BS 6656:1991

Committees responsible
Foreword
Guide
1 Scope
2 Definitions
3 General considerations
4 Transmitters and transmitter output parameters
5 Structures and spark-making mechanisms
6 Ignition of flammable atmospheres
7 Practical measurements and tests
8 Methods of assessment
9 Plant safety measures
10 Special cases
Appendices
A Electromagnetic radiated fields and examples of
    aerial characteristics
B Subdivision of group II flammable gases and vapours
C Measurement of electromagnetic fields
D Methods of measurement on structures (on-site tests)
E Orford Ness transmitter site
F Examples of full assessment procedure
G Ground-wave propagation (vertical polarization):
    calculation of field strength
H Sources of information
Tables
1 Representative gases for gas groups
2 Radio-frequency power thresholds for structures
    excluding cranes
3 Radio-frequency energy thresholds for all structures
4 Radii of vulnerable zones
5 Radii of vulnerable zone for small structures at
    frequencies less than 30 MHz
6 Maximum radii of vulnerable zones
7 Radio-frequency power threshold for cranes
8 Maximum radii of vulnerable zones for ships'
    transmitters
9 Transmitters on platforms
10 Aerials for vertical polarization, for frequencies
    up to 30 MHz
11 Aerials for horizontal polarization, for frequencies
    up to 30 MHz
12 Aerials for frequencies above 30 MHz
13 Subdivision IIA
14 Subdivision IIB
15 Subdivision IIC
16 Extent of vulnerable zones (structure perimeter p >
    40 m)
17 Extent of vulnerable zones (structure perimeter p <
    or = 40 m)
18 Transmitter data (example 1)
19 Plant data (example 1)
20 Transmitter data (example 2)
21 Plant data (example 2)
22 Effective field strength for station transmitters
    (example 2)
23 Maximum extractable power from station transmissions
    (example 2)
24 Total extractable power at fr = 1.1 MHz (example 2)
25 Total extractable power at fr = 1.2 MHz (example 2)
26 Total extractable power at fr = 1.45 MHz (example 2)
27 Transmitter data (example 3)
28 Plant data (example 3)
29 Peak field strength for radar transmitters (example
    3)
30 Energy in structure from from pulse transmissions
    (example 3)
31 Advisory bodies
Figures
1 Typical loop-type structures
2 Assessment procedure flow chart
3 On-site test procedure flow chart
4 Safe threshold field strength versus frequency for
    single unmodulated transmissions
5 Field strength versus distance (land path)
6 Field strength versus distance (sea path)
7 Modulus match powers for Qk = 5
8 Example of reduction of structure efficiency
9 Test arrangements for measurement of extractable
    power
10 Test arrangement for indcendivity tests
11 Modulus match powers for structure resonated at 1.1
    MHz

Gives advice in assessing the potential ignition hazard from the inadvertent extraction of energy from electromagnetic fields, propagated from radar, communication or other transmitting aerials to plant where there may be a potentially flammable atmosphere. Does not cover similar hazards arising from electromagnetic fields generated by other means, such as electricity generating installations, electric storms or other radiating electrical equipment, nor does it cover any hazard arising within electronic equipment (such as telecommunication). Does not consider the biological hazards of exposure to r.f fields or the hazards associated with the use of electro-explosive devices (EED). Also gives advice on how to mitigate the hazard where the assessment indicates a hazard.