Mark Andrew - GHD - Platform Carriage Interface Risks

Platform-Train Interface risks

Mark Andrew | Principal Consultant, Risk & Human Factors

What is a PTI size

that reduces risk,

SFAIRP, for as many

passenger groups as

practicable?

By-product:

specification for a

tool that could be

used by industry to

classify step / gap

sizes by risk.

Platform-Train Interface Risks ~ A SFAIRP method

Problem description

Q Why not make the gap extremely small, so that all passengers essentially

do not experience a gap?

A Gaps that are too small do not allow for train carriage side-to-side

movement, and therefore:

• the platform and carriage gets damaged

• and train running delays increase.

Q Why not make all carriage floors match the platform height, so there is no

step?

A Differences in train design and infrastructure as-built do not allow for zero

step.


Methodology overview

Three stages

A1 - Hazard log

A2 - Bow-tie scenario map

A3 - Risk scenarios identified (say 30+)

B1 - Scenario dynamics described

B2 – Evidence-based SQRA

B3 - Grouping of risks by loss type

C1 - Summation of risks by loss category

C2 - Define an Exchange Rate (harm: damage: delay)

C3 – Model gap size costs with different cohort mixes

Rich picture of the system

including candidate passenger

cohorts

Measurement of costs of loss

calculated by cohorts and step

size

Link costs to gap and step size

= design tool specification

DeliverableActivity

COHORT EXAMPLE 1: PEOPLE WITH WALKING FRAME

COHORT EXAMPLE 2: UNDER FIVES ON FOOT


Passenger can not access

carriage

Slip trip / fall

Object stuck on step

Train running delay

Passengers slip or trip

Passenger falls into train /

platform

Passenger falls down gap

Train running delay

Slip trip fall

Access restrictions

Train running delay

Object stuck / dropped

Carriage contacts platform

Platform damage

Repair costs

Train running delay

A1 - Typical hazards

Train –platform interface

Gap too

large

Step too high

Step too low

Gap too

small

ILLUSTRATIVE EXAMPLES ONLY


Prevention

Controls

Mitigation

Controls

A2 - Bow-tie representation - generic


Loss of control:

Platform-Train

interface

Gap too large

Passenger

cohort A

(e.g. <5yrs)

Step too high

Other

Slip / Trip / Fall

Entrapment

Inaccessible: delay /

cancel

Train running delay

Carriage body damaged

Train doors damaged

Other

Platform edge damage

Structural failure

Other

Passenger

cohort B

(e.g. frame)

Passenger

cohort C

(e.g. wheel

chair)

Passenger

harm

Rolling

stock

damage

Platform

damage

Gap too small

Step too low Infra-structure

Gap too large

Step too high

Other

Gap too large

Step too high

Other

Other

A2 – Bow-tie scenario map for PTI


Loss of control:

Platform-Train

interface

Gap too large

Passenger

cohort AStep too high

Other

Slip / Trip / Fall

Entrapment

Inaccessible: delay /

cancelled

Train running delay

Carriage body damaged

Train doors damaged

Other

Platform edge damage

Structural failure

Other

Passenger

cohort B

Passenger

cohort C

Passenger

harm

Rolling stock

damage

Platform

damage

Gap too small

Step too low Infra-structure

Gap too large

Step too high

Other

Gap too large

Step too high

Other

Other

A3 – Example scenario from bow-tie (one of 30+)


B1 – Scenario dynamics described

For our example candidate risk scenario:

While attempting to board an under-five year old falls

into the gap.

To measure this risk we need:

• Initiating Incident Frequency (incidence of under fives falling when boarding).

• Probability of the fall escalating to an entrapment in the gap.

• Consequential harm from under five falls into the gap (extent of injury).


B2 – Evidence-based risk analysis

For our example candidate risk scenario:

While attempting to board an under-five year old falls into the gap.

Evidence-based? > a blend of empirical data and subject-matter expertise.

Initiating Incident Frequency (incidence of under fives falling when boarding):

Records show 1:500 passengers are under fives, of which 1 in 500 slip while boarding so of the say 1,700,000 boardings per year, the Initiating Incident Frequency is 6.8 / annum

Probability of the fall escalating to an entrapment in the gap:Records show there is a one in 70 chance of entrapment following a fall.

Consequential harm from under five falls into the gap (extent of injury).Representative injury is disabling injury.


B3 – Group the risks by loss type

Infrastructuresafer:

Scenarios 2,5,9,15,27 etc

Passengers harmed:

Scenarios 6,12,16.23 etc

Passengers safer:

Scenarios 1,3,4,7 etc

Infrastructuredamaged:

Scenarios 26,17,19 etc

Bigger gap size

Smaller gap size

Smaller step size Larger step size

Some

cohorts

feature in

more than

1 cell


C1 & C2: Sum the risks by type and apply

Exchange Rate

N

…

2

Exchange Rate

Sum of all Harm

Sum of all Damage

Sum of all Delay

Global net loss calculation for gap size 1

Exchange Rates

for harm, damage

and delays have

been created in

various reference

sources


C3: Model the gap size / loss trade-off

N

…

2

Exchange Rate

Sum of all Harm

Sum of all

DamageSum of

all Delay


N

…

2

Exchange Rate

Sum of all Harm

Sum of all

DamageSum of

all Delay


N

…

2

Exchange Rate

Sum of all Harm

Sum of all

DamageSum of

all Delay


Cohort mix A Cohort mix B Cohort mix C etc >

Input variables into a spreadsheet or database to allow for SFAIRP calculations of control

costs versus losses avoided to be traded. [Different Exchange Rates will yield different

SFAIRPs]


Data sources

Exchange rates

Industry incident records

Classic texts

Manuals, guides & checklists

Standards and Regs

Weblinks and data sources

E.G. REFERENCE SOURCES

E.G. DATA REPOSITORIES

E.G. MANUALS & GUIDES

E.G. ISO / BS / ASNZ / DIN STANDARDS

E.G. COSTS OF INJURIES - SAFE WORK AUSTRALIA


Does this approach pass the SFAIRP test?

The five SFAIRP criteria:

a) the likelihood of the hazard

b) the degree of harm that might

result

c) what the person concerned knows,

or ought reasonably to know

d) the availability and suitability of

ways to eliminate or minimise the risk

e) the cost associated and if cost is

grossly disproportionate

✔ see stages A & B

Criterion addressed?

✔ see stages B & C

✔ see stages A & B

✔ see stages A, B & C

✔ see stage C


So Far As Is Reasonably Practicable (SFAIRP)

"Reasonably practicable" is a narrower

term than "physically possible" and

seems to me to imply that a

computation must be made by the

owner, in which the quantum of risk is

placed on one scale and the sacrifice

involved in the measures necessary for

averting the risk (whether in money,

time or trouble) is placed in the other;

and that if it be shown that there is a

gross disproportion between them - the

risk being insignificant in relation to the

sacrifice - the defendants discharge the

onus on them.

Lord Justice of Appeal (1949)

Acknowledgements:

The author wishes to thank GHD for permission to attend and present at this Conference.

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Mark Andrew - GHD - Platform Carriage Interface Risks

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