Analysis of past derailments
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Analysis of past derailments. Information from data bases, investigation reports and surveys. Purpose of Accident Analysis. Qualitative Analysis: To provide information on observed derailment causes.

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Analysis of past derailments

Analysis of past derailments

Information from data bases, investigation reports and surveys


Purpose of accident analysis
Purpose of Accident Analysis

  • Qualitative Analysis:

    • To provide information on observed derailment causes.

    • To identify those causes that are “single point failures” and that in most cases can be considered direct derailment causes (axle failure, wheel failure etc).

    • To identify those causes that are “contributory” and can be considered to make a derailment more likely (by eroding the safety margin, e.g. operational issues, wagon skew loading etc).

    • To identify the range of possible consequences following a derailment.

    • And therefore to provide the structure for a risk model.

  • Quantitative Analysis:

    • To provide statistical analysis of the relative frequency of individual / combinations of failures leading to a derailment.

    • To provide statistical analysis of the relative likelihood (probability) of consequences following a derailment.

    • And therefore to provide the data for a risk model.


Depth and breadth of accident analysis
Depth and Breadth of Accident Analysis

  • Accident Investigation reports from National Investigation Bodies (NIB):

    • The percentage of derailments investigated by the National Investigation Bodies varies significantly from country to country.

    • Some countries investigate a very high number of railway accidents and go far beyond what is mandatory.

  • Annual reports of National Investigation bodies:

    • For countries reporting only mandatory accidents, the annual reports of the NIBs can give some information on “non-investigated” accidents.

  • ERADIS database entries:

    • Supported by the accident investigation report where required to provide additional information.

  • Previous Agency survey

    • Significant amounts of information has also received from the Agency for the 2008 study of the Derailment Detection Device.

  • Other information sources.

  • In total we have about 700 freight train derailment accidents (although some of these are marshalling / freight yard derailments) in our database, covering 23 countries.



Accident analysis findings infrastructure
Accident Analysis Findings - Infrastructure

  • Track geometry defects account ~ 70% of infrastructure related derailments, and ~ 30% of all derailments

    • Excessive track twist 27%

    • Excessive track gauge 19%

  • Main controls are inspection, maintenance, adherence to standards etc.

  • Occur more often in station at turnouts or signals

  • However, in many cases the defect was known about.

  • Derailments due to sun curve (heat buckle) are more common in Nordic countries.


Accident analysis findings rolling stock
Accident Analysis Findings – Rolling Stock

  • Axle ruptures and wheel failures account ~ 57% of rolling stock related derailments, and ~ 20% of all derailments.

    • Bearing failure -> hot axle box -> axle journal rupture most frequent RS caused derailment scenario

  • Main wagon controls are inspection, maintenance, adherence to standards.

    • Infrastructure detection devices

45%

40%

35%

30%

25%

20%

15%

10%

5%

0%

Failure of axles

Failure of wheels

Bogie Suspension and

Others and

Unknown

(ruptures)

(composite or

Structure (spring,

monoblock)

wagon frame etc)

  • However a number of trains derailed due to a HAB had recently passed a HABD.

  • HAB failures are less common in some countries than others.


Accident analysis findings operations
Accident Analysis Findings – Operations

  • Incorrect / improper loading account ~ 25% of derailments caused by operational failures, and ~ 10% of all derailments.

  • Main controls are:

    • operational rules

    • inspection

    • functional tests

    • training & competent staff

  • Main failings are human errors / acts of omission / acts of commission.

  • Skew loading often works in combination with track geometry defects leading to derailments.


Combination of causes often necessary to cause derailment
Combination of causes often necessary to cause derailment

  • Very often the derailment is caused by a combination of several contributory causes e.g.:

    • Combination of faults of infrastructure and rolling stock

    • Combination of a Rolling stock or Infrastructure fault and unfortunate train handling/operation

  • Typical examples are:

    • Low train speed and sudden train braking action combined with:

      • Track twist, narrow curve with high cant

      • Track twist, wagon with very long wheel base

    • Track twist and twisted or skew loaded wagons

    • Track geometry fault and strong compression forces in train due to unfortunate train composition or less than optimal train handling by the driver

  • Existing measures are often directed towards control of these common causes of freight train derailment, with varying degrees of success.


Some causes in detail rolling stock
Some causes in detail – Rolling Stock

  • The event sequence bearing failure > hot axle box > sheared axle journal is the most common derailment cause accounting for about 40% of rolling stock derailments.

  • There appear to be geographic differences between countries.

  • Most, but not all, countries have hot axle box detectors trackside to provide warning:

    • But present use of HAB-detectors is far from 100 % effective


Excessive track twist most important infrastructure failure cause
Excessive track twist most important infrastructure failure cause

  • Derailments occur under presumably safe conditions

  • Upper figure shows track twist limitations for curves R > 420 m

    • UK has more lenient requirements

      • > higher proportion of track twist derailments

    • Derailment has occurred within allowable limit

      • Neulengbach (AT)

  • Lower figure shows track twist limitations for curves R < 420 m

    • Derailment has occurred within allowable limit

      • Fetsund (No) & Rosenbach (AT)


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