SIST-TP CLC/TR 50427:2005
(Main)Assessment of inadvertent ignition of flammable atmospheres by radio-frequency radiation - Guide
Assessment of inadvertent ignition of flammable atmospheres by radio-frequency radiation - Guide
This standard provides guidance in assessing the possibility of inadvertent extraction of energy from an electromagnetic field propagated from communication, radar or other transmitter aerials and the coupling of this energy to an EED in a manner capable of causing initiation. It does not cover the similar hazard arising from electromagnetic fields generated by other means, for example electrical storms, electricity generating plant or power transmission lines, nor does it cover the potential hazards that may arise in oil and gas exploration and production operations
Leitfaden zur Verhinderung der unbeabsichtigten Zündung explosionsfähiger Atmosphären durch hochfrequente Strahlung
Evaluation des risques d'inflammation des atmosphères inflammables par des rayonnements de radiofréquence - Guide
Ugotavljanje nenamernega vžiga vnetljivih atmosfer z radiofrekvenčnim sevanjem - Vodilo
General Information
Standards Content (Sample)
SLOVENSKI STANDARD
SIST-TP CLC/TR 50427:2005
01-april-2005
8JRWDYOMDQMHQHQDPHUQHJDYåLJDYQHWOMLYLKDWPRVIHU]UDGLRIUHNYHQþQLPVHYDQMHP
9RGLOR
Assessment of inadvertent ignition of flammable atmospheres by radio-frequency
radiation - Guide
Leitfaden zur Verhinderung der unbeabsichtigten Zündung explosionsfähiger
Atmosphären durch hochfrequente Strahlung
Evaluation des risques d'inflammation des atmosphères inflammables par des
rayonnements de radiofréquence - Guide
Ta slovenski standard je istoveten z: CLC/TR 50427:2004
ICS:
13.230 Varstvo pred eksplozijo Explosion protection
13.280 Varstvo pred sevanjem Radiation protection
SIST-TP CLC/TR 50427:2005 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
---------------------- Page: 1 ----------------------
SIST-TP CLC/TR 50427:2005
---------------------- Page: 2 ----------------------
SIST-TP CLC/TR 50427:2005
TECHNICAL REPORT CLC/TR 50427
RAPPORT TECHNIQUE
TECHNISCHER BERICHT December 2004
ICS 13.230; 33.060.20
English version
Assessment of inadvertent ignition of flammable atmospheres
by radio-frequency radiation –
Guide
Evaluation des risques d'inflammation Leitfaden zur Verhinderung
des atmosphères inflammables der unbeabsichtigten Zündung
par des rayonnements de explosionsfähiger Atmosphären
radiofréquence – durch hochfrequente Strahlung
Guide
This Technical Report was approved by CENELEC on 2004-08-28.
CENELEC members are the national electrotechnical committees of Austria, Belgium, Cyprus, Czech
Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy,
Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Slovakia, Slovenia,
Spain, Sweden, Switzerland and United Kingdom.
CENELEC
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
Central Secretariat: rue de Stassart 35, B - 1050 Brussels
© 2004 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.
Ref. No. CLC/TR 50427:2004 E
---------------------- Page: 3 ----------------------
SIST-TP CLC/TR 50427:2005
CLC/TR 50427:2004 – 2 –
Foreword
This Technical Report was prepared by the Technical Committee CENELEC TC 31, Electrical apparatus for
explosive atmospheres - General requirements.
The text of the draft was submitted to the formal vote and was approved by CENELEC as
CLC/TR 50427 on 2004-08-28.
___________
---------------------- Page: 4 ----------------------
SIST-TP CLC/TR 50427:2005
– 3 – CLC/TR 50427:2004
Contents
Introduction .6
1 Scope.7
2 Normative references.7
3 Terms and definitions.7
4 Symbols and abbreviations .9
4.1 Modulation codes.9
4.2 Polarization codes.10
5 General considerations .10
5.1 Radio-frequency hazard.10
5.2 Philosophy of systematic method of approach .11
5.3 Responsibility for making the hazard assessment.11
6 Transmitters and transmitter output parameters .12
6.1 Types of transmitter .12
6.2 Frequency range.12
6.3 Transmitter output power .12
6.4 Antenna gain.12
6.5 Modulation factors.12
6.5.1 General.12
6.5.2 Frequency modulation (FM).13
6.5.3 Amplitude modulation (AM).13
6.5.4 Single sideband (SSB) operation.13
6.5.5 Pulsed radar.13
7 Structures and spark-making mechanisms .14
7.1 Structures.14
7.2 Loop-type structures .14
7.3 Vertical structures .16
7.4 Spark-making mechanisms.17
8 Ignition of flammable atmospheres.17
8.1 Flammable atmospheres .17
8.2 Ignition by radio-frequency discharges .17
8.3 Criteria for ignition.18
8.3.1 Effectively continuous transmissions .18
8.3.2 Radar transmissions .18
9 Practical measurements and tests.19
9.1 Measurement of electromagnetic fields .19
9.2 Measurement of extractable power.19
9.3 Test transmissions .20
9.4 Incendivity tests.20
---------------------- Page: 5 ----------------------
SIST-TP CLC/TR 50427:2005
CLC/TR 50427:2004 – 4 –
10 Methods of assessment for determining potential RF ignition hazards on a plant
containing hazardous areas.21
10.1 General.21
10.2 Basis of the theoretical assessments .21
10.2.1 General.21
10.2.2 Initial assessment.22
10.2.3 Full assessment .22
10.3 Initial assessments.32
10.3.1 Initial assessment of the risk from a particular transmitter site.32
10.3.2 Initial assessment for a particular plant.33
10.4 Full assessment procedure.34
10.4.1 Procedure.34
10.4.2 Information to be obtained .35
10.4.3 Calculation of effective field strengths .35
10.4.4 Calculation of extractable power or energy.41
10.4.5 Comparison of the total extractable power or energy from the structure with the
threshold values detailed in Clause 8 .43
10.5 Practical on-site tests.46
10.5.1 Procedure.46
10.5.2 Plant and transmitter both in existence (Case 1 of Figure 3).46
10.5.3 Existing plant and proposed transmitter (Case 2 of Figure 3) .47
10.5.4 Existing transmitter and proposed plant (Case 3 of Figure 3) .48
11 Plant safety measures .49
11.1 General.49
11.2 Bonding.49
11.3 Insulation.50
11.4 Reducing the structure efficiency.50
11.5 De-tuning of structures.50
12 Special cases.51
12.1 Cranes.51
12.2 Mobile and portable transmitters.51
12.3 Ships.51
12.3.1 General.51
12.3.2 Ships in harbour areas.52
12.3.3 Ships at sea .52
12.4 Offshore oil and gas installations.53
12.4.1 General.53
12.4.2 Structures on offshore installations.53
12.4.3 Assessment procedures.53
12.4.4 Radio frequency transmitters and vulnerable zones.54
12.4.5 Safety measures and recommendation .55
---------------------- Page: 6 ----------------------
SIST-TP CLC/TR 50427:2005
– 5 – CLC/TR 50427:2004
Annex A (informative) Sources of information and addresses of some advisory bodies.59
Annex B (informative) Electromagnetic radiated fields and examples of radiating antenna and
unintended receiving antenna characteristics .61
Annex C (informative) Subdivision of group II flammable gases and vapours.69
Annex D (normative) Measurement of electromagnetic fields .74
Annex E (normative) Methods of measurement on structures (on-site tests).78
Annex F (informative) Derivation of vulnerable zone distances for Table 5, Table 6 and Table 10 .84
Annex G (informative) Worked examples of full assessment procedure .85
Annex H (informative) Ground-wave propagation (vertical polarization) -
Calculation of field strength .94
Bibliography.96
---------------------- Page: 7 ----------------------
SIST-TP CLC/TR 50427:2005
CLC/TR 50427:2004 – 6 –
Introduction
Electromagnetic waves produced by radio-frequency (RF) transmitters (e.g. radio, television and radar)
will induce electric currents and voltages in any conducting structure on which they impinge. The
magnitude of the induced current and voltages depends upon the shape and size of the structure relative
to the wavelength of the transmitted signal and on the strength of the electromagnetic field. When parts of
the structure normally in contact are caused to break or separate momentarily (e.g. during maintenance
or as a result of vibration) a spark may occur if the induced voltage and current is sufficiently large. If this
happens in a location where a potentially flammable atmosphere may be present a hazardous situation
can occur. However, the possibility of ignition will depend on many factors including whether the spark
can deliver sufficient energy to ignite a particular flammable atmosphere.
This European Technical Report provides a systematic approach to assist transmitter operators, plant
managers and all others concerned with a logical method for the assessment and elimination of RF
induced ignition hazards.
The assessment procedures recommended in this European Technical Report are based on
measurements of the powers and energy that can be extracted from typical structures, including cranes,
and measurements of the minimum powers and energy that are required to ignite various flammable
atmosphere gas groups.
The assessment procedures for probability of ignition recommended in this European Technical Report
are based on the assumption that worst case conditions apply at all times. The critical features are the
coincidence of the structure in resonance and the presence of the gas/air mixture in the optimum
proportions for RF spark ignition. Deviation from these optimum conditions will result in significantly
higher powers being required for ignition.
NOTE 1 Several studies have been performed which indicate that the power could be twice as great for an assumed risk as
detailed in reference [1], if due allowance is taken for probabilistic effects. In order to achieve a probability of ignition comparable
with other risks, it would be necessary for effective extractable power calculated to be twice the values determined according to this
European Technical Report. The probabilistic elements could be taken into consideration following further research work and
practical experience.
NOTE 2 If allowances for probabilities are to be applied then expert advice should be sought.
---------------------- Page: 8 ----------------------
SIST-TP CLC/TR 50427:2005
– 7 – CLC/TR 50427:2004
1 Scope
This European Technical Report provides guidance on assessing the potential ignition hazard from the
inadvertent extraction of energy from electromagnetic fields, propagated from communication, radar or
other transmitting antennas to plant where a potentially flammable atmosphere may be present. The
frequency range covered by this European Technical Report is 9 kHz to 60 GHz. This European
Technical Report does not apply to similar hazards arising from electromagnetic fields generated by other
means, such as electric storms, electricity generating installations or other radiating electrical equipment,
nor does it apply to any hazard arising within telecommunication or other electronic equipment.
NOTE 1 The methods of assessment from 9 GHz to 60 GHz are based on extrapolation of data for frequencies below 9 GHz.
NOTE 2 The ignition of dust is not covered in this European Technical Report. This European Technical Report also provides
advice on how to mitigate the hazard in cases where the assessment indicates that a hazard may exist. This European Technical
Report does not cover the hazards associated with the use of electro-explosive devices (EED) (see CLC/TR 50426), or the
biological hazards of exposure to RF fields.
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.
Publication Year Title
EN 60079-0 Electrical apparatus for explosive gas atmospheres —
Part 0: General requirements (IEC 60079-0)
EN 50020 Electrical apparatus for potentially explosive atmospheres —
Intrinsic safety “i”
EN 60079-10 Electrical apparatus for explosive gas atmospheres —
Part 10: Classification of hazardous areas (IEC 60079-10)
3 Terms and definitions
For the purposes of this European Technical Report the following terms and definitions apply.
3.1
circuit factor, Q
k
performance parameter for a structure acting as a receiving antenna (see [2])
NOTE Assuming the structure to be tuned to the transmission frequency f , Q is the ratio of f to Δf, where Δf is the difference
t k t
between those frequencies, one above and one below f , at which the structure resonates when it is re-tuned so that the open circuit
t
voltage at f has fallen by 3 dB. Q is closely related to the Q factor of a tuned circuit.
t k
3.2
extractable power, P
max
power dissipated in a resistive load connected across a discontinuity in a structure acting as a receiving
antenna
NOTE The extractable power reaches its maximum when the structure is tuned to the frequency of the transmitter (under these
conditions the impedance of the structure presents a resistive value only, with no reactive components), and the load resistance is a
value equal to that of the structure.
3.3
modulus match power, P
mm
maximum value of extractable power that can be achieved with a resistive load at a frequency to which
the structure is not tuned (see [2])
---------------------- Page: 9 ----------------------
SIST-TP CLC/TR 50427:2005
CLC/TR 50427:2004 – 8 –
3.4
structure efficiency
ratio of the extractable power that the structure can deliver to a matched load and the maximum
extractable power delivered by a lossless short dipole in free space immersed in the same field
3.5
thermal initiation time
time during which energy deposited by the spark accumulates in a small volume of gas around it without
significant thermal dissipation
NOTE For times shorter than the thermal initiation time the total energy deposited by the spark will determine whether or not
ignition occurs. For increasingly longer times, the power or rate at which energy is deposited becomes the determining factor for
ignition.
3.6
vulnerable zone
region surrounding a transmitter in which a potential hazard could arise within a hazardous area of a plant
3.7
far field
region, distant from the transmitter, in which the field strength is inversely proportional to distance in the
absence of ground reflection
NOTE The inner limit of the far field is generally regarded as the distance d from the transmitter defined as follows. For frequencies
2
up to and including 30 MHz, d = 8H /λ where H is the height of the top of the antenna above ground and λ is the wavelength. At
2
frequencies above 30 MHz, d = 2W /λ where W is the width of the antenna.
3.8
near field
region close to the transmitter which lies within the far field region
NOTE In the near field region the dependence of the field strength on distance is complex and mutual coupling effects can also
affect the value of extractable power.
3.9
flammable atmosphere
gas/air or vapour/air mixture capable of being ignited which can occur in a hazardous area
NOTE See EN 60079-10 for further information.
3.10
equivalent isotropically radiated power (EIRP)
product of the power supplied to the antenna and the antenna gain in a given direction relative to an
isotropic antenna (absolute or isotropic gain)
3.11
effective field strength
value of electric field strength due to a single transmitter which is derived from the transmitter
characteristics, modulation factors (see 6.5) and distance, and is used for the calculation of extractable
power
3.12
antenna gain
gain produced by an antenna concentrating radiation in a particular direction
NOTE 1 The gain of an antenna is always related to a specified reference antenna.
---------------------- Page: 10 ----------------------
SIST-TP CLC/TR 50427:2005
– 9 – CLC/TR 50427:2004
NOTE 2 The gain, G, of an antenna in a particular direction is given by the equation: G = (1) where R is the power in Watts, W,
that should be radiated from the reference antenna; A is the power in Watts, W, that should be radiated from the given antenna to
give the same field strength at a fixed distance in that direction.
R
G = (1)
A
where
R is the power in Watts, W, that should be radiated from the reference antenna;
A is the power in Watts, W, that should be radiated from the given antenna to give the same field strength at a fixed
distance in that direction.
NOTE 3 The gain, which is often expressed in logarithmic form, is stated in decibels.
3.13
hazard
potential source of danger to life, limb or health, or of discomfort to a person or persons, or of damage to
property
3.14
safe distance
distance outside which it is considered that there is no potential hazard
4 Symbols and abbreviations
4.1 Modulation codes
AM Amplitude-modulated speech or music transmission. Carrier power quoted.
MCW Amplitude-modulated tone transmission. Carrier power quoted.
TV Amplitude-modulated video transmission. Peak power quoted.
R ( ) Pulse-modulated radar transmission. Peak power quoted. The number in brackets indicates
the pulse duration in s where known.
FM Frequency modulation.
FSK Frequency shift keying.
GFSK Gaussian frequency shift key modulation.
SSB Single sideband transmission. Peak envelope power quoted.
CW Continuous wave.
MSK Minimum shift keying.
GMSK Gaussian minimum shift keying.
CDMA Code division multiple access.
PCM Pulse code modulation.
PSK Phase shift keying.
PM Phase modulation.
DQPSK Differential quadrature phase shift keying.
---------------------- Page: 11 ----------------------
SIST-TP CLC/TR 50427:2005
CLC/TR 50427:2004 – 10 –
4.2 Polarization codes
V Vertical polarization.
H Horizontal polarization.
V/H Either vertical or horizontal polarization, or both simultaneously.
5 General considerations
5.1 Radio-frequency hazard
For a radio-frequency hazard assessment, detailed consideration should be taken of the conditions that
have to be satisfied simultaneously for a hazard to exist. These are as follows:
NOTE 1 The simultaneous occurrence of these four conditions is unlikely.
NOTE 2 See [3] for further information.
a) electromagnetic radiation of sufficient intensity;
NOTE 3 An electromagnetic field of sufficient intensity may be generated by a fixed/mobile or portable transmitter, the
magnitude of the field depending upon the transmitted power, the antenna gain and the proximity to the site under
consideration.
NOTE 4 Intense electromagnetic fields are also generated by the intentional radio frequency sources in industrial, scientific
and medical (ISM) equipment. Field strengths in the order of 10 V/m may be present in the near vicinity of the equipment.
Typical characteristics of industrial equipment are:
2,5 GHz to 10 kW
915 MHz to 100 kW industrial microwaves
27 MHz to (10 to 50) kW
welding or drying techniques
13,56 MHz to (10 to 50) kW
b) presence of a structure capable of behaving as a receiving antenna. Only structures in a
hazardous area (as defined in EN 60079-10) should be considered (see Clause 7 and Clause 8);
c) existence of a mechanism whereby the received energy or power can be delivered as a spark;
d) presence of a flammable atmosphere (see Clause 8).
All conducting structures behave as receiving antennas, but the magnitude of induced current and voltage
depends upon the method of construction and the configuration. Experience gained in practical
measurements on structures has shown that for frequencies up to and including 30 MHz, the loop
configuration is the most efficient receiving system (see [4]). At higher frequencies all structures are large
compared with a wavelength and their behaviour is conveniently treated by the use of long dipole theory.
The behaviour of these structures is described in Clause 7.
The generation of a spark is dependent upon the appearance of a small discontinuity in a receiving
structure, for example when parts of a structure normally in contact are caused to separate, either during
maintenance or at any time by flexing, mechanical vibration or similar actions.
The spark energy required to ignite a flammable atmosphere depends upon the nature and composition
of the flammable atmosphere. In making the assessment, it is assumed that the composition is at its
optimum for ignition to take place. This in itself provides a margin of safety under most circumstances,
since the energy required for ignition of a particular atmosphere generally increases rapidly as its
composition moves away from the optimum.
---------------------- Page: 12 ----------------------
SIST-TP CLC/TR 50427:2005
– 11 – CLC/TR 50427:2004
5.2 Philosophy of systematic method of approach
This European Technical Report is based on a series of graded assessments, each requiring a
progressively more detailed analysis.
The initial assessment procedure is designed to eliminate from further consideration those locations
where it is highly unlikely that a hazard exists. It is based on “realistic worst case” estimates of the radius
of the zone around different classes of transmitter within which a hazard might result from the presence of
a structure in a hazardous area.
If the initial assessments indicate that a hazard might exist, the full assessment procedure given in 10.4
should be followed. This provides a method of computing the maximum power available in any spark
produced, based on more detailed information about the actual transmitter and plant and their relative
location. This calculated power should then be compared with the minimum power required to ignite the
particular flammable atmosphere concerned (see Table 2, Table 3 and Figure 4).
When this procedure is followed, it will quickly become apparent whether the available information is
adequate for an assessment to be made with a high degree of confidence or whether additional
information is required from practical measurements on site. If doubt exists, then expert opinion should be
sought (see Annex A).
The assessment procedures in this European Technical Report determine whether ignition is possible
under worst case conditions. No account is taken of any effects that could influence the probability of
ignition. An inherent safety factor exists for many circumstances.
The assessment procedures recommended in Clause 10 apply generally to most circumstances. For
cranes, mobile transmitters and oil rigs the special considerations described in Clause 12 should be taken
into account.
5.3 Responsibility for making the hazard
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.