Static electrical
Electrical charge will build up when there is motion or friction between two insulated or partially insulated objects. The motion does not require rubbing or sliding. The likelihood of charge being created is usually greater when the two interfacing materials are different. May activities produce static electricity. A common experience is static buildup on one’s body from walking on carpet when the air is dry. A small arc occurs when a charged person touches another person or something at a different electrical potential. Belts moving over supporting rollers, sliding bulk material, the flow of fluids through pipes and hoses, and vehicle tires on pavements produce static charge. Static charge buildup is greater when the air has low moisture content. The amount of charge buildup and release of charge at undesirable times and locations are the main concerns.
The amount of energy stored or discharged, E , through a spark or arc is
Capacitance is a property of a material. Capacitance for a person is approximately 100 pF. A walk over a carpet in dry air may produce as much as 50,000 V. A resulting spark would release 0.125 J.
Hazards
The main hazard of static electrical is creation of an arc and ignition of certain vapor or dust mixtures in air. Reference tables give minimum ignition energy for various mixtures.
Controls
One control is minimizing the buildup of charge. Using materials that do not generate or store as much change as other can help. Bonding and grounding are the simplest ways to minimize charge buildup. Grounding is preferred because it removes charge. Humidification of air in closed environments may help, but is usually more costly and less effective in reducing risks.
Grounding or bonding wires reduce hazards during fueling operations, where someone transfers fuel from one container to another, Conductive floors reduce risks in hospital operating rooms, where anesthetic gases may be explosive under the right conditions. In locations where static charge from clothing could be dangerous, works wear conductive clothing, particularly shoes. Clothing made from fabric that resists charge buildup or is treated with antistatic chemicals can reduce rick. Conductive clothing, shoes, and flooring used to control static charge may increase the hazard of electrical shock from sources other than static charge.