 10
3.1 Terms and definitions . 10
3.2 Symbols and abbreviations . 16
4 Explanation of terms . 19
4.1 Damage and loss . 19
4.1.1 Source of damage . 19
4.1.2 Types of damage . 19
4.1.3 Types of loss . 19
4.2 Risk and risk components . 20
4.2.1 Risk . 20
4.2.2 Risk components for a structure due to flashes to the structure . 21
4.2.3 Risk component for a structure due to flashes near the structure . 21
4.2.4 Risk components for a structure due to flashes to a line connected to
the structure . 21
4.2.5 Risk component for a structure due to flashes near a line connected
to the structure . 21
4.3 Composition of risk components . 22
5 Risk management . 23
5.1 Basic procedure . 23
5.2 Structure to be considered for risk assessment . 23
5.3 Tolerable risk R . 24
T
5.4 Specific procedure to evaluate the need of protection. 24
5.5 Procedure to evaluate the cost effectiveness of protection . 25
5.6 Protection measures . 27
5.7 Selection of protection measures. 28
6 Assessment of risk components . 28
6.1 Basic equation. 28
6.2 Assessment of risk components due to flashes to the structure (S1) . 28
6.3 Assessment of the risk component due to flashes near the structure (S2) . 29
6.4 Assessment of risk components due to flashes to a line connected to the

structure (S3) . 29
6.5 Assessment of risk component due to flashes near a line connected to the
structure (S4) . 30
6.6 Summary of risk components . 31
6.7 Partitioning of a structure in zones Z . 31
S
6.8 Partitioning of a line into sections S . 31
L
6.9 Assessment of risk components in a structure with zones Z . 32
S
6.9.1 General criteria . 32
6.9.2 Single zone structure . 32
6.9.3 Multi-zone structure . 32
6.10 Cost-benefit analysis for economic loss (L4). 33
Annex A (informative) Assessment of annual number N of dangerous events. 34
Annex B (informative) Assessment of probability P of damage . 42
X
62305-2  IEC:2010 – 3 –
Annex C (informative) Assessment of amount of loss L . 50
X
Annex D (informative) Evaluation of costs of loss. 57
Annex E (informative) Case study . 58
Bibliography . 85

Figure 1 – Procedure for deciding the need of protection and for selecting protection
measures . 26
Figure 2 – Procedure for evaluating the cost-effectiveness of protection measures . 27
Figure A.1 – Collection area A of an isolated structure . 35
D
Figure A.2 – Complex shaped structure . 36
Figure A.3 – Different methods to determine the collection area for the given structure. 37
Figure A.4 – Structure to be considered for evaluation of collection area A . 38
D
Figure A.5 – Collection areas (A A , A , A ) . 41
D, M I L
Figure E.1 – Country house . 58
Figure E.2 – Office building . 63
Figure E.3 – Hospital . 70
Figure E.4 – Apartment block . 81

Table 1 – Sources of damage, types of damage and types of loss according to the
point of strike . 20
Table 2 – Risk components to be considered for each type of loss in a structure . 22
Table 3 – Factors influencing the risk components . 23
Table 4 – Typical values of tolerable risk R . 24
T
Table 5 – Parameters relevant to the assessment of risk components . 30
Table 6 – Risk components for different types of damage and source of damage . 31
Table A.1 – Structure location factor C . 39
D
Table A.2 – Line installation factor C . 40
I
Table A.3 – Line type factor C . 40
T
Table A.4 – Line environmental factor C . 40
E
Table B.1 – Values of probability P that a flash to a structure will cause shock to
TA
living beings due to dangerous touch and step voltages . 42
Table B.2 – Values of probability P depending on the protection measures to reduce
B
physical damage . 43
Table B.3 – Value of the probability P as a function of LPL for which SPDs are
SPD
designed . 44
Table B.4 – Values of factors C and C depending on shielding, grounding and
LD LI
isolation conditions . 44
Table B.5 – Value of factor K depending on internal wiring . 46
S3
Table B.6 – Values of probability P that a flash to an entering line will cause shock
TU
to living beings due to dangerous touch voltages . 47
Table B.7 – Value of the probability P as a function of LPL for which SPDs are
EB
designed . 47
Table B.8 – Values of the probability P depending on the resistance R of the cable
LD S
screen and the impulse withstand voltage U of the equipment . 47
W
Table B.9 – Values of the probability P depending on the line type and the impulse
LI
withstand voltage U of the equipment . 49
W
– 4 – 62305-2  IEC:2010
Table C.1 – Type of loss L1: Loss values for each zone . 51
Table C.2 – Type of loss L1: Typical mean values of L , L and L . 51
T F O
Table C.3 – Reduction factor r as a function of the type of surface of soil or floor . 52
t
Table C.4 – Reduction factor r as a function of provisions taken to reduce the
p
consequences of fire . 52
Table C.5 – Reduction factor r as a function of risk of fire or explosion of structure . 52
f
Table C.6 – Factor h increasing the relative amount of loss in presence of a special
z
hazard . 53
Table C.7 – Type of loss L2: Loss values for each zone . 53
Table C.8 – Type of loss L2: Typical mean values of L and L . 54
F O
Table C.9 – Type of loss L3: Loss values for each zone . 54
Table C.10 – Type of loss L3: Typical mean value of L . 54
F
Table C.11 – Type of loss L4: Loss values for each zone . 55
Table C.12 – Type of loss L4: Typical mean values of L , L and L . 56
T F O
Table E.1 – Country house: Environment and structure characteristics . 59
Table E.2 – Country house: Power line . 59
Table E.3 – Country house: Telecom line (TLC) . 59
Table E.4 – Country house: Factors valid for zone Z (inside the building) . 60
Table E.5 – Country house: Collection areas of structure and lines . 61
Table E.6 – Country house: Expected annual number of dangerous events . 61
–5
Table E.7 – Country house: Risk R for the unprotected structure (values × 10 ) . 62
Table E.8 – Country house: Risk components relevant to risk R for protected structure . 62
Table E.9 – Office building: Environment and structure characteristics . 63
Table E.10 – Office building: Power line. 64
Table E.11 – Office building: Telecom line . 64
Table E.12 – Office building: Distribution of persons into zones . 65
Table E.13 – Office building: Factors valid for zone Z (entrance area outside) . 66
Table E.14 – Office building: Factors valid for zone Z (garden outside) . 66
Table E.15 – Office building: Factors valid for zone Z (archive) . 67
Table E.16 – Office building: Factors valid for zone Z (offices) . 67
Table E.17 – Office building: Factors valid for zone Z (computer centre) . 67
Table E.18 – Office building: Collection areas of structure and lines . 68
Table E.19 – Office building: Expected annual number of dangerous events . 68
–5
Table E.20 – Office building: Risk R for the unprotected structure (values × 10 ) . 69
–5
Table E.21 – Office building: Risk R for the protected structure (values × 10 ). 70
Table E.22 – Hospital: Environment and global structure characteristics . 70
Table E.23 – Hospital: Power line . 71
Table E.24 – Hospital: Telecom line . 71
Table E.25 – Hospital: Distribution of persons and of economic values into zones . 72
Table E.26 – Hospital: Factors valid for zone Z (outside the building) . 73
Table E.27 – Hospital: Factors valid for zone Z (rooms block) . 73
Table E.28 – Hospital: Factors valid for zone Z (operating block) . 74
Table E.29 – Hospital: Factors valid for zone Z (intensive care unit) . 75
Table E.30 – Hospital: Collection areas of structure and lines . 75

62305-2  IEC:2010 – 5 –
Table E.31 – Hospital: Expected annual number of dangerous events . 76
Table E.32 – Hospital: Risk R – Values of probability P for the unprotected structure . 76
–5
Table E.33 – Hospital: Risk R for the unprotected structure (values × 10 ) . 77
Table E.34 – Hospital: Risk R for the protected structure according to solution a)
-5
(values × 10 ) . 78
Table E.35 – Hospital: Risk R for the protected structure according to solution b)
-5
(values × 10 ) . 78
Table E.36 – Hospital: Risk R for the protected structure according to solution c)
-5
(values × 10 ) . 79
Table E.37 – Hospital: Cost of loss C (unprotected) and C (protected) . 79
L RL
Table E.38 – Hospital: Rates relevant to the protection measures . 80
Table E.39 – Hospital: Cost C and C of protection measures (values in $) . 80
P PM
Table E.40 – Hospital: Annual saving of money (values in $) . 80
Table E.41 – Apartment block: Environment and global structure characteristics . 81
Table E.42 – Apartment block: Power line . 81
Table E.43 – Apartment block: Telecom line . 82
Table E.44 – Apartment block: Factors valid for zone Z (inside the building) . 83
Table E.45 – Apartment block: Risk R for the apartment block depending on
protection measures . 84

– 6 – 62305-2  IEC:2010
INTERNATIONAL ELECTROTECHNICAL COMMISSION
_____________
PROTECTION AGAINST LIGHTNING –

Part 2: Risk management
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
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6) All users should ensure that they have the latest edition of this publication.
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
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 62305-2 has been prepared by IEC technical committee 81:
Lightning protection.
This second edition cancels and replaces the first edition, published in 2006, and constitutes
a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
1) Risk assessment for services connected to structures is excluded from the scope.
2) Injuries of living beings caused by electric shock inside the structure are considered.
-3 -4
3) Tolerable risk of loss of cultural heritage is lowered from 10 to 10 . The value of
-3
tolerable risk of loss of economic value (R = 10 ) is introduced, to be used when data for
T
cost/benefit analysis are not available.
4) Extended damage to surroundings structures or to the environment is considered.
5) Improved equations are provided for evaluation of

62305-2  IEC:2010 – 7 –
– collection areas relevant to flashes nearby a structure,
– collection areas relevant to flashes to and nearby a line,
– probabilities that a flash can cause damage,
– loss factors even in structures with risk of explosion,
– risk relevant to a zone of a structure,
– cost of loss.
6) Tables are provided to select the relative amount of loss in all cases.
7) Impulse withstand voltage level of equipments was extended down to 1 kV.
This bilingual version corresponds to the monolingual English version, published in 2010-12.
The text of this standard is based on the following documents:
FDIS Report on voting
81/371/FDIS 81/381/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
The French version of this standard has not been voted upon.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all the parts in the IEC 62305 series, under the general title Protection against
lightning, can be found on the IEC website.
The committee has decided that the contents of this publication will remain unchanged until
the stability 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.
– 8 – 62305-2  IEC:2010
INTRODUCTION
Lightning flashes to earth may be hazardous to structures and to lines.
The hazard to a structure can result in
– damage to the structure and to its contents,
– failure of associated electrical and electronic systems,
– injury to living beings in or close to the structure.
Consequential effects of the damage and failures may be extended to the surroundings of the
structure or may involve its environment.
To reduce the loss due to lightning, protection measures may be required. Whether they are
needed, and to what extent, should be determined by risk assessment.
The risk, defined in this part of IEC 62305 as the probable average annual loss in a structure
due to lightning flashes, depends on:
– the annual number of lightning flashes influencing the structure;
– the probability of damage by one of the influencing lightning flashes;
– the mean amount of consequential loss.
Lightning flashes influencing the structure may be divided into
– flashes terminating on the structure,
– flashes terminating near the structure, direct to connected lines (power, telecom-
munication lines,) or near the lines.
Flashes to the structure or a connected line may cause physical damage and life hazards.
Flashes near the structure or line as well as flashes to the structure or line may cause failure
of electrical and electronic systems due to overvoltages resulting from resistive and inductive
coupling of these systems with the lightning current.
Moreover, failures caused by lightning overvoltages in users’ installations and in power supply
lines may also generate switching type overvoltages in the installations.
NOTE Malfunctioning of electrical and electronic systems is not covered by the IEC 62305 series. Reference
[1]
should be made to IEC 61000-4-5 .
The number of lightning flashes influencing the structure depends on the dimensions and the
characteristics of the structure and of the connected lines, on the environmental
characteristics of the structure and the lines, as well as on lightning ground flash density in
the region where the structure and the lines are located.
The probability of lightning damage depends on the structure, the connected lines and the
lightning current characteristics, as well as on the type and efficiency of applied protection
measures.
The annual mean amount of the consequential loss depends on the extent of damage and the
consequential effects which may occur as a result of a lightning flash.
The effect of protection measures results from the features of each protection measure and
may reduce the damage probabilities or the amount of consequential loss.
___________
Figures in square brackets refer to the bibliography.

62305-2  IEC:2010 – 9 –
The decision to provide lightning protection may be taken regardless of the outcome of risk
assessment where there is a desire that there be no avoidable risk.

– 10 – 62305-2  IEC:2010
PROTECTION AGAINST LIGHTNING –

Part 2: Risk management
1 Scope
This part of IEC 62305 is applicable to risk assessment for a structure due to lightning flashes
to earth.
Its purpose is to provide a procedure for the evaluation of such a risk. Once an upper
tolerable limit for the risk has been selected, this procedure allows the selection of
appropriate protection measures to be adopted to reduce the risk to or below the tolerable
limit.
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 62305-1:2010, Protection against lightning – Part 1: General principles
IEC 62305-3:2010, Protection against lightning – Part 3: Physical damage to structures and
life hazard
IEC 62305-4:2010, Protection against lightning – Part 4: Electrical and electronic systems
within structures
3 Terms, definitions, symbols and abbreviations
For the purposes of this document, the following terms, definitions, symbols and
abbreviations, some of which have already been cited in Part 1 but are repeated here for ease
of reading, as well as those given in other parts of IEC 62305, apply.
3.1 Terms and definitions
3.1.1
structure to be protected
structure for which protection is required against the effects of lightning in accordance with
this standard
NOTE A structure to be protected may be part of a larger structure.
3.1.2
structures with risk of explosion
structures containing solid explosives materials or hazardous zones as determined in
[2] [3]
accordance with IEC 60079-10-1 and IEC 60079-10-2
3.1.3
structures dangerous to the environment
structures which may cause biological, chemical or radioactive emission as a consequence of
lightning (such as chemical, petrochemical, nuclear plants, etc.)

62305-2  IEC:2010 – 11 –
3.1.4
urban environment
area with a high density of buildings or densely populated communities with tall buildings
NOTE ’Town centre’ is an example of an urban environment.
3.1.5
suburban environment
area with a medium density of buildings
NOTE ‘Town outskirts’ is an example of a suburban environment.
3.1.6
rural environment
area with a low density of buildings
NOTE ’Countryside’ is an example of a rural environment.
3.1.7
rated impulse withstand voltage level
U
W
impulse withstand voltage assigned by the manufacturer to the equipment or to a part of it,
characterizing the specified withstand capability of its insulation against (transient)
overvoltages
[4]
[IEC 60664-1:2007, definition 3.9.2, modified]
NOTE For the purposes of this part of IEC 62305, only the withstand voltage between live conductors and earth is
considered.
3.1.8
electrical system
system incorporating low voltage power supply components
3.1.9
electronic system
system incorporating sensitive electronic components such as telecommunication equipment,
computer, control and instrumentation systems, radio systems, power electronic installations
3.1.10
internal systems
electrical and electronic systems within a structure
3.1.11
line
power line or telecommunication line connected to the structure to be protected
3.1.12
telecommunication lines
lines intended for communication between equipment that may be located in separate
structures, such as phone lines and data lines
3.1.13
power lines
distribution lines feeding electrical energy into a structure to power electrical and electronic
equipment located there, such as low voltage (LV) or high voltage (HV) electric mains

– 12 – 62305-2  IEC:2010
3.1.14
dangerous event
lightning flash to or near the structure to be protected, or to or near a line connected to the
structure to be protected that may cause damage
3.1.15
lightning flash to a structure
lightning flash striking a structure to be protected
3.1.16
lightning flash near a structure
lightning flash striking close enough to a structure to be protected that it may cause
dangerous overvoltages
3.1.17
lightning flash to a line
lightning flash striking a line connected to the structure to be protected
3.1.18
lightning flash near a line
lightning flash striking close enough to a line connected to the structure to be protected that it
may cause dangerous overvoltages
3.1.19
number of dangerous events due to flashes to a structure
N
D
expected average annual number of dangerous events due to lightning flashes to a structure
3.1.20
number of dangerous events due to flashes to a line
N
L
expected average annual number of dangerous events due to lightning flashes to a line
3.1.21
number of dangerous events due to flashes near a structure
N
M
expected average annual number of dangerous events due to lightning flashes near a
structure
3.1.22
number of dangerous events due to flashes near a line
N
I
expected average annual number of dangerous events due to lightning flashes near a line
3.1.23
lightning electromagnetic impulse
LEMP
all electromagnetic effects of lightning current via resistive, inductive and capacitive coupling,
which create surges and electromagnetic fields
3.1.24
surge
transient created by LEMP that appears as an overvoltage and/or overcurrent
3.1.25
node
point on a line from which onward surge propagation can be assumed to be neglected

62305-2  IEC:2010 – 13 –
NOTE Examples of nodes are a point on a power line branch distribution at an HV/LV transformer or on a power
substation, a telecommunication exchange or an equipment (e.g. multiplexer or xDSL equipment) on a
telecommunication line.
3.1.26
physical damage
damage to a structure (or to its contents) due to mechanical, thermal, chemical or explosive
effects of lightning
3.1.27
injury to living beings
permanent injuries, including loss of life, to people or to animals by electric shock due to
touch and step voltages caused by lightning
NOTE Although living beings may be injured in other ways, in this part of IEC 62305 the term ‘injury to living
beings’ is limited to the threat due to electrical shock (type of damage D1).
3.1.28
failure of electrical and electronic systems
permanent damage of electrical and electronic systems due to LEMP
3.1.29
probability of damage
P
X
probability that a dangerous event will cause damage to or in the structure to be protected
3.1.30
loss
L
X
mean amount of loss (humans and goods) consequent on a specified type of damage due to a
dangerous event, relative to the value (humans and goods) of the structure to be protected
3.1.31
risk
R
value of probable average annual loss (humans and goods) due to lightning, relative to the
total value (humans and goods) of the structure to be protected
3.1.32
risk component
R
X
partial risk depending on the source and the type of damage
3.1.33
tolerable risk
R
T
maximum value of the risk which can be tolerated for the structure to be protected
3.1.34
zone of a structure
Z
S
part of a structure with homogeneous characteristics where only one set of parameters is
involved in assessment of a risk component
3.1.35
section of a line
S
L
part of a line with homogeneous characteristics where only one set of parameters is involved
in the assessment of a risk component

– 14 – 62305-2  IEC:2010
3.1.36
lightning protection zone
LPZ
zone where the lightning electromagnetic environment is defined
NOTE The zone boundaries of an LPZ are not necessarily physical boundaries (e.g. walls, floor and ceiling).
3.1.37
lightning protection level
LPL
number related to a set of lightning current parameters values relevant to the probability that
the associated maximum and minimum design values will not be exceeded in naturally
occurring lightning
NOTE Lightning protection level is used to design protection measures according to the relevant set of lightning
current parameters.
3.1.38
protection measures
measures to be adopted in the structure to be protected, in order to reduce the risk
3.1.39
lightning protection
LP
complete system for protection of structures against lightning, including their internal systems
and contents, as well as persons, in general consisting of an LPS and SPM
3.1.40
lightning protection system
LPS
complete system used to reduce physical damage due to lightning flashes to a structure
NOTE It consists of both external and internal lightning protection systems.
3.1.41
LEMP protection measures
SPM
measures taken to protect internal systems against the effects of LEMP
NOTE This is part of overall lightning protection
3.1.42
magnetic shield
closed, metallic, grid-like or continuous screen enveloping the structure to be protected, or
part of it, used to reduce failures of electrical and electronic systems
3.1.43
lightning protective cable
special cable with increased dielectric strength and whose metallic sheath is in continuous
contact with the soil either directly or by use of conducting plastic covering
3.1.44
lightning protective cable duct
cable duct of low resistivity in contact with the soil
EXAMPLE Concrete with interconnected structural steel reinforcements or metallic duct.

62305-2  IEC:2010 – 15 –
3.1.45
surge protective device
SPD
device intended to limit transient overvoltages and divert surge currents; contains at least one
non-linear component
3.1.46
coordinated SPD system
SPDs properly selected, coordinated and installed to form a system intended to reduce
failures of electrical and electronic systems
3.1.47
isolating interfaces
devices which are capable of reducing conducted surges on lines entering the LPZ
NOTE 1 These include isolation transformers with earthed screen between windings, metal-free fibre optic cables
and opto-isolators.
NOTE 2 Insulation withstand characteristics of these devices are suitable for this application intrinsically or via
SPD.
3.1.48
lightning equipotential bonding
EB
bonding to LPS of separated metallic parts, by direct conductive connections or via surge
protective devices, to reduce potential differences caused by lightning current
3.1.49
zone 0
place in which an explosive atmosphere consisting of a mixture of air and flammable
substances in the form of gas, vapour or mist is present continuously or for long periods or
frequently
[5]
(IEC 60050-426:2008, 426-03-03, modified)
3.1.50
zone 1
place in which an explosive atmosphere consisting of a mixture of air and flammable
substances in the form of gas, vapour or mist is likely to occur in normal operation
occasionally
[ 5]
(IEC 60050-426:2008, 426-03-04, modified)
3.1.51
zone 2
place in which an explosive atmosphere consisting of a mixture of air and flammable
substances in the form of gas, vapour or mist is not likely to occur in normal operation but, if it
does occur, will persist for a short period only
NOTE 1 In this definition, the word "persist" means the total time for which the flammable atmosphere will exist.
This will normally comprise the total of the duration of the release, plus the time taken for the flammable
atmosphere to disperse after the release has stopped.
NOTE 2 Indications of the frequency of the occurrence and duration may be taken from codes relating to specific
industries or applications.
[5]
(IEC 60050-426:2008, 426-03-05, modified)
3.1.52
zone 20
place in which an explosive atmosphere, in the form of a cloud of combustible dust in air, is
present continuously, or for long periods, or frequently

– 16 – 62305-2  IEC:2010
[3]
(IEC 60079-10-2:2009, 6.2, modified)
3.1.53
zone 21
place in which an explosive atmosphere, in the form of a cloud of combustible dust in air, is
likely to occur in normal operation occasionally
[3]
(IEC 60079-10-2:2009, 6.2, modified)
3.1.54
zone 22
place in which an explosive atmosphere, in the form of a cloud of combustible dust in air, is
not likely to occur in normal operation but, if it does occur, will persist for a short period only
[3]
(IEC 60079-10-2:2009, 6.2, modified)
3.2 Symbols and abbreviations
a Amortization rate .
...