1、QC-06-024 Tunnel Emergency Egress and the Mid-Train Fire M.P. Colino, PE Member ASHRAE ABSTRACT This paper provides both a means for tailoring the current rail transportation tunnel emergency egress guidelines to the specifics of the individual system application and a strategy for improving the ove
2、ralljre-life safety of passengers and crew during a mid-train3re event. These dual objectives are accom- plishedvia the development ofan equation based upon the time required to complete the various activities associated with a train evacuation and subsequently rearranged to solve for the required d
3、istance intervals between successive tunnel egress elements. The paper then provides examples of how this equa- tion may be put to use for three hypothetical rail systems, as well as a correction for one of the examples as a result of a discussion on controlled evacuations. Finally, a parametric stu
4、dy is provided in order to evaluate the relative impact of changing certain variables within the equation. INTRODUCTION National Fire Protection Association VFPA) Standard 130, Fixed Guideway Transit and Passenger Rail Systems (NFPA 2003), includes guidelines for tunnel emer- gency egress provisions
5、. The 2003 edition of the standard denotes in paragraph 6.2.4.1 that “emergency exits shall be provided from tunnels to a point of safety” and in paragraph 6.2.4.2 that “within underground or enclosed trainways, the maximum distance between exits shall not exceed 2500 ft (762 m)” (NFPA 2003). The la
6、tter of these two statements is explained further in paragraph A.6.2.4.2 of the standard, which draws a parallel to NFPA Standard 101 (NFPA 2006) and its consideration of an affected, or unavailable, exit in speci%ing 2500 ft (762 m) as the maximum permissible travel distance between tunnel exits. H
7、owever, in paragraph E.B. Rosenstein 6.2.4.3.1, the 2003 edition of Standard 130 also states that “cross passageways shall be permitted to be used in lieu of emergency exit stairways to the surface where trainways in tunnels are divided by a minimum of 2 hour-rated fire walls or where trainways are
8、in twin bores” (NFPA 2003). Paragraph 6.2.4.3.2 of the standard goes on to provide seven conditions under which cross passageways may be utilized in lieu of emergency exit stairways; these conditions are noted below. 1. Cross passageways shall not be farther than 800 ft (244 m) apart. 2. Openings in
9、 open passageways shall be protected with fire door assemblies having a fire protection rating of 1-1/2 hours with a self-closing fire door. A noncontaminated environment shall be provided in that portion of the trainway that is not involved in an emergency and that is being used for evacuation. A v
10、entilation system for the contaminated tunnel shall be designed to control smoke in the vicinity of the passengers. An approved method shall be provided for evacuating passengers in the uncontaminated trainway. An approved method for protecting passengers from oncoming traffic shall be provided. An
11、approved method for evacuating the passengers to a nearby station or other emergency exit shall be provided. Figuring prominently among these conditions is the subject of the recommended distance between successive cross passageways. The 2003 edition of NFPA Standard 130 does not distinguish between
12、 the various types of fixed guide- way rail systems-Le., subway, commuter rail, or light rail- their associated train lengths, the number of persons aboard the trains, or the sizelgrowth rate of the design fire in recom- mending the 800 ft (244 m) interval. The 800 ft (244 m) guide- 3. 4. 5. 6. 7. _
13、 M.P. Colino is a senior supervising engineer and E.B. Rosenstein is a lead engineer of Parsons Brnckerhoff, Inc., New York, NY 02006 ASHRAE. 251 line also pre-dates the expanded application of Standard 130 from transit systems only (reference paragraph 3-2.4.3.aofthe 1997 edition NFPA 19971) to bot
14、h transit and passenger rail systems (reference paragraph 3-2.4.3.1 of the 2000 edition PFPA 20001). However, the stated purpose of NFPA Standard 130, as indicated in paragraph 1.2 of the 2003 edition as well as in previous editions, is to “establish minimum requirements” for fire-life safety within
15、 fixed guideway tunnel environments; therefore, the 800 ft (244 m) cross passageway spacing noted in paragraph 6.2.4.3.2( 1) should be interpreted as written-as a “not-to-exceed value for fixed guideway applications-and not as a constant design parameter to be uniformly applied to every conceivable
16、rail tunnel application. For specific rail tunnel systems, the individual parameters affecting emer- gency egress should be evaluated to determine whether they merit NFPA Standard 130s minimum fire-life safety provi- sions or whether more extensive considerations are needed. THE MID-TRAIN FIRE The p
17、rospect of a mid-train fire is one of the more trou- bling fire-life safety scenarios from the standpoints of both tunnel emergency egress and tunnel emergency ventilation. From the standpoint of egress, a mid-train fire can generally be classified as any event that tends to divide the incident pass
18、en- gercrew population into two distinct evacuation groups. If the incident area is presumed to coincide with the length of the affected train car, then any fire aboard all but the two end-cars would constitute a mid-train event. For an eight-car consist, a fire occurring aboard any of the middle si
19、x cars-or 75% of the train-would constitute a mid-train event; for a twelve-car consist, a fire occurring aboard any of the middle ten cars (see Figure 1)-or approximately 83% of the train-would be considered a mid-train event. If the incident area is presumed to be only a portion of the affected tr
20、ain car, then these percent- ages would increase for each example given. Rail tunnel emergency ventilation systems are typically designed based upon push-pull fan response modes for end- car events. The typical emergency ventilation system is capa- ble of developing the longitudinal tunnel air veloc
21、ity required to direct smoke flow away from the selected evacuation path and of preventing smoke from backlayering into that same path. These capabilities are consistent with the emergency ventilation system design characteristics recommended in the 2003 edition of NFPA Standard 130 for fixed guidew
22、ay transit and passenger rail systems (reference paragraphs 7.2.1 (1) and 7.2.1(2). However, in the case of the mid-train fire, two paths of passenger/crew evacuation are conceivable. And, while the typical emergency ventilation system would be capable of meeting the Standard 130 design guideline fo
23、r passengedcrew safety in either direction, it is usually not capable of simulta- neously meeting the Standard 130 design guideline forpassen- ger/crew safety in both directions-unless it is designed as a point-extract system, which it traditionally is not, due to space and cost considerations. (A p
24、oint-extract system would be theoretically capable of confining smoke flow to the incident car area and thus would permit immediate and simultaneous evacuations of both passengedcrew groups, in opposite direc- tions. See Figure 2.) Therefore, detailed consideration of the various mid-train fire scen
25、arios is warranted. The emergency ventilation system response to a mid-train fire must be coordinated with the evacuation plans of the End-Car Mid-train End-Car Figure 1 Mid-train cars for 12-car consist. , _1 Figure 2 Point-extract system for mid-train fire scenario, simultaneous evacuation of both
26、 passenger/crew groups. 252 ASHRAE Transactions passengerslcrew; the operation of the tunnel fans to preserve “tenable” (as defined by NFPA Standard 130, Annex B) condi- tions in one evacuation path must not further endanger the group of passengerslcrew on the opposite side of the fire. Assuming tha
27、t the mid-train fire renders the incident train car unpassable, one of three emergency evacuatiodventilation scenarios is likely+ach has its own specific benefits and drawbacks, and other scenarios are possible. (The purpose of discussing these scenarios is to provide insight into the dynamics of mi
28、d-train fire evacuations and the related venti- lation system operations.) If the fire is in its early stages of development and the tunnel conditions on both sides of the incident train are considered by the crew to be tenable, each of the two passengerlcrew groups may be directed to evacuate in op
29、posite directions. (See Figure 3.) In this scenario, the tunnel fans would not be activated during the simultaneous evacuations; only after one passenger groupmost likely the group with the shorter travel time-had reached a point of safety would fan operations be possible in support of the other pas
30、senger1 crew groups evacuation. Tunnel ingress by emergency service personnel should also be considered as part of the fan activation plan; ideally, emergency responders should enter the tunnel on the upstream side of the fire, i.e., the side where the fans are in supply mode. If the fire grows quic
31、kly and the tunnel conditions on one side of the incident train are considered to be untenable- due, for example, to a significant tunnel grade and buoy- ancy-driven smoke flow-then the passengerlcrew group on the opposite end of the incident train would be directed to evacuate first. In this scenar
32、io, the tunnel fans would not 3. be activated during the initial evacuation; the operation of the fans would pressurize the tunnel and might cause smoke flow into the occupied cars on the opposite end of the train. After the first passengerlcrew group had reached a point of safety, the fans could be
33、 operated in support of the second groups evacuation in the opposite direction. (See Figure 4.) Again, the ingress of emergency service personnel should be coordinated with the selected fan mode. If the fire grows quickly and the tunnel conditions on both sides of the incident train are considered b
34、y the crew to be untenable, then the evacuation of the two passengerlcrew groups could be conducted in sequence. In this scenario, the tunnel fans would be operated in support of both the initial evacuation-most likely by the group with the shorter travel time-and the latter evacuation. (See Figure
35、5.) Despite any residual air pressure within the cars, the oper- ation of the fans in support of the initial evacuation may cause smoke flow into the opposite end of the train, which at this time would still be occupied. Then, when the evacu- ation of the second passengerlcrew group is beginning in
36、the opposite direction, a timely flow reversal by the tunnel fan system would be required. The two most important aspects in each of these three mid-train fire scenarios are the manner in which the evacua- tions are organizedauthorized and the speed at which they occur. The first aspect is dependent
37、 upon the preparedness of the operating authority-the train crew, in particular-for such events and places added importance to the development of emergency procedures, personnel training, and incident communications. The second aspect is directly related to the number and proximity of emergency exit
38、s, cross passageways, Direction of evacuation +- - Direction of evacuation Figure 3 Mid-trainjre scenario #I, simultaneous evacuation of both passenger/crao groups. Direction of evacuation f- Direction f- ofairflow . Direction -+ of evacuation L c-1 L . 8 . ., . -.- c. .L c .I initial evacuation, Tu
39、nnel fans not activated. Figure 4 Mid-train fire scenario #2. ASHRAE Transactions Latter evacuation, Tunnel fans activated. 253 _+ Direction Direction f- of aidow of evacuation _j_ Direction Direction of evacuation of airflow f- initial evacuation, Tunnel fans activated. Figure 5 Mid-trainjre scenar
40、io #3. Direction of evacuation f- Latter evacuation, Tunnel fans activated. _+ Direction of evacuation Figure 6 Mid-train fire aligned with exit; fire location prevents use of nearest egress path. or other points of tunnel egress, i.e., station platforms or portals. These two aspects are also interc
41、onnected because any delay in organizing the evacuations will tend to increase the overall time needed to complete the evacuations, therefore exposing a greater number of evacuees to smoke flow. If the incident train happened to stop at a location where it straddled a means of tunnel egress, then a
42、timely evacuation of one passenger group via that emergency exitlcross passageway would tend to minimize human exposure to smoke during the mid-train fire event. However, if the inci- dent fire is sufficiently large, or if its location happened to directly coincide with that of an emergency exit or
43、cross passageway, then the fire may prevent use of that nearest means of egress. (See Figure 6.) In this case, the distance to the next available emergency exit or cross passageway would be an important consideration for both passengerlcrew evac- uation groups. In the context of this worst-case posi
44、tioning of traidfirelexit, an equation was developed for the dual purpose of tailoring NFPA Standard 130 tunnel egress guidelines to the individual rail system application and improving fire-life safety-the emergency egress provisions, in particuiar- during the mid-train fire event. The level of con
45、servatism associated with this worst-case event is appropriate for such static fire-life safety provisions as emergency exits andor cross passageways, since the numberllocation of each cannot be altered for specific events. EQUATIONS The basis for the equation developed was a simple compi- lation of
46、 the time-dependent activities associated with the evacuation of the first passengerlcrew group from a worst- case, mid-train fire event. In equation format, the summation of these activities was then set against the time associated with the initiation of the second passengerlcrew groups evacuation
47、in a sequenced emergency egress operation for a “true” mid- train event-i.e., at the exact mid-point of the consist. (See Equation 1 .) The evacuation of the second passengerlcrew group, which was presumed to start before the design fire reached a flashover state, would be supported by the operation
48、 of the tunnel emergency ventilation system. tdiscovety +- tcomms linitial evac i $ans active (1 1 - - tlatter evac $11 mode $ashover where - tdiscovety - tcomms - t. - initial evac - - vans active - latter evac - - - $idmode - tfashover - - the time associated with the discovery of the mid- train f
49、ire, min the time needed to communicate the details of the mid-train fire between the incident train and the operations control center and initiate the evacuation of the first passengerlcrew group, min the time needed to evacuate the first passenger1 crew group from the incident tunnel, min the run-up time of the tunnel fans preceding the evacuation of the second group, min the time at which the second passengerlcrew groups evacuation is commenced, min the time at which the tunnel fans reach full operational mode, min the time at which the mid-train fire r
