DOE-HDBK-1015/2-93Hazards of Chemicals and GasesFLAMMABLE AND COMBUSTIBLE LIQUIDSRev. 0CH-05Page 37Petroleum liquids are capable of building up electrical charges when they (a) flow throughpiping, (b) are agitated in a tank or a container, or (c) are subjected to vigorous mechanicalmovement such as spraying or splashing. Proper bonding or grounding of the transfer systemusually dissipates this static charge to ground as it is generated. However, rapid flow rates intransfer lines can cause very high electrical potentials on the surface of liquids regardless ofvessel grounding. Also, some petroleum liquids are poor conductors of electricity, particularlythe pure, refined products, and even though the transfer system is properly grounded, a staticcharge may build up on the surface of the liquid in the receiving container. The chargeaccumulates because static electricity cannot flow through the liquid to the grounded metalcontainer as fast as it is being generated. If this accumulated charge builds up high enough, astatic spark with sufficient energy to ignite a flammable air-vapor mixture can occur when theliquid level approaches a grounded probe or when a probe is lowered into a tank for samplingor gaging.This high static charge is usually controlled by reducing the flow rates, avoiding violent splashingwith side-flow fill lines, and using relaxation time, which allows time for the static charge todischarge.When flammable liquids are transferred from one container to another, a means of bondingshould be provided between the two conductive containers prior to pouring, as shown inFigure 8.In areas where flammable liquids are stored or used, hose nozzles on steam lines used forcleaning should be bonded to the surface of the vessel or object being cleaned. Also, thereshould be no insulated conductive objects on which the steam could impinge and induce a staticcharge accumulation.Nonconductive materials, such as fabric, rubber, or plastic sheeting, passing through or over rollswill also create charges of static electricity. Static from these materials, as well as static fromthe belts, can be discharged with grounded metal combs or tinsel collectors. Radioactivesubstances and static neutralizers using electrical discharges are also employed for this purpose.Bonding and grounding systems should be checked regularly for electrical continuity. Preferablybefore each fill, the exposed part of the bonding and ground system should be inspected for partsthat have deteriorated because of corrosion or that have otherwise been damaged. Manycompanies specify that bonds and grounds be constructed of bare-braided flexible wire becauseit facilitates inspection and prevents broken wires from being concealed.Electricity becomes a source of ignition where flammable vapors exist if the proper type ofelectrical equipment for these atmospheres either has not been installed or has not beenmaintained.
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