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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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