Assessment of inadvertent initiation of bridge wire electro-explosive devices by radio-frequency radiation - Guide

This standard provides guidance in assessing the potential ignition hazard from the inadvertent extraction of energy from electromagnetic fields, propagated from communication, radar or other transmitting aerials to plant where a potentially flammable atmosphere may be present. The standard is not concerned with similar hazards arising from electromagnetic fields generated by other means, such as electric storms, electricity generating installations or other radiating electrical equipment, nor is it concerned with any hazard arising within telecommunications or oter electronic equipment

Leitfaden zur Verhinderung des unbeabsichtigten Auslösens einer Zündeinrichtung mit Brückendraht durch hochfrequente Strahlung

Evaluation de la création par inadvertance de dispositifs électro-explosifs par pont métallique, par rayonnement de radiofréquence - Guide

Ugotavljanje nenamernega radiofrekvenčnega proženja elektroeksplozivnih naprav - Vodilo

General Information

Status
Published
Publication Date
31-Mar-2005
Current Stage
6060 - National Implementation/Publication (Adopted Project)
Start Date
01-Apr-2005
Due Date
01-Apr-2005
Completion Date
01-Apr-2005

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SLOVENSKI SIST-TP CLC/TR 50426:2005
STANDARD
april 2005
Ugotavljanje nenamernega radiofrekvenčnega proženja elektroeksplozivnih
naprav - Vodilo
Assessment of inadvertent initiation of bridge wire electro-explosive devices by
radio-frequency radiation – Guide
ICS 13.230; 29.260.20 Referenčna številka
SIST-TP CLC/TR 50426:2005(en)

© Standard je založil in izdal Slovenski inštitut za standardizacijo. Razmnoževanje ali kopiranje celote ali delov tega dokumenta ni dovoljeno

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TECHNICAL REPORT CLC/TR 50426
RAPPORT TECHNIQUE
TECHNISCHER BERICHT December 2004
ICS 13.230; 29.260.20; 33.060.20
English version
Assessment of inadvertent initiation of bridge wire
electro-explosive devices by radio-frequency radiation –
Guide
Evaluation de la création Leitfaden zur Verhinderung
par inadvertance de dispositifs des unbeabsichtigten Auslösens
électro-explosifs par pont métallique, einer Zündeinrichtung mit Brückendraht
par rayonnement de 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 50426:2004 E
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CLC/TR 50426:2004 – 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 50426 on 2004-08-28.
___________
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– 3 – CLC/TR 50426:2004
Contents

Introduction............................................................................................................................... 5

1 Scope ................................................................................................................................ 6

2 Normative references ....................................................................................................... 6

3 Terms and definitions ...................................................................................................... 6

4 Symbols and abbreviations.............................................................................................. 8

4.1 Modulation codes ...................................................................................................... 8

4.2 Polarization codes ..................................................................................................... 9

5 General considerations .................................................................................................... 9

5.1 Radio-frequency hazard ............................................................................................ 9

5.2 Philosophy of the systematic method of approach ................................................... 10

5.3 Responsibility for making the hazard assessment.................................................... 10

5.4 Recommended practices for radio silence in offshore operations............................. 11

6 Transmitters and transmitter output parameters.......................................................... 11

6.1 Types of transmitters............................................................................................... 11

6.2 Frequency range ..................................................................................................... 11

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) ......................................................................... 12

6.5.3 Amplitude modulation (AM).......................................................................... 12

6.5.4 Single sideband (SSB) operation ................................................................. 13

6.5.5 Pulsed radar................................................................................................ 13

7 Circuits for blasting and well perforation ..................................................................... 13

7.1 General ................................................................................................................... 13

7.2 Typical blasting circuit layouts................................................................................. 14

7.2.1 General ....................................................................................................... 14

7.2.2 Extended line blasts .................................................................................... 14

7.2.3 Benching or 3-dimensional blasts ................................................................ 15

7.2.4 Multipattern blasts ....................................................................................... 16

7.2.5 Shaft sinking................................................................................................ 16

7.2.6 Demolition work........................................................................................... 17

7.3 Circuits formed during well-perforating using wireline .............................................. 18

8 Electro-explosive devices .............................................................................................. 21

8.1 General ................................................................................................................... 21

8.2 Commercial EED ..................................................................................................... 21

8.3 EED hazard threshold ............................................................................................. 23

8.4 Common mode operation ........................................................................................ 24

9 Methods of assessment for determining potential RF ignition hazards on a site

where EED are used ....................................................................................................... 24

9.1 General ................................................................................................................... 24

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CLC/TR 50426:2004 – 4 –

9.2 Basis of the theoretical assessments for land sites.................................................. 28

9.2.1 General ....................................................................................................... 28

9.3 Initial assessment for land sites............................................................................... 36

9.3.1 Initial assessment of the risk from a particular transmitter site ..................... 36

9.3.2 Initial assessment for a particular site using EED ........................................ 36

9.4 Full assessment procedure for land sites................................................................. 37

9.4.1 Procedure.................................................................................................... 37

9.4.2 Information to be obtained ........................................................................... 37

9.4.3 Calculation of effective field strength ........................................................... 38

9.5 Safe field strength ................................................................................................... 45

9.5.1 General ....................................................................................................... 45

9.5.2 Single EED.................................................................................................. 45

9.5.3 Single EED with extended leading wires ...................................................... 46

9.5.4 EED in typical quarry/demolition firing circuits ............................................. 46

9.5.5 EED in well-perforating drilling operations ................................................... 61

9.6 Multiple transmissions ............................................................................................. 63

9.6.1 General ....................................................................................................... 63

9.6.2 Multiple-transmission assessments for quarry/demolition sites .................... 64

9.6.3 Multiple transmission assessments for well-perforating drilling operations ... 65

9.7 Assessments for offshore drilling operations............................................................ 68

10 Practical on-site testing ................................................................................................. 68

11 Safety procedures .......................................................................................................... 69

11.1 General procedures................................................................................................. 69

11.2 Alternative means of firing....................................................................................... 69

12 Special applications ....................................................................................................... 69

12.1 Semi-permanent installations .................................................................................. 69

12.2 Flammable hazard situations ................................................................................... 69

12.3 Use of transmitters in mines and quarries................................................................ 70

12.4 Safety in transit ....................................................................................................... 70

Annex A (informative) Extraction of energy from the electromagnetic field ............................................. 71

Annex B (informative) Measurement of electromagnetic fields................................................................ 72

Annex C (informative) Sources of information and addresses of advisory bodies - UK ONLY ............... 76

Annex D (informative) Electromagnetic radiated fields and examples of radiating antennas

and unintended receiving antenna characteristics............................................................................ 78

Annex E (informative) The effective resistance of the leading wires of an EED...................................... 86

Annex F (informative) Derivation of minimum distances of safe approach for Table 2 and Table 3 ....... 92

Annex G (informative) Ground-wave propagation (vertical polarization): calculation

of field strength.................................................................................................................................. 94

Annex H (informative) Worked examples to demonstrate the effects of antenna gain............................ 96

Annex I (informative) The effects of leading wire resistance, safety resistors and the use of

EED with different characteristics ................................................................................ 97

Annex J (informative) Derivation of Figure 12a) to Figure 12g) for EED alone incorporating

the resistance of leading wires and safety resistances................................................................... 100

Bibliography.......................................................................................................................... 101

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Introduction

Electromagnetic waves produced by radio-frequency (RF) transmitters (e.g. radio, television and radar)

will induce electric currents and voltages in any firing circuit including leading wires of the electro-

explosive device (EED) on which they impinge. The magnitude of the induced current and voltages

depends upon the configuration of the firing circuit and leading wires relative to the wavelength of the

transmitted signal and on the strength of the electromagnetic field. If the induced current which is

transferred to the EED is in excess of the no fire current then the EED could initiate. This European

Technical Report provides a systematic approach to assist transmitter operators, quarry managers and all

others concerned with a logical method for the assessment and elimination of the initiation of EED by RF.

The assessment procedures contained in this European Technical Report are based on measurements of

the powers and current that can be extracted from typical firing circuits and leading wires and on the

physical electrical parameters of various types of EED.
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CLC/TR 50426:2004 – 6 –
1 Scope

This European Technical Report provides guidance on assessing the possibility of inadvertent extraction

of energy from an electromagnetic field propagated from radio frequency (RF), radar or other transmitter

antennas and the coupling of this energy to an electro-explosive device (EED) in a manner capable of

causing initiation. The frequency range covered by this European Technical Report is 9 kHz to 60 GHz.

This European Technical Report only applies to bridge-wire devices which are directly initiated by radio

frequency current and does not apply to special detonators, for example, electronic detonators. It does not

cover the similar hazard arising from electromagnetic fields generated by other means, for example

electric storms, electricity generating plant or power transmission lines.
This European Technical Report does not apply to the following equipment:

− air bag igniters for automotive applications (including the igniters before they are fitted);

− special pyrotechnic devices;
− pyromechanisms;
− igniters for fireworks;
− special military devices;
− special safety equipment.

NOTE The methods of assessment from 9 GHz to 60 GHz are based on extrapolation of data for frequencies below 9 GHz.

2 Normative references
No normative references are made in this standard.
3 Terms and definitions

For the purposes of this European Technical Report the following terms and definitions apply.

3.1
duty cycle

product of pulse duration (in seconds) and the pulse repetition frequency (in pulses per second)

3.2
electro-explosive device (EED)

one shot explosive or pyrotechnic device initiated by the application of electrical energy

NOTE EED is used to refer to either a single electro-explosive device or several devices, to comply with general practice within the

industry.
3.3
hazard

potential source of danger to life, limb or health, or of discomfort to a person or persons, or of damage to

property
3.4
safe distance
distance outside which it is considered that there is no potential hazard
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– 7 – CLC/TR 50426:2004
3.5
no-fire energy/power/voltage/current

maximum energy or steady state power/voltage/current that will not cause initiation of the most sensitive

EED of any particular design

NOTE The manufacturing tolerances permitted during the production of EED will cause normal statistical variation in their firing

characteristics. The most sensitive EED permitted by this variation sets the appropriate no-fire level, which is generally accepted as

a probability no greater than 0,01 %, with a confidence level of 95 %.
3.6
round of charges (shot)

one or more primed explosive charges or shots, for example main charge, primer (if used) and detonator

3.7
toe shot
shot designed to clear the foot of a face, for example a quarry face
3.8
hazard area

area, of any shape, containing the transmission source or sources and within which the radiation

magnitude exceeds the designated hazard threshold
3.9
hazard threshold

mean power flux density or field strength that would permit only a negligible probability of EED initiation

3.10
exploder
means whereby a round of charges (shot) is fired electrically
3.11
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)
3.12
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
3.13
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.

NOTE 2 The gain, G, of an antenna in a particular direction is given by the equation:

G =
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.
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CLC/TR 50426:2004 – 8 –

NOTE 3 The gain, which is often expressed in logarithmic form, is stated in decibels.

3.14
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

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

d W λ W
frequencies above 30 MHz, = 2 / where is the width of the antenna.
3.15
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.
3.16
leading wire resistance
total d.c. resistance of the leading wires excluding that of the EED itself
3.17
bridge wire resistance
internal d.c. resistance of the EED alone
3.18
safety resistor

resistor or resistors placed within the casing of an EED in order to desensitize it to the external electrical

environment
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
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– 9 – CLC/TR 50426:2004
CDMA Code division multiple access.
PCM Pulse code modulation
PSK Phase shift keying
PM Phase modulation
DQPSK Differential quadrature phase shift keying.
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 radio-frequency hazard assessment detailed consideration should be taken of the conditions that have

to be satisfied simultaneously for the hazard to exist. These are as follows:
a) an electromagnetic field of sufficient intensity;

NOTE 1 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 of the site under

consideration.

NOTE 2 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) a means of extracting power from the electromagnetic field;

c) an EED in a situation such that it can accept power or energy from the extracting device.

The procedures contained within this European Technical Report for assessing the presence of a potential

hazard are based on a number of reasonable “worst-case” assumptions. They are based upon both

experimental evidence and engineering judgement. Taken together these give a substantial margin of

safety due to the extremely low probability of concurrence of all the worst-case factors. No extra, arbitrary,

safety factors are included.
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CLC/TR 50426:2004 – 10 –

All conducting materials behave as receiving antennas, but the magnitude of the induced current and

voltage depends upon the circuit configuration, that is, whether the EED is in a firing circuit or by itself.

Experience gained indicates that for frequencies below 7 MHz it is the loop firing circuit which is the most

sensitive whereas for higher frequencies it is the EED and its leading wires alone. The behaviour of these

circuit configurations is described in Clause 7.
5.2 Philosophy of the systematic method of approach

A potential hazard only exists in relatively few locations, with only a small number of incidents reported

that are possibly attributable to this cause.

This European Technical Report is based on a series of graded assessments, each requiring a

progressively more detailed analysis.

The initial assessments are designed to eliminate from further consideration those locations where it is

highly unlikely that a hazard exists. They are based on “realistic worst-case” estimates of the minimum

distance of safe approach around different classes of transmitter within which a hazard might exist from

the presence of a particular circuit configuration in this area.

For land based operations, if the initial assessments given in 9.3 indicate that a hazard might exist, the full

assessment procedure given in 9.4 should be followed. For offshore operations the assessment in 9.7

should be followed. These provide a method of computing the field strength available from the

transmitters, based on detailed information about the transmitters and their location relative to the site.

The calculated field strength should then be compared to those that are required to initiate an EED in

various circuit configurations, whether in a loop firing circuit or with the leading wires acting as a dipole.

When this systematic assessment 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 on-site measurements (see Clause 10 and

Annex B). If doubt exists, then expert opinion should be sought (see Annex C).

The assessment procedures recommended in Clause 9 apply generally to most circumstances. For

offshore and land based well-perforating operations the special considerations described in 7.3, 9.5.5 and

9.6.3 should be taken into account.
5.3 Responsibility for making the hazard assessment

The radio-frequency (RF) environment is becoming increasingly severe, with the proliferation of

transmitting sources and increased transmitter powers and the exploitation of new techniques.

NOTE 1 Legislation, (for example in the UK see [1]) requires that employers safeguard both their employees and others who may

be placed at risk by their activities. Hence, both operators of RF transmitters and users of EED have a responsibility to ensure safe

operation.

NOTE 2 Particular locations such as mines and quarries may exist where additional responsibilities are placed on the owners and

managers.

Operators of a proposed site in which EED are to be used should request details from the transmitter

operators about relevant transmitters in the locality of the site. The transmitter operators should include

details of transmitters for broadcast, commercial, military, air traffic and emergency services such as

police, fire and ambulance. The site operator should then use the assessment procedures given in this

European Technical Report, if necessary in consultation with the transmitter operators concerned.

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– 11 – CLC/TR 50426:2004

Similarly, an operator of a proposed new (or altered) transmitter should contact all operators of sites

where EED are used within the minimum distance of safe approach for the transmitter, and use the

procedure given in this European Technical Report to assess the potential hazard at each location.

Where both the site and the transmitter already exist but an assessment is required, the site operator

should be held responsible for ensuring that the assessment is made. If for some reason relevant

information cannot be made available to the body responsible for the assessment, the responsibility for

having the assessment carried out should be assumed by the body unable to release the necessary

information.

NOTE 3 As an aid to those who need to make a hazard assessment but do not have the necessary technical resources, a list of

sources of information and specialist organizations capable of providing consultation or test facilities is given in Annex C.

5.4 Recommended practices for radio silence in offshore operations

The position adopted by many offshore operators has been to switch off all transmissions from the

installation during the surface preparation of the explosive tool until its immersion in the well at 70 m below

sea bed level. At this point services would be restored until the explosive tool was returned to a similar

depth on the upward journey when all services would again be cut off. Following its removal from the well

and inspection to ensure its safe condition, services would be restored provided no further explosive

handling was to take place.

However, too great a reliance on all-embracing curtailment of services can itself present a potential

hazard to structures which employ radio communication for safety reasons and as an integral part of

product transportation systems (pipelines). The identification of these difficulties has highlighted the need

for the hazard to be more accurately quantified in order to minimize the disruption of other necessary

operations and to avoid the creation of further potential hazards.
6 Transmitters and transmitter output parameters
6.1 Types of transmitters

This clause provides information on various types of transmitter and transmitting systems. This information

is necessarily rather brief for certain types of radar and other military equipment but basic details are given

and further information may be sought from the specialist organizations listed in Annex C. Typical types of

antenna installations are shown in Figure D.1.
6.2 Frequency range

The main frequency range covered is 9 kHz to 60 GHz. The types of transmitter considered include the

following:

a) radio and television broadcast transmitters in specific bands in the range 0,15 MHz to 1 000 MHz;

b) fixed and mobile transmitters for communication purposes, private, commercial and amateur, in

specific bands above 0,4 MHz and for military use above 0,15 MHz;
c) radar, in specific bands at 220 MHz, 600 MHz and above 1 GHz;
d) navigational equipment, non-directional beacons, etc., from 9 kHz upwards.
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CLC/TR 50426:2004 – 12 –
6.3 Transmitter output power

Transmitter output power from several watts up to megawatts may be encountered depending on the

frequency range and the application. The method of specifying the power varies, which is significant for

the hazard assessment when highly directional antennas are in use and when considering different

modulation systems. In general, values are specified in the technical documentation for either the carrier

or peak power output from the transmitter together with the antenna gain, although the product of the two

is often quoted in the technical documentation to give the equivalent isotropically radiated power (EIRP).

6.4 Antenna gain

The reference antenna is often an isotropic antenna that radiates uniformly in all directions. Although this

is a purely hypothetical concept it is nevertheless very useful for reference purposes. When the gain of an

antenna relative to an isotropic reference antenna is stated in decibels it is denoted by dBi. In practice, the

gain of an antenna is often expressed relative to a half-wave dipole which itself has a gain of 1,64 (or

2 dB
...

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