1、BRITISH STANDARD BS 5958-2: 1991 Code of practice for Control of undesirable static electricity Part 2: Recommendations for particular industrial situations Licensed Copy: Wang Bin, na, Thu Oct 13 08:35:14 BST 2005, Uncontrolled Copy, (c) BSIBS 5958-2:1991 This British Standard, having been prepared
2、 under the direction of the General Electrotechnical Standards Policy Committee, was published under the authority ofthe Standards Board and comesinto effect on 31 January 1992 BSI 11-1998 First published December 1983 Second edition January 1992 The following BSI references relate to the work on th
3、is standard: Committee reference GEL/118 Draft for comment 90/24337 DC ISBN 0 580 20018 3 Committees responsible for this British Standard The preparation of this British Standard was entrusted by the General Electrotechnical Standards Policy Committee (GEL/-) to Technical Committee GEL/118, upon wh
4、ich the following bodies were represented: British Cable Makers Confederation British Plastics Federation British Textile Technology Group Chief and Assistant Chief Fire Officers Association ERA Technology Ltd. Engineering Equipment and Materials Users Association General Council of British Shipping
5、 Health and Safety Executive Institute of Petroleum Institution of Electrical research on the subject continues and new information is still coming to light. This Part of BS 5958 does not provide recommendations for the control of static electricity in the transport, handling, storage or testing of
6、electrostatic sensitive electronic devices (ESD) or circuits. Reference should be made to BS 5783:1987 for this purpose. Licensed Copy: Wang Bin, na, Thu Oct 13 08:35:14 BST 2005, Uncontrolled Copy, (c) BSIBS 5958-1:1991 BSI 11-1998 iii A British Standard does not purport to include all the necessar
7、y provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i to iv, pages1to 3
8、4, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover. Licensed Copy: Wang Bin, na, Thu Oct 13 08:35:14 BST 2005, Uncontrolled Copy, (c) BSIiv bla
9、nk Licensed Copy: Wang Bin, na, Thu Oct 13 08:35:14 BST 2005, Uncontrolled Copy, (c) BSIBS5958-2:1991 BSI 11-1998 1 1 Scope This Part of BS 5958 deals with static electricity problems which are encountered in particular situations during the handling of different types of materials including liquids
10、, powders, gases, sprays, explosives and electro-explosive devices. In each case, the source and nature of the electrostatic hazards and/or nuisances are identified and specific recommendations are then given for dealing with them. The static electricity problems that can occur with personnel and th
11、eir clothing are also described and the precautions are given for avoiding these problems. NOTEThe titles of the publications referred to in this standard are listed on the inside back cover. 2 Definitions For the purposes of this Part of BS 5958, the definitions given in BS 5958-1 apply. 3 Fixed me
12、tal tanks for the storage of liquids 3.1 General Static electricity hazards can arise in various operations connected with fixed storage tanks for liquids, including filling, gauging and sampling. Charge on the liquid may be generated within the tank, due, for example, to splashing or free fall, and
13、/or in the pipeline system feeding the tank. Charging may also be associated with personnel undertaking tasks on the tank, such as gauging or sampling, and with cleaning operations. An ignition hazard is created when charge is retained in the liquid, on insulated conductors or on personnel in the pr
14、esence of a flammable vapour/air mixture, mist or foam. To avoid these hazards the recommendations given in 3.2 to 3.8 inclusive should be followed. 3.2 Earthing 3.2.1 The tank and its associated pipework and fittings should all be in good electrical contact with each other and with earth, so that t
15、he resistance to earth is at all points less than 10 W. Electrical continuity checks should be made before the equipment is brought into use, and subsequently where maintenance or modification could affect electrical continuity (see clause 13 of BS5958-1:1991). 3.2.2 New tanks or tanks that have bee
16、n out of service for repairs should be inspected prior to the initial fill for any potential floating objects, such as cans, that could form insulated conductors. Such objects should be removed. 3.2.3 It should be ensured that personnel working on the tanks do not present an ignition risk (see31.3.1
17、). 3.3 Tank filling 3.3.1 Splash filling into a tank where a flammable atmosphere may exist should be avoided, in order to prevent the formation of a charged mist. This can be achieved either by bottom entry or by the use of a fill pipe reaching to the bottom of the tank without actually touching it
18、. 3.3.2 For liquids with conductivity up to and including 50 pS/m the inlet should be designed to minimize turbulence and the agitation of any heavier immiscible liquid or sediment on the tank bottom. 3.3.3 Entrained air or other gas should be avoided in liquids with conductivities up to and includi
19、ng50pS/m if there is any possibility of immiscible liquid or sediment on the tank bottom. 3.3.4 For liquids with conductivity up to and including 50 pS/m the linear flow velocity in the pipe entering the tank should not exceed 1m/s until the inlet has been covered and should be maintained at1m/s if
20、a second immiscible phase is present; an example is water suspended in oil. A precise value for the safe maximum linear velocity in the absence of a second phase in large tanks has not been established. However, experience indicates that the limitations on flow rates imposed by the present designs o
21、f pipeline systems have been adequate to maintain safe operations. There is no evidence that flow velocities up to and including 7m/s are hazardous. For storage tanks of the order of size of road/rail tanks the safe maximum linear velocity should be calculated by the procedure given in 7.3.3. 3.3.5
22、For liquids with conductivity greater than50pS/m, the recommendations of 3.3.2, 3.3.3 and 3.3.4 can be disregarded. An antistatic additive may be used to raise the conductivity of a low conductivity liquid above 50 pS/m, provided that it is compatible with the intended use of the liquid. 3.4 Filters
23、 Fine particle filters installed in the pipeline system upstream of the tank can produce a significant amount of charge. It is recommended that the methods for dealing with the charge given in clause16 be followed. 3.5 Gauging and sampling The introduction into a tank of equipment for gauging and sa
24、mpling may produce additional static electricity hazards. It is recommended that the procedures given in clause 6 be followed. Licensed Copy: Wang Bin, na, Thu Oct 13 08:35:14 BST 2005, Uncontrolled Copy, (c) BSIBS 5958-2:1991 2 BSI 11-1998 3.6 Tank cleaning Tank cleaning operations may give rise to
25、 static electricity hazards. It is recommended that the procedures given in clause 14 be followed. 3.7 Floating roof tanks When a liquid with conductivity up to and including50 pS/m is pumped into a metal tank with a floating roof, precautions for earthing (see 3.2), filling (see 3.3), fine particle
26、 filters (see clause 16) and gauging and sampling (see clause 6) are applicable until the floating roof is buoyant. Thereafter, only the earthing, gauging and sampling precautions are necessary. 3.8 Floating blankets 3.8.1 Floating blankets in tanks used for storing liquids with conductivities up to
27、 and including50pS/m should be fabricated from metal, from non-conducting material entirely coated with antistatic material or from antistatic material. The blanket should be adequately earthed. Tanks with such blankets should be treated as if the blanket were a floating roof (see 3.7). 3.8.2 Conduc
28、ting floating spheres or balls intended to suppress evaporation loss should not be used with liquids having a conductivity up to and including50pS/m. Non-conducting spheres should not be used with liquid at any conductivity level if there is any possibility of the presence of a flammable atmosphere.
29、 4 Fixed non-metallic tanks for the storage of liquids, sited partially or wholly above ground 4.1 General The charging processes and static electricity hazards associated with fixed metal storage tanks (see 3.1) are also encountered with non-metallic tanks. If tanks are made from high resistivity m
30、aterials charge may also be generated and retained on the material itself by the liquid handling operations or by internal or external rubbing. This presents additional hazards, especially if there are insulated metal components, such as bolts, flanges and valves, or if the surface is contaminated w
31、ith isolated areas of conductive material, such as water or grease. As in metal tanks, an ignition hazard is created when charge is retained on the liquid, on insulated conductors or on personnel in the presence of a flammable vapour/air mixture, mist or foam. The risk of an internal discharge from
32、the liquid surface, for example during gauging, is enhanced with tanks of high resistivity material because the dissipation of charge from the liquid is impeded and because the distribution of the field within the tank results in a greater field strength at the surface than in a metal tank. In addit
33、ion, there is increased risk outside the tank if it is situated in a hazardous area, owing to the possibility of charge on the tank itself, even when a non-flammable liquid is being handled. Recommendations for avoiding electrostatic hazards are given in 4.2, 4.3 and 4.4. They should be considered i
34、n conjunction with measures to deal with risks from other sources, e.g. the general fire risk associated with the storage of large quantities of flammable liquids in non-metallic containers and mechanical strength limitations on larger containers. 4.2 Tanks made of high resistivity materials 4.2.1 T
35、he use of large storage tanks completely fabricated from high resistivity materials, such as synthetic polymers and glass reinforced plastics having a volume resistivity greater than 10 8 Wm and/or a surface resistivity greater than 10 10W is not recommended. The exception is when it can be shown th
36、at the liquid handling operations do not produce dangerous levels of static electricity and that no charge generating processes exist outside the tank. Specialist advice should be sought before installing tanks of high resistivity materials. 4.2.2 If such a tank is installed, rubbing of its surface,
37、 e.g. in cleaning operations, should be avoided when a flammable atmosphere may be present. 4.3 Tanks made from conductive non-metallic materials Storage tanks made from conductive non-metallic materials (see 10.3.2 of BS 5958-1:1991) present no electrostatic hazards additional to those existing for metal tanks, provided that they are earthed and the precautions for metal tanks are fully implemented (see clause 3). Such tanks should be permanently marked as “Antistatic material” or “Conducting material”. Licensed Copy: Wang Bin, na, Thu Oct 13 08:35:14 BST 2005, Uncontrolled Copy, (c) BSI
