Why Stop, Drop and Roll When Your Clothes Catch Fire, Instead of Running?
― The heat of a flame races up a standing body to your face
When a sleeve catches fire, everyone wants to run. But running is the most dangerous thing you can do. The hot gas from a flame rises straight up. A standing person's body lies right in its path. Just by lying down, you let the heat leave your body and escape into the air.
It is a cold night, and you are heating a pot on a gas stove. You reach over the flame for a seasoning at the back, in a fluffy fleece sleeve.
Then you notice the cuff glowing orange. The fire is crawling up your arm much faster than you expected.
Your first thought is "run to the water." But fire services teach exactly the opposite: stop where you are, drop to the floor, and roll.
There are only two reasons not to run
The air around a flame is hot and light, and flows straight up. When you stand, the heat from a burning sleeve or hem climbs from your chest to your face.
Fire burns on the oxygen in the air. Running works like fanning with a paper fan: fresh air keeps reaching the flame.
"Stop, drop and roll" cuts off both at once. When you drop, your face moves out of the path of the heat. When you roll, the burning side is pressed to the floor and air can no longer reach it.
A standing body acts like a chimney
A flame is really glowing hot gas. Hot gas is lighter than the air around it, so it floats up. It is the same reason the water at the top of a bath is hotter.
A standing person is shaped like a tall tube. Hot gas from a burning hem or sleeve climbs along the surface of the body. On the way up, it warms the cloth above, one piece after another. Warmed cloth catches fire more easily, and the flame jumps to it. So the fire spreads from bottom to top, faster and faster.
Hang a strip of cloth upright and light the bottom edge, and the flame rushes upward. Light the top edge, and it creeps down only slowly. The heat goes up, not down.
Look at Figure 1. The slider changes the angle of the body, and with it the length of body wrapped in hot gas. Standing, everything above the flame is inside the heat. Lying down, the hot gas leaves the body and escapes into the air.
Running delivers air to the flame
The other reason is air. For a flame to keep burning, oxygen must keep arriving from around it. Even if you stand still, the rising hot gas pulls fresh air in from below.
Running adds a headwind on top of that. It is like fanning a campfire: the flames grow. And a running person cannot see the fire on their back or arms. By the time you reach water, the fire is much bigger.
Rolling is for cutting off that air. When you press the burning side to the floor, oxygen cannot reach it. Each time you roll over, another side is pressed down. Roll left and right several times, until the fire goes out.
Clothes of brushed cotton or rayon, or with long pile, can let a flame race across the surface in an instant once it touches the fine fibres. This is called "surface flash," and fire services warn about it. Fine fibres are light and heat up fast, and plenty of air surrounds them. When cooking, pick clothes with snug cuffs, and arrange things so you never reach over the flame.
So what should you do?
- StopDo not run. Running in a panic feeds air to the flame and sends heat up to your face.
- DropLie down on the floor where you are and cover your face with both hands. This takes your face out of the path of the heat and keeps you from breathing in flame.
- RollRoll left and right, pressing the burning parts against the floor. Keep going until the fire is out.
Bystanders should first turn off the stove or heater to cut the heat source. Then shout "Stop, drop and roll!" to the person on fire. If water is within easy reach, pour it on. A bath towel or coat can be pressed on from the face toward the feet to smother the fire. Even after it is out, keep cooling the burn under running tap water and call emergency services (119 in Japan) right away. If the fire spreads to furniture or walls, do not try to fight it; everyone should get outside.
Summary
The hot gas from a flame rises straight up. A standing body is in its path, and heat from a burning sleeve or hem can reach face height in under a second. Running feeds the flame air. Stopping and dropping takes your face out of the heat's path. Rolling cuts off air to the burning surface.
When you most want to flee, lie down where you are.
Flames run upward, and you cannot breathe on a floor of fire.
For why flames point upward, see "Why does a candle flame stretch upward?", and for why you crouch low to escape smoke in a fire, see "Why should you keep low when escaping a fire?"
- Boil water in a kettle and watch the steam from the spout from the side. Even if it comes out at a slant, it bends straight up partway. You can see hot air rising.
- Hold your palm about 30 cm directly above the steam. Compare the heat with holding your hand at the same distance to the side. To avoid burns, pull your hand away as soon as it feels hot.
- Practise "stop, drop and roll" once with your family on the floor. Try rolling left and right while keeping both hands over your face.
Once you see that the heat is only straight above, you can feel how far a standing body sits in the path of the heat. Never do experiments with real fire.
For those who want more ― terms, formulas and links to textbooksEach part is labelled with its level, from middle school science to university courses
- Middle schoolCovered in middle school science
- High schoolCovered in high school basic physics and chemistry
- High school+Advanced high school material, or textbook sidebars
- UniversityUniversity-level courses not taught in high school (combustion and fire engineering)
- ResearchNot yet settled textbook knowledge; researchers are still studying it
Middle schoolTerms: this phenomenon has a name
- Clothing ignition: fire spreading to the clothes you are wearing. It happens at stoves, heaters, household altar candles and so on, and is said to harm older people most.
- The three elements of combustion: fuel, oxygen and heat (temperature). Remove any one and the fire goes out. Rolling removes oxygen; pouring water removes heat.
- Updraft (fire plume): the flow of air and gas warmed by a flame, which becomes light and rises like a column.
Middle schoolHigh schoolCheck with a formula: how many seconds until sleeve heat reaches the face?
We estimate how long hot gas from a burning sleeve at chest height takes to rise 50 cm to face height. We find the rising speed from the buoyancy that the hot gas feels.
| In symbols | v ＝ √( 2 × g × h × ( T − T0 ) ÷ T ) |
| In words | Rising speed ＝ square root of 2 × gravitational acceleration × height risen × "temperature difference ÷ hot gas temperature" |
| Where it comes from | An energy balance: the buoyancy the hot gas feels because it is lighter turns into kinetic energy over the height h. "Temperature difference ÷ temperature" is how much lighter the hot gas is than the surrounding air. |
| Gravitational acceleration g | 9.8 m/s² |
| Height from sleeve to face h | 0.5 m |
| Temperature T of hot gas just above the flame | Assume about 1000 K (about 730℃) |
| Temperature T0 of surrounding air | About 300 K (about 27℃) |
| 2 × gravitational acceleration | 2 × 9.8 ＝ 19.6 |
| Multiply by height | 19.6 × 0.5 ＝ 9.8 |
| Temperature difference | 1000 − 300 ＝ 700 |
| Lightness ratio | 700 ÷ 1000 ＝ 0.7 |
| Inside the square root | 9.8 × 0.7 ＝ 6.86 |
| Speed at face height | The square root of 6.86 is about 2.6 m/s |
| Average speed on the way up (starting from 0) | 2.6 ÷ 2 ＝ 1.3 m/s |
| Time to reach the face | 0.5 ÷ 1.3 ≒ 0.38 s |
Real hot gas mixes in surrounding air, cools a little and slows down. Even so, the time is within about 1 second. The heat reaches face height before you can think "that's hot" and start to run.
| 2.6 m/s in km/h | 2.6 × 3.6 ≒ 9.4 km/h |
By this calculation, an upward wind faster than a brisk walk blows up along your body. If you lie down, this wind blows not along your body but up into the sky.
| Symbol | Meaning and unit |
| v | Rising speed of the hot gas (m/s) |
| g | Gravitational acceleration (m/s²) |
| h | Height risen (m) |
| T | Temperature of the hot gas (K, absolute temperature) |
| T0 | Temperature of the surrounding air (K) |
High schoolHigh school+Why does fire spread upward so fast?
High schoolA gas expands as its temperature rises, and its weight per unit volume (density) falls. By the Boyle–Charles law, at the same pressure the density is inversely proportional to absolute temperature. The density of 1000 K gas is about 30% that of 300 K air. This lightness becomes buoyancy and pushes the hot gas up.
High school+When a flame climbs vertical cloth, the unburnt cloth above is pre-heated by the hot gas and the flame's radiation. The more heated the cloth, the sooner it ignites, so the flame grows longer as it advances and heats the cloth ahead even more. This is called "upward flame spread," and it accelerates. In downward flame spread, heat escapes in the direction opposite to the advance, so it is slow and steady.
UniversityDiffusion flames and fire plumes
A clothing fire is a diffusion flame, which burns as fuel (gas made when cloth breaks down in heat) and air mix. The burning rate is set by how fast oxygen from the air reaches the flame. Running adds a headwind, which increases the oxygen supply and strengthens the burning. The flow above a flame is called a fire plume; it rises by buoyancy while drawing in the surrounding air. How its speed and temperature change is described by buoyant plume theory and by McCaffrey's correlations in fire science.
📖 Derivations and further reading: Diffusion combustion (Wikipedia, in Japanese) ／ Buoyancy (Wikipedia, in Japanese)
ResearchWhat is still not well understood
- How fire spreads by fabric and shape. The length of the pile, layering and loose sleeve shapes change how fast flames travel a great deal. Predicting this on a person wearing the clothes is still said to be hard.
- How well "stop, drop and roll" works. It is considered an effective teaching, but little evidence-based research exists on how many rolls are needed, or how to teach it to older or physically impaired people.
- When surface flash occurs. Whether a flame races over the surface alone depends on fibre thinness, density and dampness, and research on where the boundary lies continues.
So this article, too, is "an explanation of what is known so far." Still, that the heat of a flame rises is a sound, basic fact.
Links to textbooks (by level)
| Level | Subject / unit | Where in this article |
|---|---|---|
| Middle school | Science (combustion and oxygen, expansion of air) | Three elements of combustion; why running feeds air |
| High school | Basic physics (buoyancy, energy), basic chemistry (gas laws) | Formula for the rising speed of hot gas |
| High school+ | Advanced heat transfer | The difference between upward and downward spread |
| University | Combustion and fire engineering | Diffusion flames, fire plumes |
| Research | Fire safety engineering, flammability of textiles | Fire spread by fabric, effect of teaching methods |
| ― | Links to daily life | Clothing for cooking, care near heaters, family practice |
- Tokyo Fire Department (東京消防庁) public information, "Beware of clothing ignition" (stop, drop and roll; warning about surface flash).
- Fire and Disaster Management Agency (消防庁), Fire Service White Paper (消防白書) (causes of home fires and deaths).
- D. Drysdale, An Introduction to Fire Dynamics, 3rd ed., Wiley, 2011 (upward and downward flame spread, fire plumes).
- Japan Association for Fire Science and Engineering (日本火災学会), ed., Fire Handbook (火災便覧), 4th ed., Kyoritsu Shuppan (共立出版), 2018.
- National Fire Protection Association (NFPA) fire-safety education material, "Stop, Drop and Roll."
※This article is a science explainer for general readers. The figures given are rough guides to help you understand the mechanism. In a real fire, follow the instructions of the fire service and local authorities. If you are burned, see a medical facility rather than judging for yourself.