In order for combustion to occur inside a piping system such as a vapor collection header in a marine emission control system, there must be __________.

Correct Answer: Option D — All of the above

Combustion requires all three elements of the fire triangle: fuel (hydrocarbon vapors), oxygen (air), and an ignition source (such as static electricity or friction). Under 46 CFR 39, marine vapor control systems must manage these elements to prevent catastrophic piping explosions.