34 Other practical wellventilated situations

The previous sections have discussed the performance of leaking flammable materials from the more classic leak sources such as pipe flanges and pump compressor seals, but there are many particular situations which require specific consideration. 3.4.1 The fixed roof vented stock tank This type of tank is extremely common on most process plant for the storage of flammable materials which are normally liquid. Most of these are in well-ventilated outdoor areas and commonly have free vents to allow...

172 Electrical protection

The electrical protection of all supplies to apparatus in hazardous areas (explosive atmospheres) is of fundamental importance. Apparatus protected as described in Chapters 7 to 16 is constructed so as to be unlikely to produce an ignition-capable situation in normal operation or due to fault. It has to be remembered, however, that it is possible that in very rare circumstances it may become ignition capable. When this occurs its duration must be limited so that the chance of an ignition is...

22 22

Upon its dispersion and settling of the dust to form a layer. The layers of dust formed also create the following hazardous areas. An uncontrolled dust layer (i.e., one not contained in depth by housekeeping) will produce a Zone 20. Such layers are normally limited to the inside of vessels, etc., and because they are so thick (in excess of 5 mm) may have properties which are different to those of controlled layers. Such layers would not be acceptable outside containment such as process vessels...

204 Conductor terminations

In intrinsically safe installations, particularly where multicore cables are used, it is common to find uncertified junction boxes in installations rather, than the case in other protection concepts where any such box would need certification approval because its content would be ignition capable if sparking occurred. Junction boxes in intrinsically safe installations are used to allow individual distribution of circuits where several are included in the same cable and in individual circuits...

3913

Infallible transformer protection, 393, 394 infallible shunt safety assemblies, 396-8 infallible voltage limiters, 396, 397 insulation of wiring, 375 infallible wiring and pcb's, 398, 399 interconnections in system, 335 internal connections, 364-6 intrinsically safe apparatus, 333, 334 Electrical apparatus for explosive atmospheres (continued) intrinsically safe apparatus specification, 409-11 intrinsically safe circuit, 335, 336 intrinsically safe system, 336, 415-24 mains...

BS 5345 Part 5 1983 BSEN 50016 1995 BSEN 6007914 1997

The technique of pressurization has been in use for almost as long as the classic flameproof enclosure technique but until the advent of European Standards it was always applied in an ad hoc manner, being referred to in a Code of Practice but not having detailed requirements as a formal protection concept. This is not surprising as the technique relies upon external intervention by inputting a pressurization medium (inert gas or air) into the apparatus from an external source and monitoring it...

Area classification practice

In previous chapters the area classification of explosive atmospheres constituted of gases, vapours and mists and air have been discussed together with the legislation which addresses the total problem of explosive atmospheres. Among this legislation are requirements for the handling of combustible dusts (the term combustible is synonymous with the term flammable which is applied to gases, vapours and mists). As discussed in Chapter 1, Regulation 31(1) and 31(2) of the Factories Acts1 requires...

134 Countable and noncountable faults

Faults, be they countable or non-countable, are failures of components conductors and any other failures which are possible within the apparatus or system. There are three situations within apparatus relating to faults, and the situation in interconnecting cables is governed by cable design. Details of specifications for components, connections, cables etc., will be detailed later in this chapter. Any part of the apparatus or system which does not comply with the requirements of the protection...

BS 5345 Part 4 1977 BSEN 6007914 1997

Intrinsic safety is very different to the other protection concepts in that it does not operate by prevention of the release of ignition-capable energy, the prevention of access of the explosive atmosphere to such releases, or the control of the ignitions which result when such releases occur, but by the prevention of ignition-capable energy from entering the hazardous area and control of energy stored in the hazardous area by electrical components which can store energy, such as inductors and...

12

Another difference brought about by the source of hazard approach is the clear identification for the first time that Zone 1 as not automatically surrounded by Zone 2. While this was also true in the generalized method this fact tended to be obscured by the generality and it became common belief that Zone 1 was always surrounded by Zone 2. The source of hazard method automatically dispersed that misunderstanding as to have a hazardous area it is first necessary to identify a source of release...

174 Selection of conduit or cable systems

The cables used for interconnection of apparatus in the hazardous area to that in the non-hazardous area, and different items of apparatus in the hazardous area, are subject to essentially the same requirements whether they are associated with gas vapour mist risks or dust risks. Two features of the cable are important, namely its adequacy in respect of electrical stresses (voltage and current flow including temperature elevation resulting) and their adequacy for the environment (heat, cold,...

144 Additional requirements for certain types of nonsparking

Continuing the theme that the basic requirements for Type 'N' apparatus are normal industrial requirements which would produce a reliable item of equipment, there are only a limited set of additional requirements applied Both BS 69418 and IEC 79-1511 make the initial premiss that the machines must meet basic industrial Standards, the standard in question in the UK being BS 5000, Part 169 which details Type 'N' machines and the international Standard being IEC 3417 which is a more general...

138 Component and circuit failure modes

Failures of components and circuit connections need to be identified in the fault count unless they are not considered as subject to fault by virtue of additional constructional requirements described later in this chapter. The fault modes which need to be taken into account depend upon the component in question. 13.8.1 Wire and printed circuit tracks Wires or printed circuit tracks may be considered to become disconnected or break and in either case the action will be considered as a single...

115 Enclosures ducting and internal components

The enclosures used for pressurized apparatus are required to be sufficiently strong to withstand normal use without damage, in common with other protection concepts, and may be manufactured of metallic or non-metallic materials provided that, if non-metallic, the material of construction is not adversely affected by either the pressurization medium or any flammable material released in the enclosure. The strength of enclosures must also be such that they are not damaged by the maximum pressure...

3

Note 1 The screen is assumed to be deliberately connected to one side of the circuit which is the normal situation. Note 1 The screen is assumed to be deliberately connected to one side of the circuit which is the normal situation. Where conduit systems are used it is not possible to use separate insulated conductors as is normally the case unless the inductance, inductance resistance ratio, and capacitance of the circuit can be defined in the worst case because of the possible movement of...

BS 6467 Part 1 1985 BS 7535 1992

The approach to protection of apparatus for use in the presence of combustible dusts has always been quite different to that for gases and vapours. The fact that dust clouds are clearly visible, producing a high degree of opacity, has created a situation where processing of dusts needs a high degree of control of dust clouds so that work can take place. In addition, the prevention of entry of particulate matter such as dust into the interior of electrical apparatus is relatively easy by the...

205 Earthing and bonding connection to the potential equalization system

Earthing Connection

Any metal enclosures of items of apparatus in an intrinsically safe system should be connected to the local steelwork and the potential equalization (bonding) system in the same way as above, as are the enclosures of apparatus using all other protection concepts. Likewise, armouring applied to the cables of intrinsically safe systems, metal cable sheaths and conduits should be similarly treated (see Chapter 18). Connections between the intrinsically safe circuit and any screens used on cables...