Backdraft
Encyclopedia
A backdraft is an explosive event at a fire resulting from rapid re-introduction of oxygen
to combustion
in an oxygen-starved environment, for example, the breaking of a window or opening of a door to an enclosed space. Backdrafts present a serious threat to firefighters
, even those with a high level of experience. There is some controversy surrounding the question of whether backdrafts should be considered a type of flashover
(see below).
; consequently combustion
slows (due to the lack of oxygen) but the combustible fuel gases (primarily carbon monoxide
) and smoke (primarily hydrocarbon
free radicals and particulate matter) remain at a temperature above the ignition-point of the fuel gases. If oxygen is re-introduced to the fire, e.g. by opening a door (or window) to a closed room, combustion will restart, often resulting in an explosive effect as the gases are heated by the combustion and expand rapidly because of the rapidly increasing temperature.
Characteristic signs of a backdraft situation include yellow or brown smoke, smoke which exits small holes in puffs (a sort of breathing effect) and is often found around the edges of doors and windows, and windows which appear brown or black when viewed from the exterior. These darker colors are caused by incomplete combustion (more particulate matter in the gases darkens them). If the room contains a lot of soot (particulate matter), it indicates that the room lacks enough oxygen to permit combustion of the soot particles. Firefighters
often look to see if there is soot on the inside of windows and in cracks around in the room. The window might have cracked because of the heat. The windows of the structure may also have a slight vibration due to the varying pressure differentials. The surrounding environment (e.g. the hallway outside the suspected backdraft room) will be extremely hot.
If firefighters discover a room pulling air into itself, for example through a crack, they generally evacuate immediately, because this is a strong indication that a backdraft is imminent. Due to pressure differences, these puffs of smoke are sometimes sucked back into the enclosed space from which they emanate, which is where the term backdraft originates.
Backdrafts are very dangerous situations, often surprising firefighters, regardless of their level of experience. The most common tactic used by firefighters in defusing a potential backdraft is to ventilate from the highest point, allowing the heat and smoke to escape without igniting explosively.
as "transition to a state of total surface involvement in a fire of combustible materials within an enclosure," a broad definition that embraces several different scenarios, including backdrafts, there is nevertheless considerable disagreement regarding whether or not backdrafts should properly be considered flashovers. (A different viewpoint: ) The most common use of the term flashover is to describe the near-simultaneous ignition of material caused by heat reaching the autoignition temperature
of the combustible material and gases in an enclosure; flashovers of this type are not backdrafts as they are triggered by thermal change. Backdrafts, on the other hand, are caused by the introduction of oxygen into an enclosure that may already be hot enough for ignition; thus, backdrafts are triggered by chemical change.
, where a serial arsonist
was using them as a means of assassinating
people.
An interesting variation on the phenomenon occurred after the 1906 San Francisco earthquake
and fire. In the days after the blaze several business people opened warm safes to see if their papers were safe. The sudden inrush of oxygen into the still-hot gas of the interiors that now contained pyrolyzed
fuel gases due to the heated papers (hydrocarbons) therein, led to immediate and explosive combustion of the remaining intact contents.
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
to combustion
Combustion
Combustion or burning is the sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat and conversion of chemical species. The release of heat can result in the production of light in the form of either glowing or a flame...
in an oxygen-starved environment, for example, the breaking of a window or opening of a door to an enclosed space. Backdrafts present a serious threat to firefighters
Firefighter
Firefighters are rescuers extensively trained primarily to put out hazardous fires that threaten civilian populations and property, to rescue people from car incidents, collapsed and burning buildings and other such situations...
, even those with a high level of experience. There is some controversy surrounding the question of whether backdrafts should be considered a type of flashover
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...
(see below).
How backdrafts occur
A backdraft is a situation which can occur when a fire's product-gases are starved of oxygenOxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
; consequently combustion
Combustion
Combustion or burning is the sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat and conversion of chemical species. The release of heat can result in the production of light in the form of either glowing or a flame...
slows (due to the lack of oxygen) but the combustible fuel gases (primarily carbon monoxide
Carbon monoxide
Carbon monoxide , also called carbonous oxide, is a colorless, odorless, and tasteless gas that is slightly lighter than air. It is highly toxic to humans and animals in higher quantities, although it is also produced in normal animal metabolism in low quantities, and is thought to have some normal...
) and smoke (primarily hydrocarbon
Hydrocarbon
In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons from which one hydrogen atom has been removed are functional groups, called hydrocarbyls....
free radicals and particulate matter) remain at a temperature above the ignition-point of the fuel gases. If oxygen is re-introduced to the fire, e.g. by opening a door (or window) to a closed room, combustion will restart, often resulting in an explosive effect as the gases are heated by the combustion and expand rapidly because of the rapidly increasing temperature.
Characteristic signs of a backdraft situation include yellow or brown smoke, smoke which exits small holes in puffs (a sort of breathing effect) and is often found around the edges of doors and windows, and windows which appear brown or black when viewed from the exterior. These darker colors are caused by incomplete combustion (more particulate matter in the gases darkens them). If the room contains a lot of soot (particulate matter), it indicates that the room lacks enough oxygen to permit combustion of the soot particles. Firefighters
Firefighter
Firefighters are rescuers extensively trained primarily to put out hazardous fires that threaten civilian populations and property, to rescue people from car incidents, collapsed and burning buildings and other such situations...
often look to see if there is soot on the inside of windows and in cracks around in the room. The window might have cracked because of the heat. The windows of the structure may also have a slight vibration due to the varying pressure differentials. The surrounding environment (e.g. the hallway outside the suspected backdraft room) will be extremely hot.
If firefighters discover a room pulling air into itself, for example through a crack, they generally evacuate immediately, because this is a strong indication that a backdraft is imminent. Due to pressure differences, these puffs of smoke are sometimes sucked back into the enclosed space from which they emanate, which is where the term backdraft originates.
Backdrafts are very dangerous situations, often surprising firefighters, regardless of their level of experience. The most common tactic used by firefighters in defusing a potential backdraft is to ventilate from the highest point, allowing the heat and smoke to escape without igniting explosively.
Backdrafts and flashovers
Although ISO 13943 defines flashoverFlashover
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...
as "transition to a state of total surface involvement in a fire of combustible materials within an enclosure," a broad definition that embraces several different scenarios, including backdrafts, there is nevertheless considerable disagreement regarding whether or not backdrafts should properly be considered flashovers. (A different viewpoint: ) The most common use of the term flashover is to describe the near-simultaneous ignition of material caused by heat reaching the autoignition temperature
Autoignition temperature
The autoignition temperature or kindling point of a substance is the lowest temperature at which it will spontaneously ignite in a normal atmosphere without an external source of ignition, such as a flame or spark. This temperature is required to supply the activation energy needed for combustion...
of the combustible material and gases in an enclosure; flashovers of this type are not backdrafts as they are triggered by thermal change. Backdrafts, on the other hand, are caused by the introduction of oxygen into an enclosure that may already be hot enough for ignition; thus, backdrafts are triggered by chemical change.
In popular culture
Backdrafts entered popular consciousness through the 1991 film BackdraftBackdraft (film)
Backdraft is a 1991 action thriller film directed by Ron Howard and written by Gregory Widen. The film stars Kurt Russell, William Baldwin, Scott Glenn, Jennifer Jason Leigh, Rebecca De Mornay, Donald Sutherland, and Robert De Niro. Jason Gedrick and J. T. Walsh co-star in the film...
, where a serial arsonist
Arson
Arson is the crime of intentionally or maliciously setting fire to structures or wildland areas. It may be distinguished from other causes such as spontaneous combustion and natural wildfires...
was using them as a means of assassinating
Assassination
To carry out an assassination is "to murder by a sudden and/or secret attack, often for political reasons." Alternatively, assassination may be defined as "the act of deliberately killing someone, especially a public figure, usually for hire or for political reasons."An assassination may be...
people.
An interesting variation on the phenomenon occurred after the 1906 San Francisco earthquake
1906 San Francisco earthquake
The San Francisco earthquake of 1906 was a major earthquake that struck San Francisco, California, and the coast of Northern California at 5:12 a.m. on Wednesday, April 18, 1906. The most widely accepted estimate for the magnitude of the earthquake is a moment magnitude of 7.9; however, other...
and fire. In the days after the blaze several business people opened warm safes to see if their papers were safe. The sudden inrush of oxygen into the still-hot gas of the interiors that now contained pyrolyzed
Pyrolysis
Pyrolysis is a thermochemical decomposition of organic material at elevated temperatures without the participation of oxygen. It involves the simultaneous change of chemical composition and physical phase, and is irreversible...
fuel gases due to the heated papers (hydrocarbons) therein, led to immediate and explosive combustion of the remaining intact contents.
