NAT'L INST. OF STAND & TECH

Aiilob

Mm&M

Reference

NBSIR 83-2805

NBS

Publications

Park Service Room Fire Test

Simulations Using the Harvard

Level 5.2 Computer Fire Model

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Fire Research

Gaithersburg, Maryland 20899

June 1984

This work was partially supported by grants from the

U.S. Department of Health and Human Services and the

U.S. Park Service, Department of Interior

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U.S. DEPARTMENT OF COMMERCE

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NATIONAL BUREAU OF STANDARDS

NATIONAL BUREAU OF STANDARDS

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NBSIR 83-2805

PARK SERVICE ROOM FIRE TEST

SIMULATIONS USING THE HARVARD

LEVEL 5.2 COMPUTER FIRE MODEL

John A. Rockett

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Fire Research

Gaithersburg, Maryland 20899

June 1984

This work was partially supported by grants from the

U.S. Department of Health and Human Services and the

U.S. Park Service, Department of Interior

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

NATIONAL BUREAU OF STANDARDS, Ernest Ambler. Director

TABLE OF CONTENTS

Page

LIST OF TABLES iv

LIST OF FIGURES v

Abstract 1

INTRODUCTION 1

FUEL PARAMETERS 5

FIRE TESTS AND TEST ROOM SIMULATIONS 11

DOUBLE AND QUARDUPLE SIZE ROOM SIMULATIONS 19

CONCLUSIONS 22

REFERENCES 25

iii
LIST OF TABLES

Page

Table 1. Fuel Loading in Fire Tests 26

Table 2. Fuel Simulation Parameters 27

iv
LIST OF FIGURES

Page

Figure 1. Experimental Rate of Heat Release Versus

Time, Furniture Calorimeter Data, Bed with

Headboard Made Up with Bedding, Sidetable:

Three Repeat Tests of Nominally Identical

Furnishings 30

Figure 2. Furniture Calorimeter Rate of Heat Release

Data Compared to Free-Burn Simulation 31

Figure 3. Free Burn Simulation Rate of Heat Release

Versus Time for 2 and 3 Object Bed-Sidetable

Simulations 32

Figure 4. Experimental Rate of Heat Release Versus

Time, Room Fire Test, Gypsum Walls. Based

on Hood Stack Flow and Oxygen Concentration

Data: Two Repeat Tests of Nominally Identical

Furnishings 33

Figure 5. Gas Temperature, 0.44 m Below the Room Ceiling,

0.3 m from Left Wall and 0.3 m from Front Wall.

Also Included is the Calculated Temperature of

the Upper Layer for the 3 Object Simulation 34

Figure 6. Rate of Heat Release for the Simulated Free and

Room Burns 35

Figure 7. Rate of Heat Release for the Simulated and Room

Burns. Simulation Variables Changed to Reproduce

Better the Heat Release of the Room Burn as Recorded by the Hood Stack Sensor 36

Figure 8. Upper Gas Temperature for the Simulated and Room

Burns. Simulation Variables Changed to Reproduce Better the Heat Release of the Room Burn as Recorded by the Hood Stack Sensors 37

Figure 9. Simulated Upper Gas Temperature for Three Rooms

of Differing Area, Identical Vents: 3 Object

Bed Simulation 38

Figure 10. Mass Pyrolysis Rate, 2 Object Bed Simulation,

2 Beds, Double Room, First Bed Ignited by

Flame Contact with Burning Wastebasket, Second

Bed Ignited by Radiation from Upper Gas Layer,

Walls and Ceiling, and Flames from Other Bed 39

v

Park Service Room Fire Test Simulations

Using the Harvard Level 5.2 Computer Fire Model

John A. Rockett

Senior Scientist

National Bureau of Standards

Center for Fire Research

Washington, D.C. 20234

ABSTRACT

The Fire Center has conducted a series of full-scale tests of

hotel-like rooms. The furnishings were a bed with headboard

"made up" with bedding, and a wooden sidetable. The ignition

source was a wastebasket. The furniture was burned in the

new N.B.S. furniture calorimeter and in a 2.44 x 3.66 x 2.44

high room. As an adjunct to analysis of the test results, a series of simulations of the fire tests were run using the

Harvard Fire Simulation. This report describes the

simulations and their results.

The principal finding of the simulations was that the room

had little effect in augmenting the burning of this fuel

package. The simulation result was partially due to the burn

algorithm used and partially due to the relatively large fire area and short assumed flame radiation extinction length.

This finding might not have been true had the individual

objects been smaller in area or their flames less opaque. A

different burn algorithm might also have produced different

results

.

INTRODUCTION AND SUMMARY

The Fire Center has conducted a series of full-scale fire tests of

hotel-like rooms. The work was sponsored by the U.S. Park Service and

the fire tests involved fuel loads representative of those found in

tourist accomodations currently available in a number of our National

Parks. The furnishings were a bed with headboard, "made up" with

bedding, and a wooden side table. The ignition source was a "standard

Berkeley wastebasket" [1]. The furniture was burned in the new N.B.S.

furniture calorimeter [2] and in a 2.44 x 3.66 x 2.44 m high room. For

1
some tests the room had combustible walls, in others the walls were

plasterboard [3]. As an adjunct to analysis of the test results, a

series of simulations of the fire tests were run using the Harvard Fire

Simulation level 5.2 [1,4,5]. This report describes the simulations

and their results. Only the plasterboard wall - room tests and

associated furniture calorimeter tests were considered, as the version

of the Harvard simulation available did not include a working algorithm

for wall burning.

The specific questions addressed in carrying out the simulations were

related to the effects of room size and fuel load. To have

investigated these questions experimentally would have involved

considerable expense. A set of rooms of varying size would have had to

be built and full-scale fire tests, which are inherently expensive in

manpower and material, would have had to be conducted. The analytic

simulations, on the other hand, can readily study these effects. Six

simulations were run:

> A "free-burn" of the wastebasket igniter and a bed-sidetable unit. The free-burn condition was simulated by

specifying a very large room with a large, tall door.

> The same fuel in a room similar to that used in the room

tests.

> The same fuel in a room of twice the area of the test room. The "double" room had the same ceiling height and door size

as the test room.

> The same fuel in a room of four times the area of the test

room. Again, the ceiling height and door size corresponded

to the test room.

> The wastebasket igniter and two identical bed units in a room twice the area of the test room. In these simulations,

the two beds were positioned so that the wastebasket ignited

2
only one by flame contact. The other ignited if the fire

caused by the first bed was intense enough and of sufficient

duration to ignite the second bed by radiant and convective

heat transfer (no flame contact).

> The same "double fuel package" in a room of four times the area of the test room. The same ignition condition as in the

previous case was used.

The fuel package used in the simulation, which will be discussed in

detail presently, was adjusted to give approximate agreement between

the furniture calorimeter tests and the free-burn simulation. With one

exception, specifically discussed, these fuel parameters were then used

for all the remaining simulatons. As mentioned above, except for the

free-burn simulations, a single door of the same size for all room

sizes provided the only ventilation for the simulated fires.

The principal finding of the simulations was that, for the burn

algorithm used, the room had little effect in augmenting the burning

rate of this fuel package. This differs from the experimental burns

where a definite augmentation of rate of heat release was found in the

room as compared to the calorimeter burns. The simulation result was

partially due to the burn algorithm used and partially a result of the

relatively large fire area and short assumed flame radiation extinction

length. Under these conditions, the heat flux at the fuel surface,

which determines the fuel pyrolysis rate, was determined primarily by

the radiation from the flame immediately above the surface. Most of

the radiation from the hot gases, upper walls and ceiling, and other

fire plumes, did not penetrate through the relatively opaque flames

originating from the object itself. Thus the object's surroundings had

little effect on its burning behavior. This might not have been the

3
case had the individual objects been smaller in area or their flames

less opaque.

Due to the larger area for heat loss in the larger rooms, gas

temperatures in the upper part of those rooms were lower than in the

smaller ones for the same fuel load. For the door size used, unburned

fuel in the form of soot but no excess gaseous fuel exited from the

door for the one-bed fuel load in the smallest room.

Ventilation-limited burning did not occur. For the same fuel in the

two larger rooms, the slightly lower temperatures resulted in a

slightly higher ventilation rate - due to the slightly greater density

of the exiting, hot gases. (The reason for this is discussed in [6]

and illustrated in [6], figure 4.)

Addition of a second bed in the largest (quad) room had no effect as

the second bed did not ignite. In the double room, the second bed did

ignite but ventilation-limited burning did not occur. The increase in

fire size due to ignition of the second bed was largely offset by

exhaustion of the fuel of the initially ignited bed. The rate of heat

release for the second bed was qualitatively similar to that for the

initially ignited one but, due to the preheating of the second bed

prior to its ignition, the time scale for its burning was compressed

and its rate of heat release increased.

The concept of superposition of separate item free-burn mass loss rates

to estimate the mass loss rate for multiple objects burning in a room

4
was found to be approximately correct for the cases studied, but may

underestimate the mass loss rate to be expected in a severe room fire.

FUEL PARAMETERS

At the time this work was done, the full-scale fire tests that were to

be simulated had just been completed. Only preliminary computer runs

of the data were available. Documentation for the tests was being

prepared, but information was scattered among a number of workers and

data notebooks. The amount and type of fuel involved in these tests,

as verbally reported to the author and as used in developing these

simulations, is listed in table 1. Note, however, that this

information may not correspond exactly to that actually applicable and

which will be reported in the official test report. Any difference is

expected to be minor and would not affect the spirit of the simulations

as they attempt to capture the qualitative features of the fires, with

only approximate quantitative agreement sought.

The author had witnessed one of the fire tests and viewed video tapes

of others. He had discussed the qualitative behavior of the specific

tests of interest here with the test chief, Mr. B. Lee. The behavior

of the bed was reported to be generally similar in the room and in the

furniture calorimeter: After ignition of the wastebasket, the bedding

rapidly became involved. Fire spread over the whole surface of the bed

and, under the bed, the dust cover on the underside of the mattress

burned. This fire soon subsided as the bedding was consumed. Note

that the bedding was made-up on the bed and then rumpled to simulate a

5
"slept-in" condition. This allowed it to burn more independently of

the mattress than if it had been in the unrumpled, made-up condition

(as had been the case of the bedding in the previous mattress

simulations [1]). After passing through a minimum burning rate, the

fire grew again as the mattress and bed frame became involved. The

fire spread to include the wooden headboard and, eventually, the side

table (and, for rooms with combustible walls, the walls).

Figure 1 presents the heat release rate versus time for three furniture

calorimeter tests of a bed-sidetable unit ignited by a wastebasket.

Note that there is a distinct difference between test FB01 and tests

FB04 and FB06*. FB04 and FB06 are about as close as can be expected

for repeat full-scale fire tests. Test FB01, although differing

significantly from the other two, is qualitatively similar and still

within the quantitative agreement often found in repeat full-scale fire

tests. A fourth repeat test, FB03, is not shown as figure 1 is already

difficult to read. It was close to FB04 and FB06. An average of FB03,

04 and 06 was adopted as the typical behavior to be expected for this

fuel and the behavior to be simulated.

Figure 2 shows the result of a simulation of this fuel in a room 24.4

x 36.6 x 24.4 m high, ventilated by a single door 10.76 m wide by 24.03

m high. Thus the simulation is essentially for a "free-burn" or burn

* Test details are available in [3]. The tests were numbered FB01, 02,

... for free-burns (i.e., those conducted under the calorimeter hood)

and RB01, 02, ... for room burns (i.e., those conducted in the

enclosure whose vent discharged into the calorimeter hood).

6
"out of doors" of the fuel. Several implications of this figure are

noteworthy.

> The simulation reproduces the two separate peaks. The

simulation peaks are somewhat broader than the observed ones

and the dip between slightly deeper. The predicted heat

release rate beyond the second peak (from 850 to 1100

seconds) is somewhat above the average of the observations.

> The height of the first peak has been adjusted to an approximate average of the observed peaks for FR03, 04 and

06.

> The simulated igniting wastebasket produces a more

pronounced peak than the actual one.

The simulation presented in figure 2 uses a total of four objects.

Object 1, the igniting wastebasket, is identical to that used in [1],

For the present tests the ignition source was nominally similar to that

used in the previous study so the same parameters were used. Objects

2-4 simulated the bed and other furnishings. Object 2 was intended to

simulate the light fuel (bedding) responsible for the first peak. It

combined a relatively small amount of fuel with rapid fire development.

Its area corresponded to that of the bed top surface, increased

somewhat to account for the observation that the bedding draped over

the sides of the bed and the dust cover on the under side of the

mattress burned during the first peak period. Object 3 was to simulate

the fuel causing the second peak. It included slightly less than

one-half the remaining fuel. Its 16 kg mass was only 60% of the

combustible in the mattress and spring. It had a slower growth rate

and slightly smaller area to represent the mattress itself and the box

spring. Except for the reduced mass, relative to its size, the

parameters used to define the burning of the mattress and spring were

similar to those found satisfactory in the earlier study for the

7
simulation of a mattress [1]. Object 4 contained the remaining

mattress and spring fuel, as well as the headboard, bed frame and the

sidetable fuel. It had a smaller area and was intended to represent

the more massive parts of the bed and furnishings. These fuels would

presumably become involved later in the development of the fire.

Accordingly object 4 was positioned to ignite somewhat after objects 2

and 3.

The exact fuel parameters used are listed in table 2. They were

arrived at by a trial and error process. The selection, however, did

follow a pattern. The fire growth parameter varies the time between an

object's ignition and full involvement and, in particular, the

steepness of the rise to peak burning. The object area (provided it

has enough mass, as discussed below) sets the height of the peak. The

object's mass sets the length of steady burning once the peak has been

reached. Finally, for the algorithm used in these simulations, the

rate of decay as the fuel becomes exhausted is determined by the

burnout time constant. Transition to burnout is set by an input

parameter: the fraction of the object's initial mass at which

transition occurs. For the algorithm used, the two burnout constants

are not modified as the burning conditions vary throughout the

simulation. If the object's mass is small relative to its surface

area, the burnout phase of its behavior may encroach on the growth

phase. In this case there will be no steady burning period and the

peak burning rate will depend on the combination of all the parameters.

This is the case for objects 2 through 4 of this simulation. For

8
objects 2 and 3, the growth rate was chosen to give the observed rate

of rise ahead of the peak, the burnout time constant chosen to give the

observed slope after the peak and the object mass, area and burnout

transition chosen to give the desired peak height. In doing this, mass

was shifted between the three objects comprising the bed system, but

the total mass was always equal to the actual mass. If the burnout

phase parameters had been made functions of the heat flux incident on

the fuel surface, the extent of the overlap between the growth and

burnout phases might have been altered. A small change in the overlap

would change the peak burning rate substantially as the steeply rising

growth and sharply decaying burnout phases became more separated. The

burning area was forced by the bed dimensions but was adjusted within

a small range around this value.* The result gave too deep a trough

between the two peaks so, in the final choice of parameters, the first

peak was broadened somewhat so that the minimum between the first and

second peaks was raised. This was accomplished by increasing the

bedding mass from 3.2 to 4.14 kg. and lengthening the burnout phase of

object 2's involvement by increasing the mass fraction for the

* As stated earlier, the maximum burning area for object 2 (the

bedding) was increased over the bed's surface area to account for the

bedding draped over the sides of the bed. This worked well. The area

for object 3 (the mattress) was initially taken as the bed"s geometric

area. To reproduce the desired peak heat release rate this required a relatively small burn-out rate constant and yielded a broad, flat peak.

Reducing the area and increasing the rate constant gave the desired

shape. The area, however, was less than the bed's geometric, top

surface area. For object 4, the area had to be much less than the

geometric area for a satisfactory representation of the data. In

interpreting this, it must be remembered that the burn algorithm

assumes a circular fire, growing until it covers the entire object.

The actual fire may not be circular, but may migrate across the object

9
transition to burnout. In fitting the second peak, the logarithm of

the observed data was plotted against time. Two distinct decay regions

were found: between 700 and 900 seconds the rate of heat release

dropped rapidly; after 900 seconds, a distinctly slower rate of decay

was observed. If a single object were used to simulate the behavior

after 500 seconds either the upper part of the peak would be too broad,

or the tail (beyond 900 seconds) not well reproduced. In addition, for

a qualitatively satisfactory fit to the free-burn data, only about half

the total fuel available could be accounted for; if more fuel were

used, the second peak was much too broad. By dividing the remaining

fuel between two objects (3 and 4) the narrow peak could be simulated

while still accounting for all the fuel.

Having arrived at a satisfactory set of free-burn fuel parameters,

these were used for the remaining one-bed simulations. For simulations

involving two beds a change was necessary. The Harvard simulation used

allows for a maximum of five objects. With three objects per bed unit,

two beds could not be simulated. It was decided that the behavior

after the second peak was of less importance than that prior to and

immediately around it. Accordingly, for the two bed simulations, the

object representing the late burnout phase was eliminated. Thus five

objects, total, were used: the ignition wastebasket (object 1), the

with an irregular shape. In some cases, parts of the object ignited

early in the fire may actually burn-out before other parts become

involved. The fire may be moving across the object without growing

much in size. This is an explanation for the parameter selection found

necessary for object 4. It may not be the only explanation.

10
first bed (objects 2 and 3; object 4 omitted) and the second bed (two

objects identical to objects 2 and 3). Figure 3 compares the free-burn

rate of heat release for the 3 object and 2 object bed simulations.

One may think of these two object, two bed simulations as though the

room contained only the wastbasket and two beds made up with bedding

but without headboards. There would be no other furniture in the room.

FIRE TESTS AND TEST ROOM SIMULATIONS

Two nominally identical tests were conducted in the burn room fitted

with gypsum walls and ceiling. The observed rate of heat release

versus time for these two tests is shown in figure 4. The data shown

in figure 4 were computed from the gas mass flow rate and oxygen

concentration recorded in the exhaust stack of the hood located outside

and above the burn room door. The same procedure was used to compute

the heat release rates shown in figure 1 except, in the latter case,

the fuel was not burned in the room but, rather, on the floor outside

the room and directly under the hood. Thus the data of figure 4

includes heat released by burning occuring outside the room as well as

that in the room. Test RB01 shown in figure 4 is qualitatively similar

to tests FB04 and FB06 shown in figure 1. However, both peaks of RB01

are distinctly higher for the room burn than any of the calorimeter

("free") burns. The other room burn, RB04, is qualitatively different.

It shows three peaks: the first, corresponding in time to the first,

RB01 peak, has a much diminished amplitude although it is nearly as

high as that of FB06. The second and third peaks of RB04, on the other

11
hand, are much higher than any of the free-burn tests or the second

peak of RB01. These experimental results suggest a definite effect of

the room on the total rate of heat release.

Several observations must be made relative to figures 1 and 4. 1) A

senior CFR staff member more familiar with the rate of heat release

calorimeter than the author pointed out the possibility that,

especially during periods of high heat release rate, flames may extend

close to the hood surface; the relatively cool hood might cause some

quenching. Quenching may have occured in both the free-burn and room

tests, but, due to the differing flame geometries, would probably have

been more significant for the free-burns. Thus the rate of heat

release shown in figure 1 may be somewhat less than a true free-burn

would have recorded and the difference between the free-burn and room

burn heat release rates may be less than figures 1 and 4 suggest. 2)

The peak rate of heat release during the free burn was about 1.2 MW.

The flame plume from a pool fire entrains about sixteen times its

stoichiometric air requirement between the burning surface and the

visible flame tip, or, for this 1.2 MW fire, somewhat over 10,000 scfm

of air, the rated capacity of the hood system. Thus, this fire would

probably result in a layer of hot gas trapped in the hood between the

hood skirt and the exhaust. To the extent that a hot layer formed in

the hood, the fire would not be a true free burn, but similar to a fire

in a well ventilated room. Thus, the calorimeter burns would have

somewhat the character of a room burn; the difference between the

"free" burn and room burn tests would be reduced by this. 3) The video

12
tapes of RB01 were reviewed with particular regard to the amount of

flame visible outside the door. It was assumed that any appreciable

heat release outside the room door would be obvious as flames. Indeed

a large flame plume extended from the door for about 50 seconds at

about 250 seconds into the burn. This was preceeded and accompanied by

a considerable volume of black smoke. However, during the second

period of high heat release, from 700 to 850 seconds, no flames were

seen outside the door. The room was relatively free of smoke, but

flames extended to and across the ceiling. 4) In discussions of the

simulation and test results with CFR staff it has been suggested that

the large augmentation of the first peak for RB01 might be due to

burning of the paper on the surface of the gypsum wall board. Because

of the large amount of smoke and the camera angle relative to the fire,

the video tapes shed no light on this speculation. The author can find

little test data to confirm or refute this idea. Loftus et al [7]

report on the potential heat of gypsum board with and without the paper

coating. The net effect of the paper was +18.5 MJ per square meter of

gypsum surface. If this heat were released by burning the paper off

the room ceiling as a triangular pulse of 60 seconds duration (see

figure 4) it would produce a peak rate of heat release of almost 2 MW

or about the amount of additional heat needed to account for the

observed behavior. If the paper ignited later (at about 610 seconds,

just as the mattress began to be significantly involved) for RB04

rather than as the bedding burned (RB01), much of the disparate

behavior of these two tests could be reconciled.

13
In addition to rate of heat release, gas temperatures in the upper part

of the burn room provide a useful comparison with the simulation.

Although many temperatures may be recorded in the experiment, the

simulation calculates only an average value for all the hot gas in the

upper part of the room. In choosing a comparison temperature,

therefore, either some average must be constructed, or a single

thermocouple representative of the average should be chosen. Gas

temperatures in the burn room were recorded by a "thermocouple tree"

located 0.3 ra in from the left wall and 0.3 ra back from the front wall.

Thermocouples were located at 0.10, 0.44, 0.90, 1.44 and 1.94 m from

the ceiling. They showed that the hot-cool interface was about 1.5 m

below the ceiling after 200 seconds. Thus the three upper

thermocouples would lie in the hot gas layer. The temperatures

recorded by these three differ little throughout the test. They also

follow closely values recorded by thermocouples located near the

ceiling in other parts of the room with the exception of two near the

rear wall, left and right of the room centerline. These were about 100

K higher during the peak burning period around 700 seconds. The video

tapes of the fire suggest that these two thermocouples were near or in

the flame plume attached to the rear wall, extending from the headboard

to the ceiling and into the ceiling jet. The same three tree

thermocouples also closely followed the readings of the six uppermost

thermocouples of a "tree" mounted in the doorway. (Those from 0.1 to

0.81 m below the door soffit.) The thermocouple 0.44 m from the

ceiling has been chosen as representative of the average hot layer

temperature. Its readings are presented in figure 5. Also shown in

14
the figure is the simulation's computed hot layer temperature for the

four object fuel package in the standard room.

In addition to the "f ree-burns" described above, simulations were run

for three rooms. The basic room, corresponding to the actual fire test

room, was 2.44 by 3.66 by 2.44 m high. It had a single vent, a door,

2.03 m high by 0.76 m wide. The other two rooms had the same vent, but

were, for the "double" room, 4.88 x 3.66 x 2.44 m high, and the "quad"

room, 4.88 x 7.32 x 2.44 m high. In the smallest room, only one

bed-sidetable unit was considered, as it would not be possible to fit

two such units in the room. This simulation corresponded to the test

fires burned with non-combustible walls. The double room could

accomodate two full-size beds and some additional furniture, although

it would be a bit crowded. The quad room was about the size of a

large, contemporary motel room. Furnished with two beds and ancillary

furniture it would not be crowded. In the two larger rooms only one

bed was ignited by flame contact from the wastebasket. The other bed

was positioned so that it could only ignite by radiation from the

initially ignited bed and from the hot upper walls, room ceiling and

hot gases trapped in the room.

Simulation of the room fire tests based on the four object fuel package

discussed above and whose free-burn rate of heat release is shown in

figures 2 and 3 gave only slightly augmented heat release rates. The

free-burn and room burn results are compared in figure 6. Through the

first 600 seconds, the results are virtually identical. The second

15
peak is about 10% higher for the room than for the free-burn. As shown

in figure 5, the hot layer temperature is distinctly lower than the

experimental result. The simulation showed no ventilation-limited

burning at any time during the fire (there was always more than enough

oxygen to burn all the fuel pyrolyzed). The minimum calculated oxygen

concentration in the upper part of the room was 12 weight percent.

This is consistent with the video tape observation of no flames coming

out the door for the time around 700 to 850 seconds, but not for the

earlier peak around 250 seconds where a large flame brush extended from

the door.

To explore this discrepancy further, the simulation input was modified

to yield heat release rates closer to those shown in figure 4. This

was accomplished by delaying the burnout transition by increasing the

burnout transition mass ratio in proportion to the fraction: object

total heat flux divided by the heat flux received from only its own

flame (see table 2, note 5). The result is shown in figures 7 and 8.

Clearly the observed temperature is better simulated by this. For this

simulation, the minimum oxygen concentration in the upper layer was

10.1 weight percent at 690 seconds. The plume air entrainment was 1.63

times the stoichiometric requirement for the burning rate prevailing at

that time. Thus the simulation did not show ventilation-limited

burning even with the heat release rate increased to the experimental

value.

If the heat release rate of figure 4 is correct, then either the

16
free-burn result inferred from the calorimeter test is too low (due to

hood quenching?) or the simulation algorithm used is too insensitive

to the room conditions. The detailed simulation data sheds some light

on the latter possibility. The rate of growth of fire area and

pyrolysis rate per unit area, if not influenced by burnout, depend on

the heat flux incident on the fuel surface and thus may be increased by

placing the object in a room. During the first peak near 250 seconds

object 2 is the only significant contributor to the fire. Object 1

(the igniter wastebasket) had burned out at 130 seconds; object 4 had

not yet ignited and object 3's slowly developing fire produced two

orders of magnitude less heat than object 2. At 260 seconds, the time

that the temperature peaked, object 2's surface received just over 3%

of its heat from the hot gas layer and virtually none from the still

relatively cool ceiling and upper walls. 97% of the heat flux incident

on the surface came from its own flame plume. It seems unlikely that

this result would be much changed if the burnout parameters chosen were

made more sensitive to the incident flux (and then adjusted to yield

the free-burn result, as was done here). Thus the very large

augmentation of the first peak observed between the free and room burn

experiments cannot be explained by this model*. The second peak

occured at 720 simulation seconds. At this point object 2 was nearly

burned out and was producing two orders of magnitude less heat than

object 3. Object 4 was beginning to be a significant contributor,

providing about 16% of the heat released. Object 4 had lost very

* i.e., some other mechanism, such as the gypsum board paper surface

burning discussed above, must be invoked.

17
little of its initial weight and its burning was not influenced by the

burnout aspects of the simulation. It received slightly less than 1/3

its heat from the hot gas layer and ceiling. Thus object 4's rate of

heat release could be and was altered by the room. It provided much of

the burning rate augmentation found. Object 3 received only 18% of its

heat from the hot layer and ceiling so it would not be as strongly

influenced by its surroundings as object 4. In addition, at this time,

it had lost nearly half its initial weight and was beginning to enter

its burnout phase. This, in the present algorithm, is not sensitive to

the heat flux incident on the fuel; it is only sensitive to the mass

remaining. For this second peak, although the bulk of the heat to the

surface of object 3 came from its own flame, there was enough heat from

the room to alter its burning rate. Although this did occur, its

amount was smaller than it might have been because object 3 was

beginning to enter the burnout phase of its simulation. As a result of

the algorithm structure, the simulation probably under predicted the

effect of the room on object 3.

The level 5.2 Harvard room fire simulation wall heat transfer algorithm

assumes a simple wall construction consisting of a single, homogeneous

layer of inert material exposed on its cold side to ambient air. This

is not appropriate to the test room used in these experiments. The

test room walls were a single layer of 0.015 m thick gypsum wall board

furred out from cement block (except for the front wall containing the

door). Thus the single layer of gypsum, treated by the simulation as

the entire wall, was actually only the first layer of a multi-layer

18
wall. Treating the fire exposed layer as the entire wall may be

adequate for the short time during which heat is absorbed by the

exposed face but does not have time to penetrate through the first

layer. For longer times, the rear face of the exposed layer begins to

heat. Then the heat transfer conditions assumed for the back face of

the simple wall are no longer appropriate. One might compensate for

the overly simple wall conduction algorithm by increasing

(artificially) the thermal conductivity of the assumed single layer of

wall material. However, this would change the thermal inertia of the

material and alter its transient response in an undesirable way.

Examination of figure 7 shows that, for the "altered" simulation

parameters, the heat release rate actually exceeded the experimentally

determined heat release rate throughout the entire second peak.

Nevertheless, figure 8 shows that the predicted room temperature was

below the experimental value at and beyond the peak. Numerical

experiments done as a part of other simulations suggest that this is

partially due to inadequacies of the single layer wall heat transfer

simulation. H05.2 assumes that the lower walls and floor do not heat.

This would also result in too large a heat loss late in the fire.

DOUBLE AND QUARDUPLE SIZE ROOM SIMULATIONS

As stated earlier, simulations of the bed-sidetable fuel package were

run for rooms of twice and four times the floor area of the test room.

The predicted upper layer gas temperature for the three-object bed

19
simulation in the three room sizes is shown in figure 9. The effect of

the increased surface for heat transfer (loss) is clear. Altering the

wall conduction algorithm would change this result slightly with all

three curves moved up late in the fire. The effect prior to 900

seconds would be small as, up to this time, little heat has penetrated

to the rear face of the fire exposed wall layer.

The behavior of a two bed fuel package was simulated for the two larger

rooms. In these simulations each bed was simulated by only two

objects, those representing the bedding, and the mattress and spring.

The object representing the bed frame, headboard and the sidetable was

omitted for each fuel package for the reasons explained earlier. The

second bed was positioned relative to the igniter wastebasket and

primary bed so that it could only ignite as a result of radiant heating

from the wastebasket and primary bed fires. Flames from these fires

could not contact the second bed. It was close to the primary bed, to

simulate the furniture arrangement commonly found in hotel rooms fitted

with a pair of similar beds. In the larger room the second bed heated

but did not reach its ignition temperature. In the smaller (double

size) room the second bed did ignite. It is of some interest that, had

its ignition temperature, 450 centigrade, been only slightly higher (10

degrees) it would not have ignited. The mass pyrolysis rate for this

simulation is shown in figure 10. Arrows on the time axis point to the

ignition times for the two beds. Comparing the mass pyrolysis rate of

the primary bed (from 50 to 700 seconds) with that of the second bed

(dotted curve from 710 seconds on) shows that they are generally

20
similar but that the time scale for the second bed's involvement is

somewhat compressed and the peak pyrolysis rates raised. This is

because the primary bed was cold when ignited whereas the second bed

had been preheated until its surface reached ignition conditions. Thus

flame spread across the second bed would be rapid and more of the heat

flux incident on its surface would be available to pyrolyze fuel, while

less would be needed to heat its interior.

It is also seen from figure 10 that the peak mass loss rate for the two

bed case is only slightly higher than for one-bed. This is because of

the limited fuel available in the first bed. At the time the second

bed ignited 56% of the mass of the first bed had already been consumed

and, at the time the second bed's bedding peaked (820 seconds), 72% of

the mass of the first bed was gone. Had the beds been more massive, or

the second bed ignited earlier (for example, because of a lower

ignition temperature), a higher total peak mass loss rate would have

been achieved. Because the first bed was burning out as the fire on

the second bed grew, ventilation-limited burning did not occur in this

room with its vent size and with this fuel load. The minimum

calculated oxygen mass fraction in the upper gas layer was 13% at 700

seconds, when the first bed burning peaked, and 11.9% at 1090 seconds,

just after the second bed burning peaked. The upper gas layer

descended to 0.94 m from the floor at 630 seconds. This still gave

0.34 m clearance between the bed surface and the layer, enough for the

fire plume to entrain more than enough air for the then current

pyrolysis rate. The closest approach to ventilation-limited burning

21
occured at 1080 seconds when the plume entrained 1.9 times the

stoichiometric air requirement.

It has been suggested that free-burn pyrolysis rates for each object in

a room can be added to give the post flashover behavior of a

multi-object fuel load in the room [8]. The pyrolysis rates for the

objects which became involved at flashover would be added to that of

the primary fire with their free-burn ignitions shifted to the time of

flashover. Figure 10 shows that this would be only approximately true.

Even where the room causes little augmentation of the burning for the

first object ignited, preheating of subsequently ignited objects may

significantly alter their free-burn behavior.

CONCLUSIONS

The experimental data shown in figures 1 and 4 suggests that there was

a considerable augmentation of burning as a result of the fire being

within a room. While the simulation suggests that some augmentation

may have occured, the amount was much less than these two figures

indicate. It is proposed that the experimental and simulation fire

situations may not be strictly comparable since the gypsum walls and

ceiling of the room, assumed inert by the simulation, may have

contributed much of the augmentation as their paper surface burned off.

Nevertheless , the pyrolysis rates may have been increased more by the

room than the simulation showed because of limitations in the

simulation's treatment of the burnout phase of an object's burning

22
cycle. The burnout phase of the algorithm is empirical; no

satisfactory physical mechanism has yet been proposed which would cause

the observed burnout behavior. Thus it is not possible to suggest a

physical mechanism by which burnout might be made sensitive to incident

heat flux. The present data provides some basis for a change in the

empirically derived algorithm used, but further confirmation should be

sought before a change is made.

The simulation did not show any period of ventilation limited burning

but the video tapes of the fire did show a considerable flame brush

exiting from the room door as the bedding fire peaked. It is suggested

that, at this time, the gypsum board's paper surface might have been

burning. The appearance of flames out the door might have been simply

a consequence of a vigorous fire located so near the vent that its

natural flame was too long .to be accomodated entirely in the room.

Note that appearance of a flame out the door is not necessarily the

result of ventilation-limited burning; it may simply be caused by the

location and flame size of the fire.

The concept of superposition of free-burn pyrolysis rates to estimate

the post flashover burning of multiple objects is only approximately

valid. Although the room may not greatly alter the behavior of one

object, there can be substantial changes in burning behavior as a

result of preheating of objects in the room prior to flashover. This

cannot be readily inferred from the free-burn (furniture calorimeter)

test data although it might be estimated from material properties using

23
techniques similar to those embodied in the Harvard burn algorithm.

It should be possible to design a test which would demonstrate the

effect, if any, on the rate of heat release, of a substantial flame

brush impinging on a gypsum wall-board ceiling. Since the resultant

flame might extend a significant distance from the room door for a long

enough time to cause ignitions outside the room of origin (even though

that room had not flashed over in the conventional sense), it would

seem desirable to clarify this point.

The Harvard fire simulation wall-conduction algorithm should be

extended to allow more accurate treatment of multi-layer walls

including air spaces. H05.2 should also be altered to allow for the

heating of the lower walls and floor. The current H05.2 simulation of

the burnout phase of an object's behavior may be in error because it is

insensitive to incident heat flux.

24
REFERENCES

1] Rockett, J.A., "Modeling of NBS Mattress Tests with the

Harvard Mark V Fire Simulation", NBSIR 81-2440, U.S. Nat.

Bur. of Stds., Washington, D.C., 20234, May 1983

2] Babrauskas, V, Lawson, J.R., Walton, W.D. and Twilley,

W.H., "Upholstered Furniture Heat Release Rates Measured

with a Furniture Calorimeter", NBSIR 82-2604, U.S. Nat.

Bur. of Stds, Washington, D.C., 20234, December, 1982

3] Lee, B.T., "Effect of Wall and Room Surfaces on the Rates

of Heat, Smoke, and Carbon Monoxide Production in a Park

Lodging Bedroom Fire", to be published as an NBSIR in 1983

4] Mitler, H.E., "The Physical Basis for the Harvard Computer

Fire Code", Home Fire Project Report No. 34, Harvard

University, Cambridge, MA, October, 1978

5] 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, Cambridge, MA, October, 1981

6] Rockett, J.A. , "Fire Induced Gas Flow in an Enclosure", Combustion

Science and Technology, 1976, Vol 12, pp. 165-175

7] Loftus, J.J., Gross, D. and Robertson, A.F., "Potential

Heat", Proceeding of the American Society for Testing

and Materials, Philadelphia, PA, Vol 61, 1961

8] Walton, D. and Nelson, H. , personal communication of work

in progress, to be published.

25
Table 1

Fuel Loading in Fire Tests

Fuel Item

Filled Wastebasket

Bedding (1)

Mattress and Box Spring

Headboard

Night Table

Total Combustible Furnishings

Combustible Weight in Kilograms

0.75

3.2

24.7

14.4

10.6

53.7

Notes

1) Two pillows, two pillow cases, two cotton sheets, one blanket

26
Table 2

Fuel Simulation Parameters

Fuel Item

1 - Wastebasket and contents

Parameter Value

X 0.434 m

Y location coordinates 2.13 m

Z 0.32 m

Thickness 0.25 m

Equivalent Radius 0.2 m

Maximum Burning Radius 0.2 m

Density 35. kg/m**3

Heat of Pyrolysis 3.98E+5 J/kg

Initial mass 0.35 kg

Flame Spread Parameter 2.78E-2 m/sec

- Bedding

Parameter Value

X 1.22 m

Y location coordinates 2.74 m

Z 0.6 m

Thickness 0.1 m

Equivalent Radius 0.913 m

Maximum Burning Radius 1.263 m

Density 19.32 kg/m**3

Heat of Combustion (1) 3.00E+7 J/kg

Heat of Pyrolysis 2.00E+6 J/kg

Initial Mass 4.14 kg

Ignition temperature 723. K

Smoke fraction 0.25 gm/gm

Flame Spread Parameter 1.60E-2 m/sec

Burn-out Time Constant 40. sec Burn-out Rate Constant (5) 0.52/0. 55

- Mattress and Box Spring

Parameter Value

X 1.22 m

Y (2) location coordinates 1.44 m

z 0.48 m

Thickness 0.25 m

Equivalent Radius 0.913 m

27
Maximum Burning Radius

Density

Heat of Combustion (1)

Heat of Pyrolysis

Initial Mass

Ignition temperature

Smoke fraction

Flame Spread Parameter

Burn-out Time Constant

Burn-out Rate Constant

4 - Bed Frame, Headboard,

0.843 m 54.0 kg/m**3

3.00E+7 J/kg

2.00E+6 J/kg

16.0 kg

723. K

0.25 gm/gra

5.00E-3 m/sec

60. sec

(5) 0.5/0.66

Sidetable

Parameter Value

X (3)

Y location coordinates

Z

Thickness

Equivalent Radius (3)

Maximum Burning Radius (4)

Density

Heat of Combustion (1)

Heat of Pyrolysis

Initial Mass

Ignition temperature

Smoke fraction

Flame Spread Parameter

Burn-out Time Constant

Burn-out Rate Constant (5)

2.088 m

1.44 m

0.48 m

0.25 m

0.43 m

0.469 m

54.0 kg/m**3

3.00E+7 J/kg

2.00E+6 J/kg

32.66 kg

723. K

0.25 gm/gm

5.00E-3 m/sec

600. sec 0.4/0.72

Notes:

1) For all objects the program default values were used unless

values are given in this table. The default value for the

fraction of the heat of combustion actually realized . = 0.65

The heat released by an object is proportional to the

product of its heat of combustion and the fraction actually

released. Two to three figure accuracy heats of combustion

can be found for many materials, but . values for turbulent,

diffusion flames amount to little more than educated guesses.

Because of the large uncertainty in . , use of exact heats of

combustion is not particularly important.

2) Physically, objects 2 and 3 are centered near the same

point. They were separated to see if this (a) made any

difference to the simulation and (b) alleviated a poor

convergence (excessive iterations) near the second peak.

It had no effect on either, but the centers were kept

separated

28
3) Center placed to cause ignition at about 475 sec. This placed the peak burning for this object at close

to 900 sec. The equivalent radius and location of object

together with its rate of flame spread determine the

ignition time for object 4.

4) The simulation is not particularly sensitive to the

choice of this radius.

5) Second value used for simulation adjusted to produce

the experimental rate of heat release around the

second peak of RB01 (result shown in figures 7 and 8).

29

RATE

OF

HEAT

RELEASE

(MW)

TIME (seconds)

Figure 1. Experimental rate of heat release

versus time, furniture calorimeter

data, bed with headboard made up

with bedding, sidetable: three

repeat tests of nominally identical

furnishings
HEAT

RELEASE

RATE

(kW)

Figure 2. Furniture calorimeter rate of heat

release data compared to free-burn

simulation
1400

1200

1000

800

600

400

200

0

3 object simulation

2 object simulation

300 600 900 1200

TIME (seconds)

1500

Figure 3. Free burn simulation rate of heat

release versus time for 2 and 3

object bed-sidetable simulations

1800
HEAT

RELEASE

RATE

(MW)

TIME (seconds)

• Figure 4. Experimental rate of heat release versus time, room fire test,

gypsum walls. Based on hood stack flow and oxygen concentration

data: two repeat tests of nominally identical furnishings
900

800

700

600

500

400

300

200

100

500 1000 1500

TIME (seconds)

Figure 5. Gas temperature, 0.44 m below the room ceiling, 0.3 m from left wall

and 0.3 m from front wall. Also

included is the calculated temperature of the upper layer for the 3

object simulation
RATE

OF

HEAT

RELEASE

(kW)

TIME (seconds)

Figure 6. Rate of heat release for the

simulated free and room burns
HEAT

RELEASE

RATE

(MW)

Figure 7. Rate of heat release for the simulated and room burns.

Simulated variables changed to reproduce better the heat

release of the room burn as recorded by the hood stack

sensors
1000

900

800

700

600

500

400

300

200

100

0 500

I I I 1000 1500

TIME (seconds)

Figure 8. Upper gas temperature for the simulated and room burns.

Simulation variables changed to reproduce better the heat

release of the room burn as recorded by the hood stack

sensors
UPPER

LAYER

GAS

TEMPERATURE

(K)

TIME (seconds)

Figure 9. Simulated upper gas temperature

for three rooms of differing area,

identical vents: three object bed

simulation
PYROLYSIS

RATE

(g/s)

CM

Figure 10. Mass pyrolysis rate, 2 object bed

simulation, 2 beds, double room,

first bed ignited by flame contact with burning wastebasket,

second bed ignited by radiation

from upper gas layer, walls and

ceiling, and flames from other

bed
NBS-114A (REV. 2-80

U.S. DEPT. OP COMM. 1. BIBLIOGRAPHIC DATA

SHEET (See instructions)

PUBLICATION OR

REPORT NO.

2. Performing Organ. Report NoJ 3. NBSIR 85-2805

Publication Date June 1984

4. TITLE AND SUBTITLE

Park Service Room Fire Test Simulations Using the Harvard

Level 5.2 Computer Fire Model

5. AUTHOR(S)

John A. Rockett

6. PERFORMING ORGANIZATION (If joint or other than N BS, see in struction s) 7. Contract/Grant No. national bureau of standards

DEPARTMENT OF COMMERCE 8. Type of Report & Period Covered

WASHINGTON, D.C. 20234

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

Partially supported by the US Department of Interior

US Department of Health and Human Services and Park Service

Washington, DC Washington, DC

10. SUPPLEMENTARY NOTES

| | Document describes a computer program; SF-185, FIPS Software Summary, is attached.

11.

ABSTRACT (A 200-word or less factual summary of most significant information. I f document includes a significant

bibliography or literature survey, mention it here)

The Fire Center has conducted a series of full-scale tests of hotel-like rooms.

The furnishings were a bed with headboard "made up" with bedding, and a wooden

sidetable. The ignition source was a wastebasket. The furniture was burned in

the new NBS furniture calorimeter and in a 2.44 x 3.66 x 2.44 high room. As an adjunct to analysis of the test results, a series of simulations of the fire

tests were run using the Harvard Fire Simulation. This report describes the

simulations and their results.

The principal finding of the simulations was that the room had little effect in

augmenting the burning of this fuel package. The simulation result was partially

due to the burn algorithm used and partially due to the relatively large fire

area and short assumed flame radiation extinction length. This finding might not

have been true had the individual objects been smaller in area or their flames

less opaque. A different burn algorithm might also have produced different

results

12.

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

Full scale fire tests; furniture calorimeter; rate of heat release;

room fires

13.

AVAILABILITY 14. NO. OF

PRINTED PAGES

| X| Unlimited

| | For Official Distribution. Do Not Release to NTIS

| | Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D.C.

20402.

(~X| Order From National Technical Information Service (NTIS), Springfield, VA. 22161

45

15. Price

$8.50

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