Fire

Table of contents

Introduction

What causes fires?

What factors affect the force of a fire?

Types of Fires

Introduction

Fire is created when combustible materials, heat and oxygen come together. A fire both uncontrolled and unsupervised easily develops into a large fire. The result can be the burning of property or infrastructure. Domestic fires have turned furnishings into nothing but ashes, and fires out in the open have totally consumed thousands of acres of forests. Such results are destructive, but deadly fires have also brought about massive loss of life.

Fires pose a direct threat to the human body: damages are inflicted by the fire and the heat. There are also indirect threats in the side effects of a fire (smoke inhalation and asphyxiation, building collapse as the heat melts the foundations, etc.).

A fire might be its own emergency or the result of another emergency (an earthquake, a hazardous materials event, etc.).

The damages inflicted by a fire are extensive, and require long-term rehabilitation (a forest damaged by a forest fire may require several decades of rehabilitation). They may even be irreversible.

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What causes fires?

The setting and spread of a fire are generated by the coming together of three basic factors:

1. Combustible material: Most materials found on earth are combustible. In terms of their burning, the only difference between one material and another is the temperature needed for combustion to take place. The degree of sensitivity of a given material to combustion is the direct result of its combination of elements. Every material in nature may appear in one of the following three states: solid, liquid and gas. Usually, the state can be regulated and affected through heat and cold. There is a connection between the state of the material and its sensitivity to combustion.

2. Oxygen: Combustion is a process through which a given material combines with oxygen, i.e. the chemical element oxygen which makes up about 20% of the air in the atmosphere. Oxygen is a colorless, odorless and tasteless gas that appears as an element, and also in organic and inorganic compounds.

3. Heat: A combustible material will burn in the presence of oxygen and heat. In order for a material to catch fire, it requires a certain temperature; each material has its specific temperature, known as its “combustion point.”

Ignition sources may be natural causes such as lightning strikes or volcanic eruptions. Fires may also be purposely started. In Israel, of course, there are no active volcanoes. The chance that a lightning strike will cause a serious fire in Israel is also very slight. In Israel, lightning is a winter phenomenon, usually accompanied by heavy rains that wet the vegetation and the ground. Under such conditions, chances are that even if a fire is started by a lightning strike, that fire will not have a chance to spread, and will, in all likelihood, go out on its own.

However, the main reason that oxygen, heat and combustible materials come together is negligence. Most fires in Israel and the world are the result of carelessness: farmers burning deadwood who disregard safety rules; sparks that fly off during welding procedures; bonfires that are not properly put out, and are left unattended with glowing embers, etc. Such factors together with dry conditions and strong winds are liable to cause fire to spread to areas of planted forests or adjacent wild vegetation, a fire that might be very difficult to control.

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What factors affect the force of a fire?

Experience teaches us that three main factors make the difference between a local event and a disaster of massive proportions:

1. Early preparations and the behavior of the people at the site: A fire that starts in an organized setting (home, factory, office) where there are means for putting the fire out and people who know what to do, does not have the chance to spread and endanger or harm lives.

2. The amount and particular characteristics of the combustible material: As most fires start as brush fires or ground fires, great importance attaches to the amount of combustible material there is close to the ground. This includes combustible materials and combustible solids (indoors), or low-growing flora, pruned branches and dry remnants of annual plants (outdoors) which very much increase the risk of fire and its quick spread.

3. Attendant factors: These include high winds, electricity, and more.

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Types of Fires

There are five types of fires:

1. Solid combustible fires: This type of fire includes combustible solids such as wood, cloth, rubber and more. These solids all have their particular combustion point, the critical point at which a fire can be ignited. When the material reaches the combustion point, it breaks down into its elements, some of which react with the oxygen in the air, causing combustion.

2. Liquid combustible fires: This type of fire includes the group of flammable and combustible liquids such as benzene, diesel fuel, alcohol, tar, and more.

Flammable and combustible liquids have three critical points in terms of a fire:

· The flashpoint: The temperature at which the liquid gives off enough vapor to create an initial ignitable mixture. At this point, an ignition source is required for the mixture to ignite. Burning ceases once that source is removed.

· The flammable range: The range of temperatures at which the liquid gives off enough vapors consistently to create a flammable vapor-air mixture. In the presence of an ignition source, a flame ignites, and the flame turns into a fire even if the source of ignition is then removed.

· The auto ignition temperature: This is the minimum temperature at which a vapor-air mixture will spontaneously ignite, without the necessity of a spark or a flame. The liquid’s flashpoint determines its susceptibility to ignition. In general, the lower the flashpoint, the greater the hazard of a flammable liquid.

3. Electrical fires: Any fire in which electricity is involved, whether actively or passively.

4. Gas fires: This type of fire includes the entire group of flammable gases such as hydrogen, acetylene, and more. Flammable gases, in certain mixtures and proportions, are explosive.

5. Light metals fires: This type of fire includes metals such as magnesium, lithium, and aluminum, as well as their compounds.

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