gavin astin 29 september 2011 derailment risk model frequency analysis and scenario development

Gavin Astin 29 September 2011

Derailment Risk Model

Frequency analysis and scenario development

Freight train derailment risk model29 September 2011

Agenda

2

1. Background

2. Frequency Assessment

3. Consequence / Impact Assessment

4. Summary


Risk Model Structure

Traditional bow-tie approach.

Hazard = derailment.

Freight train risk reduction measures shown as controls in the bow-tie structure.

3

Hazard

Basic causes Intermediate causes

Hazard/ What - if

Fully developed consequences

Developing consequences

Primary controls

Secondary controls

Fault Tree Analysis Event Tree Analysis Mitigation 2 Outcome Yes 1

Mitigation 1 Yes No 2

Yes 3 No

No 4

= Key risk reduction measures


4

Background to Risk Model Data

Previous freight train derailment accident reports:- 201 accident reports collected by DNV from various sources.- The Agency provided access to accident summaries used for their previous work. After

elimination of duplicates, those which were not derailments etc. the usable Agency data was 355 accident summaries from a range of European countries.

- The total volume of information used was 556 accident reports / summaries.

Undertook research to establish other freight train derailment causes, not necessarily occurring in the accident data. (Although if not occurring in 500+ accidents then we can conclude that such causes are very low contributors.)

These data populate frequency (“fault tree”) and scenario (event tree) models.

Observations:- Not many accident reports identify root causes. This makes analysis difficult. Hot axle box

may have caused a derailment, but what caused the HAB? - Systematic analysis of accident data on an annual basis may identify national differences,

good practice and trends (not just limited to freight train derailment accidents).


Agenda

5

1. Background



4. Summary


Fault Tree Extract

6

OPS_DRL

Operational failures leading directly to, or which are the primary cause of a freight train

derailment

Page 1

O_1_DRL

Freight train composition failure

O_2_DRL

Improper loading of wagons

Page 4

O_3_DRL

Failure to perform brake check /

inspection

O_4_DRL

Incorrect setting of points/turnouts leading to, or primary cause of derailment

(mainly yards with no interlocking)

O_5_DRL

Mishandling of train en-route

O_6_DRL

Items left under train

O_7_DRL

Other operational failures l

O_1A

Unfavourable train composition formation (empties before loaded

wagons)

O_1B

Other train composition failure

O_3A

Speed not set according to brake

performance

O_3B

Brakes not properly checked or tested

O_3C

Brakes not set with respect to load or

speed of brake application

0_4A

Wrong setting in relation to movement authority

0_4B

Point moved whilst occupied by train

O_5A

Driver overspeeding

O_5B

Other mishandling of train

O_5A1

Excessive speed through turnout in deviated position

O_5A2

Excessive speed elsewhere

This is part of a set of fault trees, although they were used to quantify the analysis.


Alternative Frequency Analysis Approach

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Hazard: Freight Train Derailment

Infrastructure

Rolling Stock

Operations

% contribution cause 1

% contribution cause 1

.

.

% contribution cause n

Cause 1 leads to high or low speed

derailment?

Cause n leads to high or low speed

derailment?

Calculation flow

Annual number of significant derailments per year = 500 (from Eurostat and Agency data)

A severe derailment is one which has the potential for loss of containment. A significant derailment is one which has the potential to become severe.


Some Statistics for Accidents with Single or Dominant Cause

About 75% of derailments have single or dominant cause:- > 65% Inf derailments result from track geometry defects (track width dominant from single

causes, although when combinational causes included track twist becomes dominant).- > 70% RS derailments result from wheel / wheel set failures (HAB dominant).- ~ 25% Ops derailments result from loading errors (although dominant single cause is brake

checking errors including handbrake left on)

Example: HAB = 75% * 41% * 38% = about 12% (60 in number) of all derailments.

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Accident Causes Breakdown

33%

41%

24%

1%0%

5%

10%

15%

20%

25%

30%

35%

40%

45%

Infrastructure Rolling stock Operational failure Others(environment etc)


Some Statistics for Accidents with Several Causes

Track geometry defects appear in about 50% of accidents where more than one cause is present, with track twist the most significant appearing in about 30%.

Wheel profile defects appear in about 20% of accidents where more than one cause is present.

Wagon wrongly loaded appears in about 10% of accidents where more than one cause is present.

Train mishandling appears in 10% of accidents where more than one cause is present.

Our assumption is that removal of a one of these causes will prevent the derailment.

9


10

Derailment Frequency Assessment Results

Derail numbers.docx


Agenda

11

1. Background



4. Summary


12

Derailment Event Tree Considerations and Some Data

Factors include:- Derailment location.- Immediate consequences:

- Severe (e.g. overturn, mechanical impact causes loss of containment)- Not immediately severe:

- Is derailment detected?- Is train brought to a safe stop?

About 70% of low speed derailments occur in or around stations.

About 25% of low speed derailments are immediately severe (potential for loss of containment).

About 30% of high speed derailments occur in or around stations.

About 50% of high speed derailments are immediately severe.


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Partial Event Tree (preceding branches are speed & location)


Derailment Outcomes (about 170 in total, but simplify to…)

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Consequence DescriptionSD1 Severe derailment occurring immediately, contents spilling, fouling adjacent line and affecting passenger train

on adjacent lineSD2 Severe derailment occurring immediately, contents spilling, fouling adjacent line and affecting freight train on

adjacent lineSD3 Severe derailment occurring immediately, contents spilling, fouling adjacent line but no affect on adjacent lineSD4 Severe derailment occurring immediately, contents spilling but no affect on adjacent lineSD5 Severe derailment occurring immediately , fouling adjacent line and affecting passenger train on adjacent lineSD6 Severe derailment occurring immediately , fouling adjacent line and affecting freight train on adjacent lineSD7 Severe derailment occurring immediately , fouling adjacent line but no affect on adjacent lineSD8 Severe derailment occurring immediately but no contents spill or no affect on adjacent lineSD9 Occurring some time after initial derailment (detected by driver/others but unable to apply safe

stop/undetected), contents spilling, fouling adjacent line and affecting passenger train on adjacent lineSD10 Occurring some time after initial derailment (detected by driver/others but unable to apply safe

stop/undetected), contents spilling, fouling adjacent line and affecting freight train on adjacent lineSD11 Occurring some time after initial derailment (detected by driver/others but unable to apply safe

stop/undetected), contents spilling, fouling adjacent line but no affect on adjacent lineSD12 Occurring some time after initial derailment (detected by driver/others but unable to apply safe

stop/undetected), contents spilling, but no affect on adjacent lineSD13 Occurring some time after initial derailment (detected by driver/others but unable to apply safe

stop/undetected), no contents spilling, fouling adjacent line and affecting passenger train on adjacent lineSD14 Occurring some time after initial derailment (detected by driver/others but unable to apply safe

stop/undetected), no contents spilling, fouling adjacent line and affecting freight train on adjacent lineSD15 Occurring some time after initial derailment (detected by driver/others but unable to apply safe

stop/undetected), no contents spilling, fouling adjacent line but no affect on adjacent lineSD16 Occurring some time after initial derailment (detected by driver/others but unable to apply safe

stop/undetected) but no contents spill or affect on adjacent lineNSD1 Number of non severe derailments per year. Must be without contents spill and no affect on adjacent line


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Derailment Event Tree Statistics

Imm Sev DG Non Immed Sev DG Immed Sev Normal Non Immed Sev Normal Detected and safe Detected not safe stop19 11 165 93 204 8

3.7% 2.2% 33.1% 18.6% 40.7% 1.7%

Each outcome has an impact in terms of:- Potential loss of life.- Operational disruption.- Track damage.- Wagon damage.- Environmental events (contamination).

We estimate:- About 4 fatalities per year (almost exclusively from DG incidents).- About 17,000 hours operational disruption per year.- About 720 km track damage per year.- About 2,400 damaged wagons per year.- About 65 contamination events per year.


Agenda

16

1. Background



4. Summary


17

Summing Up

Risk model predicts impacts.

Benefits of identified measures are determined in terms of avoided derailments / reduced impacts.

Potential costs of new measures are defined by the application scope, measure cost and maintenance parameters and effectiveness of each measure

Hazard

Basic causes Intermediate causes

Hazard/ What - if

Fully developed consequences

Developing consequences

Primary controls

Secondary controls

Fault Tree Analysis Event Tree Analysis Mitigation 2 Outcome Yes 1

Mitigation 1 Yes No 2

Yes 3 No

No 4

= Key risk reduction measures


18

End of Session - Any Questions


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Safeguarding life, property and the environment

www.dnv.com

gavin astin 29 september 2011 derailment risk model frequency analysis and scenario development

Documents

severe derailment

accident summaries

summary slide

accident reports summaries

dominant cause

single causes

dominant single cause

frequency assessment