WHAT IS STATIC ELECTRICITY?
It is defined as a surface phenomena which involves high voltage and low current produced by separation and contact of two dissimilar bodies. (Static Electricity Definition)
STATIC ELECTRICITY EXAMPLES:
- Automobile moving on the road
- Person moving/walking on insulated flooring
- Belt moving on pulleys/rollers
- Air craft flying in the car
- Light petroleum products flowing in pipe lines
- Leakage of steam from pipe line
- Pneumatic transferring of dust
- Manufactures of cotton, silk, rayon, woolen fabrics
- Filtering, crushing, grinding, sieving, mixing/blending, pouring, pumping Petrol/Naphtha light solvent
HAZARDS OF STATIC ELECTRICITY
TYPE OF INDUSTRY PRONE TO FIRE/EXPLOSION
- Dust Processing
WHAT CAUSES STATIC ELECTRICITY/ HOW TO MAKE STATIC ELECTRICITY?
It poses danger under three conditions.
- An inflammable explosive atmosphere must be present.
- An electric charge must be generated and accumulated on PLAT/PRODUCT/OPERATOR and produced in electric field strength of surrounding atmosphere to produce a SPARK.
- The resulting SPARK must have energy greater than the minimum spark ignition energy of the surrounding atmosphere.
NOTE: Fire or explosion can not occur if any of the above three condition is not satisfied.
- Safety precaution therefore arises at elimination of one or more of the above conditions/factors(with minimum interference to the operation of the plant and process)
HOW TO STOP STATIC ELECTRICITY(HOW TO DISCHARGE STATIC ELECTRICITY)?
HOW IS STATIC ELECTRICITY DIFFERENT FROM ELECTRIC CURRENT?
Control of Charge Generation:
- To reduce unnecessary friction process/operation
- By controlling flow velocity.(Ensure streamline flow instead of turbulence flow)
- To avoid/reduce free fall(Ensure surface filling)
Reduce Charge Accumulation:
- Do bonding/grounding (for conducting bodies)
- Maintain relative humidity 60-70 % minimum
- Use fairly conductive materials as additive for non metallic bodies.
- Ionize surrounding atmosphere (with proper care)
- Use anti static foot wears / flooring
Eliminate Flammable/Explosive Atmosphere
Reduce Stoichiometric Concentration to 50%
Stoichiometric Concentration, C = 100
4.85 x N – 1.425 %
Where N = No. of O2 atom required for complete combustion of one mol. of the vapour
CH4 + 2H2O = CO2 + 2H2O N for CH4 = 4
- (2) (1) (2)
∴C = 100 = 5.563% = 5.56%
4.85 x 4 – 1.425
Possibility of Combustion is reduced, if concentration is reduced to ½ x 5.56% i.e. 2.78%
Minimize Possibility of Spark
- Use intrinsically safe electric equipment (With very low current and voltage)
- Use Pressurization
- Use Segregation