upright=1.5, Fire fighters simulating boilover to demonstrate the risks. Length of the sequence 2.4 seconds. it was 1 kg cooking oil and 1 litre of water.
A boilover (or boil-over) type of
fire
Fire is the rapid oxidation of a material (the fuel) in the exothermic chemical process of combustion, releasing heat, light, and various reaction products.
At a certain point in the combustion reaction, called the ignition point, flames ...
refers to an extremely hazardous situation where an attempt is made to extinguish semi-enclosed
oil
An oil is any nonpolar chemical substance that is composed primarily of hydrocarbons and is hydrophobic (does not mix with water) & lipophilic (mixes with other oils). Oils are usually flammable and surface active. Most oils are unsaturated ...
or
petrochemical
Petrochemicals (sometimes abbreviated as petchems) are the chemical products obtained from petroleum by refining. Some chemical compounds made from petroleum are also obtained from other fossil fuels, such as coal or natural gas, or renewabl ...
fueled fire with
water
Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as ...
. The hazard results due to the difference in
density
Density (volumetric mass density or specific mass) is the substance's mass per unit of volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' can also be used. Mathematicall ...
between oil and water.
NFPA defines boil-over as: ''An event in the burning of certain oils in an open-top tank when, after a long period of quiescent burning, there is a sudden increase in fire intensity associated with expulsion of burning oil from the tank.''
Boilover is also common in the home as a
chip pan fire when cooking.
Mechanism
As water is poured onto the fuel, it quickly sinks to the bottom of the container due to the water's higher density, and has little effect on extinguishing the flames on the surface. Under certain conditions, after some time, the water on the bottom rapidly
vaporise
Vaporization (or vaporisation) of an element or compound is a phase transition from the liquid phase to vapor. There are two types of vaporization: evaporation and boiling. Evaporation is a surface phenomenon, whereas boiling is a bulk phenomenon ...
s into steam, causing it to expand more than 1700 times in
volume
Volume is a measure of occupied three-dimensional space. It is often quantified numerically using SI derived units (such as the cubic metre and litre) or by various imperial or US customary units (such as the gallon, quart, cubic inch). ...
. The rapidly expanding steam (possibly
superheated) expels the oil or fuel above upward and out of the tank, resulting in the discharging of burning oil onto a large and uncontrolled area outside of the container.
Mathematical modelling of the phenomenon is difficult and complicated,
making boilover prediction unreliable.
Image:Chip-pan-fire-cross-section-1.png, Oil gets so hot that it catches fire all by itself
Image:Chip-pan-fire-cross-section-2.png, Water is poured into the container
Image:Chip-pan-fire-cross-section-3.png, Water is denser than oil, so it sinks to the bottom. Since the boiling point of water is much below the boiling point of oil, water is heated above its boiling point and instantly vaporizes.
Image:Chip-pan-fire-cross-section-4.png, The water vapour expands rapidly, ejecting the upper burning oil out of the container and into the air where its surface area increases hugely and combustion proceeds much faster, forming a fireball.
Image:Chip-pan-fire-4.jpg, Oil is heated strongly
Image:Chip-pan-fire-3.jpg, After some time, it gets hot enough to catch fire
Image:Chip-pan-fire-2.jpg, Pouring a very small amount of water into the fire ejects a plume of fire
Image:Chip-pan-fire.jpg, The plume rises and spreads against the ceiling; hopefully nothing flammable is in the way
Image:Chip-pan-fire-5.jpg, With all the oil burned, there is no more fuel to supply the fire
See also
*
Chip pan fire, a common domestic boilover accident
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Expansion ratio
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Fire extinguisher foams
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Fire class#Class F/K
*
Phreatic eruption
A phreatic eruption, also called a phreatic explosion, ultravulcanian eruption or steam-blast eruption, occurs when magma heats ground water or surface water. The extreme temperature of the magma (anywhere from ) causes near-instantaneous evap ...
- a similar concept in volcanic eruption
*
Wax fire
References
External links
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{{DEFAULTSORT:Boilover (Fire)
Fire
Petroleum production
Articles containing video clips
