What must be present in order for combustion to occur inside a piping system such as a vapor collection header in a marine emission control system?

Correct Answer: Option D — All of the above

The fire triangle dictates that combustion requires fuel, oxygen, and an ignition source. In a vapor collection header, these elements can coexist if the system is not properly inerted or monitored. Eliminating any one of these three components is necessary to prevent an internal explosion within the piping.