Feasibility study

Feasibility study A smoke extraction system for FCC S. La Mendola DGS/SEE A. Henriques DGS/SEE

Smoke propagation in case of longitudinal ventilation Advantages for 100 % longitudinal ventilation system, with respect to Safety • Provides fresh air for occupants during access Disadvantages for 100 % longitudinal ventilation system: • Propagation and contamination of smoke to others volumes of the tunnel, • Even if the ventilation is stopped , the smoke still propagates S. La Mendola DGS/SEE A. Henriques DGS/SEE

Smoke propagation in case of longitudinal ventilation 5 MW 1 MW 500 kW 100 kW 50 kW From the presentation by F. Corsanego EDMS 1236477 ver. 1 10 kW See also the presentation «A simplified model for tunnel fire dynamics predictions» by S. La Mendola EDMS 1278776 The back layering length (Lb) is limited to a few tens of meters upstream the fire at worst Fr = Froude number: ratio between flow inertia and buoyancy Forced ventilation Lb Ventilation ON – 1.2 m/s u H Stratification Mixing Region I Fr ≤ 0.9 Region III Fr > 10 Region II 0.9 ≤ Fr ≤ 10 S. La Mendola DGS/SEE A. Henriques DGS/SEE

Smoke propagation in case of ventilation stop 4 m2 petrol pool fire (about 10 MW), The handbook of tunnel fire safety From the presentation by F. Corsanego EDMS 1236477 ver. 1 5 MW 1 MW 500 kW 100 kW 50 kW 10 kW Fire origin 1 MW Fire 300 m Smoke propagates along 300 m in both directions after about 12 minutes in a tunnel with a 6 m diameter S. La Mendola DGS/SEE A. Henriques DGS/SEE

Smoke propagation in case of transverse ventilation Advantages for 100 % transverse ventilation system, with respect to Safety • Limit the propagation and contamination of smoke to others volumes of the tunnel • Provide dynamic confinement localized near the fire Disadvantages for 100 % transverse ventilation system: • Large ducts are needed  occupy ~50 % of the tunnel volume • Tunneling costs S. La Mendola DGS/SEE A. Henriques DGS/SEE

Smoke propagation in case of transverse ventilation Vitiated air exhaust duct Fresh air supply duct Fresh air supply duct Vitiated air exhaust duct Normal operations Fire conditions Smoke extraction solution proposed for CLIC, CLIC Conceptual Design Report – Geneva 2012 S. La Mendola DGS/SEE A. Henriques DGS/SEE

A proposal for a “Hybrid” smoke extraction system • Longitudinal Ventilation for normal operations • Provide the requirements for occupational health – Fresh air, temperature, humidify • Dedicated smoke extraction system • Limit propagation and contamination of smoke to others volumes of the tunnel • Provide the dynamic confinement • Reduce the cross section of the smoke extraction ducts. S. La Mendola DGS/SEE A. Henriques DGS/SEE

Proposal - Dedicated extraction system • Example of a section of the FCC tunnel: • Nominal conditions Shaft Dedicated smoke extractor Dedicated smoke extraction duct Smoke control dampers … Fresh air Tunnel S. La Mendola DGS/SEE A. Henriques DGS/SEE

Proposal - Dedicated extraction system • Example of a section of the FCC tunnel: • Accidental scenario – e.g. Fire • Longitudinal ventilation is stopped • Smoke extraction is ON Dynamic Confinement … Length of Smoke Compartment S. La Mendola DGS/SEE A. Henriques DGS/SEE

Proposal - Dedicated extraction system • Fire Detection system : • Shall be able to identify the fire location within a certain length, to ensure that the dampers open in the correct location … Length of Smoke Compartment S. La Mendola DGS/SEE A. Henriques DGS/SEE

Feasibility Assessment • First approximation for extraction flow rate: 1 m3/s/100 m2 French “Code du travail ” • Velocity in the extraction duct of 10 m/s S. La Mendola DGS/SEE A. Henriques DGS/SEE

Pressure Drop • Linear pressure drop only, assuming maximum duct length of 8 km • , where Q is the volume flow rate. Zoom S. La Mendola DGS/SEE A. Henriques DGS/SEE

Evaluation of smoke volume production - Mathcad model See “An introduction to fire dynamics”, D. Drysdale Smoke extraction flow rate = 11 m3/s for a tunnel diameter of 6 m and 8 m3/s for a diameter of 4.5 m. That gives a smoke compartment length of about 200 m taking into account the flow rate requirement from the code du travail (1 m3/s/100m2) S. La Mendola DGS/SEE A. Henriques DGS/SEE

Fire Dynamics Simulation (FDS) model Fire Dynamics Simulator (FDS), developed by the National Institute of Standards and Technology (NIST) of the United States Department of Commerce, is a computational fluid dynamics (CFD) model of fire-driven fluid flow. The software solves numerically a large eddy simulation form of the Navier-Stokes equations appropriate for low-speed, thermally-driven flow, with an emphasis on smoke and heat transport from fires. Virtual measurement stations (temperature, velocity, concentration of species, etc.) Up to 1’372’800 cells 200 m to 600 m No longitudinal ventilation Open ends boundary conditions, 4 smoke extraction dampers Constant power 1 MW fire @ 100 m F = 6 m S. La Mendola DGS/SEE A. Henriques DGS/SEE

Preliminary simulations 25 m 50 m 50 m 50 m 25 m Open boundary condition Open boundary condition Q/4 Q/4 Q/4 Q/4 No longitudinal ventilation Constant 1 MW fire S. La Mendola DGS/SEE A. Henriques DGS/SEE

Preliminary simulations results: the problem of extraction efficiency 12 m3/s Smoke propagates outside the smoke compartment 24 m3/s Smoke confined 36 m3/s (!) Left tunnel opening Smoke extraction station Smoke extraction station Fire location For a smoke extraction flow rate up to 24 m3/s, smoke propagates beyond the smoke compartment. A flow rate of 36 m3/swould be necessary to confine smoke in this configuration (extraction efficiency between 1/2 and 1/3). In this configuration (36 m3/s ), the smoke extraction duct would be too big (φ ≈ 3 m) and that would reduce greatly the utility of the proposed system. Smoke curtains are proposed to keep the extraction flow rate at a feasible value (12 m3/s). S. La Mendola DGS/SEE A. Henriques DGS/SEE

Smoke curtains (EN 12101-1): a possible solution Pictures taken from the paper “Flexible Devices for smoke control in road tunnels”, M. Bettelini et Al, AMBERG Engineering S. La Mendola DGS/SEE A. Henriques DGS/SEE

Smoke curtains (EN 12101-1): a possible solution Roller smoke curtain EN 12101-1 Fixed smoke curtain Fire resistance test EN 12101-1 S. La Mendola DGS/SEE A. Henriques DGS/SEE

Similar solution used for the ESS S. La Mendola DGS/SEE A. Henriques DGS/SEE

Smoke curtains: a possible solution Modeled smoke curtain. Height from floor of design smoke layer = 2 m Smoke curtain H - h = 3 m H = 5 m h = 2 m Full confinement within the 200 m compartment for a 1 MW fire and 12 m3/s Full confinement within the 200 m compartment for a 2 MW fire and 12 m3/s Partial confinement within the 200 m compartment for a 5 MW fire and 12 m3/s This system provides a good smoke confinement also in off-design conditions S. La Mendola DGS/SEE A. Henriques DGS/SEE

Smoke extraction duct – cross section to scale Considering: Extraction duct Ø 1.2 m • Extraction flow rate of 12 m3/s; • Velocity in duct of 10 m/s; • Linear pressure drop of ≈ 6 kPa; • Smoke compartment length of 200 m Provides an extraction duct of 1.2 m S. La Mendola DGS/SEE A. Henriques DGS/SEE

Smoke extraction duct – smoke curtains layout Fixed curtain Roller curtain S. La Mendola DGS/SEE A. Henriques DGS/SEE

Future activities • Quantitative design optimization (n. of smoke extraction dampers, dimensions, distance, n. and dimension of smoke screens, etc.) with respect to soot propagation. • System virtual test w.r.t to different “real” fires: electrical cabinet, cable trays (different length and height), etc. • Take into account the delay of the fire detection system and the inertia of the ventilation system. • Study on the compatibility of the smoke extraction system with a cryogenic release. S. La Mendola DGS/SEE A. Henriques DGS/SEE

Feasibility study