INTERNATIONAL SEMINAR Desafo para el Diseo, Construccin y Operacin - - PowerPoint PPT Presentation

INTERNATIONAL SEMINAR LONG TUNNELS

17, 18 y 19 de Octubre 2012 Santiago, Chile

PROGRESS IN RISK ASSESSMENT FOR PERFORMANCE-BASED ASSESSMENT OF ROAD TUNNEL SAFETY

Bernhard Kohl, MSc ILF Consulting Engineers (Austria)

Desafío para el Diseño, Construcción y Operación Challenges for Design, Construction and Operation

PIARC CHILE

1

2

INTRODUCTION

Bernhard Kohl, MSc ILF Consulting Engineers Head of branch office Linz (Austria) Member of PIARC TC3.3

• Leader of new WG

“Feedback from experience on tunnel safety”

• and former WG

“Manage and improve tunnel safety”

3

OUTLINE

(1) Basic principles of performance based approach (2) Risk analysis methods (3) Approach for risk evaluation (4) Practical application of risk analysis (5) Research activites and new developments (6) Conclusions (1)    Basic principles of performance based approach

4

BASIC PRINCIPLES OF PERFORMANCE BASED APPROACH

Basic principle of road tunnel safety: Holistic approach

Safety / Emergency Services Maintenance Project Management Structural Engineering Operational Procedures Ventilation Electric Infrastructure Traffic Management / Vehicles / Drivers

5

BASIC PRINCIPLES OF PERFORMANCE BASED APPROACH

Different approaches to road tunnel safety

Prescriptive approach Risk based approach

A tunnel is safe if it is designed in line with valid regulations A tunnel is safe if it meets predefined risk criteria

• Technical specification of safety features of a

tunnel

• Easy to implement, but scarcely taking

specific characteristics into account

• Residual risk (even if all requirements are met)

– is not addressed

• Structured, harmonised and holistic safety

analysis – basis for decision making

• Consideration of specific characteristics of a

tunnel

• Quantitative evaluation of residual risk / of

effects of safety measures

Risk 

  

k , i k ik k ik ik m

G ) A ( A H R

Frequency Consequences

Frequency Consequences

x =

Consequences Frequency

6

BASIC PRINCIPLES OF PERFORMANCE BASED APPROACH

Different approaches to road tunnel safety Prescriptive based approach and risk based approach have to be used as complementary elements of the safety assessment process.

7

BASIC PRINCIPLES OF PERFORMANCE BASED APPROACH

Risk assessment process

RISK ASSESSMENT Start Start Definition of the system Definition of the system Hazard identification Hazard identification Probability analysis Probability analysis Consequence analysis Consequence analysis Risk estimation Risk estimation (additional) safety measures (additional) safety measures Acceptable risk? Acceptable risk? Yes No Risk reduction Stop Stop Risk criteria Risk criteria Risk evaluation Risk evaluation Risk analysis Report: Risk Analysis For Road Tunnels Risk evaluation Report: Risk Evaluation 8

BASIC PRINCIPLES OF PERFORMANCE BASED APPROACH

Risk assessment process

• Risk analysis:

systematic approach to analyse sequences and interrelations in potential incidents or accidents, identifying weak points in the system and recognising possible improvement measures

• Risk evaluation:

directed towards the question

• f

acceptability

• f

the identified risks – judged against particular risk criteria that have been defined

• Risk reduction:

required if the estimated risk is considered as acceptable, additional safety measures have to be proposed to reduce risk.

9

BASIC PRINCIPLES OF PERFORMANCE BASED APPROACH

Different types of risk Different types of risk can be addressed in a risk analyses:

• Societal risk:

harm to a specific group of people

• Individual risk:

harm to an individual person

• Economical loss
• Damage to environment
• Damage to immaterial values

   Focus on societal risk of tunnel users

10

BASIC PRINCIPLES OF PERFORMANCE BASED APPROACH

Different types of risk representation

• Expected risk value (EV)

long-term average number of statistically expected fatalities per year

• FN diagram

shows magnitude of consequences in relationship to the (cumulated) frequency of a hazard

1,00E-11 1,00E-10 1,00E-09 1,00E-08 1,00E-07 1,00E-06 1,00E-05 1,00E-04 1,00E-03 1,00E-02 1,00E-01 1,00E+00

1 10 100 1.000 10.000

Frequency / per year Damage [fatalities] 11

OUTLINE

(1) Basic principles of performance based approach (2) Risk analysis methods (3) Approach for risk evaluation (4) Practical application of risk analysis (5) Research activites and new developments (6) Conclusions (2)    Risk analysis methods

12

RISK ANALYSIS METHODS

• In general, there is a big variety of different approaches,

methods and complex models combining various methododical components for specific tasks

• For road tunnels in particular, there are two big families of

methods

• Qualitative or semiquantitative scenario based methods
• Quantitative system-based methods

13

RISK ANALYSIS METHODS

Qualitative or semiquantitative scenario based Approach: analyses a set of relevant scenarios obtaining information on frequency/consequences for each individual scenario

Select relevant scenarios Select relevant scenarios scenario 1 scenario 1 scenario 2 scenario 2 scenario 3 scenario 3 … Analyse development

• f scenarios

Analyse development

• f scenarios

Investigate effects and consequences

• f scenarios

Investigate effects and consequences

• f scenarios
• eg. evacuation
• ptimize

design

• ptimize

design

14

Quantitative system based Approach: investigates an

• verall

system in an integrated process,

• btaining risk values for the whole system

Mechanical accidents ( statistics) (model results)

RISK ANALYSIS METHODS

Probability calculation- Input parameters

Accident type Traffic composition scenario evolution Accident rates Traffic volume vehicles involvements

Probability calculation- Input parameters

Accident type Traffic composition scenario evolution Accident rates Traffic volume vehicles involvements

X

Logical tree

initial event accident scenarios

RISK

Results Results Expected risk value (fatalities/year)

dangerous goods fires mechanical accidents

Risk distribution (F-N-Curve)

15

Damage values – Input parameter

Tunnel type, ventilation system, Emergency exits

Damage values – Input parameter

Tunnel type, ventilation system, Emergency exits

OUTLINE

(1) Basic principles of performance based approach (2) Risk analysis methods (3) Approach for risk evaluation (4) Practical application of risk analysis (5) Research activites and new developments (6) Conclusions (3)    Approach for risk evaluation

16

APPROACH FOR RISK EVALUATION

Background of risk evaluation:

• Risk analysis: “What might happen?”
• Scientific process: Identification, structuring, assessment of

probabilities and consequences

• Risk evaluation: ”Is the risk acceptable?”
• Socio-political process including ethical, political and societal

aspects

• Strongly influenced by risk perception
• Risk perception: is influenced by many parameters such as

perceived benefits, voluntariness, controllability or catastrophic potential    No “right” or “wrong” risk evaluation criteria

17

APPROACH FOR RISK EVALUATION

Basic principles for risk evaluation:

• Absolute

criteria risk is acceptable as long as assessed risk is lower than a defined absolute threshold

18

APPROACH FOR RISK EVALUATION

Basic principles for risk evaluation:

• Relative

criteria risk is acceptable, as long as assessed risk is lower than an established risk profile Concept of “Reference Tunnel”: theoretical tunnel similar to tunnel under assessment, but fully complying with all requirements, conditions etc. defined in relevant regulations.

acceptable risk level

19

APPROACH FOR RISK EVALUATION

Basic Principles for risk evaluation:

• Cost-effectiveness approach

Comparison of efficiency

• f safety measures and

their risk reduction potential A tunnel is safe, if all cost-effective measures are implemented

Optimum = Minimum

Safety Measures

Loss E xpenses Cost for S afety Measures Total Cost

Cost

Optimum = Minimum

Safety Measures

Loss E xpenses Cost for S afety Measures Total Cost

Cost 20

APPROACH FOR RISK EVALUATION

Practical example for a relative approach: Evaluation of safety measures for existing tunnel Influence of mechanical ventilation in a unidirectional tunnel without ventilation

EV (fire risk) FN-curve (overall risk) Model tunnel: 0,6 km unidirectional; 70.000 veh/d; vaulted cross section

• Tunnel 3n:

natural ventilation

• Tunnel 3l:

longitudinal ventilation

1,00E-11 1,00E-10 1,00E-09 1,00E-08 1,00E-07 1,00E-06 1,00E-05 1,00E-04 1,00E-03 1,00E-02 1,00E-01 1,00E+00 1 10 100 1.000

frequency of event per year and km consequences of event (fatalities)

5,09E-02 2,60E-03

Tunnel 3n Tunnel 3l 21

OUTLINE

(1) Basic principles of performance based approach (2) Risk analysis methods (3) Approach for risk evaluation (4) Practicl application of risk analysis (5) Research activites and new developments (6) Conclusions (4)    Practical application of risk analysis

22

PRACTICAL APPLICATION OF RISK ANALYSIS

Typical applications for a performance based approach

• to check general consistency of safety planning
• to choose between alternatives
• to demonstrate safety in case of deviations from

prescriptions

• to optimize safety planning in terms of cost-effectiveness
• application as decision making tool – for safety relevant

decisions in the design phase of new tunnels as well as in the upgrading process of existing tunnels

23

PRACTICAL APPLICATION OF RISK ANALYSIS

Typical practical examples for the application of risk analysis

• Investigation of specific design features of a tunnel

(e.g. steep gradient, specific cross section, cross passage distance)

• Investigation of specific traffic situations

(e.g. congestion, high share of lorries, DG-transports)

• Decision on ventilation system (design phase)
• Investigation of alternative measures as compensation for

deviations from prescriptions (upgrading of existing tunnels)

• Decision on admissibility of DG-transport in a tunnel

24

PRACTICAL APPLICATION OF RISK ANALYSIS

Why applying risk analysis for decision making?

• The safety standard of road tunnels in Europe in general is

high

• (Further) improvements of tunnel safety are (very) cost-

intensive

• The financial resources available for further improvements

are more and more limited

• Focus on extreme scenarios may result in an unbalanced

safety level and disproportionate cost

• In most cases there are different options to reach a safety

goal; sometimes there are low cost alternatives Conclusion There is an increasing need for informed decisions supported by well defined decision making tools

25

PRACTICAL APPLICATION OF RISK ANALYSIS

Regulative background for decision making on the basis of a risk analysis

• On European level
• EC Directive 2004/54/EC:

Derogations of the requirements in annex I are allowed under specific conditions Principle: Alternative Safety measures, resulting in an equivalent / higher safety level

• In national regulations (examples)
• Austrian Tunnel Safety law:

Same principle generally applied for all prescriptive requirements of annex I – only for tunnels not on the TERN network

• German tunnel guideline RABT:

Risk based decision on ventilation system for tunnels (600 m - 1.200 m) with bidirectional or congested traffic

• Directive

2004/54/EC RABT STSG

26

Case study: Tunnel Učka (Croatia) Initial situation

• Tunnel Učka is a 5,062 km long road tunnel in Istria (Croatia)

with one tube and bidirectional traffic

PRACTICAL APPLICATION OF RISK ANALYSIS

27

PRACTICAL APPLICATION OF RISK ANALYSIS

Case study: Tunnel Učka (Croatia) Initial situation

• Tunnel Učka is a 5,062 km long road tunnel in Istria (Croatia)

with one tube and bidirectional traffic

• The tunnel is equipped with a longitudinal ventilation system

and has no emergency exits

• Being aware of the difficult situation, the operator – BINA-

ISTRA – optimised the existing systems and established a set

• f well coordinated operational safety measures –

embedding it in a highly developed safety culture

• The system is well-proven and tested in everyday operation,

including real incidents, accidents and fires

28

PRACTICAL APPLICATION OF RISK ANALYSIS

Case study: Tunnel Učka (Croatia) Problem: decision on ventilation system

• In the next years, a second tube shall be built

29

PRACTICAL APPLICATION OF RISK ANALYSIS

Case study: Tunnel Učka (Croatia) Problem: decision on ventilation system

• In the next years, a second tube shall be built
• In Croatia there are no specific national tunnel regulations;

in practice the Austrian design guidelines RVS are applied

• In RVS 09.02.31 a limit of 3 km length is defined for the

application of longitudinal ventilation systems

• Although tunnel Učka is longer, the operator BINA-ISTRA

wants to maintain the longitudinal ventilation system also for the new tunnel configuration

• The main reasons are:
• big technical problems (existing tube),
• high cost
• limited benefit

 A risk assessment study was performed to demonstrate that this is acceptable (system – based approach – Austrian Tunnel Riks Model TuRisMo)

PRACTICAL APPLICATION OF RISK ANALYSIS

Case study: Tunnel Učka (Croatia) Additional safety measures In comparison to a standard safety level the following additional safety measures are in place in tunnel Učka and will also be maintained in future

• Early detection of accidents, incidents and fires by optimised

CCTV system and well trained, highly motivated staff (efficiency documented by statistical data / incident reports)

• Fast and efficient tunnel closure (by barriers at toll stations at

both tunnel portals and inside tunnel)

• Tunnel Učka is a 5,062 km long road tunnel in Istria (Croatia)

with one tube and bidirectional traffic

31

PRACTICAL APPLICATION OF RISK ANALYSIS

Case study: Tunnel Učka (Croatia) Results – model values for fire scenarios (consequences / event – without probabilities) Comparison longitudinal ventilation – transversal ventilation (with additional safety measures)

Fire scenarios Tube 1 Tube 2 longitudinal transversal longitudinal transversal 5 MW (2,0) 0,2 0,2 (1,7) 0,4 0,6 30 MW (4,4) 0,8 4,3 (4,8) 0,8 4,4 100 MW (29,0) 12,4 5,8 (35,5) 13,3 6,2

 The additional safety measures already in place reduce the consequences of the 5 MW and 30 MW fire scenarios with longitudinal ventilation below the respective values with transverse ventilation

 The model values for the 100 MW scenario are reduced as well,

but are still higher

32

PRACTICAL APPLICATION OF RISK ANALYSIS

Case study: Tunnel Učka (Croatia) Results

• There is a (very limited) benefit of a transversal ventilation

system

• Longitudinal ventilation can be accepted, because

additional measures reduce risk below risk of reference tunnels (relative approach for risk evaluation)

33

PRACTICAL APPLICATION OF RISK ANALYSIS

Case study: Tunnel Učka (Croatia) Conclusions

• The overall risk / the relevant partial risks of tunnel Učka

are below the respective values of the reference tunnel (“EC Directive” as well as “RVS-transversal ventilation”)

• The future tunnel configuration will be sufficiently safe with

respect to

• the minimum safety requirements defined in the EC Directive

2004/54/EC

• the requirements of RVS 09.02.31
• Hence a longitudinal ventilation system is acceptable
• The fire risk in the new tunnel Učka will be very low

(appr. 2 %); hence the influence of measures specifically influencing fire risk (e.g. Ventilation) will be low as well

34

PRACTICAL APPLICATION OF RISK ANALYSIS

Case study: influence of tunnel cross section on fire risk

• The model calculations were performed with a 2-lane

vaulted tunnel cross section

• Recent research results show, that there is a relevant

influence of height, width and shape of tunnel cross section

• n (fire) risk

EV (fire risk) FN-curve (overall risk) Influence of tunnel geometry (bidirectional tunnel)

Model tunnel: 1,2 km bidirectional; 20.000 veh/d; longitudinal ventilation

• Tunnel 1:

vaulted cross section

• Tunnel 4:

rectangular cross section

1,00E-11 1,00E-10 1,00E-09 1,00E-08 1,00E-07 1,00E-06 1,00E-05 1,00E-04 1,00E-03 1,00E-02 1,00E-01 1,00E+00 1 10 100 1.000

frequencyof event per year and km consequencesof event (fatalities)

9,10E-03 1,55E-02

Tunnel 1 Tunnel 4

Influence of tunnel cross section on fire risk in a bidirectional tunnel with longitudinal ventilation (research project “Sicherheitsbewertung RABT-konformer Tunnel” – Heimbecher, Kohl 2011)

35

OUTLINE

(1) Basic principles of performance based approach (2) Risk analysis methods (3) Approach for risk evaluation (4) Practicl application of risk analysis (5) Research activites and new developments (6) Conclusions (5)    Research activites and new developments

36

RESEARCH ACTIVITIES AND NEW DEVELOPMENTS

• There is a trend towards more complex integrated models
• There is a trend to implement more and more statistical data

(the data base in Europe improved a lot as a consequence

• f the EC-Tunnel Safety Directive)
• The new generation of risk models is able to cover more

relevant parameters in a more specific way

• The continuous improvement of risk models makes the

evaluation of even complex problems possible, thus providing a better basis for an informed decision for people responsible for tunnel safety

37

RESEARCH ACTIVITIES AND NEW DEVELOPMENTS

Example: Austrian Tunnel Risk Model TuRisMo

• Implementation of a combined 1D / 3D smoke propagation

model

• To cover all relevant (global and local) factors influencing

smoke propagation in the tunnel

38

RESEARCH ACTIVITIES AND NEW DEVELOPMENTS

Example: Austrian Tunnel Risk Model TuRisMo

• Implementation of an integrated evacuation simulation tool

in the smoke propagation model

• The smoke propagation model calculates obscuration and

concentration of toxic gases in dependence of time at 1,6 m height, transferring it directly into the evacuation model

39

RESEARCH ACTIVITIES AND NEW DEVELOPMENTS

Enhanced use of statistical traffic data

• So far the fire risk damage values were calculated on the

basis of the AADT, hence for an average situation

• It is envisaged to take at least 3 different traffic scenarios into

account (for low, average and high traffic situations)

• These values shall be defined on the basis of statistical traffic

data of one complete year

• This approach allows to take effects into account which

directly depend on the traffic situation (air flow conditions, exposure)

40

OUTLINE

(1) Basic principles of performance based approach (2) Risk analysis methods (3) Approach for risk evaluation (4) Practicl application of risk analysis (5) Research activites and new developments (6) Conclusions (6)    Conclusions

41

Conclusions (1)

• A risk performance-based approach is a valuable

supplement to prescriptive guidelines

• The application of risk analysis allows a structured,

harmonised and transparent assessment of the risk of a specific tunnel in a quantitative way

• It covers different fields of application such as risk-based

decision making or performance-based assessment of safety standards

• The selection of the most suitable method depends on the

specific requirements of the problem to be investigated

• All methods exhibit specific advantages and disadvantages

– none can claim to be generally the most suitable

42

Conclusions (2)

PIARC elaborated 2 reports addressing a risk based approach:

• Report “Risk analysis for road tunnels”

(published http://www.piarc.org/en/publications/technical-reports/)

• Provides a description of basic principles and characteristic

methodologies of the risk assessment process

• Presents 6 practical methods and gives recommendations for

the use of risk anlaysis

• Report “Current practice for risk evaluation for road tunnels”
• Provides a description of basic principles and practical

methods of risk evaluation

• Includes an update/ completition of the practical methods

described in the previous report

43

DI Bernhard KOHL, ILF Consulting Engineers, Harrachstraße 26, 4020 Linz, Austria

Thank you for your attention!

contact: bernhard.kohl@ilf.com +43 (0) 699 14 530 158 PROGRESS IN RISK ASSESSMENT FOR PERFORMANCE – BASED ASSESSMENT OF ROAD TUNNEL SAFETY

44