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We all know what fire looks like and does but what is
it? Fire is the simple chemical reaction in which combustible
materials, (such as wood, coal, oil, paper, etc.), burn to
give heat and light energy. Fire can be very useful, as it
provides light, heat for cooking, and heating in many industrial
processes, but can also be very dangerous when due respect
is not given and precautions taken.
However fire is not always the major threat. It should
be remembered that quite often extreme heat is a cause of
fire. Any sources of large heat should be treated carefully
as they can lead to fire.
So, fire can be man made and controlled but also occurs frequently due to natural causes. Because of this statement fire is a natural hazard. It is a naturally occurring phenomena that has the potential to cause loss of life or damage to property. Because people interact with fire so closely and because of its unpredictability it is a very real and potent threat.
When fires start naturally in a natural environment, such as a forest or prairie, and take hold, burning uncontrollably they are called Wildfires. Wildfires are often very difficult to put out and spread easily, often putting homes, property and lives in danger. This is the most commonly perceived form of fire as a natural hazard as it starts in a natural environment and then spreads to endanger humans and/or their interests. Fire of course is a natural hazard within built up areas such as cities. However as built up areas are heavily populated fires are spotted sooner and reacted to more easily and faster than in a natural environment as precautions and a fire service are present. Add to this that in today?s modern world cities there is not as much combustible material as in the natural environment and it can be seen that fire is much more of a natural hazard in the natural environment than in cities. Because of this I will be writing predominantly on Wildfires.
Wildfires are difficult hazards to classify. They may be caused by natural events, such as lightning strikes, or by human actions, such as sparks from a campfire. This means that in the causal scheme of classification they can be positioned in two places depending upon how the fire was started. If the fire was started naturally, e.g. By lightning, then it can be classified as a Biological Hazard. However if the fire is started due to a human?s action then it can be classified as a Quasi-Natural Hazard as it is artificially started but continued, and often made worse, by nature. Because of this it cannot be clearly classified in the causal classification system.
Wildfires, natural or human-caused fires that burn forest vegetation, are usually distinguished by three types of forest fires:
It is not uncommon for two or three types of fires to occur simultaneously. As mentioned previously wildfires can be started both naturally or by humans. Naturally, fires can be started by any natural source of heat, however the only really realistic natural ignitions for fires are lightning and lava flows. Human causes of wildfires include sparks from campfires, cigarette butts, children playing, industrial equipment and, unfortunately the most common, arson.
Much data is recorded on the causes of wildfires. In the table below the number of fires burned and the percentage of the total for each cause is shown. I have highlighted some figures:
| Cause | Fires | % of Total |
| Lightning | 525 | 13% |
| Camp Fires | 89 | 2% |
| Smoking | 59 | 2% |
| Debris | 873 | 22% |
| Arson | 1065 | 26% |
| Equipment | 216 | 5% |
| Rail Road | 56 | 2% |
| Children | 290 | 7% |
| Unknown | 512 | 13% |
| Miscellaneous | 342 | 8% |
| TOTAL | 4027 | 100% |
These figures are for wildfires in the USA in 1997.
(Source) National Parks Service (USA) web site.
All wildfires develop because material is sufficiently dry to burn and prevailing weather conditions encourage the fire to spread. Unusually hot, dry weather is the main common factor.
Having just said that wildfires develop because material
is sufficiently dry to burn and prevailing weather conditions
encourage the fire to spread it therefore follows that wildfires
will occur only where these conditions are located. Fires
are most common and fierce in those places where a warm wet
season is followed by a long hot dry season. A warm wet
season allows plants to put out a lot of growth. Then, when
the weather turns dry, many of the plants will shed their
leaves covering the ground with tinder dry material that
will catch fire easily.
Apart from Antarctica no continent is entirely free from
the combinations of ignition source, e.g. Lightning, Camp
Fires etc., fuel and weather conditions which provide a potential
wildfire hazard. This means that the most hazardous zones
tend to have either a Mediterranean or a continental climate
with their appropriate vegetation?s. Even high latitude areas,
such as Alaska, can have very dry vegetation and a high fire-risk
during the long mid-summer days.
Australia is the most fire-prone country in the world. Fires have started naturally there for millions of years and most native vegetation is adapted to regular burning. According to Cunningham (1984), the crescent of south-eastern Australia is the most hazardous wildfire region on earth. One major reason is the nature of the fuel in this area. Most Australian forests accumulate a great deal of fuel on the forest floor. These forest like many other in Australia, are dominated by Eucalyptus, which itself promotes fire. The eucalyptus tree contains a great deal of oil, which makes the trees explode as soon as they light .
In the USA the main problem areas are in the mid-western prairies and in the area in and around California. However having said this fires happen all over the USA and occur all around the globe.
As previously mentioned wildfires often start during a hot, dry season preceded by warm, wet season. Because of this a ?fire season?, as it is known, occurs at different times of the year for different countries. Generally because of this there will only be one fire season per year. However this does not mean that fires will not occur out of the fire season - the fire season is simply the time when fire hazard is at its highest level. In California the ?fire season?, where fire hazard is most extreme, is during September and October - the hottest months of the year here which coincide with easterly Santa Ana winds which dry fuel for the fires.
Not only do different countries have their fire seasons at varying times, fire seasons can occur at different times within a country. Australia is a prime example.
Wildfires can range in size from small isolated fires to huge, blazing fires that cover huge areas of land engulfing everything in their paths. The magnitude of the hazard is increased with proximity to built up areas where people live. As the areas most prone to wildfires have the most sought after climate for holidays (e.g. California, the Med) this further increases the size of the hazard as there will be more people in the area (tourists) to be in danger. These tourists also increase the possibility of a fire as they are not educated as to what precautions must be taken to prevent such fires occurring.
In modern years there has been an expansion of human activities
into areas of predominantly natural vegetation and not only
has this led to increased number of wildfires but it also
has led to more tangible losses to life and property.
For example, in May 1987 a wildfire burned an estimated
10,000 km2 in China, killed 191 people, destroyed 12,000
homes and forced 56,000 people to flee their homes. This
fire started when oil leaked out of a bush cutting machine
and caught fire. Gale force winds were blowing and in the
dry days of early summer the bushes soon caught alight and
the fire was quickly out of control.
Another case study to illustrate how large and dangerous
wildfires can be as a hazard is in Australia. On Ash Wednesday
in February 1983 fires were caused by classic wildfire weather.
Temperatures of 40°C combined with 40 knot winds to create
a raging wildfire. 76 people were killed, 8,000 were made
homeless and losses were put at an estimated cost of $A 200
million.
These two cases show the extent to which fires can wreak havoc.
One characteristic of wildfires is their size. In Australia and the USA, as well as in some other countries, major fires can extend over 1,000,000 ha - 1,000,000 football pitches.
However, the major characteristic of Australian fires
is the speed with which they spread. Wildfires in Australia
can engulf up to 400 ha of forest in 30 minutes compared
with as little as 0.5 ha over the same time in coniferous
forests of the northern hemisphere.
It has been found that
the rate of fire spread is closely related to the surface
wind strength, though this is not the only reason for rapid
fire spread in Australia. Other factors here include the
dry nature of ?bush? vegetation and the explosive nature
of eucalyptus trees.
?Spotting? is another characteristic of wildfires. This occurs when ignited fuel is blown a head of an advancing fire front by strong winds to create ?spot? fires. These spot fires increase the speed of fire spread. In Australia some of the longest spotting distances in the world have been recorded, with distances of 30km or more authenticated. These large distances are due once again the explosive nature of eucalyptus trees and is yet another factor for the fast speed of fire spread in Australia.
A final characteristic of wildfires is that most damage has been found to be done during a relatively short period of time - usually a few hours - compared with the total duration of the fire. This is because wildfires can accelerate and change direction very readily, catching people out unexpectedly. Fire acceleration can also be greatly aided by the shape of the land.
As I have already shown the consequences of wildfires can be devastating - killing people, destroying homes and property and causing mass disruption to human ways of life.
Wildfires also have a huge effect on the environment. However as I have already talked about fires are natural and occur to aid in the natural processes of the environment. For example, any rain may wash acidic ash into rivers releasing minerals gently enriching the aquatic systems to the advantage of fish, and seeds and bulbs will thrive in the newly fertilised soil.
There are disadvantages of fire for the environment aswell however. Many animals will die and those that survive will often find their home destroyed. A fire has a ripple effect on life in forests that continues until the next fire.
The main human response to an unwanted wildfire is to fight it and try to put it out. Many techniques are used, here are some of them.
Fires feed on the dead material of trees that lie on the floor. This material includes fallen leaves, twigs and other material. The first thing fire fighters try to do therefore is to remove this material.
Next water or fire suppressing chemicals are sprayed onto the fire to slow its progress across the land. These first two measures are general and can be used on any of the three types of fire.
The third measure is to dig a Fireline. This can
only be done though if firefighters can get close enough
to the fire. A fireline is used on surface fires and is done
by clearing the surrounding area of low vegetation and litter,
or digging emergency furrows to confine the area.
Ground fires, once established, are difficult to extinguish.
When the humus layer is not very deep, a ground fire may be
extinguished with water or sand. Most ground fires, however,
are controlled by digging trenches around the burning area
and allowing the fire to burn itself out.
These methods are known as firebreaks and as much as
possible, advantage is taken of streams, open areas, and
other natural obstacles when establishing a firebreak.
Crown fires are difficult to extinguish. They may be allowed to burn themselves out, they may be halted by streams, or they may be limited by backfired areas. Backfiring consists of carefully controlled burning of a strip of forest on the leeward side of the blaze, so that when the fire reaches the burned area it can go no farther.
Aeroplanes are often used to drop water or chemicals over
large fires where firefighters cannot get to on the ground.
Finally, people known as ?Smoke Jumpers? may be used. These people parachute into a fire area to dig a fireline around a fire that would otherwise be hard to reach.
There are times however when fighting the fire does not work and people and their homes are put in danger by fires. At this point people must leave their homes, taking as many possessions as possible, and flee the area. This is one of the problems with living in an place near to areas that are prone to wildfires.
To prevent things like this happening fires must be attacked and put out before they can get past a stage where they cannot be stopped. To do this experts try to predict where the most likely areas for fire are at certain times. In countries like the USA ?Fire Danger Forecasts' are made daily.
In the USA a Wildland Fire Assessment System (WFAS) is in place generating national maps of selected fire weather, and fire danger components of the National Fire Danger Rating System (NFDRS). NFDRS computations are based on once-daily observations from the Fire Weather Network. This network is comprised of some 1500 weather stations throughout the Conterminous United States and Alaska. These observations are reported to the Weather Information Management System (WIMS) where they are used each afternoon to generate maps from the day's weather observations. Each afternoon Fire Weather Forecasters from the National Weather Service also view these local observations and issue trend forecasts for fire weather forecast zones. As you can see wildfires in the USA are taken very seriously.
Along with these maps the National Parks Service makes a situation summary report daily. This report is then distributed to the media so that the general public can be made aware of the danger and number of fires in nearby areas. These reports are easily accessible off the web. See them by visitingwww.nifc.nps.gov and clicking on 'Fire Information'. On these daily situation summaries fires are listed with a name, number, the date they started, the time the fire was observed, the size of the fire, the strategy being used to control it and the status of the fire, whether it be under control or not.
As you can see from these two sources of information predicting where fires will occur is taken very seriously and from what I have seen of it the information is very informative and easy to access. This gives a feeling of security against a natural hazard that may not be felt about other natural hazards.
As well as predicting where fires occur experts try to formulate ways in which wildfires can be prevented.
In Australia community preparedness, including plans for the early detection and suppression of wildfires, is a key element in disaster reduction. In populated areas lookout points may be sufficient for early detection but in more remote regions regular surveys by aircraft may be necessary. General tools to help volunteer firefighter are available and include earth-moving plant to construct access tracks and firelines.
Since human actions now represent the major proportion of ignition of wildfires it seems necessary that fire prevention education for the general public is in greater need. The persuasive approach of signs and posters can be accompanied in a variety of ways. For example, the provision of barbecues set up by local authorities in safe clearings alongside roads tends to discourage fire lighting at more dangerous spots.
Finally I will talk about people?s perceptions of fire as a hazard. The attraction of a rural environment, together with effective commuting facilities has led to urban sprawl in cities such as Sydney, Melbourne and Adelaide in Australia, and Los Angeles and San Francisco in the USA meaning an invasion of natural bushland. People moving to these communities have little real appreciation of wildfire hazard. Without the right guidance they may build with highly flammable materials, deliberately retain vegetation close to their homes and disregard the need for adequate fire fighting equipment. This is an example of where people are unaware of the danger they are in.
Compared to some natural hazards, such as earthquakes and volcanoes, wildfires can be predicted well and there are many different ways of fighting the fires and preventing them in the first place, as I have shown. Because of this many people believe that it is not such a threat as they will have adequate time if a fire develops. Though as I have shown fires can accelerate and change direction rapidly and deaths have occurred. Having said that people are not weary of fires, people living near danger zones are well educated and so know to some extent what the fires can do. People find comfort and safety in their knowledge and the confidence that fires will be predicted and spotted though his may not always be the case.
As I talked about at the start, fires can happen in both natural environments and built up areas. However as built up areas are heavily populated, fires are spotted sooner and reacted to more easily and faster than in a natural environment as precautions and a fire service are present. Add to this that in today?s modern world cities there is not as much combustible material as in the natural environment and it can be seen why wildfires are a greater hazard than in cities. However this has not always been the case.
One of the largest fire disasters in cities happened in London in the 17th century. In 1666 one of the world?s largest fires started in a baker?s shop in London. At this time many of London?s houses were really slum comparable to the conditions experienced in many third world country cities today. They were built with wood frames, wood floors and were roofed with thatch. All the houses were very close together. There was no mains water supply and if a fire occurred people had to do the best they could and put it out themselves.
The summer of 1666 had been very hot and dry and by September
everything was very dry. This, along with the lack of a fire
service and houses built of combustible material very close together
precipitated the fire and allowed it to spread easily.
Other factors that encouraged the fire to spread rapidly
and out of control was a strong wind that carried sparks
and lit surrounding houses roofs. By six o?clock the next
morning the houses on London bridge were burning and the
fire was out of all control. Thousands of people fled for their lives.
The wind that had sped the spread of the fire blew all Monday and Tuesday until it died on the Tuesday evening. However the fire continued to burn and the main flames did not subside until Thursday, four days after the fire had started.
Very few people were killed in the fire but 80 % of the city?s buildings had been destroyed including a total of 13,000 houses covering 160 hectares. The fire left three quarters of the city?s population homeless.
The human response to the fire was bold. Sir Christopher Wren, a famous architect at the time was asked to suggest how the city should be rebuilt to prevent such a disaster recurring. He stipulated that wider roads were needed to prevent the speed of the spread of the fire, and that buildings should be built of stone to reduce the risk of such an event happening again.
As you can see fires on old cities were a great hazard. Today they are not so much because building are made of concrete and steel, are spread out and there is an organised fire service. However this is not the case in a lot of developing world countries city?s. Here conditions are similar to those of the fire described in London. Houses are made of combustible material and there is no real fire service. Because of this fires in developing world cities are still a major hazard.
The worst scenario in a city fire is a firestorm. A city can burn so fiercely that huge convection currents can be created as huge masses of heated air rise rapidly. Air from around the city rushes in to fill the space left by the rising air. This air coming in can race in at hurricane force speeds of upto 80 mph.
This happened during World War II when cities like Warsaw in Poland were hit by millions of incendiary bombs. At the heart of a firestorm no one can survive. It is impossible to breathe as the fire uses up all the air and temperatures reached can be tremendous. People will die of the heat, burns or suffocation within seconds. Just outside the central zone of devastation winds are so strong that people are blown towards the centre of the fire where they suffer the same fate.
Firestorms are truly devastating phenomena that can kill thousands of people in seconds.
I hope I have shown what fires are, how they
occur, how they are a hazard to humans and how humans respond
to them.
I have talked mostly about wildfires as these are the most common form of fire as a hazard in the developed world. I have shown that wildfires can be started naturally or artificially and that humans are the main cause of wildfires. I have shown when and where wildfires occur - during hot, dry, windy weather in continental areas with a Mediterranean climate. I have shown case studies to illustrate the scale of the hazard and what damage wildfires can cause. I have talked about what types of fire there are and what methods are used to fight them. I have also shown how humans try to predict and prevent such fires occurring.
As well as showing these aspects of wildfires I also talked briefly on fires in cities and how modern cities no longer suffer from major fires. In this section I also talked about the awesome destruction and killing wreaked by a firestorm.
In general fires are a natural phenomena that in modern times are caused more frequently by humans than naturally. When out of control they can be devastating, but with the right education and precautions taken the risks can be greatly reduced. Also, when spotted early, fire can be controlled.
Of all the natural hazards, fire is possibly one of the more predictable, and certainly one of the more preventable. However when out of control it can cause great destruction.
Sources
My sources for this essay were :