Background
Problem of fires
Fire is appreciated only when under control. When out of control fire becomes dangerous posing risk to property and life. There are approximately 500 deaths and 11,000 serious injuries due to fires in the UK each year. As bad as it sounds it is only a small fraction of the problem worldwide where estimates suggest 300,000 deaths and millions of injuries due to fires every year. From the financial point of view the cost of fires is 1-2% of the GDP for the UK as well as 14 other countries where such statistics are available. In the United States alone annual losses due to fires are estimated at $200bn.
Financial and human losses are not the end. It is estimated that approximately 1% of the Earth’s surface is burned every year. This figure in some parts of the globe, such as Australia, reaches 2- 4%. Fires have a heavy ecological toll which is manifested mainly in their large contribution to the CO2 emissions. They are also responsible for creation of arid, leached of nutrients, landscapes and loss of wildlife.
To put statistics into the context of a single fire, let’s look at the largest fire on record, the Black Dragon Fire, which took place on the border between the Soviet Union and the Republic of China in May 1987. The fire is estimated to have burned over 18 million acres of land and destroyed prime timber land of the size of Scotland. China responded by mobilising two armies of regular troops and thousands of forest workers. The USSR adopted ‘let it burn’ policy. Due to small population density only 200 people died and 250 were injured.
Fighting fires
Fires like the Black Dragon Fire in China as well as thousands of smaller ones have been causing death and destruction since time immemorial. Over the centuries numerous measures of fighting them have been developed. Unfortunately, there are still many fires difficult or impossible to bring under control. This is the main driver for research of new, alternative ways of fighting fires.
Fire prevention
The most obvious and cheapest way of fighting fires is to prevent them form happening. Fire prevention is mainly comprised of observation, education and forest management. Wildland areas, including forests, grass, and shrub-lands are constantly monitored for fires. If these are detected early there is a better chance of their early suppression. By educating people about the risks and dangers of fires it is possible to greatly reduce their number. Tragedies such as the cigarette-caused fire in the Mont Blanc Tunnel in 1999, where 39 people were killed with over $1bn losses to the region, could have been prevented. Lastly, forest management plays an important role in preventing fires by segregation of fuels, back-burning and creation of water access points.
Fire suppression
When prevention fails fires are fought by suppression. This is done using direct or indirect attack techniques.
Direct attack is the picture most of us associate with fire-fighters when standing on the ground or suspended in a cherry-picker they douse the fire with large quantities of water. Over the years many mechanisms helping in fighting fires have been developed This includes application of wetting agents making water more effective, and deployment of air-planes allowing for fighting fires difficult to reach form the ground.
An alternative way is to use indirect attack techniques, whereby fire is starved of fuel. This is done by making fire-breaks which are strips of land with no fuel that can burn. Fire-breaks can be made by hand-crews who remove all plants and turn the soil up side down, but more often the ground is cleared by burning all the fuels using torches in a technique called ‘back-burning’. More unusual methods of creating fire-breaks include deployment of incendiaries from the air, or making trenches by exploding rods of dynamite .
Having suppressed flames fire-fighting continues as there is still combustion going on underground and in large pieces of fuel such as timber logs. It is usual for fire-fighters stay in the burned area clearing it of any leftover fuels in what is called ‘mop-up’. The reason behind it is to ensure that fire does not reignite.
Counter-firing
Indirect attack techniques described above present themselves as an attractive alternative compared to the conventional fire-fighting methods. The fact that they require no water makes them applicable to large wildlife fires. On the downside, they require substantial human resources in order to clear and control the fire-break. Access to such resources is costly and not always readily available.
A potential solution to this problem is counter-firing, a technique in which a small fire is placed at a certain distance form the wildfire and, as a result of in-draft, drawn-in by it thereby creating a fire-break. Counter-firing presents a number of challenges. To begin with it is not applicable in numerous fire scenarios including forest and high-canopy fires. Counter-firing may, but may not work depending on topography, weather, fuels and the uniformity of the wildfire front. Moreover, little is known about the distance at which counter-fires should be placed to work effectively. As a result counter-firing is used only as a last resort.
Extensive benefits of counter-firing are a driving force behind their research aiming to overcome any problems associated with their application. Due to the nature of the problem conventional experimental field studies would be highly time-consuming and costly. CFD presents itself as an alternative, potentially viable way of investigating counter-fires.
Fire is appreciated only when under control. When out of control fire becomes dangerous posing risk to property and life. There are approximately 500 deaths and 11,000 serious injuries due to fires in the UK each year. As bad as it sounds it is only a small fraction of the problem worldwide where estimates suggest 300,000 deaths and millions of injuries due to fires every year. From the financial point of view the cost of fires is 1-2% of the GDP for the UK as well as 14 other countries where such statistics are available. In the United States alone annual losses due to fires are estimated at $200bn.
Financial and human losses are not the end. It is estimated that approximately 1% of the Earth’s surface is burned every year. This figure in some parts of the globe, such as Australia, reaches 2- 4%. Fires have a heavy ecological toll which is manifested mainly in their large contribution to the CO2 emissions. They are also responsible for creation of arid, leached of nutrients, landscapes and loss of wildlife.
To put statistics into the context of a single fire, let’s look at the largest fire on record, the Black Dragon Fire, which took place on the border between the Soviet Union and the Republic of China in May 1987. The fire is estimated to have burned over 18 million acres of land and destroyed prime timber land of the size of Scotland. China responded by mobilising two armies of regular troops and thousands of forest workers. The USSR adopted ‘let it burn’ policy. Due to small population density only 200 people died and 250 were injured.
Fighting fires
Fires like the Black Dragon Fire in China as well as thousands of smaller ones have been causing death and destruction since time immemorial. Over the centuries numerous measures of fighting them have been developed. Unfortunately, there are still many fires difficult or impossible to bring under control. This is the main driver for research of new, alternative ways of fighting fires.
Fire prevention
The most obvious and cheapest way of fighting fires is to prevent them form happening. Fire prevention is mainly comprised of observation, education and forest management. Wildland areas, including forests, grass, and shrub-lands are constantly monitored for fires. If these are detected early there is a better chance of their early suppression. By educating people about the risks and dangers of fires it is possible to greatly reduce their number. Tragedies such as the cigarette-caused fire in the Mont Blanc Tunnel in 1999, where 39 people were killed with over $1bn losses to the region, could have been prevented. Lastly, forest management plays an important role in preventing fires by segregation of fuels, back-burning and creation of water access points.
Fire suppression
When prevention fails fires are fought by suppression. This is done using direct or indirect attack techniques.
Direct attack is the picture most of us associate with fire-fighters when standing on the ground or suspended in a cherry-picker they douse the fire with large quantities of water. Over the years many mechanisms helping in fighting fires have been developed This includes application of wetting agents making water more effective, and deployment of air-planes allowing for fighting fires difficult to reach form the ground.
An alternative way is to use indirect attack techniques, whereby fire is starved of fuel. This is done by making fire-breaks which are strips of land with no fuel that can burn. Fire-breaks can be made by hand-crews who remove all plants and turn the soil up side down, but more often the ground is cleared by burning all the fuels using torches in a technique called ‘back-burning’. More unusual methods of creating fire-breaks include deployment of incendiaries from the air, or making trenches by exploding rods of dynamite .
Having suppressed flames fire-fighting continues as there is still combustion going on underground and in large pieces of fuel such as timber logs. It is usual for fire-fighters stay in the burned area clearing it of any leftover fuels in what is called ‘mop-up’. The reason behind it is to ensure that fire does not reignite.
Counter-firing
Indirect attack techniques described above present themselves as an attractive alternative compared to the conventional fire-fighting methods. The fact that they require no water makes them applicable to large wildlife fires. On the downside, they require substantial human resources in order to clear and control the fire-break. Access to such resources is costly and not always readily available.
A potential solution to this problem is counter-firing, a technique in which a small fire is placed at a certain distance form the wildfire and, as a result of in-draft, drawn-in by it thereby creating a fire-break. Counter-firing presents a number of challenges. To begin with it is not applicable in numerous fire scenarios including forest and high-canopy fires. Counter-firing may, but may not work depending on topography, weather, fuels and the uniformity of the wildfire front. Moreover, little is known about the distance at which counter-fires should be placed to work effectively. As a result counter-firing is used only as a last resort.
Extensive benefits of counter-firing are a driving force behind their research aiming to overcome any problems associated with their application. Due to the nature of the problem conventional experimental field studies would be highly time-consuming and costly. CFD presents itself as an alternative, potentially viable way of investigating counter-fires.
Devastation caused by fire (Courtesy of http://www.guardian.co.uk/world/gallery)
Fighting fires directly (Courtesy of http://www.superiorsafety.ca/fire-equipment.asp)
Indirect methods of fighting fires (Courtesy of http://www.guardian.co.uk/world/gallery)
Back-firing (Courtesy of http://www.guardian.co.uk/world/gallery)
Counter-firing (Courtesy of http://www.fireparadox.org/suppression_fire.php)
