a common ignition source within chemical plants is sparks resulting from static charge buildup and sudden discharge. static electricity is perhaps the most elusive of ignition sources.Despite considerable efforts,serious explosions and fires caused by static ignition continue to plague the chemical process industry.
the best design methods for preventing this type of ignition source are developed by understanding the fundamental relevant to static charge and by using these fundamental to design specific feature within a plant to prevent the accumulation of static charge or to recognize situation where the buildup of static electricity is inevitable and unavoidable. For unavoidable static buildup design feature are added to continuously and reliably inert the atmosphere around the regions where static sparks are likely.
fundamentals of static charge
static charge buildup is result of physically separating a poor conductor from a good conductor another poor conductor. When different materials touch each other,the electrons move across the interface from one surface to the other. Upon separation, more of the electrons remain on one surface than on the other; one material become positively charged and the other negatively charged.
if both the materials are good conductors,the charge buildup as a result of separation is small because the electrons are able to scurry between the surfaces. if,however,one or both of the material are insulators or poor conductors,electrons are not as mobile and are trapped on one of the surfaces,and the magnitude of the charge is much greater.
Household example that result in a buildup of statics charge are walking across a rug,placing different materials in a tumble dryer,removing a sweater,and combing hair.the clinging fabrics and sometimes audible sparks are the result of the buildup of static charge.