• Home
  • Download PDF
  • Order CD-ROM
  • Order in Print
Figure 7  Grounding Above-Ground Storage Tanks
Figure 8  Bonding During Container Filling

Chemistry Volume 2 of 2
Page Navigation
  107    108    109    110    111  112  113    114    115    116    117  
DOE-HDBK-1015/2-93 Hazards of Chemicals and Gases FLAMMABLE AND COMBUSTIBLE LIQUIDS Rev. 0 CH-05 Page 37 Petroleum  liquids  are  capable  of  building  up  electrical  charges  when  they  (a)  flow  through piping,  (b) are agitated in a tank or a container, or (c) are subjected to vigorous mechanical movement such as spraying or splashing.  Proper bonding or grounding of the transfer system usually dissipates this static charge to ground as it is generated.  However, rapid flow rates in transfer lines can cause very high electrical potentials on the surface of liquids regardless of vessel grounding.  Also, some petroleum liquids are poor conductors of electricity, particularly the pure, refined products, and even though the transfer system is properly grounded, a static charge  may  build  up  on  the  surface  of  the  liquid  in  the  receiving  container.    The  charge accumulates  because static electricity cannot flow through the liquid to the grounded metal container as fast as it is being generated.  If this accumulated charge builds up high enough, a static spark with sufficient energy to ignite a flammable air-vapor mixture can occur when the liquid level approaches a grounded probe or when a probe is lowered into a tank for sampling or gaging. This high static charge is usually controlled by reducing the flow rates, avoiding violent splashing with side-flow fill lines, and using relaxation time, which allows time for the static charge to discharge. When  flammable liquids are transferred from one container to another, a means of bonding should  be  provided  between  the  two  conductive  containers  prior  to  pouring,  as  shown  in Figure 8. In  areas  where  flammable  liquids  are  stored  or  used,  hose  nozzles  on  steam  lines  used  for cleaning  should be bonded to the surface of the vessel or object being cleaned.  Also, there should be no insulated conductive objects on which the steam could impinge and induce a static charge accumulation. Nonconductive materials, such as fabric, rubber, or plastic sheeting, passing through or over rolls will also create charges of static electricity.  Static from these materials, as well as static from the  belts,  can  be  discharged  with  grounded  metal  combs  or  tinsel  collectors.    Radioactive substances and static neutralizers using electrical discharges are also employed for this purpose. Bonding and grounding systems should be checked regularly for electrical continuity.  Preferably before each fill, the exposed part of the bonding and ground system should be inspected for parts that  have  deteriorated  because  of  corrosion  or  that  have  otherwise  been  damaged.    Many companies specify that bonds and grounds be constructed of bare-braided flexible wire because it facilitates inspection and prevents broken wires from being concealed. Electricity  becomes a source of ignition where flammable vapors exist if the proper type of electrical  equipment  for  these  atmospheres  either  has  not  been  installed  or  has  not  been maintained.







Western Governors University

Privacy Statement
Press Release
Contact

© Copyright Integrated Publishing, Inc.. All Rights Reserved. Design by Strategico.