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Forensic Fire Investigation

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Introduction

BTEC National Diploma in Forensic Science Year 2 Forensic Fire Investigation Assignment One Laura Oakley Sources of Ignition There are four stages to the start of a fire; Pre-ignition/Pre-heating, Ignition and Combustion and in order for the fire to begin three things are needed; Heat, Oxygen and a Fuel as shown The Fire Triangle. There is a large amount of potential sources of ignition these can vary for the uses of cigarettes or matches to mechanical machinery which could not function correctly or could create sparks. A full list of potential sources of ignition is listed below: * Open Flames- This can be from Welders, Cigarettes, Matches or Cutters. * Hot Surfaces- This can be from Dryers, Heaters etc. * Heat from Machinery * Electrical Discharges- A spark of anything over 1mJ can ignite a dust cloud. * Electrostatic Discharges * Smouldering or Burning Dust In order to lower the risk of a potential fire all potential sources of ignition should be effectively controlled in any hazardous areas for example prohibition of smoking or use of matches in certain areas; also machinery which would use electricity should be checked and classified for the area in which it is used. ...read more.

Middle

* Flaming Stage- This stage involves the vapours igniting and the flames are beginning to grow. * Heat Stage- The burning has progressed to there the fire is still small but generating heat to warm the air which would send warm products of combustion upwards using convection. The speed of combustion depends on the amount of oxygen needed to combine with the fuel but it can also depend on the conditions surrounding the fire. Extinction The chemistry of fire extinction involves the removal of one of the elements which will cause a fire; these are illustrated of the Fire Tetrahedron. Completing one of the following principles can stop the fire as it will remove one of the elements. * Smothering- By removing the oxygen surrounding the fire the fir can be extinguished. This method can be achieved by using a flame proof fabric to cover the fire. * Starvation- This can achieved by removing the fuel which is being used in the fire. If the fuel is gaseous substance the valves in which are giving this substance out can be turned off. ...read more.

Conclusion

When constructing a house the builders need to be sure they follow rules such as: * All walls and ceiling are made of a reasonable material which will resist the spread of flames over that surface and if ignited can have a reasonable rate of heat release. Buildings must be constructed so in case of fire: * Stability will be able to last for a certain period of time. * Walls joining on to more buildings will resist the spread of fire so other buildings will not catch fire. * Fire spread will be stopped with fire resisting walls and floors. * Concealed areas will be sub-divided to restrict unseen spread of flames. Yet there is still old buildings in our towns which are made of old features such as wood which could be the support for the ceiling and walls, if any of this kind of building were to set alight then this would consume the whole building. This is why more modern buildings contain steel girders which will not ignite or crumple under the pressure. ...read more.

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