A flame is a chemical reaction you can see with the naked eye. Fuel combines with oxygen and gives off heat, while glowing soot and excited atoms emit light. Light a fire and put it out by taking away the sides of its triangle one by one, match the right extinguisher to each fire, look deep into a candle flame like Michael Faraday, balance a combustion equation, identify metals by the color of their flame, and see why flour in the air can be more dangerous than a log.
Simplified model: a wood flame goes out when it runs out of fuel, when the air holds less than about 15% oxygen, or when the fuel cools below its ignition temperature (for wood we assume about 300 °C — it depends on the species and moisture). In a real fire the flame heats the fuel itself; here you set the temperature with the slider.
Choose a type of fire, then an extinguishing agent.
✓ right choice · ~ only for small fires or with caveats · – ineffective · ✗ dangerous. Fire classes follow the European standard EN 2; for live electrical equipment the extinguisher must be marked as approved for it (usually up to 1,000 V).
The emergency number 112 works throughout the European Union. In Poland you can also call the fire brigade at 998. Speak calmly: what is burning, where (the address), and whether anyone is inside.
A guide after Faraday — choose a step:
Jar: the candle stands in a saucer of water. Cover it and watch what happens to the flame and the water.
The candle flame temperatures are approximate — measurements vary with the method and the candle. The jar model is simplified (1 L of air, water vapor condenses at once, CO₂ doesn't dissolve), but it shows the right proportions.
Burning 1 m³ of methane takes about 9.5 m³ of air. A Bunsen burner premixes only part of that air with the gas (primary air); the flame draws the rest from its surroundings. Temperatures are approximate.
Simplification: hydrogen combines with oxygen into water first, and carbon gets the rest of the oxygen. In a real flame the products always mix a little differently (hydrogen H₂ also forms, for example), but the trend is the same: the less oxygen, the more CO and soot and the less energy. Energy from enthalpies of formation, water as vapor.
Bar: lower heating value (water in the exhaust as vapor); tick: higher heating value (vapor condensed). Natural fuels vary (the range is shown lighter). Typical values, in MJ/kg.
Carbon monoxide is colorless, odorless and non-irritating. It forms during incomplete combustion — when a stove, boiler or fireplace doesn't get enough air. It binds to hemoglobin more than 200 times more strongly than oxygen, so the blood stops carrying oxygen around the body. The first symptoms resemble a cold or tiredness: headache, dizziness, nausea, drowsiness.
Most poisonings happen during the heating season, from autumn to spring. An alarm is no substitute for working ventilation and inspections.
Thresholds from standard EN 50291-1 for home alarms. ppm — the number of CO molecules per million molecules of air.
Draw a sample and identify the metal by its flame color and the lines in the spectroscope.
The spectroscope shows the main atomic lines and the molecular bands (e.g. SrOH, CaOH, CuCl) that form in the flame. Line positions are real; brightnesses are approximate. Colors on screen only resemble the real ones.
A hot flame kicks the electrons of metal atoms up to higher energy levels. A moment later they fall back and give the energy off as light. The spacing between levels is different for every element, so each one glows with its own set of colors — like a fingerprint.
For sodium's yellow line λ = 589 nm, so E ≈ 2.1 eV. Potassium's violet (404 nm) means higher-energy photons, about 3.1 eV.
Blue is the hardest firework color: the glowing copper compound (CuCl) breaks down when the flame is too hot. White and golden sparks come from glowing specks of metals such as magnesium, aluminum, titanium or iron.
Model: cube-shaped pieces of wood with a density of 500 kg/m³. We estimate the burn time of a single particle surrounded by air with the d² law (t ≈ d²/K, K ≈ 1 mm²/s) — only an order of magnitude. The animation is sped up or slowed down so you can see it.
We use the classic explosive limits of methane in air: about 5% and about 15% by volume (newer standards give 4.4% and 17%). The most violent burning is in a mixture close to stoichiometric, about 9.5% methane.
Combustible dust — flour, sugar, wood or coal dust — explodes only when all of these happen at once: there is a lot of it, it hangs in the air as a cloud, it has access to oxygen, a spark or hot surface appears, and the whole thing is enclosed in a room or silo. Removing any one condition prevents the explosion.
Methane in coal mines. Coal seams, including those in Upper Silesia in southern Poland, hold trapped methane — miners call it firedamp. Its explosions used to be the greatest danger underground. Today mines measure methane levels constantly, ventilate the workings, and automatically shut down electrical machinery long before the explosive limit is reached.
The Davy lamp (1815). A flame surrounded by fine metal gauze: the gauze carries heat away so fast that the flame can't pass outside. The height of the blue “cap” above the flame let miners judge how much methane there was. George Stephenson built a similar lamp at the same time.
Engines and rockets. In an engine cylinder the fuel–air mixture burns in a fraction of a second, but in a precisely metered dose. A rocket carries its own oxidizer, because there is no air in space. It's still the same combustion — just fast and under control.
Exactly when humans learned to use fire is still debated. Traces from about 1 million years ago (Wonderwerk Cave in South Africa) are disputed; stronger evidence, such as burned flints and seeds at Gesher Benot Ya'aqov in Israel, is about 780,000 years old. Regular use of hearths seems widespread from about 400,000 years ago. Fire brought warmth, protection, light and cooking, which makes food easier to digest.
For almost a hundred years people believed that combustible bodies contain “phlogiston,” which escapes in fire. Antoine Lavoisier weighed substances before and after burning: metals got heavier after roasting. He explained that burning is combining with a gas discovered by Scheele and Priestley, which he named oxygen (oxygène). 2.4 g of magnesium gives about 4.0 g of magnesium oxide — mass is gained, not lost.
A match head contains, among other things, potassium chlorate and sulfur, while red phosphorus is on the striking strip of the box. When you strike it, the heat of friction turns a tiny bit of red phosphorus into a more reactive form, which ignites the head. The idea of the Swede Gustaf Pasch (1844) was popularized by the Lundström brothers of Jönköping. Earlier matches made with white phosphorus poisoned the workers who made them and were banned in the early 20th century.
In some ecosystems fire is a natural visitor. The cones of jack pine and lodgepole pine in North America are sealed with resin and open only at high temperatures — after a fire, the seeds land on bare soil enriched with ash. In Poland, however, almost all forest fires are started by people, and the greatest risk comes in dry springs and summers.
The fire started in a bakery on Pudding Lane and over four days consumed most of the medieval City — about 13,000 houses, 87 churches and St Paul's Cathedral. Dense wooden buildings, drought and a strong wind fed the flames. Afterward London was rebuilt in brick and stone, building regulations were introduced and fire insurance took off.
The Sun doesn't “burn” like coal — there's no oxygen there for combustion. It shines thanks to nuclear fusion: hydrogen nuclei fuse into helium, and the lost mass turns into energy (E = mc²). If the Sun were a lump of coal burning with the same power, it would burn out in a few thousand years. Yet it has been shining for 4.6 billion years.
Cellular respiration is combustion without a flame: glucose combines with oxygen into the same products as in a campfire, but enzymes break the reaction into dozens of small steps, and the energy goes into ATP molecules instead of escaping as heat and light.
Combustion is a fast reaction between a fuel and an oxidizer — usually oxygen from the air. The reaction is exothermic: the bonds in the products (CO₂, H₂O) are stronger than in the reactants, so the excess energy is released as heat and light.
Wood doesn't catch fire by itself at room temperature, because the molecules first have to get over a barrier — the activation energy. A match supplies it in one spot, and then the flame itself heats the next portions of fuel to their ignition temperature. A chain reaction runs in the flame: free radicals (H•, OH•, O•) break apart fuel molecules and create more radicals. Extinguishing powder and the halons of old break this chain — that's the fourth side of the “fire tetrahedron.”
With plenty of oxygen, the carbon in the fuel ends up as CO₂. When oxygen runs short, poisonous carbon monoxide CO forms, and with even less oxygen — pure carbon, that is, soot. Glowing specks of soot give candles and campfires their yellow light; a flame with excess oxygen (a burner with the air hole open, a gas stove) is blue, because excited CH and C₂ molecules glow in it and there is no soot.
Combustion happens at the surface of the fuel. Pieces ten times smaller mean ten times more surface, and a single speck burns up to a hundred times faster. So a cloud of dust, or gas mixed with air, can burn up in a fraction of a second — that's deflagration, an explosion. A mixture explodes only within a certain range of concentrations: too lean and it can't carry the flame, too rich and it has too little oxygen.
Simplifications: the models on this page show trends, not specific devices. Flame temperatures, heating values and thresholds are typical and approximate. This page contains no instructions for experiments with fire — real experiments belong only in a lab or under adult supervision.