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January 17, 2017

Causes of fluid leaks and their contributions to vehicle fires

Hoses and tubes are used extensively throughout vehicle engine compartments and undercarriages. They are made from many different materials to accommodate several different pressure classifications, and contain several different types of fluids. One thing is consistent: they all have the potential to release a flammable liquid that can start a quickly progressing fire. Although every detail of vehicle hydraulic systems can’t be covered in a short article, the following is a general overview of some common causes of fluid leaks in commercial and passenger vehicles.

Hose failures can vary significantly and result from a range of causes from abrasion and mechanical degradation, to chemical corrosion, to bursting. Rubber and plastic hoses are often consumed by the blaze, leaving little to no evidence of how they first failed. However, an analysis can still be performed on the burned vehicle to determine what happened.

In most engine compartment vehicle fires, bursting from over pressurization occurs at some point in the system and can either be the cause or result of the fire. Determining which is complicated and involves consideration of the hose or tube construction, the fluid it was carrying, and the system of which it was a component. While at first it may appear that a fire was caused by a large burst pipe, especially if it sits directly over a known ignition point such as a turbocharger or exhaust component, without proof of how it burst prior to the fire, it could easily be classified as a consequence of the fire and not a cause. Investigators should also consider the system as a whole to look for evidence of a larger problem. Likely causes of an over pressurization include clogged filters or vent lines, overloading of the machine, or improper maintenance. Simply noting a burst line as the cause of a fire is not sufficient for a cause determination. Other evidence explaining the cause of the burst, if it occurred prior to the fire, should be analyzed to prove that over-heating was not the culprit.

Although bursting (from over pressurization) is a common type of hose failure, other failures can occur. If maintenance was recently performed on one of the hydraulic systems in the vehicle, further investigation into the placement of clamps, hose routing and proper supports installed on the system may be required. If a line was improperly supported or poorly routed, it may rub against sharp components, resulting in abrasion. If it was allowed to dangle, travelling on a bumpy road may have caused the hose end to migrate off the joint over time.

Chemical attack of the lines is another type of failure. For example, steel braided hoses installed in an industrial or acidic environment can corrode, which significantly decreases their maximum working pressure. Microscopic examination of the hose strands can confirm whether there was a tensile failure (the result of bursting) or chemical attack that resulted in hose degradation to the point of failure. Rubber or plastic hoses can be subject to hardening or selective corrosion if low quality fuels or oils are used extensively. This can cause brittleness and cracking in the hoses that allows fluid to escape.

Determining the cause of a fluid leak requires a scientific, evidence-based approach. ‘First glance’ conclusions must be avoided. In an extensive fire, it is likely several fluid lines could have been compromised in one way or another, and a comprehensive investigation is the only way to establish which occurred first. Sintra Engineering employs a team of both experienced fire investigators and engineering experts that can work together to properly diagnose these complex fire scenarios.

By Ryan Hazlett


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