Transcript Human Reliability

Human Reliability Analysis:
Accounting for Human Error on Light Rail
Transportation Systems
SYSM 6309 Advanced Requirements Engineering
By: Michael Murphy
Agenda
Motivation
Case Study
Human Reliability Analysis (HRA) Tools
 Technique for Human Error Rate Prediction (THERP)
 Error Rates
 Event Tree
 Swiss Cheese Model
Possible Light Rail System Solutions
Questions
Motivation
Federal Transit Administration’s (FTA) Office of Safety and
Security compiled a report of light rail safety statistics from
2003 to 2008 that grouped light rail accident types with light
rail accident causes.
5 Types: Rail Grade Crossing (RGX) Collisions, NonRGX Collisions, Derailments, Fire and Other
4 Causes: Equipment Failure, Workforce Behavior,
Customer Behavior and Public Behavior
Within that time span, there were 3,665 reported accidents.
Of the 3,665 reported accidents, 583 (16%) were caused by
Workforce Behavior.
Case Study: San Francisco Railroad
Accident
Date: July 18, 2009
Time: 2:50 pm, Pacific daylight time
Property Damage: $4.5 million
Injuries: 48 (28 serious)
Accident: L train 1433 struck the rear end of standing K train 1407
 K train was at the end (aka platform) of the West Portal Tunnel, waiting to
merge onto the K line.
 L train, controlled by automatic train control system (ATCS), pulled into
tunnel.
 L train operator “cut out” of ATCS to manually pull ahead to the platform.
 L train was moving about 5 mph when the operator “blacked out” until
impact.
Accident Simulation
Platform
Tunnel
Outbound
K
L
K
L
KA-BLAM!!!
Inbound
LK
Train
Train
arrives
in
tunnel,
tunnel,
K no
Train
cars
still
atat
platform.
platform.
L Train
changes
Karrives
Train
toinmanual
pulls
ahead
and
to
pulls
platform.
ahead
to platform.
Cause of Accident
Human Error
L Train Operator failed to request permission of OCC
management to disengage ATCS.
L Train Operator failed to keep the train in automatic
mode until reaching the station stop at the West Portal
platform.
Would have been a safe guard against his “black
out”
OCC failure to monitor and enforce requirement that
the operator wait until reaching the platform before
changing operating mode of the train.
Corrective Action
Bulletin issued reminding the train operators
not to “cut out” of the ATCS without OCC
permission.
The final sentence of the bulletin read,
“Failure to comply with these existing rules
outlined in the Rules and Instruction
Handbook will result in discipline, up to and
including termination.”
Human Reliability Analysis
(HRA)
Role is to provide the foundation for calculating
the probability that the human element of an
operator/process or system interaction will fail.
Majority of HRA methods were developed in the
1980’s due to concern caused by the accident
at Three Mile Island.
Technique for Human Error
Rate Prediction (THERP)
 Best known human performance reliability prediction technique
which involves 5 steps:
 Define the system or process.
 Identify and list all human operations performed and their
relationships to the system or process tasks and functions.
 Predict error rates for each human operation or group of
operations.
 Determine the effect of human errors on the system or
process -> Event Tree.
 Develop and recommend changes that will reduce the
system or process failure rate.
Error Rates
 Probability that a class of errors will lead to system failure is:
Qi = 1 – (1 – FiPi)^nj
 Error Rate Tables

http://panko.shidler.hawaii.edu/HumanErr/
Event Tree
Swiss Cheese Model
Possible Light Rail System
Improvements
Utilize THERP when building new or expanding current
systems.
Additional training of established operating procedures.
Threat of disciplinary action when established operating
procedures are not followed.
The German Aerospace Center has developed a Railway
Collision Avoidance System (RCAS)
 Safety overlay that can be deployed on top of any existing
safety infrastructure in train networks.
 Provides train position and vehicle dimensions to all other
trains in the area using ad-hoc train-to-train
communications.
Questions?
References
 “Collision of Two Municipal Transportation Agency Light Rail
Vehicles, 7/18/2009, San Francisco, CA,”
http://www.ntsb.gov/investigations/reports.html
 “Human Reliability,” http://en.wikipedia.org/wiki/Human_reliability
 E. Hollnagel “Human Reliability Analysis,” 2002,
http://www.ida.liu.se/~eriho/WhatIsHRA_M.htm
 “Technique for Human Error Rate Prediction.”
http://en.wikipedia.org/wiki/Technique_for_Human_Error_Rate_Pre
diction
 Barbara Gregory, MPH, Victoria S. Kaprielian, MD “Anatomy of
Error – Swiss Cheese Model,”
http://patientsafetyed.duhs.duke.edu/module_e/swiss_cheese.html