Process Safety: Hot Work, Flammable Gases

Friday, November 13, 2015 @ 03:11 PM gHale

Just over nine years ago three contract workers were installing a pipe between two oil production tanks at the Partridge-Raleigh oilfield in Mississippi when welding sparks ignited flammable vapor that was escaping from an open-ended pipe near the welding activity.

The resulting blast killed the three contract workers and a fourth worker ended up seriously injured.

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When it comes to safety incidents, there are the huge incidents that live on forever like Bhopal, India or BP Texas City to name a few.

But then there are other incidents that have garnered immediate headlines, but then go forgotten, but they prove to be learning experiences. In an occasional series, ISSSource will edit reports about incidents that showed how a small mistake, or series of mistakes, led to a big safety incident.

The incident started when contract workers were connecting piping between two recently moved tanks. Several days earlier, crude oil residue ended up removed from Tank 4 and the tank flushed with water. However, the contractors did not clean out or purge the crude oil residue from Tank 2 or Tank 3.

Before starting to weld, the welder checked for flammable vapors in Tank 4 by inserting a lit welding torch into it, an unsafe act known as flashing the tank. Then, as the CSB report said, “The foreman climbed to the top of Tank 4. Two other maintenance workers climbed on top of Tank 3; they then laid a ladder on the tank roof, extending it across the 4-ft space between Tanks 3 and 4, and held the ladder steady for the welder. The welder attached his safety harness to the top of Tank 4 and positioned himself on the ladder.”

Almost immediately after the welder started welding, flammable hydrocarbon vapor venting from the open-ended pipe attached to Tank 3 ignited. The fire flashed back into Tank 3, spread through the overflow connecting pipe from Tank 3 to Tank 2, and caused Tank 2 to explode. The lids of both tanks blew off and the two maintenance workers and foreman ended up thrown off the tanks to the ground. The blast threw the welder off the ladder, but his harness prevented him from falling to the ground.

The root cause of this incident was hot work conducted in the presence of a flammable atmosphere without using any safe work permitting procedure. The workers should have used a gas detector to test for flammable vapor. There was no cap on the open pipe on Tank 3. Nor did they isolate the open pipe. All of the tanks were interconnected, and some of the tanks still contained flammable residue and crude oil.

Lessons learned: Safe work practices, such as hot work permits, are necessary to ensure a safe work environment when hazardous chemicals, in this case flammable vapors, are present. The contractor, Stringer’s Oilfield Services, did not require the use of safe work procedures, specifically hot work permits in this case.

Contractors need to end up managed in such a way as to ensure they know about and use safe work practices. The owner of the wells and tanks, Partridge-Raleigh, relied on contractors to do most of its well commissioning work, such as installing tanks, pumps, and piping, which is a common practice. Partridge-Raleigh did not, however, manage the contractors to make sure they used safe work practices.

Companies need to be aware of and follow best industry practices. Several National Fire Protection Association (NFPA) and American Petroleum Institute (API) guidelines cover this situation.

If Partridge-Raleigh or Stringer’s Oilfield Services had adopted any of these industry standards, this incident could have been prevented.