Post on 03-Nov-2014
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Static ElectricityHazards & Controls
Static Electricity Generation When ? When two dissimilar materials come in contact with each other or they remain in contact while they are in motion there is a transfer of electrons between them which results in Static electricity generation.If any one of these materials is a non conductor then accumulation of electron occurs on them.
Static Electricity Generation How ?All materials are made of atoms. Atoms contains positively charged Protons neutrally charged Neutrons in Nucleus.
Electrons are moving in different orbits around nucleus. Various orbits can accommodate different no.s of Electrons e.g. 2,8,18,18,32Atoms have tendency to become stable by accepting or donating electrons from the outer orbits.
Static Electricity Generation How ?Sometimes electrons from outer orbits are separated from stable atoms due to rubbing action between them. Materials with deficiency of electrons becomes positively charged & excess of electrons becomes negatively charged resulting into potential difference between them.
Static Electricity Precautions for plant safetyRemember, Static Electricity is one of the less acknowledged reasons for fire and explosion in Chemical Processing. Its generation is not realized and accumulation is not identified till it discharges in the form of Electrical spark.
Static Electricity Precautions for plant safetyLiquid flowing in pipelines.If the liquid or the pipeline is non conducting, it leads to the charge build-up in liquid or pipeline or isolated conducting parts.
Static Electricity Precautions for plant safetyDischarge of liquid or powder from pipe.Pneumatic conveying of powders. If the pipeline is non-conducting, then both pipe and also the powders get charged.
Static Electricity Precautions for plant safetyPouring of liquid or powder into/ from a container.While pouring liquids or powder from a container, if the container or the material is non-conducting will lead to accumulation of charges. Adding material into reactor through man-hole is dangerous.
Static Electricity Precautions for plant safetySpraying of liquid through a nozzle.Spray drying, spray painting etc. are some to the operations of this type. This is the reason for powder coating the job is kept charged to attract paint particles.
Static Electricity Precautions for plant safetyStirring of material in a reactor.If the material is non-conducting or the reactor is glass-lined, the charges will build up in liquids. The problem is more pronounced if the reactor is glass lined.
Static Electricity Precautions for plant safetyUse of normal plastic containers and liners.Normal plastics have high resistance, this leads to charge generation and accumulation. Plastic containers can not be easily discharged by Earthing and Bonding. Antistatic/ Static dissipative plastics are available.
Static Electricity Precautions for plant safetyBelt moving on a pulleyIf the belt used is normal and not antistatic, then it will lead to the build of charges on the belt.
Characteristics of Materials Materials have tendency to release electrons Leather Glass Wool Human hair Aluminum Materials have tendency to accept electrons Hard Rubber Vinyl (PVC) Silver Polyester Acrylic
Examples of Static Electricity Generation Static Electricity is usually generated when two dissimilar materials are rubbed against each other. e.g.Wool on plastic Plastic comb on dry hair Shoes sole on carpet
Static Electricity Generation in Industry Solid SolidBetween Belt & Pulley
While Grit / Sand BlastingCharging dust or powder in Hopper
Static Electricity Generation in Industry Solid LiquidLiquids flowing through pipeline While Filling liquids in Storage tanks
Static Electricity Generation in Industry Solid GasSteam coming out from pin hole Gas coming out from nozzle.
Static Electricity Generation in Industry Liquid LiquidWater settling in Hydrocarbon filled tan Liquid Gas Air bubble rising through tank filled with liquid
Static Electricity Generation in Industry during various operations Loading - Unloading While loading or unloading materials from tankers, drums, carboys there are chances of Static charge generation. Generation of charge depends on type of container & materials which are to be unloaded.
Static Electricity Generation in Industry during various operations Agitation, Mixing or Blending While Agitation operation there are chances of rubbing actions between material & Agitator or Reactor. During mixing rubbing action can also occur between two materials which are to be mixed.
Accumulation of Static charge Generation of Static charge is not a hazard on its own. Accumulation of Static charge occurs when out of two material, one is non conductor. Accumulation of charge also occurs if generated charge is not discharged or rate of generation is higher than rate of dissipation or discharge. This process is also known as Electrostatic Induction
Accumulation of Static charge Examples
Non Conductive Filter bags
Plastic Suction devices
Electrostatic Discharge Accumulated Electrostatic charge can discharge in following ways:Sparks Brush Discharge Corona Discharge Lightning like Discharge.
Electrostatic Discharge Sparks
Discharge occurs between two conductors.Discharge occurs in a sudden burst.Equivalent Energy=0.2 mJ
Radius of curvature is >=5cm
Electrostatic Discharge Brush Discharge
Discharge occurs between conductors & charged conductive surface.Rapid Discharge gives overall impression of brush.Equivalent Energy=3 mJ
Luminous phenomenon emitted from conductor ends in a gap. Radius of curvature is 0.5cm
Electrostatic Discharge Corona DischargeDischarge occurs between conductive point & charged conductors.Luminous phenomenon emitted from conductive point gives shape of Corona. Radius of curvature is