A demolition technician noted an elevated combustible gas lower explosive limit (LEL) on a pipe that was being tested prior to cutting (No. 2 pipe). The No. 2 pipe was one of four pipes being tested. The other three pipes tested less than detectable for combustible hydrogen gas. Testing involves tapping the pipe and connecting the pipe to an Explosive Gas Detector via a tube. When an elevated LEL is identified, the pipe is allowed to vent and then retested prior to cutting. After tapping the No. 2 pipe, the work crew left the pipe open to vent and departed the area for the end of shift.

At approximately 7"45 PM on the same day, a crew was on overtime to support roofing activities. Since additional workers were available, the craft supervisor decided to re-enter the viewing room pipe trench to remove pipe. A pre-job briefing on the planned work included a discussion with the demolition technician of the previous hydrogen gas testing results. During this pipe-cutting activity, the craft supervisor directed the removal of the No. 2 pipe that had not yet undergone the follow-up hydrogen gas testing. The pipe was removed without incident, however, this is considered a deviation from the work procedure for removing the pipe. Note that the craft personnel on overtime were not the same personnel that initially tapped the pipes during the day.

When the crew entered the viewing room, they verified that the No. 2 pipe had been removed and that a retest for combustible gas had not been completed.

Incident Date
Sep 27, 2000
  • Piping/Fittings/Valves
  • Piping
Damage and Injuries
When Incident Discovered
Lessons Learned

Management should ensure that a complete and thorough review of the previous work activities identified in the work package is performed at the pre-job briefing for the planned work. Work activities should be discontinued if any confusion exists concerning how to execute procedure steps. A process should be put in place to positively mark pipes that have been tested and retested to ensure proper identification when testing for acceptable levels of hydrogen.