The autoignition temperature or self-ignition temperature, often called spontaneous ignition temperature or minimum ignition temperature (or shortly ignition temperature) and formerly also known as kindling point, of a substance is the lowest temperature at which it spontaneously ignites in a normal atmosphere without an external source of ignition, such as a flame or spark. [1] This temperature is required to supply the activation energy needed for combustion. The temperature at which a chemical ignites decreases as the pressure is increased.
Autoignition temperatures of liquid chemicals are typically measured using a 500-millilitre (18 imp fl oz; 17 US fl oz) flask placed in a temperature-controlled oven in accordance with the procedure described in ASTM E659. [2]
When measured for plastics, autoignition temperature can also be measured under elevated pressure and at 100% oxygen concentration. The resulting value is used as a predictor of viability for high-oxygen service. The main testing standard for this is ASTM G72. [3]
The time it takes for a material to reach its autoignition temperature when exposed to a heat flux is given by the following equation: [4]
where k = thermal conductivity, ρ = density, and c = specific heat capacity of the material of interest, is the initial temperature of the material (or the temperature of the bulk material).
Temperatures vary widely in the literature and should only be used as estimates. Factors that may cause variation include partial pressure of oxygen, altitude, humidity, and amount of time required for ignition. Generally the autoignition temperature for hydrocarbon/air mixtures decreases with increasing molecular mass and increasing chain length. The autoignition temperature is also higher for branched-chain hydrocarbons than for straight-chain hydrocarbons. [5]
| Substance | Autoignition [D] | Note |
|---|---|---|
| Barium | 550 °C (1,022 °F) | 550±90 [1] [C] |
| Bismuth | 735 °C (1,355 °F) | 735±20 [1] [C] |
| Butane | 405 °C (761 °F) | [6] |
| Calcium | 790 °C (1,450 °F) | 790±10 [1] [C] |
| Carbon disulfide | 90 °C (194 °F) | [7] |
| Diesel or Jet A-1 | 210 °C (410 °F) | [8] |
| Diethyl ether | 160 °C (320 °F) | [9] |
| Ethanol | 365 °C (689 °F) | [7] |
| Gasoline (Petrol) | 247–280 °C (477–536 °F) | [7] |
| Hydrogen | 535 °C (995 °F) | |
| Iron | 1,315 °C (2,399 °F) | 1315±20 [1] [C] |
| Lead | 850 °C (1,560 °F) | 850±5 [1] [C] |
| Leather / parchment | 200–212 °C (392–414 °F) | [8] [10] |
| Magnesium | 635 °C (1,175 °F) | 635±5 [1] [B] [C] |
| Magnesium | 473 °C (883 °F) | [7] [B] |
| Methane | 537 °C (999 °F) | |
| Molybdenum | 780 °C (1,440 °F) | 780±5 [1] [C] |
| Paper | 218–246 °C (424–475 °F) | [8] [11] |
| Phosphorus (white) | 34 °C (93 °F) | [7] [A] [B] |
| Silane | 21 °C (70 °F) | [7] or below |
| Strontium | 1,075 °C (1,967 °F) | 1075±120 [1] [C] |
| Tin | 940 °C (1,720 °F) | 940±25 [1] [C] |
| Triethylborane | −20 °C (−4 °F) | [7] |
| A On contact with an organic substance, melts otherwise. |
| B There are two distinct results in the published literature. Both are separately listed in this table. |
| C At 1 atm. The ignition temperature depends on the air pressure. |
| D Under standard conditions for pressure. |
Combustion, or burning, is a high-temperature exothermic redox chemical reaction between a fuel and an oxidant, usually atmospheric oxygen, that produces oxidized, often gaseous products, in a mixture termed as smoke. Combustion does not always result in fire, because a flame is only visible when substances undergoing combustion vaporize, but when it does, a flame is a characteristic indicator of the reaction. While activation energy must be supplied to initiate combustion, the heat from a flame may provide enough energy to make the reaction self-sustaining. The study of combustion is known as combustion science.
A thermocouple, also known as a "thermoelectrical thermometer", is an electrical device consisting of two dissimilar electrical conductors forming an electrical junction. A thermocouple produces a temperature-dependent voltage as a result of the Seebeck effect, and this voltage can be interpreted to measure temperature. Thermocouples are widely used as temperature sensors.
A calorimeter is a device used for calorimetry, or the process of measuring the heat of chemical reactions or physical changes as well as heat capacity. Differential scanning calorimeters, isothermal micro calorimeters, titration calorimeters and accelerated rate calorimeters are among the most common types. A simple calorimeter just consists of a thermometer attached to a metal container full of water suspended above a combustion chamber. It is one of the measurement devices used in the study of thermodynamics, chemistry, and biochemistry.
An Otto cycle is an idealized thermodynamic cycle that describes the functioning of a typical spark ignition piston engine. It is the thermodynamic cycle most commonly found in automobile engines.
A flame is the visible, gaseous part of a fire. It is caused by a highly exothermic chemical reaction made in a thin zone. When flames are hot enough to have ionized gaseous components of sufficient density, they are then considered plasma.
The flash point of a material is the "lowest liquid temperature at which, under certain standardized conditions, a liquid gives off vapours in a quantity such as to be capable of forming an ignitable vapour/air mixture".
A backdraft, backdraught or smoke explosion is the abrupt burning of superheated gases in a fire caused when oxygen rapidly enters a hot, oxygen-depleted environment; for example, when a window or door to an enclosed space is opened or broken. Backdrafts are typically seen as a blast of smoke and/or flame out of an opening of a building. Backdrafts present a serious threat to firefighters. There is some debate concerning whether backdrafts should be considered a type of flashover.
A flashover is the near-simultaneous ignition of most of the directly exposed combustible material in an enclosed area. When certain organic materials are heated, they undergo thermal decomposition and release flammable gases. Flashover occurs when the majority of the exposed surfaces in a space are heated to their autoignition temperature and emit flammable gases. Flashover normally occurs at 500 °C (932 °F) or 590 °C (1,100 °F) for ordinary combustibles and an incident heat flux at floor level of 20 kilowatts per square metre (2.5 hp/sq ft).
Homogeneous Charge Compression Ignition (HCCI) is a form of internal combustion in which well-mixed fuel and oxidizer are compressed to the point of auto-ignition. As in other forms of combustion, this exothermic reaction produces heat that can be transformed into work in a heat engine.
In electrical and safety engineering, hazardous locations are places where fire or explosion hazards may exist. Sources of such hazards include gases, vapors, dust, fibers, and flyings, which are combustible or flammable. Electrical equipment installed in such locations can provide an ignition source, due to electrical arcing, or high temperatures. Standards and regulations exist to identify such locations, classify the hazards, and design equipment for safe use in such locations.
Mixtures of dispersed combustible materials and oxygen in the air will burn only if the fuel concentration lies within well-defined lower and upper bounds determined experimentally, referred to as flammability limits or explosive limits. Combustion can range in violence from deflagration through detonation.
Char cloth, also called char paper, is a material with low ignition temperature, used as tinder when lighting a fire. It is the main component in a tinderbox. It is a small swatch of fabric made from a natural fibre that has been converted through pyrolysis.
Smouldering or smoldering is the slow, flameless form of combustion, sustained by the heat evolved when oxygen directly attacks the surface of a condensed-phase fuel. Many solid materials can sustain a smouldering reaction, including coal, cellulose, wood, cotton, tobacco, cannabis, peat, plant litter, humus, synthetic foams, charring polymers including polyurethane foam and some types of dust. Common examples of smouldering phenomena are the initiation of residential fires on upholstered furniture by weak heat sources, and the persistent combustion of biomass behind the flaming front of wildfires.
Spontaneous combustion or spontaneous ignition is a type of combustion which occurs by self-heating, followed by thermal runaway and finally, autoignition. It is distinct from pyrophoricity, in which a compound needs no self-heat to ignite. The correct storage of spontaneously combustible materials is extremely important considering improper storage is the main cause of spontaneous combustion. Materials such as coal, cotton, hay, and oils should be stored at proper temperatures and moisture levels to prevent spontaneous combustion.
A thermal oxidizer is a process unit for air pollution control in many chemical plants that decomposes hazardous gases at a high temperature and releases them into the atmosphere.
A combustible material is a material that can burn in air under certain conditions. A material is flammable if it ignites easily at ambient temperatures. In other words, a combustible material ignites with some effort and a flammable material catches fire immediately on exposure to flame.
Fire-safe polymers are polymers that are resistant to degradation at high temperatures. There is need for fire-resistant polymers in the construction of small, enclosed spaces such as skyscrapers, boats, and airplane cabins. In these tight spaces, ability to escape in the event of a fire is compromised, increasing fire risk. In fact, some studies report that about 20% of victims of airplane crashes are killed not by the crash itself but by ensuing fires. Fire-safe polymers also find application as adhesives in aerospace materials, insulation for electronics, and in military materials such as canvas tenting.
A cool flame is a flame having a typical temperature of about 400 °C (752 °F). In contrast to an ordinary hot flame, the reaction is not vigorous and releases little heat, light, or carbon dioxide. Cool flames are difficult to observe and are uncommon in everyday life, but they are responsible for engine knock – the undesirable, erratic, and noisy combustion of low-octane fuels in internal combustion engines.
This is an alphabetized glossary of terms pertaining to lighting fires, along with their definitions. Firelighting is the process of starting a fire artificially. Fire was an essential tool in early human cultural development. The ignition of any fire, whether natural or artificial, requires completing the fire triangle, usually by initiating the combustion of a suitably flammable material.
Oxygen compatibility is the issue of compatibility of materials for service in high concentrations of oxygen. It is a critical issue in space, aircraft, medical, underwater diving and industrial applications. Aspects include effects of increased oxygen concentration on the ignition and burning of materials and components exposed to these concentrations in service.
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