WHY PRESSURIZED EXITS FOR TRANSPORTATION TUNNELS MAY NOT MAKE SENSE

Kenneth J. Harris, Bob Melvin WSP | Parsons BrinckerhoffCalifornia, USAE-mail: harris@pbworld.com

INTRODUCTION Jurisdiction requirement Derives from building environment Tunnel ventilation Complex controls Tunnel vs. building environments

BASIS OF PRESSURIZED EXITS3

Protect building occupants. Smoke control Door opening forces Incident floor fire Egress to point of safety Pressure differential bounding constraints

Pressure Force

NFPA 101 87.5 pa (0.35 in. wc) 133 N (30 lbf)

Design range 12.5-25 pa (0.05-0.10 in. wc.) 19-38 N (4-8 lbf)

ROAD AND RAIL TUNNEL SMOKE CONTROL DESIGN4

Confined spaces Space smoke control Point of safety

Location exterior to facility OR Protected space

Tenable environment-permits self-rescue or survival Smoke control in the tunnel

ROAD AND RAIL TUNNEL SMOKE CONTROL DESIGN5

Longitudinal ventilation Upstream protection and tenable environment Prevention of backlayering

Pressure Force

NFPA 101 87.5 pa (0.35 in. wc) 133 N (30 lbf)

Design range 12.5-25 pa (0.05-0.10 in. wc.) 19-38 N (4-8 lbf)

NFPA 130 & 502 146 pa (0.58 in. wc.) 222 N (50 lbf)

Design range 125-375 pa (0.5-1.5 in. wc.) 190-570 N (43-129 lbf)

BUILDING SMOKE CONTROL 6

Complications in building smoke control Stack effect Stairwell pressurization Elevator pressurization Combined systems

Seasonal extremes

BUILDING SMOKE CONTROL DESIGN7

NFPA 92, Standard for Smoke Control Systems

Fstruc/Fbldg Door opening force (N)

Fr Residual force to overcome any door closer and friction (N)

Figure 1. Exit door arrangement.

(1)

(2)

BUILDING SMOKE CONTROL DESIGN8

Figure 2. Stairwell pressurization.

TUNNEL SMOKE CONTROL AND EGRESS DESIGN 9

Figure 3. Longitudinal ventilation

Figure 4. Extraction ventilation

TUNNEL EGRESS PRESSURIZATION REQUIREMENTS10

(3)

(4)

(5)

(6)

(7)

POSITIVE AND NEGATIVE TUNNEL PRESSURE BOUNDS11

Positive tunnel pressure 203kPa (0.815 in.

wc.)

Negative tunnel pressure-215 Pa (-0.863 in.

wc.).

(8)

(9)

TUNNEL VENTILATION SMOKE CONTROL12

Figure 5. Longitudinal ventilation in a transit tunnel.

DISCUSSION 13

Code and Standard requirements Exit path

Buildings. Protecting exit path from the incident area. Tunnels. The exit path is protected by the tunnel ventilation system.

Door opening force Buildings. Pressures necessary to control smoke result in low door opening

forces. Tunnels. Pressure necessary to control smoke result in high door opening forces. Tunnels. Controls necessary for flow and pressure make systems complex.

SUMMARY 14

Requirements for pressurized exits derive from building industry. Barrier separation Common exit path and its protection from incident space

Tunnels have no occupancy barriers Ventilation system control smoke spread in incident space. Proposed systems have higher door opening forces Proposed systems are more complex and may not work as intended.

By understanding how tunnel smoke control systems work, resources can be focused on measures that provide real benefit.