Efecto de los procesos

Vehicle fires have been occurring for as long as people have been using automobiles. A broken fuel line resulting in a spray of petroleum on a hot engine, overheating of a braking system and electrical spark malfunctioning are all possible causes of vehicle fire (Lee 2001). There is also a possibility of vehicle fire due to deliberate acts such as arson and collision. According to USFA (1999), the causes of a vehicle fire generally fall under the following four categories; the result of a faulty vehicle, the result of an act of carelessness such as discarded cigarettes on the upholstery, the result of arson or the aftermath of a collision.

There are many factors that could contribute to the cause of a fire hazard in a motor vehicle. Lee (2001) has provided a range of possible causes of a vehicle fire due to faulty vehicle, act of carelessness and arson. A few of these fire scenarios will be discussed in the subsequent section.

Engine and the fuel system fire (Lee 2001)

The engine is the heart of the vehicle. It converts heat into motion when the engine is started. The gasoline or diesel in the fuel tank is drawn through a filter system into the carburettor or direct injectors mounted on the engine top. Mixing of gasoline and air occurs and the mixture is fed into the engine cylinders. For the gasoline to burn as energy, it must be vaporized. The problem arises when the connection from the fuel line to the carburettor is a poorly fitted. When gasoline flows and collects on top of the hot manifold, it can give off vapours resulting in a fire in the presence of an ignition source.

Exhaust system fire (Lee 2001)

Some vehicle fire incidents are related to the emission control system (e.g. catalytic converter – Figure 4.1) connected to the vehicle’s exhaust. Waste products are removed from the car’s engine when the gases enter the exhaust pipe, the muffler and out to the rear

Chapter 4 Statistic on Vehicle Fire in Singapore and International Fire Incidents in Road Tunnels

while the exhaust gases passes through; the reaction of the chemical substance with the hydro-carbon exhaust converts them into water and carbon dioxide through further burning of the pollutants. The temperature of the exterior converter can be very high due to the reaction that occurs inside the catalytic converter. A heat shield is often provided to protect the under body of the vehicle.

Figure 4.1: Catalytic converter location in exhaust system (reproduced from Lee (2001))

An example of vehicle fire hazard can be due to poor repair work or improperly positioning the catalytic converter too close to the underside of the vehicle body. If the normal design clearance on a proper vehicle assembly is not followed, the carpeting at the rear end of the vehicle is likely to catch fire.

Friction and tyre fire (Lee 2001)

In the presence of flammables such as petroleum or oil, a fire can occur if sparks are produced when parts are rubbed together. An example would be a fire caused by brake fluid spilling on the brake lining.

Chapter 4 Statistic on Vehicle Fire in Singapore and International Fire Incidents in Road Tunnels

frequent stop and go driving caused by the road surface friction. When their ignition temperature is reached, the tyres catch fire.

Turbo charger fire (Lee 2001)

The function of a turbo charger is to increase the engine power output allowing the vehicle to move faster by increasing the amount of fuel and air delivered to its engine cylinders. For this to work, a small turbine wheel is mounted in the exhaust system where flow of gases can cause the turbine to spin and drive a compressor in the intake manifold. This allows the compressor to force more air and fuel into the engine cylinders allowing a higher power output. However, the nature of this design often results in the turbocharger to operate at extremely high temperature. In the event where there are flammable materials in its proximity due to fuel leakage or faulty fuel line, a fire may occur.

Electrical system fire (Lee 2001)

The battery in the vehicle provides the flow of electric current and boots the voltage required to fire the spark plugs for engine ignition. In addition, it provides the electrical energy to operate headlights, interior lights signals, horn and other electrical accessories. The alternator is a generator which produces alternating current (AC) by connecting it to the belt of the engine crankshaft when the engine is operating. A voltage regulator is used to control electric output from the alternator to prevent the battery from overcharging. The rectifier converts the AC current to direct current (DC) to charge the battery.

During charging, electrolysis separates each water molecule into two parts hydrogen and one part oxygen within a storage battery. For continuous charging over a long period of time, the mixture in the ullage space may remain hydrogen rich. Generally there is small vent hole in the battery to allow hydrogen to escape into the surrounding air. Hydrogen can be extremely flammable when mixed with oxygen with an ignition temperature of approximately 579oC.

The alternators can be another source of a vehicle fire. Connectors used in these units can develop high resistance if they are not properly connected. The heat output generated from the high resistance may cause melting resulting in a fire.

Chapter 4 Statistic on Vehicle Fire in Singapore and International Fire Incidents in Road Tunnels

Smoldering material on upholstery (Lee 2001)

The result of an act of carelessness such as discarded cigarettes on the upholstery could lead to a fire occurring in a vehicle. According to Lee (2001), there is an experiment conducted where a lighted cigarette was placed on the seat cushion with the vehicle doors closed. Flames could be observed in the area where the cigarette was placed and shortly after, the seats and the entire passenger compartment were fully engulfed in flames.

Arson fire (Lee 2001) & (Kocsis 2002)

Arson is a serious offence and often results in substantial financial losses and environmental damage. The motives of an arsonist can be grouped into six categories. A profit motive; where the offender could benefit from an insurance claim on the property destroyed by the fire. Animosity crime; by using fire as a tool for revenge. Crime concealment; an attempt to destroy evidence from another crime. Vandalism; an abnormal fire-setting behaviour. Personality disorders and political objectives; where arson is committed to achieve political goals such as terrorism (Kocsis 2002). Details on the used of materials that are easily obtainable and not leaving trace of hydrocarbon related with accelerated fire by arson can be find in Lee (2001).