OSHA Hazard Information Bulletins
Static Electricity Buildup in Plastic Pipe
September 30, 1988
- LEO CAREY
- Office of Field Programs
- EDWARD J. BAIER
- Directorate of Technical Support
- Safety Hazard Information Bulletin on Static Electricity Buildup in Plastic Pipe
The Dallas Regional Office has brought to our attention a potential hazard associated with the buildup of static electricity in plastic pipe used in the conveyance of flammable gas. Accidents including a fatality have been noted in investigations conducted by the Lubbock, Texas and Columbus, Ohio Area Offices. Explosions occurred due to the combination of a flammable gas-air mixture and the discharge of static electricity by arcing. These occurrences should not be confused with fires caused by heat generated by high pressure flammable gas discharges caused by small leaks.
Static charge on a plastic pipe can be generated by friction during the physical handling of the pipe in storage, shipping, installation, and repairing operations. Also, flowing gas in an operational plastic pipe containing particulate matter in the form of scale, rust, or dirt can generate static electricity. Other causes of static charge include gas flow disrupters such as pipe elbows, valves, neckdowns, and leaks.
The American Gas Association (AGA) in its February, 1985 Plastic Pipe Manual for Gas Service (Catalog No. XR0185, American Gas Association, 1515 Wilson Blvd., Arlington, VA 22209) states: "When conditions exist that a flammable gas-air mixture may be encountered and static charges may be present, such as when repairing a leak, squeezing off an open pipe, purging, making a connection, etc., arc preventing safety precautions are necessary." (Squeezing off involves clamping down a plastic pipe to stop flow upstream of a leak or rupture. This can be done with smaller-diameter pipe, typically two inches or less.)
The AGA Plastic Pipe Manual in Chapter VI, p. 57, "Maintenance, Operation, and Emergency Control", also urges the following recommended additional precautions:
Other similar techniques such as dissipating the static charge buildup with wet rags or a bare copper wire are used but may not be as effective.
- The use of a grounded wet tape conductor wound around or laid in contact with the entire section of the exposed piping.
- If gas is already present, the pipe should be wet with a very dilute water solution of dishwasher-type detergent starting from the ground end. The tape should then be applied immediately and left in place.
- The tape should be kept wet by occasional applications of water. Where ambient temperatures below 0 degrees C. (32 degrees F.) are encountered, glycol may be added to the water to maintain tape flexibility. The tape should be grounded with a metal pin driven into the ground.
- Do not vent gas using an ungrounded plastic pipe or tubing. Even with grounded metal piping, venting gas with high scale or dust content could generate a charge in the gas itself and could result in an arc from the dusty gas cloud back to the pipe and ignition. When venting, it should be done at a down-wind location remote from personnel or flammable material.
- Ground the tools, such as saws, etc., that come in direct contact with the pipe.
- In all cases, appropriate safety equipment such as flame-resistant clothing appropriately treated to avoid static buildup and respiratory protection equipment should be used.
Please note that requirements for operation and maintenance of pipelines, including plastic pipelines, are specified in 49 CFR 192. These requirements are enforced by the Department of Transportation, Office of Pipeline Safety, for those operations under its regulatory authority. Operations not so covered would normally fall under OSHA jurisdiction.
Please distribute this bulletin to Area Offices, State Plan States and Consultation Projects.