A jet fire is an intense, directional flame created when flammable gas, vapor or liquid escaping under pressure from a leak or rupture ignites and keeps burning while fuel flows.
A jet fire is a turbulent, high-velocity flame produced when a flammable gas, vapor, liquid or two-phase mixture escapes under pressure from a hole, crack, flange or broken pipe and ignites. The momentum of the release pushes the flame outward in a long, narrow, intense plume, much like a blowtorch, that keeps burning as long as fuel continues to flow from the source.
Jet fires are a key concern in process safety for oil and gas production, refineries, chemical plants, gas pipelines, compressor stations, LPG facilities and hydrogen systems. They can occur after a leak from a pressurized line or vessel finds an ignition source, either immediately or after a short delay.
Compared with a pool fire, which burns from a puddle of liquid, a jet fire releases heat into a smaller area at a much higher intensity. Flames that strike nearby equipment, a condition called flame impingement, can weaken steel quickly, cause vessels and pipes to fail and trigger escalation into larger fires and explosions. Understanding how jet fires behave is central to plant layout, equipment protection and emergency planning.
A jet fire requires three things: a fuel stored or flowing under pressure, a loss of containment, and ignition. Common release points include flanges, valve stems, pump and compressor seals, small-bore connections, instrument tubing, corroded pipe and damaged hoses. The size and length of the flame depend mainly on the hole size, the pressure and the type of fuel.
Workers close to a jet fire face severe thermal radiation and burn injuries, as well as noise from the release, smoke and toxic combustion products. Escape may be blocked if the flame crosses walkways or exits. Even workers farther away can be injured by radiant heat if they cannot move behind a barrier or out of line of sight of the flame.
Jet fire risk is managed through process safety programs. In the United States, facilities that handle threshold quantities of highly hazardous chemicals fall under OSHA's Process Safety Management standard, 1910.119, which requires process hazard analysis, mechanical integrity, management of change and emergency planning. Jet fire scenarios are commonly evaluated in hazard studies and quantitative risk assessment to estimate flame lengths and which equipment could be affected.
Fast detection and isolation shorten how long a jet fire can burn. Fixed gas detection and flame detectors can trigger alarms and automatic shutdowns. Emergency shutdown valves isolate the leaking section, and emergency depressurization or blowdown systems route remaining inventory to a flare, reducing the pressure that feeds the flame. Because a jet fire cannot be safely put out until the fuel source is stopped, isolation is the most important control.
Passive fire protection (PFP) protects structures and equipment from failing during the time it takes to isolate and depressure a system. Common types include:
Not all PFP products perform well against jet fires, since the high velocity flame can erode coatings that work against pool fires. Products intended for jet fire exposure are usually tested to specific jet fire test methods, such as ISO 22899-1, and the required protection time is set by the facility's fire hazard analysis.
Water deluge systems, monitors and water spray can cool exposed equipment and structures. However, water spray is generally not effective at cooling an area of direct jet flame impingement, so it is used mainly to protect nearby equipment and reduce escalation.
At a gas processing plant, a small-bore drain connection on a high-pressure gas line cracked due to vibration from a nearby compressor. The escaping gas ignited, producing a horizontal jet fire that struck the support legs of a pipe rack. Flame detectors activated the emergency shutdown system, which closed isolation valves and opened the blowdown valves to route remaining gas to the flare. Operators evacuated the area using a route on the opposite side of the unit and gathered at the muster point.
The fire burned out within minutes as pressure dropped. The steel supports had been coated with passive fire protection rated for jet fire exposure, and the pipe rack remained standing. The investigation found that the small-bore connection had no bracing and had not been included in vibration surveys. The plant added bracing to small-bore connections on vibrating equipment, updated its mechanical integrity program and reviewed other areas where PFP was missing.
A jet fire is driven by a pressurized release and forms a fast, directional flame. A pool fire burns from a liquid spill on the ground or a surface. Jet fires usually produce more intense heat over a smaller area.
If the flame is put out while gas is still escaping, the gas can build up into a flammable cloud that may find another ignition source and explode. The usual approach is to isolate the fuel and let the fire burn out while cooling nearby equipment.
Passive fire protection is coatings, insulation and barriers that slow the heating of structures and equipment during a fire without needing activation. It buys time for isolation, depressurization and evacuation.
They are most likely where flammable gases or liquids are handled under pressure, such as in refineries, gas plants, offshore platforms, pipelines, compressor stations and LPG or hydrogen facilities.
Part of SafetyIQ's EHS glossary: plain-English definitions of workplace health and safety terms.
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