OSHA Hazard Information Bulletins
September 30, 1988
| MEMORANDUM FOR: |
REGIONAL ADMINISTRATOR |
| THROUGH: |
LEO CAREY
Director
Office of Field Programs |
| FROM: |
EDWARD J. BAIER
Director
Directorate of Technical Support |
| SUBJECT: |
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:
1. The use of a grounded wet tape conductor wound around or laid in
contact with the entire section of the exposed piping.
2. 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.
3. 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.
4. 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 op flammable material.
5. Ground the tools, such as saws, etc., that come in direct
contact with the pipe.
6. In all cases, appropriate safety equipment such as
flame-resistant clothing appropriately treated to avoid static buildup and
respiratory protection equipment should be used.
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.
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.
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