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Tunnel emergency egress and the mid-train fire.

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 overall fire-life safety of passengers and crew during a mid-train fire event. These dual objectives are accomplished via the development of an equation based upon the time required to complete the various activities associated with a train evacuation and subsequently rearranged to solve for the required distance intervals between successive tunnel egress elements. The paper then provides examples of how this equation 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 study is provided in order to evaluate the relative impact of changing certain variables within the equation.

INTRODUCTION

National Fire Protection Association (NFPA) Standard 130, Fixed Guideway Transit and Passenger Rail Systems (NFPA 2003), includes guidelines for tunnel emergency egress provisions. 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 latter 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 specifying 2500 ft (762 m) as the maximum permissible travel distance between tunnel exits. However, in paragraph 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 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 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.

3. 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.

4. A ventilation system for the contaminated tunnel shall be designed to control smoke in the vicinity of the passengers.

5. An approved method shall be provided for evacuating passengers in the uncontaminated trainway.

6. An approved method for protecting passengers from oncoming traffic shall be provided.

7. An 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 the various types of fixed guide-way rail systems--i.e., subway, commuter rail, or light rail--their associated train lengths, the number of persons aboard the trains, or the size/growth rate of the design fire in recommending the 800 ft (244 m) interval. The 800 ft (244 m) guide-line also pre-dates the expanded application of Standard 130 from transit systems only (reference paragraph 3-2.4.3.a of the 1997 edition [NFPA 1997]) to both transit and passenger rail systems (reference paragraph 3-2.4.3.1 of the 2000 edition [NFPA 2000]).

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 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 rail tunnel application. For specific rail tunnel systems, the individual parameters affecting emergency egress should be evaluated to determine whether they merit NFPA Standard 130's minimum fire-life safety provisions or whether more extensive considerations are needed.

THE MID-TRAIN FIRE

The prospect of a mid-train fire is one of the more troubling 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 passenger/crew 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 six 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 train car, then these percentages would increase for each example given.

[FIGURE 1 OMITTED]

[FIGURE 2 OMITTED]

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 capable of developing the longitudinal tunnel air velocity 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 guideway 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 for passenger/crew safety in either direction, it is usually not capable of simultaneously meeting the Standard 130 design guideline for passenger/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 point-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 passenger/crew groups, in opposite directions. See Figure 2.) Therefore, detailed consideration of the various mid-train fire scenarios is warranted.

The emergency ventilation system response to a mid-train fire must be coordinated with the evacuation plans of the evacuation of both passenger/crew groups. passengers/crew; the operation of the tunnel fans to preserve "tenable" (as defined by NFPA Standard 130, Annex B) conditions in one evacuation path must not further endanger the group of passengers/crew on the opposite side of the fire. Assuming that the mid-train fire renders the incident train car unpassable, one of three emergency evacuation/ventilation scenarios is likely--each 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 mid-train fire evacuations and the related ventilation system operations.)

1. 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 passenger/crew groups may be directed to evacuate in opposite directions. (See Figure 3.) In this scenario, the tunnel fans would not be activated during the simultaneous evacuations; only after one passenger group--most likely the group with the shorter travel time--had reached a point of safety would fan operations be possible in support of the other passenger/crew group's 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.

2. If the fire grows quickly 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 buoyancy-driven smoke flow--then the passenger/crew group on the opposite end of the incident train would be directed to evacuate first. In this scenario, the tunnel fans would not 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 passenger/crew group had reached a point of safety, the fans could be operated in support of the second group's evacuation in the opposite direction. (See Figure 4.) Again, the ingress of emergency

service personnel should be coordinated with the selected fan mode.

[FIGURE 3 OMITTED]

[FIGURE 4 OMITTED]

3. If the fire grows quickly and the tunnel conditions on both sides of the incident train are considered by the crew to be untenable, then the evacuation of the two passenger/crew 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 5.) Despite any residual air pressure within the cars, the operation 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 evacuation of the second passenger/crew group is beginning in 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 evacuations are organized/authorized and the speed at which they occur. The first aspect is dependent 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 exits, cross passageways, or other points of tunnel egress, i.e., station platforms or portals. These two aspects are also interconnected 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.

[FIGURE 5 OMITTED]

[FIGURE 6 OMITTED]

If the incident train happened to stop at a location where it straddled a means of tunnel egress, then a timely evacuation of one passenger group via that emergency exit/cross passageway would tend to minimize human exposure to smoke during the mid-train fire event. However, if the incident fire is sufficiently large, or if its location happened to directly coincide with that of an emergency exit or 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 passenger/crew evacuation groups. In the context of this worst-case positioning of train/fire/exit, 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 particular--during the mid-train fire event. The level of conservatism associated with this worst-case event is appropriate for such static fire-life safety provisions as emergency exits and/or cross passageways, since the number/location of each cannot be altered for specific events.

EQUATIONS

The basis for the equation developed was a simple compilation of the time-dependent activities associated with the evacuation of the first passenger/crew 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 passenger/crew group's evacuation 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 passenger/crew group, which was presumed to start before the design fire reached a flashover state, would be supported by the operation of the tunnel emergency ventilation system.

[t.sub.discovery] + [t.sub.comms] + [t.sub.initial evac] + [t.sub.fans active] = [t.sub.latter evac] [greater than or equal to] [t.sub.full mode] [greater than or equal to] [t.sub.flashover] (1)

where

[t.sub.discovery] = the time associated with the discovery of the mid-train fire, min

[t.sub.comms] = 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 passenger/crew group, min

[t.sub.initial evac] = the time needed to evacuate the first passenger/crew group from the incident tunnel, min

[t.sub.fans active] = the run-up time of the tunnel fans preceding the evacuation of the second group, min

[t.sub.latter evac] = the time at which the second passenger/crew group's evacuation is commenced, min

[t.sub.full mode] = the time at which the tunnel fans reach full operational mode, min

[t.sub.flashover] = the time at which the mid-train fire reaches flashover, min

The first two terms in Equation 1, [t.sub.discovery] and [t.sub.comms], are elapsed-time entries that may be either determined via training exercises or estimated for the individual rail system application based upon such factors as train length, crew size, vehicle fire alarm/extinguishing provisions, personnel emergency procedures, etc. (The identification of the incident train car location is essential to the recognition of a mid-train fire event. For best emergency response planning, the location of the incident train car should also be quickly determinable, either locally or remotely, versus both the nearby tunnel egress provisions and the closest mechanical ventilation shafts.)

The time required to safely evacuate the first passenger/crew group, [t.sub.initial evac], can be estimated through the use of three additional terms: (1) the time required for the first evacuee in the group to reach the most constricting element in the evacuation path, or [t.sub.first evacuee]; (2) the time required for the entire group of evacuees to pass through the most constricting element in the evacuation path, or [t.sub.constrict element]; and (3) the time required for the last evacuee in the group to travel from the most constricting element in the evacuation path to a point of safe refuge, or [t.sub.last evacuee]. (Refer to Equation 2.)

[t.sub.initial evac] = [t.sub.first evacuee] + [t.sub.constrict element] + [t.sub.last evacuee] (2)

The time required for the first evacuee in the group to reach the most constricting element in the evacuation path can be computed by dividing the distance traveled, [D.sub.fe], by the speed of travel, V, or [D.sub.fe]/V. If the most constricting element in the evacuation path is either the vehicle door or the bench walkway, then the length of travel for the first evacuee to reach this element, and consequently the term [D.sub.fe]/V, will have a relatively minor impact upon the equation.

Then, the time required for the entire group of evacuees to pass through the most constricting element in the evacuation path can be computed by dividing the incident train's evacuee population, [P.sub.t], by the product of the egress flow capacity through the most constricting element, Q, and the usable width, [w.sub.c], of the element, or [P.sub.t]/(Q[w.sub.c]). For the true mid-train event, however, the initial evacuee population would consist of one-half of the train's passenger/crew load, or [P.sub.t]/2. An additional, nondimensional parameter, y, can be included in the denominator of this term to reflect the number of active egress elements during the initial evacuation; therefore, the final form of this term in the equation is [P.sub.t] /(2Q[w.sub.c]y).

Finally, the time required for the last evacuee in the group to travel from the most constricting element in the evacuation path to a point of safe refuge would then be the distance of travel, [D.sub.le], divided by the speed of travel, V, or [D.sub.le]/V. In order to relate this term to the proper spacing of tunnel egress elements, the parameter [D.sub.le] can be represented by the distance that must be traveled to reach a tunnel egress element, [D.sub.l], minus one-half of the train length, [L.sub.t] /2, divided by the number of active egress elements, y, or [D.sub.le] = [D.sub.l] - ([L.sub.t]/2y). However, in order to accurately reflect the distance to each available egress element during the initial evacuation, the term [D.sub.l] can be represented by the product of the number of active egress elements during the initial evacuation, y, and the required distance between the successive egress elements, [D.sub.x]. Therefore, the final form of this term in the equation is (y[D.sub.x] - ([L.sub.t]/2y))/V, and the rewritten form of Equation 2 is then

[t.sub.initial evac] = [D.sub.fe]/V + [P.sub.t]/(2Q[w.sub.c]y) + (y[D.sub.x] - ([L.sub.t]/2y))/V. (3)

Inserting the expanded form of [t.sub.initial evac] back into Equation 1 yields

[t.sub.discovery] + [t.sub.comms] + [D.sub.fe]/V + [P.sub.t]/(2Q[w.sub.c]y) + (y[D.sub.x] - ([L.sub.t]/2y))/V + [t.sub.fans active] = [t.sub.latter evac] [greater than or equal to] [t.sub.full mode] [greater than or equal to] [t.sub.flashover]. (4)

As for the remaining term on the left-hand side of Equation 4, the elapsed-time entry [t.sub.fans active] was included to reflect the presumption that the evacuation of the second passenger/crew group would occur under the smoke-flow protection of the emergency ventilation system and that the tunnel fans would have a run-up time before reaching full mode capability. According to paragraph 7.2.1(3) of the 2003 edition of NFPA Standard 130, "the emergency ventilation system shall be designed to ... be capable of reaching full operational mode within 180 seconds." The impact of this term on the overall computation, however, can be minimized if the tunnel fan system is activated in advance of commencing the second passenger/crew group's evacuation. However, activating the tunnel fan system prior to the completion of the first group's evacuation will expose some of those evacuees to smoke flow, which, at this point, may be diluted due to the impact of the tunnel fan operations.

It is presumed that the commencement of the second passenger/crew group's evacuation, [t.sub.latter evac], does not exceed the time at which the tunnel fans reach full operational mode capability, [t.sub.full mode], and that full-mode tunnel fan operations precede the point when the mid-train fire reaches its flashover condition, [t.sub.flashover], the point at which all combustible materials within the affected train car are presumed to be engaged in the fire. Typical fire size data for selected rail vehicles is provided in chapter 13 of ASHRAE Handbook-HVAC Applications under the heading "Rapid Transit" and the subheading "Emergency Ventilation" (ASHRAE 2003). Fire growth rate data are both incident- and vehicle-specific; consequently, they are not provided in the Handbook.

Reconfiguring Equation 4 to solve for the desired variable, [D.sub.x], the required distance between successive tunnel egress elements, yields

[D.sub.x] = [V x ([t.sub.latter evac] - ([t.sub.discovery] + [t.sub.comms] + [D.sub.fe]/V + [P.sub.t]/(2Q[w.sub.c]y) + [t.sub.fans active])) + ([L.sub.t]/2y)]/y, (5)

where the definitions provided for Equation 1 apply, and

[D.sub.x] = the required distance between successive tunnel egress elements, ft (m) (see Figure 7);

V = the speed of travel, ft/min [fpm] (m/min);

[D.sub.fe] = the distance traveled by the first evacuee in the group to reach the most constricting element in the path of evacuation, ft (m);

[FIGURE 7 OMITTED]

[P.sub.t] = the total number of passengers/crew aboard the incident train, persons;

Q = the egress flow capacity through the most constricting element in the path of evacuation, persons/in.-min [pim] (persons/mm x min);

[w.sub.c] = the usable width of the most constricting element in the path of evacuation, in. (mm);

y = the number of active egress elements during the initial evacuation, nondimensional; and

[L.sub.t] = the total length of the incident train, ft (m).

ANALYSES

Of all the variables shown in Equation 5, only Q, the egress flow capacity, and V, the egress travel speed, are not application-specific and can thus be standardized.

Chapter 5 of the 2003 edition of NFPA Standard 130 provides factors for use in computing emergency egress times. Though specifically intended for station egress planning, the Standard 130 factors may provide insight toward estimating passenger evacuation rates from tunnels. Among these factors are an egress flow capacity of 2.27 pim (0.0893 p/mm x min) and an egress travel speed of 200 fpm (61 m/min) on platforms, corridors, and ramps sloped at less than 4%. These general factors, which were subsequently adjusted by NFPA 130 Committee via Technical Interim Amendment in October 2004, may be considered reflective of timely/orderly station evacuations in that they do not specifically address slower-moving persons, such as children, the elderly, mobility-disadvantaged/handicapped individuals, or those injured during the event--each of whom may reduce the overall egress flow capacity or travel speed of the evacuation group. Computer modeling may be used to provide more realistic predictions of passenger egress flow capacity and travel speed in tunnels.

Since these factors are specifically intended for station planning in the 2003 edition of NFPA Standard 130, they should be considered non-ideal for tunnel evacuation analyses. For example, paragraph 5.5.3.3.1.1 of the standard recommends that egress paths should be a minimum of 5 ft 8 in (1.73 m) wide, and paragraph 5.5.3.3.1.2 recommends that when computing capacity is available, 1 ft (0.3048 m) should be deducted from each side wall and 1 ft 6 in (0.4572 m) from each platform edge. A traditional 30 in. (762 mm) wide tunnel bench walkway is significantly smaller than the minimum egress path width recommended in paragraph 5.5.3.3.1.1 and provides no usable width for egress flow capacity calculations when evaluated against the recommendations of paragraph 5.5.3.3.1.2. It should be recognized that in order to achieve a usable walkway width of 30 in. (762 mm), a 60 in. (1524 mm) wide tunnel bench would be required. Nevertheless, in the absence of other specific flow capacity or travel speed data for tunnel egress applications, Q will be assumed as 2.27 pim (0.0893 p/mm x min) and V will be taken as 200 fpm (61 m/min) in the following analyses.

The balance of the data required by Equation 5 was selected for three distinct rail system classifications: commuter rail, subway, and light rail. The data entries selected were purely hypothetical and not intentionally representative of any particular fixed guideway tunnel system.

Train Data Inputs

The train data entries associated with Equation 5 include the train length, [L.sub.t]; the passenger/crew load, [P.sub.t]; the distance to the most constricting element in the evacuation path, [D.sub.fe]; and the time for the fire to reach flashover, [t.sub.flashover]. In the analyses that follow, these data entries were arbitrarily selected for each hypothetical rail system application and were not intended to represent either any particular fixed guideway system or an average of several. The entries were, however, selected in a manner that attempted to address the comparative differences between the three rail system classifications. For example, the variations in the train length and passenger/crew load entries were based on the assumptions that the commuter rail system would have the longest train for the largest passenger/crew load and that the light-rail system would have the shortest train for the smallest passenger/crew load. The related subway system entries fall between the commuter and light-rail system entries.

It was also assumed that each of the respective commuter rail, subway, and light-rail trains had side doors for easy access to the tunnel bench walkway and that these double-width doors were wider than the tunnel bench walkway, which made the walkway the more constricting element in the path of evacuation. The tunnel bench walkway was, in fact, assumed to be the narrowest, most constricting passage within the entire evacuation path. Therefore, the distance traveled by the first evacuee in the group to reach the most constricting element was approximated as the distance from the centerline of the train car to the centerline of the bench walkway. These entries were varied for the individual rail system applications based upon hypothetical train widths, where the commuter rail system was presumed to have the widest train, the light-rail system the narrowest, and the subway system midway between these two.

For the fire flashover time, a distinction was made in terms of the actual location of the fire. An assumption was made that the commuter rail train experienced a coach fire, whose close proximity to the majority of combustible components aboard the train resulted in a relatively short time to reach flashover. Conversely, both the subway and light-rail system trains were presumed to have undercarriage fires, where the growth/spread of the fire to the combustible components within the coach area, which enable it to reach its flashover state, was delayed by fire-rated vehicle flooring. In all three cases, it was assumed that the mid-train fire either directly or indirectly caused the incident train to stop within the tunnel and was serious enough to necessitate an evacuation. It is important to note that the time required for the fire to reach flashover is not an active variable within Equation 5; [t.sub.flashover] serves only as a limiting factor on the time available to both complete the evacuation of the initial passenger/crew group and at least commence the evacuation of the second passenger/crew group. The evacuation of the second group is also presumed to occur under the protection of an active tunnel emergency ventilation system.

Elapsed-Time Entries

The elapsed-time data entries in Equation 5 include the time related to the fire discovery, [t.sub.discovery]; the time needed for pre-evacuation communications, [t.sub.comms]; and the time associated with the activation of the tunnel fan system, [t.sub.fans active]. With the exception of the fan activation time, which has the aforementioned limiting factor of 180 seconds via NFPA Standard 130, paragraph 7.2.1(3), these entries are entirely specific to the individual rail system application. For the sake of variation in the analyses, these hypothetical data entries were varied in accordance with the following assumptions.

It was assumed that the commuter rail system conductor's greater mobility--i.e., for ticket-checking activities, etc.--would lend itself to a more timely fire discovery than in a subway system. Furthermore, a light-rail system may be automated, which may lend itself to the least timely fire discovery. It was also presumed that subway systems, due to their longer association with the guidelines of NFPA Standard 130, would have more efficient emergency communications than either the commuter rail or light-rail systems. Finally, in recognition of its greater passenger/crew load, it was assumed that the commuter rail system would activate the tunnel fan system earlier than either the subway or the light-rail systems. However, as previously noted, activating the tunnel fan system prior to the completion of the first passenger/crew group's evacuation may expose some of those evacuees to hazardous smoke flow.

The time selected for the commencement of the second passenger/crew group's evacuation in each individual rail system application was based upon the limitations identified in Equation 4, where [t.sub.latter evac] was to precede both the time at which the tunnel fans reached full mode operation, [t.sub.full mode], and the time at which the fire reached its flashover state, [t.sub.flashover]. Beyond that, it should also be recognized that the mid-train fire is burning from time = 0 seconds in these scenarios/analyses and that [t.sub.flashover] should not be considered a grace period for completing all decision-making, communications, emergency systems response planning, and personnel evacuations. From the moment the mid-train fire begins, the incident passengers/crew are in danger; therefore, the variable [t.sub.latter evac] should be set as low as deemed practical.

Results

The results of six particular calculations are presented in Table 1. Unless otherwise indicated, Equation 5 was solved for the required distance between successive tunnel egress elements, [D.sub.x]. "Commuter Calc #1" presents the results of an analysis for a hypothetical commuter rail system application; "Commuter Calc #2" demonstrates the impact of adding a second active egress element during the initial passenger/crew evacuation. "Subway Calc #1" presents the results of an analysis for a hypothetical subway system application; "Subway Calc #2" provides the result of back-calculating [t.sub.latter evac] using the Standard 130-recommended guideline (NFPA 2003) for cross passageway spacing, 800 ft (244 m), as an input for [D.sub.x]. "Light-Rail Calc #1" presents the results of an analysis for a hypothetical light-rail system application; "Light-Rail Calc #2" provides the result of back-calculating [t.sub.latter evac] using the Standard 130-recommended guideline for cross passageway spacing, 800 ft (244 m), as an input for [D.sub.x].

DISCUSSION

The focal point of the analyses presented in Table 1 is the computed distance between successive tunnel egress elements, [D.sub.x]. The value of this term was determined using Equation 5 for the analyses Commuter Calc #1, Commuter Calc #2, Subway Calc #1, and Light-Rail Calc #1. In the remaining two analyses, Subway Calc #2 and Light-Rail Calc #2, [D.sub.x] was assumed to be 800 ft (244 m) for the sake of comparison with the guidelines in the 2003 edition of NFPA Standard 130. Each of the respective rail system analyses is discussed in the following paragraphs.

Upon inspection of the results for Commuter Calc #1, it is evident that a negative value was produced for the distance between successive tunnel egress elements, [D.sub.x] = -58.64 ft (-17.9 m). This result simply means that the combination of train data, elapsed time entries, and passenger flow capacity/travel speed inputs to Equation 5 exceeded the time limit imposed on the analysis via the data input for [t.sub.latter evac] and [t.sub.flashover]. Comparing the inputs to Commuter Calc #1 with those of the subway and light-rail calculations, it is also evident that the summation of the elapsed time entries, [t.sub.discovery], [t.sub.comms], and [t.sub.fans active], were smallest, and that the usable width of the tunnel bench walkway was greatest for the commuter rail calculation. Therefore, the factors that contributed to this negative result were mainly the number of passengers/crew involved in the initial evacuation and the growth rate of the mid-train fire. The results of Commuter Calc #1 were included in Table 1 to make a distinct point: that a single means of tunnel egress may not be sufficient for evacuation of the first passenger/crew group based upon the combination of inputs to Equation 5.

[FIGURE 8 OMITTED]

Hence, the variable y in Equation 5 was utilized in Commuter Calc #2 to introduce a second means of tunnel egress during the first passenger/crew group's evacuation. This improvement generated the desired positive result for the distance between successive tunnel egress elements, [D.sub.x] = 408.84 ft (124.6 m)--but with the caveat that an equal number of evacuees were presumed to flow through each active exit (see Figure 8). The significance of this result is that the specific combination of train data, elapsed time entries, and passenger flow capacity/travel speed inputs to Equation 5 for the commuter rail analysis generated an interval between successive egress elements that was roughly one-half the maximum distance recommended by NFPA Standard 130. This is not to say that all commuter rail applications will require twice the number of tunnel egress elements as that recommended in the 2003 edition of the standard, but it does signify that certain combinations of rail system data may necessitate greater tunnel egress provisions than those cited by the standard in order to safely evacuate passengers/crew during a mid-train fire event.

The results of Subway Calc #1 indicate what the distance between successive tunnel egress elements, [D.sub.x] = 613.41 ft (187.0 m), would be for a different combination of Equation 5 inputs (see Figure 9). Despite greater elapsed time for both fire discovery and fan activation and the selection of a narrower tunnel bench width, the subway analysis generated greater spacing between tunnel egress elements than did the commuter rail analyses. This was largely attributed to the reduced number of passengers/crew, [P.sub.t], involved in the subway train evacuation and the greater time input for [t.sub.latter evac]. In the case of the latter variable, 12.5 min was randomly selected as the time to commence the evacuation of the second passenger/crew group, even though the mid-train fire did not reach flashover until 30 min had elapsed. This relatively conservative selection of [t.sub.latter evac] data reflects the fact that the mid-train fire is growing from time = 0 seconds.

Subway Calc #2 was completed to check the results of Subway Calc #1 against the 2003 NFPA Standard 130 guidelines for tunnel cross-passageway spacing. To do this, Equation 5 was re-arranged to solve for [t.sub.latter evac], while [D.sub.x] was taken to be 800 ft (244 m). The predictable result was that [t.sub.latter evac] increased by slightly less than a minute to account for the additional 186.59 ft (57.0 m) of tunnel bench travel at 200 fpm (61 m/min). The decision as to whether faster (12.5 min vs. 13.4 min via reduced egress element spacing) initial evacuations are warranted would ultimately rest with the authority having jurisdiction (AHJ) for the individual subway system.

[FIGURE 9 OMITTED]

[FIGURE 10 OMITTED]

The results of Light-Rail Calc #1 indicate what the distance between successive tunnel egress elements, [D.sub.x] = 1128.23 ft (343.9 m), would be for another combination of Equation 5 inputs (see Figure 10). Despite the largest data inputs for fire discovery, communication, and fan activation times and the selection of the narrowest usable width for tunnel bench travel, the light-rail analysis generated greater spacing between tunnel egress elements than did either of the other analyses. This was largely attributed to the small number of passengers/crew, [P.sub.t], involved in the light-rail train evacuation and the 15 minute timeframe input for [t.sub.latter evac]. Even though the mid-train fire wasn't presumed to reach flashover until 30 min had elapsed, 15 min was randomly selected as the time to commence the evacuation of the second passenger/crew group to reflect the fact that the mid-train fire is growing from time = 0 seconds.

The significance of this result is that this specific combination of train data, elapsed time entries, and passenger flow capacity/travel speed inputs to Equation 5 for the light-rail analysis generated an interval between successive egress elements that was almost 50% greater than the maximum distance for cross-passageway spacing recommended by NFPA Standard 130. This is not to say that all light-rail applications will require 50% fewer tunnel egress elements than that recommended in the 2003 edition of the standard, but it does signify that certain combinations of rail system data may require fewer tunnel egress provisions than those cited by the standard and still have sufficient means available to safely evacuate passengers/crew during a mid-train fire event.

As in the subway analyses, Light-Rail Calc #2 was completed to check the results of Light-Rail Calc #1 against the 2003 NFPA Standard 130 guidelines for tunnel cross-passageway spacing by taking [D.sub.x] as 800 ft (244 m) and solving for [t.sub.latter evac]. The predictable result was that [t.sub.latter evac] decreased by about 1.6 min to account for the reduction of 328.23 ft (99.9 m) in tunnel bench travel at 200 fpm (61 m/min). The decision as to whether slower (15.0 min vs. 13.3 min via increased egress element spacing) evacuations are warranted would ultimately rest with the AHJ for the individual light-rail system.

Controlled Evacuations

Regardless of the manner in which the evacuation occurs during a train fire, emergency egress should be "controlled"--that is, organized and led by a qualified member of the crew. Paragraph 6.1.2.2 of the 2003 edition of NFPA Standard 130 (NFPA 2003) recommends that train evacuations take place only under the "guidance and control" of an authorized and trained transit system employee or other authorized and trained personnel. Upon reporting the details of the event to an operations control center and receiving evacuation orders from same, crew members should be expected to proceed toward the door(s) at which the passengers will exit the train and assume a leadership position for the group of evacuees. In addition to achieving a sense of order, crew-based leadership of the evacuation would be beneficial in terms of adhering to the instructions of the operations control center, recognizing tunnel signage (including that for the egress elements), avoiding other sources of harm, and continuing the flow of evacuees toward their ultimate destination--be it a station, portal, non-incident tunnel/rescue train, or the surface level via an exit stair.

For all of the analyses in Table 1 except Commuter Calc #2, the manner of the controlled evacuation from the mid-train fire would be similar--i.e., the evacuations of both the first and second passenger groups would be led by a different crew member, in opposite directions, toward a single tunnel egress element. In Commuter Calc #2, however, the presence of the second active egress element during the evacuation of each passenger/crew group would have a tangible effect on the manner in which the evacuation is controlled and thus upon the desired result, [D.sub.x]. The form of Equation 5 presumes an equal distribution of the first evacuation group between the two active egress elements, when in fact the actual distribution would be determined by the manner in which the initial evacuation is controlled, which can be very incident-specific.

To show the dependence of tunnel egress element spacing upon the manner by which the evacuation is controlled, the results of Commuter Calc #2 were reconsidered based on the assumption that the evacuees would exit the tunnel via the closest egress element in their forward path. With this assumption, the even distribution of evacuees between the two active egress elements that is inherent to Equation 5 was adjusted for the percentage length of train with respect to the location of the egress elements. Since Commuter Calc #2 has a train length, [L.sub.t], of 900 ft (274.3 m) and a calculated tunnel egress element spacing, [D.sub.x], of 408.84 ft (124.6 m), the percentage, %, of first evacuees that can be assumed to utilize the nearer egress element in this example would be:

% = [D.sub.x]/([L.sub.t]/2) x 100 = 408.84 ft/(900 ft/2) x 100 = 90.85

[or, % = [D.sub.x]/([L.sub.t]/2) x 100 = 124.6 m/(274.3 m/2) x 100 = 90.85]

Since there are [P.sub.t]/2, or 750, evacuees in the first group, then about 0.9085 x 750 = 681 persons would attempt to use the nearer of the two egress elements. A simplified version of Equation 4 was created to evaluate the time needed to complete this controlled evacuation:

[t.sub.discovery] + [t.sub.comms] + [D.sub.fe]/V + [P.sub.z]/(Q[w.sub.c]) + [D.sub.z]/V + [t.sub.fans active]

= [t.sub.latter evac] [greater than or equal to] [t.sub.full mode] [greater than or equal to] [t.sub.flashover] (6)

where the variables are similar to Equation 4, except

[P.sub.z] = number of passengers/crew using the nearer tunnel egress element, persons

y = 1, since only one egress element is involved in the calculation

[D.sub.z] = the distance of travel along the tunnel bench walkway to the nearest egress element, ft (m)

[L.sub.t] = 0 ft (0 m), since the egress element being evaluated is within the length of the train

Solving Equation 6 for [t.sub.latter evac] with [P.sub.z] = 681 persons, [D.sub.z] = 1.0 ft (0.3048 m) assuming a best-case scenario of a nearly coincident train car door and tunnel exit door, and the other data inputs taken from Commuter Calc #2 yielded 11.54085 min, which exceeded the time frame associated with fire flashover, [t.sub.flashover] = 10 min, by approximately 1.5 min. Therefore, with the controlled evacuation based upon percentage evacuee flow to the nearest forward exit, the distance between successive tunnel egress elements must be reduced further in order to achieve the 10 min time frame required for [t.sub.latter evac]. To determine the maximum number of evacuees, [P'.sub.z], that can use the nearer of the two active tunnel egress elements within 10 minutes, Equation 6 can be rearranged and simplified once more as

[P'.sub.z] = (Q[w.sub.c])[[t.sub.latter evac] - ([t.sub.discovery] + [t.sub.comms] + [D.sub.fe]/V + [D.sub.z]/V + [t.sub.fans active])]. (7)

With [t.sub.latter evac] = 10 min, [D.sub.z] = 1.0 ft (0.3048 m), and the other data inputs taken from Commuter Calc #2, Equation 7 yielded [P'.sub.z] = 576 persons. Then, the percentage, %', of first evacuees who could utilize the nearer egress element within a 10 min timeframe would be

%' = [P'.sub.z]/([P.sub.t]/2) x 100 = 576/(1500/2) x 100 = 76.80.

Finally, solving for the percentage train length-adjusted tunnel egress element spacing, [D'.sub.x], based on the maximum number of evacuees that can utilize the nearest active egress element within a 10 min time frame, yielded

[D'.sub.x] = ([L.sub.t]/2) x (%'/100) = (900 ft/2) x (76.80/100) = 345.60 ft

[or, [D'.sub.x] = ([L.sub.t]/2) x (%'/100) = (274.3 m/2) x (76.80/100) = 105.4 m] (see Figure 11).

Thus, the impact of reconsidering the results for Commuter Calc #2 based upon a different assumption for the controlled evacuation served to further reduce the interval spacing between successive tunnel egress elements from 408.84 to 345.60 ft (124.6 to 105.4 m). This is not to say that the "percentage train length" method of approximating the controlled evacuation is more accurate than the equal distribution method that is inherent to Equation 5. The purpose of this example was to demonstrate that the manner in which the controlled evacuation is carried out may influence computations of tunnel egress element spacing when determined as a function of mid-train fire evacuation times.

It is ultimately up to the individual rail system operator and the AHJ to determine the manner in which train evacuations will be remotely organized from an operations control center and locally controlled by crew members. Once determined, the impact of the controlled evacuation upon the results of Equation 5-based analyses can be computed. The controlled evacuation method(s) should then become part of the emergency procedures--on which both the system operators and the train crew should be trained and practiced--for tunnel fire events. Emergency responders should also be cognizant of the manner in which the incident train evacuation is to be controlled so that firefighter ingress and paramedic resources can be directed to the proper location(s).

[FIGURE 11 OMITTED]

PARAMETRIC STUDY

The results of the Equation 5 analyses depend upon all of the data inputs shown in Table 1, though some inputs affect the results more than others. Therefore, a parametric study was completed in order to demonstrate the effects of changing the values of certain variables in the Equation 5-based analyses. Two variables were altered for each rail system type--generating a new Calc #3 and a new Calc #4, respectively, for each application. The basis for Commuter Calc #3 and Commuter Calc #4 was the original data from Commuter Calc #2, the basis for Subway Calc #3 and Subway Calc #4 was the original data from Subway Calc #1, and the basis for Light-Rail Calc #3 and Light-Rail Calc #4 was the original data from Light-Rail Calc #1. The results of the parametric study are presented in Table 2.

In Commuter Calc #3, the time needed to communicate the details of the mid-train fire was increased to 2.0 minutes; no specific reason for the additional time is necessary for the parametric study, but it may be a function of either mis-communication or unpreparedness. In Commuter Calc #4, the egress flow capacity was reduced to 1.82 pim (0.0716 p/mm x min); this parametric analysis relates to the aforementioned uncertainties inherent to using NFPA Standard 130 station egress guidelines for tunnel analyses.

In Subway Calc #3, the usable width of the most constricting element in the path of evacuation was increased to 29 in. (737 mm). Though it is not possible to change the width of an egress element in the course of an event, this parametric analysis was completed to highlight the significance of this variable in Equation 5. In Subway Calc #4, the egress travel speed was reduced to 160 fpm (48.8 m/min); this parametric analysis relates to the aforementioned uncertainties inherent to using NFPA Standard 130 station egress guidelines for tunnel analyses.

In Light-Rail Calc #3, the length of the incident train was increased to 330 ft (100.6 m). This parametric study reflects the consideration that within the same rail transportation system, trains of differing lengths may be operated at different times of the day or week. In Light-Rail Calc #4, the evacuee population was reduced to 450 persons to address the fact that the number of passengers/crew aboard the incident train will also vary depending upon the time of day or week.

As compared with the results of Commuter Calc #2, increasing the communications time, [t.sub.comms], in Commuter Calc #3 from 1.0 to 2.0 minutes served to reduce the distance between successive egress elements, [D.sub.x], from 408.84 to 308.84 ft (124.6 to 94.1 m). This is a predictable result since the elapsed time entries, including [t.sub.discovery] and [t.sub.fans active], inversely affect the outcome--either positively or negatively--as a function of the travel speed, V, divided by the number of active egress elements, y. In this case, a 1.0 minute increase multiplied by V/y reduced the distance between successive egress elements by 100 ft (30.5 m). Changes to the other time-dependent variables in Equation 1.2 will generate similar results, whereby the impact upon the calculation can be determined as the net change in the variable multiplied by V/y.

In Commuter Calc #4, a ~20% reduction in the egress flow capacity (1.82 pim [0.0716 p/mm x min] vs. 2.27 pim [0.0893 p/mm x min]) through the most constricting element in the evacuation path yielded a ~44% reduction in the egress element spacing (228.51 ft [69.7 m] vs. 408.84 ft [124.6 m])--with all other values in Commuter Calc #2 held constant. This is a logical result because a reduction in the egress flow capacity lengthens the time needed for the evacuees to pass through the most constricting element in their path, therefore necessitating closer egress element spacing to achieve the same overall evacuation time. This parametric analysis was included to show the impact of the egress flow capacity, Q, which affects Equation 5 as a function of the passenger/crew load, [P.sub.t], and the usable width, [w.sub.c], of the most constricting element, on the overall result.

As compared with the results of Subway Calc #1, increasing the usable width of the most constricting element in Subway Calc #3 from 27 to 29 in. (686 to 737 mm) served to increase the distance between successive egress elements, [D.sub.x], from 613.41 to 725.94 ft (187.0 to 221.3 m). This is a logical result because an increase in the usable width reduces the time needed for the evacuees to traverse the most constricting element in their path, therefore permitting wider egress element spacing to achieve the same overall evacuation time. This parametric analysis was included to show the impact of the usable width, [w.sub.c], which affects Equation 5 as a function of the egress flow capacity, Q, and the passenger/crew load, [P.sub.t], on the overall result.

In Subway Calc #4, a ~20% reduction in the evacuees' travel speed (160 fpm [48.8 m/min] vs. 200 fpm [61 m/min]) netted only a ~10% reduction in the egress element spacing (549.73 ft [167.6 m] vs. 613.41 ft [187.0 m])--with all other values in Subway Calc #1 held constant. This is a predictable result because slower walking speeds correspond to longer travel times and require closer egress element spacing to achieve the same overall evacuation time. The imbalance between the percentage change in the variable and the percentage change in the result is attributed to the weight of the various terms in Equation 5, where the variables that were held constant between Subway Calc #1 and Subway Calc #4 would seem to contribute more to the calculated result.

As compared with the results of Light-Rail Calc #1, increasing the length of the train in Light-Rail Calc #3 from 300 to 330 ft (91.5 to 100.6 m) served to increase the distance between successive egress elements, [D.sub.x], from 1128.23 to 1143.23 ft (343.9 to 348.5 m). This is a predictable result because the train length affects the outcome--either positively or negatively--as a function of itself over two times the number of active egress elements, [L.sub.t] /2y. In this case, a 30 ft (9.1 m) increase divided by the product of 2y, with y = 1, increased the distance between successive egress elements by 15 ft (4.6 m).

In Light-Rail Calc #4, a 10% reduction in the passenger/ crew load (450 persons vs. 500 persons) netted an ~8% increase in the egress element spacing (1220.01 ft [371.9 m] vs. 1128.23 ft [343.9 m])--with all other values in Light-Rail Calc #1 held constant. This is a predictable result because fewer evacuees correspond to reduced exiting times and allow wider egress element spacing to achieve the same overall evacuation time. This parametric analysis was included to show the impact of the passenger/crew load, [P.sub.t], which affects Equation 5 as a function of the egress flow capacity, Q, and the usable width, [w.sub.c], of the most constricting element on the overall result.

RECOMMENDATIONS

The following recommendations are made based upon the development/analyses of Equation 5:

* The emergency exit and cross-passageway spacing guidelines within NFPA Standard 130 (NFPA 2003) should be interpreted as not-to-exceed values for rail system applications and not as constant design parameters to be uniformly applied to all tunnels regardless of their train length, walkway width, passenger/crew load, fire growth rate, etc.

* The mid-train fire presents an extremely problematic situation for both tunnel emergency egress and tunnel emergency ventilation, whereas unless emergency ventilation is designed as a point-extract system, the emergency egress provisions can be enhanced above those recommended by NFPA Standard 130 to improve fire-life safety.

* The keys to a mid-train fire response are event recognition and speed of response. Rail system authorities should have a visual depiction of the entire tunnel network to quickly determine the location of the incident train, the reported position of the fire with respect to the train length, the tunnel egress paths, and the mechanical ventilation shafts.

* Equation 5 should be used for computing the distance between successive tunnel egress elements for mid-train fires in rail tunnels. If the result exceeds the NFPA Standard 130 guidelines, then the standard's maximum cross-passageway spacing distance criteria should be observed; if the result is less than the NFPA Standard 130 guidelines, then additional tunnel egress elements should be considered.

* The values utilized in these analyses to represent the egress flow capacity, Q, and the egress travel speed, V, during tunnel evacuations were taken from the NFPA Standard 130 guidelines (NFPA 2003) for station egress planning. Better data are needed to simulate the actual egress flow capacities and travel speeds during tunnel evacuations (see Fruin [1971]).

* Subject to approval by the AHJ, passenger evacuations should be controlled by the rail system authority via the train crew. The manner in which the controlled evacuation is planned/executed will have a tangible effect upon the time required to evacuate the train, in general, and on the results of tunnel egress element spacing calculations using Equation 5, in particular.

* The parametric study presented here showed the results of Equation 5-based analyses when six of the data inputs were altered while the other variables were held constant. More parametric study may be completed (as needed) by the designers of underground rail systems in order to select the best possible emergency egress solution for the specific tunnel application.

* If one or more of the active variables in Equation 5 are unknown or undeterminable for a particular rail system application due to information availability, construction sequencing, etc., then the default condition for this particular system application would be to implement the 2003 NFPA Standard 130 design guidelines for tunnel egress element spacing.

* The determination of whether a particular tunnel egress element is an emergency exit or a cross passageway should depend upon emergency response/ingress requirements, the tunnel depth below the surface, the number of parallel tunnels, rescue train availability, special considerations for disabled evacuees, and the relative safety of any designated refuge areas.

* Tunnel emergency ventilation systems should be designed in accordance with NFPA Standard 130, the ASHRAE Handbook--HVAC Applications, and the Subway Environmental Design Handbook (UMTA 1976). Though related to the manner in which a particular rail system authority deals with a tunnel fire event, the actual design and operation of the emergency ventilation system is beyond the scope of this paper.

REFERENCES

ASHRAE. 2003. 2003 ASHRAE Handbook--HVAC Applications, chapter 13. Atlanta: American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc.

ASHRAE. 2005. 2005 ASHRAE Handbook--Fundamentals, chapter 38. Atlanta: American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc.

Fruin, J.J. 1971. Pedestrian Planning and Design. New York: Metropolitan Association of Urban Designers and Environmental Planners.

NFPA. 2006. NFPA Standard 101, Life Safety Code. Quincy, MA: National Fire Protection Association.

NFPA. 2003. NFPA Standard 130, Fixed Guideway Transit and Passenger Rail Systems. Quincy, MA: National Fire Protection Association.

NFPA. 2000. NFPA Standard 130, Fixed Guideway Transit and Passenger Rail Systems. Quincy, MA: National Fire Protection Association.

NFPA. 1997. NFPA Standard 130, Fixed Guideway Transit and Passenger Rail Systems. Quincy, MA: National Fire Protection Association.

UMTA. 1976. Subway Environmental Design Handbook, Volume 1: Principles and Applications, 2d ed. Washington, DC: Urban Mass Transportatio n Administration.

DISCUSSION

Mohammad Tabarra, Arup, London, England: (1) In your parametric study, which factors had the largest impact on the Dx (the required maximum distance between egress elements)

(2) While the breakdown of evacuation time into smaller components is appreciated and is a positive step toward clarifying the issues, the overall time period not exceeding flashover time can undermine the usage of this approach since this parameter (flashover time) is itself subject to much debate and assumption. It may be better to define an agreed maximum period (say, 30 minutes or flashover time, whichever is shorter) for the purposes of design.

M.P. Colino: (1) The factors that had the greatest impact on the calculated spacing between egress elements were the length of the incident train, the number of incident passenger/crew evacuees, the egress flow capacity of passengers/crew through the most constricting element in the evacuation path, the width of that most constricting element, and the timeframe under which the evacuation occurred. The impact of changes in these factors were evaluated to varying degrees in both the analysis of Equation 5 (Table 1) and the parametric study (Table 2).

(2) The time at which flashover occurs is a definitive point in the fire load curve of a rail vehicle; it is a point at which the conditions in the tunnel will decidedly worsen. Flashover is also a fundamental parameter associated with the design of tunnel ventilation systems in terms of both its duration and magnitude. Similar to the design of tunnel ventilation systems and all related infrastructure, a calculation methodology for tunnel egress element spacing that uses flashover as an upper boundary will be a function of the accuracy with which the time of flashover was determined. However, since the time to flashover is only an upper boundary in the calculation--and not an active variable in Equation 5--the egress element spacing is not wholly dependent upon the flashover time. As the reviewer infers in his latter comment, a lengthy time to flashover would be counter-productive toward the timely evacuation of incident passengers/crew and, thus, the spacing of tunnel egress elements, if the two were inseparably linked. This is not the case. This matter was addressed in the paper via the calculations/discussions provided for the hypothetical subway and light-rail system examples, where the selected evacuation time was in advance of the assumed flashover time--in recognition of the fact that the fire presents a safety hazard from the moment that it starts and that a lengthy flashover time should not be taken as a "grace" period for untimely actions.

Paul Miclea, Tech Director, Earth Tech, Inc., Oakland, CA: Congratulations for tackling a difficult/controversial issue. The automatic/immediate start of EVS was not addressed. Reversing the ventilation direction should not be corrected. More work is necessary.

Colino: The paper does not advocate an automatic/immediate start of the emergency ventilation system since the location of the fire, with respect to both the incident train and the local tunnel egress elements, will dictate the operational mode under which the tunnel fans are activated. The paper recognizes, via mid-train fire scenario #3, that a certain set of circumstances may necessitate a reversal in the ventilation airflow direction. However, the calculation methodology provided for tunnel egress element spacing is not dependent upon a reversal in the direction of ventilation airflow.

Robert Till, Associate Professor of Fire Science, John Jay College of Criminal Justice, New York, NY: I agree that speed and capacity data should be collected for evacuees walking in queues along a raised tunnel walkway. The capacities that you currently use in your model are based on data collected for much wider planes that allowed people to move in between each other. I don't believe these capacities are applicable to queues on a tunnel walkway where people can't pass each other without letting go of a handrail and taking the risk of falling off the walkway.

NFPA 130 TIA 03-1/Log797 (issued August 4, 2004) reduced the maximum passenger walking speed on a plane from 200 fpm to 124 fpm. Could you please include your results for this walking speed in additional tables?

Colino: The egress flow capacity (Q) and egress travel speed (V) values used in the analyses were clearly stated as being taken from the 2003 edition of NFPA Standard 130 and explicitly classified as being applicable to station, not tunnel, analyses. This point was further emphasized in the fifth bullet item under "Recommendations," where the need for tunnel-specific data was recognized. With this in mind, there is no useful tunnel information to be gained from altering the travel speed in the analyses from 200 fpm to 124 fpm, where the latter value reflects a post-2003 amendment to the referenced standard and is also applicable to station analyses. The tables were included in the paper to give the reader examples of Equation 5-based calculations for randomly selected data inputs. The paper does not advocate the use of 200 fpm in tunnel egress analyses; this is why the parameter V remains a variable, not a constant, within Equation 5.

Kai Kang, Hatch Mott MacDonald, New York, NY: What will be the first reaction of the passengers/crews to the mid-train fire, and would the author consider evacuation through the trains?

Colino: Upon discovery of a mid-train fire, it is expected that the first reaction of the passengers would be to move away from the fire (in both directions) toward the train end-cars. The first reaction of the passengers is expected to occur within the train--so long as the interior environment of the non-incident cars remains tenable. Depending on the nature of the event, the number of crew members in the immediate vicinity, and the equipment within the incident train car, the crew may organize/lead this passenger migration toward the end-cars, attempt to suppress the fire, or communicate the details of the fire to the train engineer and/or the central supervising station. Per NFPA Standard 130, the crew should also lead/control the evacuation of passengers when they leave the train.

M.P.Colino, PE

Member ASHRAE

E.B. Rosenstein

M.P. Colino is a senior supervising engineer and E.B. Rosenstein is a lead engineer of Parsons Brinckerhoff, Inc., New York, NY.
Table 1. Results of Analyses for Equation 5*

 Commuter Commuter
Variable Units Calc #1 Calc #2

[t.sub.flashover] min 10 10
[t.sub.latter evac] min 10.0 10.0
[t.sub.discovery] min 0.5 0.5
[t.sub.comms] min 1.0 1.0
[t.sub.fans active] min 0 0
V fpm (m/min) 200 (61) 200 (61)
[D.sub.fe] ft (m) 6 (1.83) 6 (1.83)
[P.sub.t] persons 1500 1500
Q pim (p/ 2.27 (0.0893) 2.27 (0.0893)
 mm x min)
[w.sub.c] in (mm) 30 (762) 30 (762)
[L.sub.t] ft (m) 900 (274.3) 900 (274.3)
y none 1 2
[D.sub.x] ft (m) -58.64 408.84
 (-17.9)## (124.6)##

 Subway Subway
Variable Units Calc #1 Calc #2

[t.sub.flashover] min 30 30
[t.sub.latter evac] min 12.5 13.43292##
[t.sub.discovery] min 0.75 0.75
[t.sub.comms] min 0.5 0.5
[t.sub.fans active] min 1.5 1.5
V fpm (m/min) 200 (61) 200 (61)
[D.sub.fe] ft (m) 5 (1.52) 5 (1.52)
[P.sub.t] persons 1000 1000
Q pim (p/ 2.27 (0.0893) 2.27 (0.0893)
 mm x min)
[w.sub.c] in (mm) 27 (686) 27 (686)
[L.sub.t] ft (m) 600 (182.9) 600 (182.9)
y none 1 1
[D.sub.x] ft (m) 613.41 (187.0)## 800 (244)

 Light-Rail Light-Rail
Variable Units Calc #1 Calc #2

[t.sub.flashover] min 30 30
[t.sub.latter evac] min 15.0 13.35885##
[t.sub.discovery] min 1.0 1.0
[t.sub.comms] min 1.5 1.5
[t.sub.fans active] min 3.0 3.0
V fpm (m/min) 200 (61) 200 (61)
[D.sub.fe] ft (m) 4 (1.22) 4 (1.22)
[P.sub.t] persons 500 500
Q pim (p/ 2.27 (0.0893) 2.27 (0.0893)
 mm x min)
[w.sub.c] in (mm) 24 (610) 24 (610)
[L.sub.t] ft (m) 300 (91.5) 300 (91.5)
y none 1 1
[D.sub.x] ft (m) 1128.23 (343.9)## 800 (244)

* Calculated values are shown in shaded cells. Metric conversion factors
are from chapter 38, ASHRAE Handbook--Fundamentals (ASHRAE 2005).

* Calculated values are shown indicated with ##.

Table 2. Results of Parametric Study*

 Commuter Commuter
Variable Units Calc #3 Calc #4

[t.sub.flashover] min 10 10
[t.sub.latter evac] min 10.0 10.0
[t.sub.discovery] min 0.5 0.5
[t.sub.comms] min 2.0** 1.0
[t.sub.fans active] min 0 0
V fpm (m/min) 200 (61) 200(61)
[D.sub.fe] ft (m) 6 (1.83) 6(1.83)
[P.sub.t] persons 1500 1500
Q pim (p/ 2.27 (0.0893) 1.82 (0.0716)**
 mm x min)
[w.sub.c] in (mm) 30 (762) 30 (762)
[L.sub.t] ft (m) 900 (274.3) 900 (274.3)
y none 2 2
[D.sub.x] ft (m) 308.84 228.51
 (94.1)## (69.7)##

 Subway Subway
Variable Units Calc #3 Calc #4

[t.sub.flashover] min 30 30
[t.sub.latter evac] min 12.5 12.5
[t.sub.discovery] min 0.75 0.75
[t.sub.comms] min 0.5 0.5
[t.sub.fans active] min 1.5 1.5
V fpm (m/min) 200 (61) 160 (48.8)**
[D.sub.fe] ft (m) 5 (1.52) 5 (1.52)
[P.sub.t] persons 1000 1000
Q pim (p/ 2.27(0.0893) 2.27 (0.0893)
 mm x min)
[w.sub.c] in (mm) 29 (737)** 27 (686)
[L.sub.t] ft (m) 600 (182.9) 600 (182.9)
y none 1 1
[D.sub.x] ft (m) 725.94 549.73
 (221.3)## (167.6)##

 Light-Rail Light-Rail
Variable Units Calc #3 Calc #4

[t.sub.flashover] min 30 30
[t.sub.latter evac] min 15.0 15.0
[t.sub.discovery] min 1.0 1.0
[t.sub.comms] min 1.5 1.5
[t.sub.fans active] min 3.0 3.0
V fpm (m/min) 200 (61) 200 (61)
[D.sub.fe] ft (m) 4 (1.22) 4 (1.22)
[P.sub.t] persons 500 450**
Q pim (p/ 2.27 (0.0893) 2.27 (0.0893)
 mm x min)
[w.sub.c] in (mm) 24 (610) 24 (610)
[L.sub.t] ft (m) 330 (100.6)** 300 (91.5)
y none 1 1
[D.sub.x] ft (m) 1143.23 1220.01
 (348.5)## (371.9)##

*Altered values are shown in bold type; calculated values are shown in
shaded cells. Metric conversion factors are from chapter 38, ASHRAE
Handbook--Fundamentals (ASHRAE 2005).

Note: Altered values are shown in indicated with **; calculated values
are shown in indicated with ##.
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No portion of this article can be reproduced without the express written permission from the copyright holder.
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Article Details
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Author:Colino, M.P.; Rosenstein E.B.
Publication:ASHRAE Transactions
Geographic Code:1USA
Date:Jul 1, 2006
Words:11232
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