What Are Backfire Flame Arrestors on a Boat?

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Backfire flame arrestors serve a vital safety function on watercraft. They are legally required and must be Coast Guard approved on inboard and stern-drive boats that use gasoline engines. Engine compartments can build up gas vapors and fumes that can ignite with a stray spark or flame. Occasionally engines can backfire, sending a flame up through the carburetor and into the engine compartment. The backfire flame arrestor's function requires it to muffle and delete any such spark or flame, which could result in an onboard explosion.

Backfire Flame Arrestor Contruction

  • The backfire flame arrestor has a solid metal construction very similar to the older style air cleaner housings on cars and trucks. Most of the casing shells have circular designs, whereas some can use oval or square configurations. They attach solidly to the upper lip of the carburetor throat via a clamp, and bolt from the top into the carburetor body. They possess an interior baffle grid that resists flame, oil and fuel contamination. The airtight seal and grid within the flame arrestor halts and dissipates backfire flames from the carburetor.

Backfire Flame Arrestor Concept

  • When fuel and air can sustain combustion, they have a flammability factor. The internal combustion engine uses this ignition to power the cylinders. When a backfire occurs, the combustion process temporarily changes direction and travels up through the air intake passage. Hydrocarbon molecules need space and oxygen to ignite and propagate. When they enter the flame arrestor as a result of a backfire, their travel speed is drastically reduced, held in check by striking the interior grid element. The confined space inside the flame arrestor does not allow enough oxygen to continue the burn. The renegade flame is snuffed before it can expand.

Noise Levels

  • Backfire flame arrestors reduce and muffle combustion noise to a lower level. Since the flame arrestor completely seals the intake portion of the engine, engine noise becomes trapped within the confines of the grid. A backfire, which can cause high level shockwave noise, gets dissipated instantly with a back-flow pressure. This confines and mutes the explosion.

Regulations

  • Backfire flame arrestors must be permanently installed on vessels that have stern-drive or inboard motors. Outboard motor and diesel engines need not use them. The flame arrestor must be in adequate and serviceable condition, as prescribed by the U.S. Coast Guard, Underwriters Laboratories. The flame arrestor can not have any holes in the grid surface, nor oil or raw gas in the grid compartment. It must be sealed tight against pressure escape. Flame arrestors need to be inspected regularly,cleaned with soap and water and then refitted for proper seal.

References

  • Photo Credit Thomas Northcut/Photodisc/Getty Images
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