Safe roads, Reliable journeys, Informed travellers Tunnels, Risks & Design Mitigation Eamonn Colgan HA Senior Project Manager & John Celentano Mouchel Ltd, Tunnel Technical Director
Introduction Eamonn Colgan Highways Agency Senior Project Manager M25 Area Tunnel Refurbishments Netserve Tunnel Team Leader
Highways Agency Executive Agency of Department for Transport responsible for the operation maintenance and improvement of the strategic road network. The Highways Agency network forms 2.5 % of road length in England but carries around one third of all car journeys and two thirds of HGV traffic. There are Ten Tunnels on the network, five on the Trans European Road Network (TERN)
M62/M1 Lofthouse (A57Mottram) Planned A50 Meir A1(M) Hatfield M25 Holmesdale M25 Bell Common A282 Dartford east and west A27 Southwick A20 Roundhill A38 Saltash
Highways Agency Tunnel Assets. Name Length Opened A1(M) Hatfield TERN 1150 1986 M25 Holmesdale TERN 700 1984 M25 Bell Common TERN 470 1984 A282 Dartford N bound TERN 1430 1963 A282 Dartford S bound TERN 1430 1980 A20 Roundhill 370 1993 A27 Southwick 536 1995 A38 Saltash 400 1988 A50 Meir 284 1997 M62 M1 Lofthouse Interchange 155 1998
M25 Area Tunnel Refurbishment M25 Holmesdale, M25 Bell Common and A1(M) Hatfield Tunnels were constructed in the early 1980 s and are on TERN Tunnel mechanical and electrical systems were at the end of their design life and are beyond economic repair. Manufacturers no longer support spares Tunnel refurbishment programme developed in line with Current HA Standards, EU Road Tunnel Safety Directive and current best practice EU TERN Tunnels to be upgraded by 2014
M25 Tunnel Refurbishment Progress M25 Holmesdale Refurbishment 75m Started May 2006 Completed September 2007 M25 Bell Common Refurbishment 90.5m Started October 2008 completion April 2010 A(1)M Hatfield Tunnel Refurbishment (DBFO) Started June 2009 Completion April 2011
What Are The Improvements? Upgrade tunnel equipment in line with new standards Full replacement of mechanical and electrical plant Removal of raised walkways Passive fire protection of structure Additional operational safety mitigation measures Make provision for future D4 Widening Scheme
Delivery Challenges One of the busiest tunnels in Europe carrying 120,000 vehicles a day Close to the strategic Junction 27 with the M11 Three lanes to remain open during the day Delays to limited to around 10 15 minutes at peak times Provision for future M25 improvements
Presentation Objective Current Safety Approach in Tunnel Design Risk Terminology Tunnel Risks Holmesdale Tunnel - Risk Based Design Methodology. Holmesdale tunnel Consequence Reduction Measures Conclusions Contra-Flow During Refurbishment
Current Tunnels Safety Approach to Design Risk Presently there are two approaches to Design for Operational Risk in tunnels. Prescriptive Approach Where it is considered that a tunnel is safe if it is designed in line with current standards This is normally achieved where particular safety systems are included in the design without considering the individual characteristics or needs of the tunnel. Risk Based Approach Where a tunnel is safe if it meets a predefined risk criteria This normally allows a structured assessment of risks to meet the individual needs of a tunnel resulting in the installation of appropriate measures to reduce the consequences of the risk. Tunnel Industry is still debating the best approach
Risk Terminology Confusion on Definition of Risk HSE Website defines Hazard :- Something with the potential to cause harm Risk :- Likelihood of potential harm from that hazard being realised The Website expands on this and quantifies that Risk is dependant on:- Likelihood of harm (Probability) Potential Severity (Consequence) Risk is a function of two variables, Risk = {Frequency of hazard occurring} x {Consequence of hazard}
Tunnel Hazards Tunnel hazards are not dissimilar to those found on the open road, Fire Collisions Breakdown Spillage etc
Tunnel Hazards Frequency Research (PIARC) has concluded that the Frequency of these hazards are also not dissimilar to those found on the open road.
Tunnel Consequences Tunnel Consequences vary dramatically from Open Road. Primarily due to the containment effect of the tunnel structure. Recent tunnel disasters such as Mont Blanc, Tauern & St Gotthard tunnels are examples where increased consequence of tunnel hazards are apparent
Mont Blanc
Tauern
St Gotthard
Introduction EU Directive
Holmesdale Tunnel Design Risk Assessment Approach Article 13 of the EU Directive led to the development of a Risk Assessment model which allowed not only the Probability of the hazard to be assessed but when combined with other tools the potential consequence. The approach was undertaken in two phases, Hazard Identification Qualitative. Risk Evaluation Quantitative Output from the Risk model led to the development of the Outline Design & Performance Specification for the mitigation measures.
Hazard Identification Qualitative Developed with the Tunnel Design & Safety Consultation Group (TDSCG-Tunnel stakeholders). Comprehensive list of hazards identified based on operational knowledge. Identified Ranked Spreadsheet based tool.
Quantitative Risk Assessment Output from the model quantified the Probability and Magnitude" of key operational hazards, Probability-Magnitude Matrix Fire Risk, A small fire of 5 MW 1 in 3 years A medium size fire of 50 MW 1 in 15 years A Large fire of 100MW 1 in 32 years Spillage Risk Hazardous Spillage (1 in 76) Major Hazardous Spillage (1 in 196 years) HRR (MW) Probability Years 5 0.325 3.08 15 0.056 17.92 25 0.056 17.79 50 0.068 14.60 100 0.023 32.92 Model Output Fire Size Probability Matrix Traffic Collisions Major Road Traffic Collision (1 in 1.5 years)
Quantitative Output Ventilation Performance Model output set the design constraints for the conceptual design. Ventilation, Analysis concluded that the potential for a 100MW fire was 1 in 32 years. Design Standards suggest Ventilation systems should have a 25 Year design life. Design Life = 25 years 100 MW Fire Probability = 32 Years System Requirement = Design Life Probability of Fire Size = 25 years 32 years = 78% The model concluded a 78% probability that a fire Could occur during the life of the system. Based on the Balance of Probabilities. Model concluded ventilation design size -100MW
Quantitative Output Structural Protection Since the European tunnel fires research concluded that greater need to protect tunnel structure from the risk of fire. In Holmesdale, Probability of a 100MW fire occurring every 1 in 32 years Remaining structure life of 100 years Conclusion using Balance of Probabilities suggested that the Structure could experience at least 3 large fire events in the remainder of its life. Conclusion Tunnel Required Structural Protection. Structural resilience determined by CFD & FEA
Model Output Vehicle Incidents & Life safety Systems The Risk Model also has the capability to assess the frequency of vehicle related incidents such as, Single vehicle Breakdowns Single and multiple vehicle accidents. Accident of vehicles from different classes Spillages of Dangerous & Hazardous Goods Accident Type Probability In Years CAR 0.30 LGV 31.25 HGV 16.53 Car-Car 1.52 Car-LGV 7.72 Car-HGV 5.61 LGV-LGV 156.25 LGV-HGV 56.82 HGV-HGV 82.64 Car-Car-Car 1.88 Car-Car-LGV 6.31 Car-Car-HGV 4.60 Car-LGV-LGV 60.11 Car-LGV-HGV 22.25 Car-HGV-HGV 32.80 Model Output - Vehicle Incident matrix
Consequence Mitigation Holmesdale Tunnel - Installed Systems
Mitigation Measures QRA Model Output set the performance constraints on to the choice of Fire & Life Safety Engineering Systems. Tunnel Incidents have three Key Areas where Consequence mitigation is addressed Early Incident Detection Incident Control Evacuation.
PASSIVE FIRE PROTECTION (PFP) Why PFP? To avoid structural collapse in the case of fire. To improve network resilience. To avoid an estimated economic impact of 1M/hour to UK Plc in the case of a tunnel closure. The performance is designed to withstand a 100 megawatt fire and prevent concrete failure for up to 2 hours.
FIRE MAIN Designed in consultation with Fire & Rescue Services. Ring main system. Runs through both bores with Fire Hydrants at each Emergency Distribution Panel (EDP). Delivers 25 Litres/sec at 4 Bar
EMERGENCY DISTRIBUTION PANELS At 50m intervals in each bore. Contain: Fire extinguishers (2 No 6kg AFFF) Fire hydrant Emergency Telephone Radio communication system Incident Detection System Control
SMOKE CONTROL PANELS 4 panels one at each portal. Enables HA Traffic Officers to take control of essential tunnel M&E with ERCC agreement. Controls: - Ventilation fans - Connecting bore doors - Lighting - Drainage system Contains: - Emergency telephone - Maintenance telephone
VENTILATION SYSTEM
VENTILATION SYSTEM Two Ventilation Buildings - One at each entry portal. 5 Fans in each Ventilation Building. Automatic operation with Manual intervention at Control centre. Manual control at Smoke Control Panels by an authorised HA Traffic Officer. Capable of controlling smoke from a 100MW fire.
PUBLIC ADDRESS SYSTEM (PA) 20 speakers per bore. Located every 50m. Made of fire retardant material. Plays up to six pre-recorded messages
CONNECTING BORE DOORS 3 off located every 100 m. Normally locked under operational conditions. When unlocked an Emergency Exit Sign is illuminated. Manual Operated individually or as a group by the Control Centre Emergency Telephone adjacent.
EMERGENCY WAY FINDING SIGNS Illuminated distance to exit signs installed at 50m intervals Each indicates the direction and distance to the portals. Additional signs installed either side of the connecting bore doors.
VIDEO AUTOMATIC INCIDENT DETECTION 12 fixed cameras per bore. Fixed in pairs at approx. 80m intervals. Fully automated system. Detects changes to normal conditions within the tunnel, e.g. - smoke - debris - pedestrians - animals - Vehicles travelling the wrong way - standing traffic. Monitored at Control Centre
CCTV 4 new low profile cameras per bore fixed at 140m intervals located on sill beam or soffit.
Environmental Monitoring System 3 groups of sensors per bore Located at approx. 220m intervals Measures levels of: NO CO Opacity / Visibility 2 Anemometers per bore Monitored at Control Centre
Conclusions Tunnel hazards are generic and identical to hazards on the Open road Probabilities of tunnel hazards are not dissimilar to those of the open road. Consequence of tunnel hazards are potentially far greater than those of the Open road. Consequences of tunnel hazards can result in large numbers of fatalities, loss of asset and long term network disruption. Mitigation measures for Hazards in tunnels should be Performance Based and not Prescriptive as no two tunnels have the same Risk Profile Risk Assessment tools are now available to assess consequences of tunnel hazards, this was developed for the Highways Agency on the M.25 tunnels by Mouchel Ltd following introduction of the EU Directive in 2004. These Risk tools allow the Designer/Stakeholder to choose appropriate mitigation measures for individual tunnel needs.