BS 6656:2002 pdf download – Assessment of inadvertent ignition of flammable atmospheres by radio-frequency radiation — Guide
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 British Standard 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 assessment The radio-frequency (RF) environment is becoming increasingly severe, with the proliferation of transmitting sources, increased transmitter powers and the exploitation of new techniques.
NOTE 1 UK legislation [5], 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 plant in which a flammable atmosphere may be present 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 plant in which a flammable atmosphere may be present should send details to the transmitter operators and request information about relevant transmitters in the locality of the site. If a potential hazard is indicated, the plant operator should then use the assessment procedures given in this British Standard, in consultation with the transmitter operators concerned. Similarly, the operator of a proposed new (or altered) transmitter should contact all operators of plant with potentially flammable atmospheres within the vulnerable zone for their transmitter, and use the procedure given in this British Standard to assess the potential hazard at each location. Where both plant and transmitter already exist but an assessment is required, the plant operator should be held responsible for ensuring that an assessment is made. If for some reason relevant information cannot be made available to the body responsible for the assessment, the responsibility for having an assessment carried out should be assumed by the body unable to release the necessary information. NOTE 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 A.
6 Transmitters and transmitter output parameters
6.1 Types of transmitter 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 A. Typical types of antenna are shown in Figure B.1.
6.2 Frequency range
The main frequency range covered in this guide 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.