NBSIR 87-3567

Comparisons of NBS/Harvard VI

Simulations and Full-Scale, Multi-Room

Fire Test Data

John A. Rockett, Masahiro Morita and Leonard Y. Cooper

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Fire Research

Gaithersburg, MD 20899

July 1987

U.S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANOAR08

NBSIR 87-3567

COMPARISONS OF NBS/HARVARD VI

SIMULATIONS AND FULL-SCALE, MULTI-ROOM

FIRE TEST DATA

John A. Rockett, Masahiro Morita and Leonard Y. Cooper

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Fire Research

Gaithersburg, MD 20899

July 1987

U.S. DEPARTMENT OF COMMERCE, Malcolm Baldrige, Secretary

NATIONAL BUREAU OF STANDARDS, Ernest AmMer, Difctor
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TABLE OF CONTENTS

Page

LIST OF TABLES iv

LIST OF FIGURES iv

ABSTRACT 1

1. INTRODUCTION AND OBJECTIVE 1

2. DESCRIPTION OF THE TESTS 1

3. TEST RESULTS AND THE PARAMETERS SIMULATED 3

4. PRESENTATION OF THE TEST DATA AND THE PREDICTIONS 4

5. DISCUSSION OF RESULTS AND ADDITIONAL SIMULATIONS 5

5.1 Orifice Coefficients and the Subdivision of Large Spaces 5

5.2 Temperature Rise and Overall Heat Losses 6

5 . 3 Layer Depth Comparisons 9

6. CONCLUSIONS 10

7. REFERENCES 11

iii
LIST OF TABLES

Page

Table 1. Figure Numbers Versus Test Parameters 13

Table 2. Input Data 14

LIST OF FIGURES

Figure 1. Sketches of the four test configurations with indications of

the locations of vertical instrument arrays (A,B,C,D, and E)

and of video cameras (V) 15

Figure 2a. 100 kW fire, Corridor and Lobby configuration: layer heights. 16

Figure 2b. 100 kW fire, Corridor and Lobby configuration: X, pressure

difference and average temperature rises 17

Figure 3. Vertical temperature profiles, 100 kW fire. Corridor and Lobby

configuration at 200 sec 18

Figure 4a. 25 kW fire, 1/2 Corridor configuration: layer heights 19

Figure 4b. 25 kW fire, 1/2 Corridor configuration: A, pressure

difference and average temperature rises 20

Figure 5a. 25 kW fire, 3/4 Corridor configuration: layer heights 21

Figure 5b. 25 kW fire, 3/4 Corridor configuration: A, pressure

difference and average temperature rises 22

Figure 6a. 25 kW fire. Full Corridor configuration: layer heights 23

Figure 6b. 25 kW fire, Full Corridor configuration: A, pressure

difference and average temperature rises 24

Figure 7a. 25 kW fire. Corridor and Lobby configuration: layer heights.. 25

Figure 7b. 25 kW fire. Corridor and Lobby configuration: A, pressure

difference and average temperature rises 26

Figure 8a. 100 kW fire, 1/2 Corridor configuration: layer heights 27

Figure 8b. 100 kW fire, 1/2 Corridor configuration: A, pressure

difference and average temperature rises 28

Figure 9a. 100 kW fire, 3/4 Corridor configuration: layer heights 29

IV
LIST OF FIGURES (cont.)

Page

Figure 9b. 100 kW fire, 3/4 Corridor configuration: X, pressure

difference and average temperature rises 30

Figure 10a. 100 kW fire, Full Corridor configuration: layer heights 31

Figure 10b. 100 kW fire. Full Corridor configuration: A, pressure

difference and average temperature rises 32

Figure 11a. 100 kW fire. Full Corridor configuration, 1/2 width door

burn room to corridor: layer heights 33

Figure 11b. 100 kW fire. Full Corridor configuration, 1/2 width door

bum room to corridor: A, pressure difference and average

temperature rises 34

Figure 12a. 100 kW fire. Full Corridor configuration, 1\4 width door

burn room to corridor: layer heights 35

Figure 12b. 100 kW fire. Full Corridor configuration, 1\4 width door

bum room to corridor: A, pressure difference and average

temperature rises 36

Figure 13a. 100 kW fire. Full Corridor configuration, 1/8 width door

burn room to corridor: layer heights 37

Figure 13b. 100 kW fire. Full Corridor configuration, 1/8 width door

burn room to corridor: A, pressure difference and average

temperature rises 38

Figure 14a. 225 kW fire, 1/2 Corridor configuration: layer heights 39

Figure 14b. 225 kW fire, 1/2 Corridor configuration: A, pressure

difference and average temperature rises 40

Figure 15a. 225 kW fire, 3/4 Corridor configuration: layer heights 41

Figure 15b. 225 kW fire, 3/4 Corridor configuration: A, and average

temperature rises 42

Figure 16a. 225 kW fire. Full Corridor configuration: layer heights 43

Figure 16b. 225 kW fire, Full Corridor configuration: A, pressure

difference and average temperature rises 44

Figure 17a. 225 kW fire. Corridor and Lobby configuration: layer heights. 45

V
LIST OF FIGURES (cont.)

?age

Figure 17b. 225 kW fire, Corridor and Lobby configuration: A, pressure

difference and average temperature rises 46

Figure 18a. Ramp fire, 1/2 Corridor configuration: layer heights 47

Figure 18b. Ramp fire, 1/2 Corridor configuration: A, pressure

difference and average temperature rises 48

Figure 19a. Ramp fire, 3/4 Corridor configuration: layer heights 49

Figure 19b. Ramp fire, 3/4 Corridor configuration: A, pressure

difference and average temperature rises 50

Figure 20a. Ramp fire. Full Corridor configuration: layer heights 51

Figure 20b. Ramp fire. Full Corridor configuration: A, pressure

difference and average temperature rises 52

Figure 21a. Ramp fire. Corridor and Lobby configuration: layer heights.. 53

Figure 21b. Ramp fire. Corridor and Lobby configuration: A, pressure

difference and average temperature rises 54

Figure 22a. 100 kW fire, Corridor (subdivided into 3 rooms) and Lobby:

layer heights, 55

Figure 22b. 100 kW fire. Corridor (subdivided into 3 rooms) and Lobby:

A, pressure difference and average temperature rises 56

Figure 23. Burn room vertical temperature distribution at 200 seconds,

100 kW fire: 1/8 normal width door 57

Figure 24. Burn room vertical temperature distribution at 200 seconds,

normal door, 100 kW fire: full, 3/4 and 1/2 corridors sizes. 58

Figure 25. Burn room vertical temperature distribution at 200 seconds,

normal door, corridor plus lobby: 25 and 225 kW fires 59

vi
COMPARISONS OF NBS/HARVARD VI SIMULATIONS AND

FULL-SCALE, MULTI -ROOM FIRE TEST DATA

John A. Rockett, Masahiro Morita and Leonard Y. Cooper

ABSTRACT

The NBS/Harvard VI multi -room fire model computer code was used to

simulate results of previously reported full-scale, multi-room fire

experiments. The tests and simulations involved: four different compartment

configurations made up of two or three rooms connected by open doorways, four

different fire types generated by a methane burner located in the room

identified as the bum room, and up to four different doorway openings between

the burn room and the adjacent space. A total of nineteen different tests

were carried out and simulated. Comparisons between simulated and measured

parameters of the fire -generated environments are reviewed. While the

computer code is generally found to provide favorable simulations for the

entire range of tests, several areas in modeling detail are identified as requiring clarification, research, and further improvement. The improvements

should be incorporated in future versions of the NBS/Harvard Multi-Room Fire

Model.

Key words: Computer models; compartment fires; fire models, full-scale fire;

multi room fires; simulation; validation

1. INTRODUCTION AND OBJECTIVE

The NBS/Harvard VI compartment -fire simulator is a computer code which

predicts the dynamic environment generated by fires in multi-room enclosures.

The development of the computer code in its original Harvard VI form [1,2] was carried out at Harvard University as an outgrowth of the Harvard V, single

room compartment fire simulator [3,4]. The continued development and further

enrichment of the code is being carried out at the Center for Fire Research of

the U.S. National Bureau of Standards [5].

Reference [6] describes the results of an extensive series of

full-scale, multi -room enclosure fire tests. The purpose of the work reported

here was to use the NBS/Harvard Code to simulate the results of this experimental study and to describe and analyze the results of a comparison between

the predictions and the actual data tabulated in [6]

.

2. DESCRIPTION OF THE TESTS

The following description of the test program is a summary of the

presentation in [6]

.

The reader is referred to that work for additional

clarification.

1
The test program of [6] consisted of a series of separate tests

involving a variety of compartment configurations and fire energy release

rates. For a given test, the compartment involved either two or three rooms,

all having a nominal 2.36 m ceiling height, connected by open doorways. The

wall and ceiling surfaces of all rooms were lined with 0.013 m thick gypsum

board, and the floors were concrete. During the course of the test program

the space was partitioned to yield four different configurations ranging in

total plan area from 40.6 m^ to 89.6 m^. These configurations are sketched in

Fig. 1. The doorway between the burn room and its adjacent space (designated

as the corridor) was 2.0m high and 1.07 m wide. The doorway between the

corridor and the next adjacent space (the lobby) was 2.01 m high and 1.32 m wide

An attempt was made to seal cracks and penetrations in the bounding

surfaces of the test space. A 0.15-m (high) x 0.94-m (wide) hole with clear

opening to the outside (through an unused room and open window of the test

facility) was provided next to the floor in a wall surface of the corridor.

The hole was to provide the major leakage path for mass exchange between the

test space and the outside environment.

Each test used the same burn room of 14.0 m^ area. The room contained a 0.30 m X 0.30 m square methane diffusion burner whose surface was positioned

0.24 m above the floor and approximately in the center of the room. After

ignition from a pilot flame, fuel supply to the burner was controlled manually

from an outside metering system to produce one of four energy release rates:

a constant rate, Q, of 25 kW, 100 kW, or 225 kW; or a time varying energy

release rate, Qramp(^)»

Qranjp(t) - 30 t kW, 0 < t (t in minutes) (1)

where the time from ignition, t, never exceeded 10 min.

The free-bum characteristics of the particular burner used in these

tests were studied in [7]. Using methane for a fuel, and for fires between 50

kW and several hundreds of kW, it was found that, of the total energy release

rate of the fire, a fraction, , of approximately 0.24 is radiated away from

the combustion zone. For a 25 kW fire X^ was found to be 19 percent.

With methane as a fuel the burner produced very little smoke. In order

to have a visual tracer of the combustion products as they spread throughout

the compartment, an artificial source of smoke (a commercially available, non- toxic smoke candle) was introduced into the ceiling jet of the burn room. Thus, in every test, a highly visible white smoke was generated by a smoke

candle and mixed with the fire's products of combustion near their source for

up to 5 min. Effective visualization of the upper smoke layers was achieved

by placing fluorescent light fixtures on the floor of the corridor and lobby.

For each of the four spatial configurations of Fig. 1, a separate burn

test was run for each of the four energy release rates <16 test runs). For

the 100 kW fire and full corridor configuration of Fig. 1, three additional

tests were also run. In these tests, the burn room- to-corridor doorway width

was reduced to 1/2, 1/4, and 1/8 of its full value of 1.07-m.

2
The test instrumentation is described in detail in [6]

.

It consisted of

five thermocouple "trees” located as shown by A-E in Fig. 1. There were eight

thermocouples on each tree and, except for the doorway, they were 0.30 m

apart, the lowest one being 0.15 m from the floor and the uppermost 0.07 m

from the ceiling. Photometers measured the growth of the smoke layer, and

video tapes were made during each test allowing post- test analysis of the

smoke layer growth by noting the extent of smoke obscuration of vertical

scales mounted within the field of vision of the cameras (at positions V of

Fig. 1). A single pair of pressure taps located at A and C (see Fig. 1)

measured the pressure difference between the burn room and the corridor at the

ceiling elevation.

3. TEST RESULTS AND THE PARAMETERS SIMULATED

The NBS/Harvard VI code simulates the fire -generated environment within

each room of a compartment as having two homogeneous horizontal gas layers

separated by a sharp interface: an elevated temperature, combustion-product

contaminated (i.e., smoky) upper layer and a lower layer of uncontaminated air

at ambient temperature. Observations during the reference [6] tests and

during other, similar fire tests suggest that this two-layer description is

frequently a reasonable, albeit distinctly idealized approximation of the

actual phenomena. The approximation is idealized in that the actual interface

between the gas layers is not sharp. In some cases there is a relatively

narrow, in others a relatively broad transition region across which the gas

temperature, smoke opacity and product of combustion densities change.

Further, in many fires, the gas in the lower part of the rooms is, at later

times, neither free of smoke nor at ambient temperature [6,8,10].

Reference [6] uses three rules for defining a layer interface height

based on the experimental data: (1) the height at which the gas temperature

rise above ambient is N percent of the temperature rise at the topmost

thermocouple or at least 0.5 K; (2) an analogous rule applied to the

photometer data; and (3) visual observation as determined from video tapes.

In [6], data for selected runs and at selected thermocouple locations are used

to provide the time -dependent interface heights based on rule 3, and based on rules 1 and 2 for N - 10, 15, and 20. Tabulated interface heights according

to rules 1 and 2 for N - 10, and to rule 3 are provided in [6] for each room

during all nineteen tests.

Reference [6] presents vertical temperature distributions for only one of the nineteen tests, and for this at only one corridor thermocouple tree

location and at only one instant of time. In general, only three time-varying

measures of the thermocouple tree data are presented for each room during all runs. The first of these measures is the floor- to-ceiling-averaged

temperature. As it turned out, for each test, the history of this vertically

averaged tempera- ture was found to be substantially the same at all (up to

three) thermocouple tree locations in the corridor. Accordingly, only the

vertically averaged temperatures at location D are tabulated for the corridor

in [6] and reported in this work. The second measure of the dynamic

temperature distribution in the test spaces is the above-mentioned interface

3
elevation according to rule 1 with N - 10. The third dynamic measure of the

thermocouple data is a result of analysis on the first of these measures.

This leads to estimates of the instantaneous total rates of heat transfer to

bounding surfaces of the test space (given in terms of a fraction, A, of the

instantaneous burner power output) which are tabulated in [6] for all test

runs

Five types of comparisons between NBS/Harvard VI simulations and the

experimental data are presented in this paper. In one, the histories of

predicted floor- to-ceiling-averaged temperatures are compared with the

corresponding histories as tabulated in [6]

The second type of comparison

involves predicted two -layer interface elevations and experimentally

determined, N - 10 interface elevations. Thirdly, the vertical distribution

temperature test data (archived at the National Bureau of Standards) were

consulted. For a few test scenarios and at the arbitrarily selected test time

of 200 s, these are compared to the predicted temperature distributions. ,The

fourth type of comparison is between the experimental and predicted

time -varying rate of total heat transfer loss to the bounding surfaces of the

test space. Finally, comparisons are made between experimental and predicted

near-ceiling, cross-wall, bum- room- to -corridor pressure differentials.

Each of the nineteen tests are indicated by groups of numerical entries

in Table 1. Simulations were carried out for all runs. The entries in the

table refer to the numbers of the figures (to be introduced and discussed

below) in which the above-mentioned comparisons between simulation and test

data are displayed.

The input data for the computer runs are presented in Table 2.

4. PRESENTATION OF THE TEST DATA AND THE PREDICTIONS

The first simulation results to be presented will be for the 100 kW

fire, full corridor and lobby test configuration with full burn room- to

corridor doorway. For each of the three rooms, computed results and

corresponding experimental data for the time -dependent interface elevations

are plotted in Figure 2a. Plotted in Figure 2b are (1) the computed and

measured vertically-averaged temperature rise histories based on thermocouple

tree data at locations A, D and E as noted on figure 1: AT^ (burn room), AT^

(corridor), ATg (lobby), (2) the burn room- to-corridor cross-doorway pressure

differential, Ap, and (3) the heat transfer parameter, A. The heat transfer

parameter A is defined as the fraction of Q(t) which is lost by radiation and

convection to the bounding surfaces of the test space. A(t) is estimated from

the AT(t) data and Q(t) according to Eqs. (4) and (5) of [6].

Figure 3 compares the predicted and measured vertical temperature

distributions in the three rooms at 200 seconds. As mentioned earlier, the

200 second experimental data, which are not documented in [6], were obtained

from magnetic tapes archived at NBS.

4
Plots similar to Figure 2a and 2b are provided in Figures 4-21 for the

remaining 18 tests of Table 1. Discussion of these results will be presented

in the next section along with results of selected additional simulations

involving variants in the original calculations

.

5. DISCUSSION OF RESULTS AND ADDITIONAL SIMULATIONS

5.1 Orifice Coefficients and the Subdivision of Large Spaces

Typical applications of zone compartment fire models tacitly assume that

openings (vents) between contiguous spaces are small enough that flows through

them can be modeled as orifice- type flows (constant orifice coefficient)

between relatively quiescent regions. If a vent is too large (e.g., if the

width of the vent approaches the characteristic width of either of the contiguous spaces) then some modification to the analysis is appropriate. Analysis

and experimental results presented in [9] suggest that an adequate modification in this regard involves a variable rather than a constant orifice coefficient; the coefficient varies, approaching unity as the ratio of vent opening

width to exiting room width approaches unity.

Consistent with the above, the NBS/Harvard VI code incorporated the

orifice coefficient formula recommended in [9]

.

To test this new capability

the 100 kW, bum room- corridor -lobby test was simulated a second time. This

test was chosen for comparison because, in this case, the predicted burn room

average temperature rise was in good agreement with the experiment whereas the

burn room- to -corridor pressure difference was not. The corridor test space

was conceptually partitioned into three identical, contiguous spaces with

joining vents having the full corridor width and height 10 cm less than the

corridor height. (10 cm was used based on previous, unpublished experience in

simulating corridor flows.) The center corridor section (Room 3, per the 3-

space corridor data of Table 2) included the doorway vent to the burn room and

the pressure tap. It also shared a "full" vent with each of the two end

sections, one a "deadend" (Room 2, the left portion of the corridor as seen in

Figure 1) and one with the doorway to the lobby (Room 4, the right portion of

the corridor as seen in Figure 1)

.

Results of the new fire-room simulation are plotted in Figure 22a (layer

heights) and Figure 22b (vertically averaged temperatures, cross-door pressure

differential and heat transfer parameter) . These two Figures are to be com- pared to Figures 2a and 2b, respectively. Review of these results leads to

the following observations:

There is a slight difference between calculated values of

lobby and bum room layer heights, plotted in Figures 2a

and 22a, and of Ap, A and AT^ plotted in Figures 2b and

22b.

Due to the amount of scatter in the data, it is not

possible to tell if subdividing the corridor improves the

layer height simulation. The predicted average

5
temperature rises vary along the corridor more than the

measured values AT(, and AT^ at the locations C and D

indicated in Figure. 1.

The predicted ceiling pressure difference between the burn

room and the corridor sub -room in which the corridor pressure was measured is in better agreement with the data

than that for the undivided corridor.

The computed burn room- to -corridor pressure difference exceeds the

measured values as shown in Figure 2 and Figures 4-21 for all the tests except

those for the smallest (25 kW) fire, Figures 7-10. The discrepancy increases

with fire size. While this could have resulted from inadequately sealed leaks

in the burn room, the improved agreement for the subdivided corridor simulation suggests that this was probably not the case. Rather, the slight pressure change along the corridor as one moves away from the burn room door is

more likely responsible. (Note that the gas flow in the corridor upper layer

is away from the bum room door in both directions; the corridor ceiling pressure is highest near the door and, therefore, the burn room- to -corridor pressure difference is smallest there. Thus, the average burn room- to -corridor

pressure difference should be smaller than the local burn room- to -corridor

pressure difference • just outside the door.) This is partially compensated for

by subdividing the corridor. Bearing this in mind, the predicted and measured

pressure differences are satisfactory.

5.2 Temperature Rise and Overall Heat Losses

Figures 2b and 4b- 21b show the vertically averaged temperature rise in

the several rooms. The most striking feature observed on comparing these

Figures is the distinct break in the computed temperature rise for the larger

fires in the smaller spaces which is not reproduced in the data. (See, for

example. Figures 8b, 9b and 10b as compared to Figure 2b, Figures 14b through

17b and Figures 18b through 21b) . This is due to an inadequate treatment in

the modeling of "oxygen limited burning". The simulation always models the

upper layer gas as being so depleted of oxygen that it will not support

combustion. For the cases considered here and, indeed, for many other

scenarios, the assumption is not adequate. Thus, in a simulation, when the

upper layer descends to the height of the surface of a burning object (in the

present case, the burner), the object continues to pyrolyze, but none of the

fuel evolved is assumed to burn. This is in difference to the fact that until

much of the upper layer oxygen is used up, burning rate will not be reduced

significantly. This defect in the simulation has been identified for

correction in a revised version of the simulation. All predicted results

presented here should be disregarded beyond times of the above-mentioned

"breaks .

In a number of the cases, the predicted temperature rises faster at the

beginning of the test than the experimental data (Figures 2, 7, 8 and 19).

This is by no means always the case, however, as shown by Figures 5, 20 and

21. In Figure 8 the experimental temperature data suggest.® that the gas flow

6
to the burner was decreased slightly at about 150 seconds. Taken together,

these results suggest that manual adjustment of the gas flow to the burner did

not produce as rapid a build-up to steady gas flow rate as assumed in the

calculation.

The gas burner algorithm does not account properly for the heat needed

to bring the burner itself to operating temperature. If the algorithm were

improved in this respect the temperature would rise somewhat more slowly than

it now does . This would improve agreement with some tests and make it less

satisfactory for others.

Besides the above, two distinct trends appear when comparing the

simulation results with the experimental data. One is observed as fire size

varied, the other, as the bum room door size varied. As for the first

(Figures 2, 7 and 17 and Figures 3 and 25), the simulation seems to predict

higher- than-measured burn room temperatures for the larger fires, and smaller

ones for the smaller fires. The reverse tendency may be present in the

corridor and lobby although the temperature rise is so small in these spaces

that this is somewhat less obvious. For the ramp fires (Figure 21), the

prediction lies consistently above the experimental data for all times.

The X plots indicate no consistent trend in comparisons of measured and

predicted heat loss to the boundary surfaces of the compartment. For these,

there is general agreement between the experiments and simulations after an

initial period. The A calculation is for heat losses throughout the entire

space. Thus, for any given test run, good agreement between measured and

predicted values of A could be obtained, for example, even if predicted losses

were over-estimated significantly in the bum room and under -estimated

significantly in the other spaces. Were it not for the ramp fires, where the

trend is uneven, the A plots together with the average temperature rise plots

suggest that the simulation heat transfer is under -estimated for the higher

temperatures, and over-estimated for the lower ones. In assessing simulation

A values versus those values derived from experiment, note that in the

experimentally derived values, temperatures at only one location in each of

the rooms were used. This may limit significantly the accuracy of the

measured values of A. On the other hand, many approximations are embedded in

the A estimate of the simulation and these may limit significantly its

accuracy.

Tests 10-13 varied the bum room door size. Figures 10-13 and Figures 3 and 23 compare the experimental and simulation results for these tests. The

simulation underestimated significantly the bum room temperature for the

smallest door, with improving agreement as the door is increased in size.

There are three possible reasons for this discrepancy. First, the simulation

does not Include the effect of mixing between the hot gas exiting from the

room and cool gas entering. (Mixing of the exiting upper layer gas with that

entering the lower layer through the same vent.) It has been shown that this

can be important [8] and, when modeled [10], raises the gas temperature in the

burn room. The effect would be more pronounced for the smaller doors. The

second possible reason involves the door flow algorithm. The data suggests

that too much flow exits from the narrower doors. Note, however, that data

for steady gas burner fires in a room with various openings [11] was well7
modeled by the same door flow algorithm used here [10]. The third reason

relates to the overall modeling of convective heat transfer. In the present

model a single heat transfer coefficient is used where this is based on the

difference between the (average) upper layer temperature and that of the

(average) ceiling surface. The actual convective heat transfer is driven by

the differences between plume-driven ceiling/wall boundary flow temperatures

and ceiling wall surface temperatures. These latter temperature differences

and the corresponding distribution of heat transfer coefficient can be

expected to vary significantly from peak values at plume-ceiling impingement

to relatively low values at distant ceiling and upper-wall surface elements

[12-15]. A more detailed model for the upper layer- to-ceiling convective heat

transfer might improve agreement for these and other tests. It is also

likely, that such a model would have an impact on the aforementioned

simulation A estimates.

Figures 3, 23, 24 and 25 present typical vertical temperature profiles

together with the corresponding simulation result. For the burn room, the

experimental data clearly show two nearly- isothermal gas layers separated by a roughly 20 cm thick transition region. The predicted layer depth is in

satisfactory agreement with the data. Note that in each case there is some

increase in lower layer temperature above ambient. For 3 case of the 100 kW

fire (Figure 3), where the measured and predicted average temperature rise are in best agreement, this agreement is obtained from a predicted upper layer

temperature which is too high combined with a lower layer temperature which is

too low. Were layer mixing at the vent included, the lower layer temperature

would rise due to the effects of mixing. Also, the predicted upper layer

temperature would be expected to rise somewhat due to decreased radiation heat

loss through the lower layer to the floor. For constant fire size, narrowing

the vent increases the mixing; Figures 3 and 23 illustrate this. For constant

vent size, decreasing the fire size decreases mixing; Figures 3 and 25

illustrate this.

No attempt was made to simulate the effect of the smoke candle. (Note

that no test was re-run without artificial smoke to assess its effect.)

Raising the smoke production significantly above that for a relatively weakly

radiating methane fire would have lowered the predicted upper layer

temperature, the effect being more pronounced for the larger fires.

While the two -layer model seems satisfactory for the burn room, the

vertical temperature data for the corridor and lobby (Figure 3) show that,

away from the burn room, the assumption of two distinct, isothermal gas layers

is a much more questionable idealization. The two- layer model is based on the

assumption of well-mixed layers. In reality, the process by which the hot

layer is formed seems to involve the development of successive, stably

stratified layers [17, 18]. When hot gas first enters a compartment it

spreads as a "gravity current" under the ceiling to form a thin, nearly

uniform thickness hot layer. This spreads until it reaches the compartment

walls where it turns flowing back under itself. During this process the gas

forming the ceiling layer loses heat to the ceiling and may be mixed with the

cool gas already present in the room. We may think of one "complete ceiling

layer" to have been formed when the returning flow reaches the entry point. A

second layer then begins to form over the earlier one. The newest, hottest

8
layer forms under the ceiling pushing the older layers down as it forms.

Where there are suitable vents, the bottom-most layers may be siphoned off and

cool gas allowed to enter the lower part of the room. Eventually, as the

temperature difference between the newest and older layers decreases , a nearly

isothermal layer "stack" may be found. However, for times allowing only the

initial filling process to occur, this fill mechanism will not produce a pair

of well -mixed layers. Thus, it is not to be expected that the two- isothermal

layer model, based as it is on the assumption of well mixed layers, would be

entirely satisfactory for the corridor and lobby for tests studied here. For

the corridor and lobby a more detailed transient model for the layer growth

may be desirable. Even so, as will be shown in the next section, the two

layer model does seem to give adequate overall predictions of the temperature

and layer depth in these spaces.

5.3 Layer Depth Comparlsona

Turning now to the layer depth comparisons (figures 2a - 22a), the

computed layer interface heights are seen to be generally higher than those

given by applying the 10 percent temperature rise rule to the experimental

data. Where the temperature data suggests a more rapid fire buildup for the

calculation than the actual fire, the computed layer descends more rapidly

than the data indicates. This is to be expected if the computed and actual

fires do not develop in the same way, as already discussed. Otherwise the

comparisons are satisfactory. The computed layer depths depend on the plume

entrainment algorithm used. In NBS/Harvard VI the plume arises from an area

source, calculated using a virtual point source located below the actual fire

surface height. Alternate plume models might be used and different layer

depths predicted [16]. It is possible that some improvement might be found.

However, to date, no provision has been made in NBS/Harvard VI to change the

plume model.

If the layer depths are too small, the layer temperature will be high.

However, the vertically averaged temperature will be much less sensitive to

changes in layer depth. Changing the plume model, while possibly improving

the layer depth agreement, would alter the other results. A plume model which

increased layer depth would increase the door flows. This would increase the

convective heat loss from the bum room, lower its average temperature and

raise the temperature in the adjacent spaces. Considering the scatter of the

experimental data, the results are satisfactory. They do, however, suggest

use of either a layer interface definition by the "N percent rule" [6] with N

greater than the 10 percent or an alternate plume algorithm.

The use of artificial smoke to allow the hot layer behavior to be

visually tracked was not simulated in the calculations use and may have

influenced the comparisons . This would be expected to have more influence on

the configurations producing higher upper layer temperatures than those where

upper layer temperatures were lower. The simulation can treat gas as well as particulate radiation and, with empirically- altered input data to account for

the artificial smoke, it might have produced for favorable comparisons.

However, the empirical adjustment of input to produce a "best fit" to

9
experimental data must be used with caution when assessing the capability of a model. This was not done here.

6 . CONCLUSIONS

The simulations generally compare favorably with the experiments. As

the compartment geometry or fire size were varied the trends found experimentally were reproduced by the simulations. There were differences in detail,

however. In some cases the experimental data and simulations differed in ways

that are most likely due to differences between assumed and actual experimental conditions. For example, in the burner gas flow rate during the first two

minutes of the fire, and the radiation from the natural gas fire and its plume

which was assumed to be negligible, but which, due to the use of artificial

smoke, may not have been.

A known weakness of the simulation is its modeling of "oxygen limited

burning" which came into play here for the larger fires in the smaller spaces.

This is a known weakness of the simulation, scheduled for rectification.

Revised physics to account more properly for burning at times when the hot gas

layer nearly reaches or even envelopes a burning object should be included as soon as possible.

Mixing of the hot and cool layer gases as they pass through a vent

should be included in the simulation. Mixing occurs on both sides of a vent

and both should be included. This would likely improve the agreement between

the experimental data and the predictions studied here, especially in the

partially open bum room door cases

.

More detailed modeling of convective heat transfer could lead to

significant improvements in all aspects of temperature predictions. This is

especially true for fire scenarios, like the ones studied here, where

temperature increases of the upper layers are not so high that radiation

dominates the heat transfer processes (e.g., fire scenarios where upper layers

are within a few hundred K above ambient)

.

Provision for the use of alternative plume entrainment algorithms should

be considered. It is possible that use of a different available algorithm

might lead to better agreement with experiment.

The variable orifice coefficient capability of NBS/Harvard VI will be

useful in simulating fire -generated environments in corridor spaces having

segments with different cross-sections, or in other large area spaces having

irregular floor plans or varying ceiling heights.

Improvement of the gas burner algorithm to account for the heat absorbed

by the burner body early in the fire is worth considering.

Perhaps the most important conclusion of this study is that the

NBS/Harvard VI multiroom compartment fire model computer code can be expected

to provide useful predictions of fire-generated environments in multiroom fire

10
scenarios similar to those studied experimentally in [6]. These can be

characterized mainly by fire sizes on the order of several hundred kW and

total room areas of the order of 100 m^

.

7 . REFERENCES

[1] Gahm, J.B., "Computer Fire Code VI", NBS-CCR-83-451 (2 volumes), U.S.

Department of Commerce, Nat. Bur. of Stands., Gaithersburg, MD 20899,

December 1983.

[2] Ramsdell, J., "Variable Elimination in the Home Fire Code", ASME/AIChE

National Heat Transfer Conferences, paper 81-HT-3, Milwaukee, Wisconsin,

Aug. 2-5, 1981.

[3] Mitler, H. , "The Physical Basis for the Harvard Computer Fire Code",

Home Fire Project Technical Report No. 34, Division of Applied Sciences,

Harvard University, Cambridge, MA, October 1978.

[4] Mitler, H.E. and Emmons, H.W.

,

"Documentation for CFC V, The Fifth

Harvard Computer Fire Code", Home Fire Project Technical Report No. 45,

Division of Applied Sciences, Harvard University, October 1981.

[5] Rockett, J.A. and Morita, M. , "The NBS/Harvard VI Multi-Room Fire

Simulation", Fire Science and Technology, Vol 5, No 2, 1985 (159-164),

Tokyo, Japan.

[6] Cooper, L.Y.

,

Harkleroad, M. , Quintiere, J.G. and Rinkinen, W. , "An

experimental study of upper hot layer stratification in full-scale

multiroom fire scenarios". Jour, of Heat Transfer, Vol. 104, p. 741,

November 1982.

[7] McCaffrey, B. , "Measurements of the Radiative Power Output of Some

Buoyant Diffusion Fl£unes", Western States Section, Combustion Institute,

WSS/CI 81-15, Pullman, WA, 1981.

[8] McCaffrey, B.J. and Rockett, J.A., "Static pressure measurements of

enclosure fires". Jour, of Research of the Nat. Bur. of Stands.,

Vol. 82, No. 2, p. 107, 117, Sept. -Oct. 1977.

[9] Steckler, K.D.

,

Baum, H.R. and Quintiere, J.Q., "Fire Induced Flow

Through Room Openings - Flow Coefficient", NBSIR 83-2801, U.S. Nat. Bur.

of Stands., Gaithersburg, MD 20899, March 1984.

[10] Rockett, J. A., "Modeling of NBS Mattress Tests With the Harvard Mark V

Fire Simulation", Fire and Materials, Vol 6, No 2, pp 80-95, June 1982

[11] Steckler, K.D.

,

Quintiere, J.G. and Rinkinen, W.J., "Flow Induced by

Fire in a Compartment", NBSIR 82-2520, U.S. National Bureau of

Standards, Washington, D.C., Sept. 1982

11
[12] Alpert, R.L. , Fire Induced Turbulent Ceiling-Jet" , FMRC Serial No.

19722-2 May 1971, Factory Mutual Research Corporation, 1151 BostonProvidence Turnpike, Norwood, MA 02062

[13] Veldman, C.C., Kubota, T. and Zukoski, E.E., "An Experimental

Investigation of the Heat Transfer from a Buoyant Gas Plume to a Horizontal Ceiling - Part 1, Unobstructed Ceiling", NBS-GCR-77-97

Part 2, Effects of Ceiling Layer, NBS-GCR-77-98 U.S. Nat. Bur. of

Sts., Washington, D.C.

,

1977

[14] Cooper, L.Y.

,

"Heat Transfer from a Buoyant Plume to an Unconfined

Ceiling", Journal of Heat Transfer, Vol 104, Aug., 1982

[15] Cooper, L.Y. and Stroup, D. , "Thermal Response of Unconfined Ceilings

Above Growing Fires and the Importance of Convective Heat Transfer",

Journal of Heat Transfer, Vol. 109, Feb., 1987.

[16] Rockett, J.A., McCaffrey, B.J. and Levine, R. , "Naval fire fighting

trainers: Effect of ventilation on fire environment (Model calculations

for 19F3 FFT)", NBSIR 85-3238, U.S. Nat. Bur. of Stds. Washington, D.C.

,

December 1985

[17] Tangren, E.N.

,

Sargent, W.J. and Zukoski, E.E., "Hydraulic and Numeric

Modeling of Room Fires", Daniel and Florence Guggerheim Jet Propolsion

Center, California Institute of Technology, Pasadena, CA, June, 1978.

[18] Zukoski, E.E., and Kubota, T. , "Experimental Study of Environment and

Heat Transfer in a Room Fire, Final Report", California Institute of

Technology, Division of Engineering and Applied Science, Pasadena, CA

July 1984.

12
Table 1. Figure Nunbera Versus Test Parameters

Configxiration

Full

Fire

1/2

Corridor

3/4

Corridor

FuU

Corridor

Full

Corridor

1/2 Door

Full

Corridor

1/4 Door

Full

Corridor

1/8 Door

Corridor

and Lobby

25 kW 4 5 6 7, 25

100 kW 8 9 10 11. 24 12, 24 13. 23 2, 3, 22

225 kW 14 15 16 17. 25 Ramp 18 19 20 21

13
Tabl* 2. Input Data

Fuel Properties :

Heat of combustion 55. S MJ/Kg

Fraction of heat released

Stoichiometric air/ fuel mass ratio Gr C02 produced per gr fuel burned

Gr H20 produced per gr fuel burned

Gr CO produced per gr fuel burned

0.99

17.25 2.75

2.25

0.019 Gr soot produced per gr fuel burned

Flame absorption coefficient

0.008

1.55 1/m

Thermal Pronerties of Walls:

Thickness 0.0254 m

Density 800. kg/mg

Specific heat 1062. J/kg-deg C Thermal conductivity 0.134 W/m-deg C Room Dimensions;

Single Space Corridor

Rm. 1 - bum room:

2

- full corridor:

2-3/4 corridor:

2 - 1/2 corridor:

3 - lobby:

3-Space

1 - bum room:

2 - left corridor:

3 - middle corridor:

4 - right corridor:

5 - lobby:

4.22 X 3.35 X 2.44 high

18.97 X 2.41 X 2.44

14.23 X 2.41 X 2.44 9.48 X 2.41 X 2.44

3.00 X 15.40 X 2.44

Corridor

4.22 X 3.35 X 2.44

6.32 X 2.41 X 2.44

6.33 X 2.41 X 2.44 6.32 X 2.41 X 2.44

3.00 X 15.40 X 2.44

Vent Geometries:

Single Space Corridor* 3-Space Corridor** Rm 1

1

1

12

2

Rm 2: 1.07 X 2.03 high (f\all door) Rm 1 - Rm 3: 2: 0.54 X 2.03 (1/2 door) 2-3:

2: 0.27 X 2.03 (1/4 door) 3-4:

2: 0.13 X 2.03 (1/8 door) 4-5:

3: 1.25 X 2.01 3 - outside

outside: 0.94 X 0.15

1.07 X 2.03 high

2.41 X 2.43 2.41 X 2.43

1.25 X 2.01

0.94 X 0.1

*Rm 1 - bum room Rm 2 - corridor Rm 3 - lobby

**Rm 1 - bum room Rm 2 - left corridor Rm 3 - middle corridor Rm 4 - right corridor Rm 5 - lobby

14
15

Figure

1.

Sketches

of

the

four

test

configurations

with

indications

of

the

locations

of

vertical

instrument

arrays

(A,B,C,D,

and

E)

and

of

video

cameras

(V)
Figure 2a. 100 kW fire, Corridor and Lobby configuration: layer heights.

16
Q.<

UiO

z

UJs

UJ

u.

tL5

UJs

3

CO

CO

UJs

0.

Figure 2b. 100 kW fire, Corridor and Lobby configuration:

difference and average temperature rises.

X, pressure

17
HEIGHT

(m)

HEIGHT

(m)

HEIGHT

(m)

Figure 3.

FIRE ROOM

CORRIDOR

LOBBY

~r-'

1

1

1 Measurement at E

i d

L-' Prediction

100 kW fire

- 1'!

t = 200 sec

I-' /! 1

-

1

! !' ^ 1 Measured average

' IT Predicted average

(.

j

1

1 1 0 20 40 60

TEMPERATURE RISE C»C)

Vertical temperature profiles, 100 kW fire, Corridor and Lobby

configuration at 200 sec.

18
LAYER

HEIGHT

(m)

.

LAYER

HEIGHT

(m)

Figure 4a. 25 kW fire, 1/2 Corridor configuration: layer heights.

19
Figure 4b.

and average temperature rises.

20
LAYER

HEIGHT

(m)

LAYER

HEIGHT

(m)

Figure 5a. 25 kW fire, 3/4 Corridor configuration: layer heights.

21
Figure 5b. 25 kW fire, 3/4 Corridor configuration: A,

and average temperature rises.

pressure difference

22
LAYER

HEIGHT

(m)

LAYER

HEIGHT

(m)

Figure 6a. 25 kW fire, Full Corridor configuration: layer heights.

23
0 500 TIME (sec) Figure 6b. 25 kW fire, Full Corridor configuration: A, pressure difference

and average temperature rises.

24
Figure 7a. 25 kW fire, Corridor and Lobby configuration: layer heigh

25
AVERAGE

TEMPERATURE

RISE

(*0

Figure 7b. 25 kW fire, Corridor and Lobby configuration:

difference and average temperature rises.

A, pressure

26
H

X

g

ili X

X

UJ>

<

Figure 8a

TIME (s)

100 kW fire, 1/2 Corridor configuration:

500

layer heights

27
Figure 8b.

o

Ui(0s

UJ

cc3

H*<X

Ui0. 2

Ui

UJO

<X

UJ>

<

and average temperature rises.

pressure difference

28
LAYER

HEIGHT

(m)

_

LAYER

HEIGHT

(m)

Figure 9a. 100 kW fire, 3/4 Corridor configuration: layer heights.

29
Figure 9b. 100 kW fire, 3/4 Corridor configuration:

and average temperature rises.

X, pressure difference

30
LAYER

HEIGHT

(m)

2.5

X

g

UJX

X

LU>

<

TIME (s)

Figure 10a. 100 kW fire, Full Corridor configuration: layer heights

31
0 500

TIME (sec)

O

tii s

U1

(T3

K

<

CCUi

a.2

ui

UJo

<

oeUi>

<

Figure 10b. 100 kW fire, Full Corridor configuration: A,

and average temperature rises.

pressure difference

32
2.5

Figure 11a. 100 kW fire, Full Corridor configuration, 1/2 width door burn room

to corridor: layer heights.

33
TIME (sec) Figure lib. 100 kW fire, Full Corridor configuration, 1/2 width door burn roc to corridor: A, pressure difference and average temperature

rises.

34
LAYER

HEIGHT

<m)

LAYER

HEIGHT

(m)

Figure 12a. 100 kW fire, Full Corridor configuration, 1\4 width door bur

to corridor: layer heights.

35
Figure 12b. 100 kW fire, Full Corridor configuration, 1\4 width door burn room

to corridor: A, pressure difference and average temperature

rises.

36
LAYER

HEIGHT

(m)

LAYER

HEIGHT

(m)

TIME (sec)

Figure 13a. 100 kW fire, Full Corridor configuration, 1/8 width door burn r to corridor: layer heights.

37
TIME (s)

Figure 13b. 100 kW fire, Full Corridor configuration, 1/8 width door burn room

to corridor: A, pressure difference and average temperature

rises.

38
LAYER

HEIGHT

(m)

LAYER

HEIGHT

(m)

Figure 14a. 225 kW fire, 1/2 Corridor configuration: layer heights.

39
Figure 14b. 225 kW fire, 1/2 Corridor configuration: X, pressure difference

and average temperature rises.

40
LAYER

HEIGHT

(m)

LAYER

HEIGHT

(m)

TIME (sec)

Figure 15a. 225 kW fire, 3/4 Corridor configuration: layer heights.

41
Figure 15b. 225 kW fire, 3/4 Corridor configuration: A, and average

temperature rises

.

42
LAYER

HEIGHT

(m)

^

LAYER

HEIGHT

(m)

Figure 16a. 225 kW fire, Full Corridor configuration: layer heights.

43
0 500 TIME (sec) Figure 16b. 225 kW fire, Full Corridor configuration: A, pressure difference

and average temperature rises.

44
TIME (sec) Figure 17a. 225 kW fire, Corridor and Lobby configuration: layer he

45
AVERAGE

TEMPERATURE

RISE

(*C)

Figure 17b. 225 kW fire, Corridor and Lobby configuration: X, pressure

difference and average temperature rises.

46
LAYER

HEIGHT

(m)

LAYER

HEIGHT

(m)

47“
TIME (S«C) Figure 18b. Ramp fire, 1/2 Corridor configuration: A, pressure difference and

average temperature rises

.

48
LAYER

HEIGHT

(m)

.

LAYER

HEIGHT

(m)

Figure 19a. Ramp fire, 3/4 Corridor configuration: layer heights.

49 ~
Figure 19b. Kamp fire, 3/4 Corridor config\iratlon: A, pressure difference and

average temperature rises

.

50
LAYER

HEIGHT

(m)

LAYER

HEIGHT

(m)

TIME (sec)

Figure 20a. Ramp fire, Full Corridor configuration: layer heights.

51
0 500 TIME (sec) Figure 20b. Ramp fire, Full Corridor configuration: A, pressure

difference and average temperature rises.

52
Figure 21a. Ramp fire, Corridor and Lobby configuration: layer heights.

53
o

600

TIME (sec)

Figure 21b. Ramp fire, Corridor and Lobby configuration:

difference and average temperature rises.

, pressure

54
55

500

0

TIME

(sec)

TIME

(sec)

Figure

22a.

100

kW

fire,

Corridor

(subdivided

into

3

rooms)

and

Lobby:

layer

heights,
a.<I

UJo

z

UJK

UJo

UJc

3

0} CO

UJE

0.

Ulo

<E

UJ>

<

Figure 22b. 100 kW fire, Corridor (subdivided into 3 rooms) and Lobby

A, pressure difference and average temperature rises.

56
HEIGHT

(m)

Figure 23. Bum room vertical temperature distribution at 200 seconds,

100 kW fire: 1/8 normal width door.

57
HEIGHT

(m)

HEIGHT

(m)

HEIGHT

(m)

TEMPERATURE RISE (®C)

Figure 24. Burn room vertical temperature distribution at 200 seconds,

normal door, 100 kW fire: full, 3/4 and 1/2 corridors sizes.

58
HEIGHT

(m)

Figure 25. Bum room vertical temperature distribution at 200 seconds,

normal door, corridor plus lobby: 25 and 225 kW fires.

59
U.S. DEPT. OP COMM. 1. PUBLICATION OR 2. Performing Organ. Report NoJ

BIBLIOGRAPHIC DATA

REPORT NO.

SHEET (See instructions) NBSIR-87-3567

ruMicati«n Dat*

July 1987 4.

TITLE AND SUBTITLE

5. Comparisons of NBS/Harvard VI Simulations and Full-Scale, Multi-Room Fire Test Data

AUTHOR(S)

John A. Rockett, Masahiro Morita and Leonard Y. Cooper

6.

PERFORMING ORGANIZATION (If joint or other than NBS, see Instructions)

NATIONAL BUREAU OF STANDARDS

U.S. DEPARTMENT OF COMMERCE

GAITHERSBURG, MD 20899

9.

SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City, State, ZIP)

7. Contract/Grant No.

I. Type of Report & Period Covered

10.

SUPPLEMENTARY NOTES

I I Document describes a computer prosram; SF*I85, FIPS Software Summary, Is attached.

11.

ABSTRACT (A 200^word or less factual summary of most significant Information. If document Includes a significant

bibliography or literature survey, mention It here)

The NBS/Harvard VI multiroom fire jnodel computer code was used to simulate results of

previously reported full-scale, multi—room fire experiments. The tests and simulations

involved: four different compartment configurations made up of two or three rooms

connected by open doorways, four different fire types generated by a methane burner

located in the room identified as the bum room, and up to four different doorway

openings between the bum room and the adjacent space. A total of nineteen different

tests were carried out and simulated. Comparisons between slmnlated and measured

parameters of the fire-generated environments are reviewed. While the computer code

is generally found to provide excellent simulations for the entire range of tests,

several areas in modeling detail are identified as requiring clarification, research,

and further improvement. The improvements should be incorporated in future versions of

the NBS/Harvard Multi-Room Fire Model.

12.

KEY WORDS (S»x to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolons)

computer models; compartment fires; fire models^ full-scale compartment fire experiment!

multi-room fires; simulation; validation

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