Flame Arresters: The Last Line of Defense

Flame arresters are designed to prevent catastrophe. How do they work, and which type is right for your application?

The unassuming process-safety devices installed in flare lines, on flammable-liquid storage tanks, in vapor-control systems, and on processing vessels at your plant are called flame arresters. They may even be hiding in plain sight every day on your commute. At your local gas station, for example, the small threaded components at the ends of the underground gas tank-venting lines are likely end-of-line atmospheric deflagration flame arresters rated for National Fire Protection Agency (NFPA) Group D vapors.

Flame arresters comprise a diverse array of safety devices, ranging from small, end-of-line units with threaded connections to massive, custom-built flanged behemoths weighing several tons. They are available with different element designs, housing shapes, and materials of construction to handle various deflagration and detonation explosions, vapor (or explosion) groups, installation positions, operating pressures and temperatures, and allowable burn times. The sheer magnitude of options and configurations can be daunting to the novice user or rookie engineer. However, all flame arresters have the same purpose: to protect people and property from the impact of a safety event that is already in progress, and to serve as the last line of defense against a tragic accident.

Regular maintenance, including frequent inspections, cleaning, and occasional part replacement, is critical to ensure the long-term functionality of flame arresters. Despite their rugged appearance, the guts of flame arresters can be quite fragile. Maintenance staff must be especially careful to avoid damaging internal elements. A dropped wrench or hammer can irrevocably damage a flame arrester.

While many engineers are exposed to the basics of relief valve sizing, combustion, explosions, and other process safety fundamentals, flame arrester theory and application criteria are not typically included in courses or training. To novice engineers, flame arrester functionality and application principles can seem like a mysterious black box.

Because engineers and other personnel are often unfamiliar with flame arrester fundamentals, misapplication is quite common. This article covers the basics of flame arresters to help prevent misapplications, which can have catastrophic results.