The document discusses why pressurized exits used in buildings may not be suitable for transportation tunnels. In buildings, pressurized exits are used to protect the exit path from smoke in the event of a fire by acting as a barrier. However, tunnels do not have the same compartmentalization as buildings. Instead, tunnel ventilation systems are designed to control smoke spread. Applying the high pressures needed to pressurize tunnel exits could result in door opening forces that are too strong. Such pressurized exit systems in tunnels may also be complex and may not function as intended. It is better to understand how tunnel smoke control systems work and focus on measures that provide real safety benefits.

1. WHY PRESSURIZED EXITS FOR
TRANSPORTATION TUNNELS
MAY NOT MAKE SENSE
Kenneth J. Harris, Bob Melvin
WSP | Parsons Brinckerhoff
California, USA
E-mail: harris@pbworld.com

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

3. BASIS OF PRESSURIZED EXITS
3
 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)

4. ROAD AND RAIL TUNNEL SMOKE CONTROL DESIGN
4
 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

5. ROAD AND RAIL TUNNEL SMOKE CONTROL DESIGN
5
 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)

6. BUILDING SMOKE CONTROL
6
 Complications in building smoke control
 Stack effect
 Stairwell pressurization
 Elevator pressurization
 Combined systems
 Seasonal extremes

7. BUILDING SMOKE CONTROL DESIGN
7
 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)

8. BUILDING SMOKE CONTROL DESIGN
8
Figure 2. Stairwell pressurization.

9. TUNNEL SMOKE CONTROL AND EGRESS DESIGN
9
Figure 3. Longitudinal ventilation
Figure 4. Extraction ventilation

10. TUNNEL EGRESS PRESSURIZATION REQUIREMENTS
10
(3)
(4)
(5)
(6)
(7)

11. POSITIVE AND NEGATIVE TUNNEL PRESSURE BOUNDS
11
 Positive tunnel pressure
203kPa (0.815 in. wc.)
 Negative tunnel pressure
-215 Pa (-0.863 in. wc.).
(8)
(9)

12. TUNNEL VENTILATION SMOKE CONTROL
12
Figure 5. Longitudinal ventilation in a
transit tunnel.

13. 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.

14. 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.