On September 13, 2007, a subcontractor was implementing a hot tap into a carbon steel pipe.
The explosion was caused by the heat from the acetylene torch kindling the residual vapor inside, attaching to the polyvinylchloride (PVC) piping.
Shrapnel pieces were blown up to 100 feet outwards due to the force of the explosion.
The two workers who were closest to the explosion were guarded by an alcove wall. However, the explosion resulted in four other workers, who were standing 25 feet away, suffering temporary hearing loss.
Lessons Learned
From this situation we can conclude that before anything is started on, all potential hazards need to be identified and addressed.
Workers should be able to avoid assumptions from previous experiences, and be familiar with the dangers associated with their work.
Source http://www.hss.energy.gov/csa/analysis/oesummary/oesummary2008/2008-05-03.pdf