Flames can reach astonishing heights under the right conditions. The height a flame can reach depends on several factors, including the type and amount of fuel available, environmental conditions like wind, and the geometry of the fire itself.
What determines the height of a flame?
There are three main factors that determine how high flames can reach:
- Fuel – The type and amount of fuel burning determines how much energy is released and available to power the rising air column.
- Wind – Strong vertical drafts of wind can rapidly accelerate the rise of hot gases, boosting flames higher.
- Geometry – Fires with a continuous area of burning fuel tend to reinforce air entrainment and reach greater heights.
Of these factors, the type and quantity of fuel has the greatest influence. With enough continuous fuel and a strong, steady wind, flames can reach astonishing heights.
What fuels allow the highest flames?
Light fuels like grass, leaves, and thin branches allow relatively small, low-intensity fires. Heavier fuels like wood, coal, oil, and gas have much more potential energy per unit of mass, allowing bigger, hotter fires. Here are some fuels that can produce extreme flame heights under the right conditions:
- Wood – Timber forest fires fueled by heavy logs can produce flames over 100 ft high.
- Coal – Underground coal seam fires often burn unattended for years, generating flames up to 300 ft.
- Oil – Crude oil and fuels like gasoline have very high energy densities, capable of flame heights over 500 ft.
- Natural gas – Highly pressurized gas leaking from pipes has fueled flames over 1,000 ft high.
Wood Fires
Wood releases approximately 8,000 BTU of energy per pound when burned completely. Logs and heavy timber provide a dense, slow-burning fuel source capable of sustaining intense fires for long durations.
The intense radiant heat output of large timber fires pre-heats surrounding fuel, driving further combustion and extreme fire behavior. Stacked piles of timber can fuel convection columns so strong that 100+ ft flame lengths are possible under windy conditions.
Coal Fires
Coal produces over 10,000 BTU per pound when burned, making it an extremely energy-dense fuel. While most coal is burned in controlled settings like power plants and factories, coal seam fires in mines historically produced flames hundreds of feet tall.
The uncontrolled burning of coal seams in underground mines is a dangerous phenomenon capable of raging for years. With abundant fuel and oxygen, turbulence caused by cave-ins, and natural vents creating strong drafts, flames up to 300 ft tall have been recorded from mine fires.
Oil and Gas Fires
Crude oil and natural gas produce approximately 17,000 BTU and 20,000 BTU per pound respectively when burned, making them some of the most energy-dense fuels available. When ignited in large, uncontrolled quantities, oil and gas can drive flames to phenomenal heights.
Pressurized gas from ruptured pipelines and storage facilities has been known to produce stable flames over 1,000 ft tall. The famous Cleveland gas refinery fire of 1944 burned for 5 days, with flames reaching 1,000+ ft due to gas escaping under high pressure.
What are the tallest flames on record?
Some of the largest recorded flame heights include:
| Fire | Fuel Source | Flame Height |
|---|---|---|
| Cleveland Gas Refinery Fire | Natural Gas | 1,000+ ft |
| Milford Haven Refinery Fire | Crude Oil | 500 ft |
| 1949 Mann Gulch Fire | Timber | 250 ft |
| 1937 Blackwater Fire | Coal Seam | 300 ft |
The most extreme flame heights occur when heavy fuels burn uncontrolled, combining with high winds to create enormous convection columns. The greatest documented flames result from pressurized gas leaks, which can funnel huge amounts of energy into stable jets of burning fuel.
What environmental factors allow the highest flames?
Certain environmental conditions can accelerate and intensify the upward movement of heat and gases, boosting flames to exceptional heights. These include:
- Wind – Strong vertical wind drafts enhance entrainment and flame height.
- Slope – Fires burning uphill take advantage of rising slope and natural chimney effect.
- Venturi Effect – Passing fire through a narrow opening increases draft velocities.
Wind Effects
Wind provides additional momentum and turbulence that enhances the induction of ambient air into the rising column above a fire. This added entrainment feeds greater combustion intensity and higher flames. Wind also bends flames sideways, further increasing the area affected by radiant heat.
Studies have demonstrated that wind velocities of 7-10 mph can increase flame heights by up to 50%. Extreme winds during blowup fires can rapidly accelerate flame heights to 100 ft or more as the fire draws energy from the passing weather system.
Slope Effects
When burning up a hillside, the rising slope naturally adds momentum to the thermal updraft produced by the fire itself. This combined convection column fuels greater intensity through enhanced entrainment. Slope angles of 30% (about 15 degrees) typically double the rate of spread and flame heights compared to flat terrain.
Venturi Effects
As flames or smoke pass through a narrow gap between rocks, cliffs, or manmade structures, the venturi effect constricts them and increases flow velocities. This venturi mechanism can locally boost flame heights and tilt angles as winds accelerate through obstructions.
During the Freeway Fire in Los Angeles in 2008, 50 mph winds blowing through a narrow underpass produced turbulent eddies. This created a vortex that twisted flames into a whirlwind over 1,000 ft in height.
How can flame height be minimized for safety?
There are several strategies firefighters and land managers use to reduce flame heights and fire intensity:
- Reducing surface and ladder fuels – Eliminating flammable ground debris diminishes potential flame heights.
- Establishing fuelbreaks – Areas cleared of vegetation inhibit fire spread and convection columns.
- Backfiring – Controlled burning robs advancing fire of fuels and weakens its intensity.
- Water application – Water cools fuels, resulting in shorter flame lengths.
Carefully managed forested areas with regular fuel treatments exhibit lower fire severity and flame lengths compared to overgrown, neglected forests. Smart land use planning can help reduce the risks to people and property from intense wildland fire behavior.
Conclusion
Flames can reach astonishing heights, with well-documented cases over 1,000 ft tall. The type of fuel, environmental conditions, and fire geometry all play a role in determining flame height. The most extreme flames result from uncontrolled burning of heavy fuels like gas, oil and coal in combination with strong winds. Fire suppression tactics aim to reduce flame length by decreasing fuel supply and fire intensity for safer control.