Ignition of flammable mixture in diesel engine silencer / spark arrestor

Exhaust silencer/spark arrestor failed on an emergency generator during an annual overspeed trip ,emitting a localised flame and pressure wave.

• The trip was initiated by isolating the fuel and closing the air intake flaps (rigsaver)

• Five to ten seconds later as the machine was running down and had almost stopped rotating, a loud bang occurred
• Flame and pressure were emitted from the failed exhaust silencer/spark arrestor into the generator room
• Fortunately, no injuries were incurred by those carrying out the trip test