Reference

NAT L INST. OF STAND & TECH

NBS

PUBLICATIONS

;iR 84-2897

AlllDt

Jefferson National Memorial

Historical Site Analysis of

Impact of Fire Safety Features

Harold E. Nelson

U S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Fire Research

Gaithersburg, MD 20899

March 1985

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84-2897

1985

Sponsored by:

National Park Service

Department of Interior

Washington, DC 20240

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NBSIR 84-2897

» • r JEFFERSON NATIONAL MEMORIAL

HISTORIAL SITE ANALYSIS OF

IMPACT OF FIRE SAFETY FEATURES

NATIONAL BUREAtJ OF STANDARDS UBRARy

- /O o

Harold E. Nelson

U S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Fire Research

Gaithersburg, MD 20899

March 1985

Sponsored by:

National Park Service

Department of Interior

Washington, DC 20240

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

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director
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TABLE OF CONTENTS

Page

List of Figures iv

List of Tables v

Foreward vi

Background 1

Assumptions 1

Procedure 3

Hazard Growth A

Impact of Emergency Smoke Removal 5

Response of Automatic Fire Sprinklers 6

Operation of Smoke Detectors 7

Emergency Egress of Visitors 7

Emergency Egress from the Memorial Arch 7

Analysis 9

References 9

Appendix A A-1

Appendix B B-1

-iii-
LIST OF FIGURES

Page

Figure 1. Facility Floor Plan 10

Figure 2. "Semi-Universal Fire Curve" 11

Figure 3. Fire Environment 12

Figure 4. Fire Conditions 13

Figure 5. Sprinkler Response 14

Figure 6. Normally Expected Egress Capacity 15

Figure 7. Optimum Egress Capacity 16

-iv-
LIST OF TABLES

Page

Table 1. Time to Development of Critical Conditions for Typical

Fire Safety Arrangements 17

Table 2. Calculated Number of Persons Who Can Be Evacuated Prior

to Advent of Firest Critical Condition Shown in Table 1 . . . 18

Table of Appendix B B-5

-V-
FOREWARD

This report discusses the application of specific fire safety features and

their impact on visitor safety. It is the product of a unique effort in

intergovernmental cooperation. The report demonstrates the direct benefits

of the National Bureau of Standards, Center for Fire Research program as implemented at specific facilities.

We are especially pleased with this combined effort which was aimed at

utilizing these concepts. In particular, this information has been useful

to National Park Service management for application at Jefferson National

Expansion Memorial (JNEM). The result is a better understanding of both

the technical research and of its direct, practical benefits.

Because of this joint effort, the National Park Service will be able to

safely accommodate additional visitors at JNEM for relatively low additional costs. This permits the Service to apply fire safety features in

the most cost-effective manner with a clear assurance of their effecGeorge Gowans

Chief, Engineering and Safety

Services Division

National Park Service

Washington, D.C. 20013-7127

March 1, 1985

tiveness

.

VI
Jefferson National Memorial Historical Site

Analysis of Impact of Fire Safety Features

Background

This analysis has been conducted by staff members of the National

Bureau of Standards as part of the ongoing project to develop improved

fire safety evaluation approaches for the National Park Service. The

study at the Jefferson National Memorial Historical Site was undertaken

both as a feasibility study to assist the National Bureau of Standards in

appraising practicality of analytical approaches, and as assistance to the

National Park Service in their ongoing efforts to provide effective fire

safety in an efficient manner.

The approach used in this analysis consisted of application of fire

dynamics calculation methods to predict the rate of development of fire

nroducts (smoke and hot gases) , the impact of those products within the

facility, the relationship of such fire development to the emergency

evacuation of visitors, and the response and operation of fire detection

and fire protection systems.

Figure 1 is a floor plan of the museum and lobby component of the facility.

In addition the facility involves the Memorial Arch rising over the space

diagrammed in Figure 1. The footings of the arch appear as large triangles

in Figure 1. The arch is accessible to visitors. Normal access is through

the lobby descending to tram loading stations located approximately two

floors lower than the lobby. Emergency egress can be made through the

lobby or through alternative exits located on the lobby side of the doors

that separate the tram loading area from the lobby. These are located

on the ramp descending from the lobby to the tram loading doors. The doors

separating the tram loading area from the lobby are located one floor lower

and directly beneath the main museum entrance doors.

Assumptions

The current ability to calculate fire phenomena required several assumptions

In some cases the assumptions may differ from the expected situation. In

1
these instances, however, a conservative engineering position was taken to

increase the likelihood that the predictions developed are on the safe side.

The principal assumptions made were:

1. A severe fire occurs in the museum area. The hypothesized fire exceeds

that likely from the fixed exhibits. It represents the maximum burning rate

that might occur during an exhibit unpacking and construction operation which

involves packing material, pallets, and other similiar loose combustibles in

addition to a significant quantity of exhibit materials. To simulate this

condition, a fire curve developed by Cooper [1] was used. This curve, which

Cooper has named "a semi-universal fire curve" represents a rapidly growing

fire based on a compilation of fire test data. This curve is shown in Figure 2.

2. The fire generates smoke and hot gases which rise in a relatively narrow

plume towards the ceiling. Air is entrained into the plume as it rises

increasing its volume but decreasing its temperature. When the plume reaches

the ceiling it spreads like an impacting fluid jet forming a smoke layer. As

the fire progresses this reasonably homogeneous smoke layer descends towards

the floor. The air below the layer remains at roughly room temperature and

is relatively free of smoke. As the temperature of the smoke layer increases,

thermal heat radiation will be transmitted towards the floor, heating objects

below the smoke layer. Figure 3 shows a schematic diagram of the fire environment. The general correctness of this assumption has been repeatedly demonstrated in tests and experiments.

3. The smoke produced is assumed to be both dense and intolerable. The density

and toxicity of the smoke will be a function of the specific material involved

in a fire and may actually be tolerable to some degree or not as dense as assumed

in these calculations. The actual condition however is difficult to access and

this assumption is therefore appropriate to maintain a conservatively safe

calculation

.

4. The ceiling is smooth. Actually the ceiling is onlv semi-smooth with

concentric baffles in the museum area and coffered areas in the lobby. The

assumption of smoothness impacts on the prediction of temperature and the

response of temperature actuated devices. The actual ceiling configurations

provide greater heat transfer surfaces than assumed in the preditions.

2
As a result the predicted average smoke layer temperature will be somewhat

higher than that which would actually occur given any particular fire

incident. The channelization produced by the baffles, however, would have

the reverse effect in the space between the baffles directly over the fire

and would likely cause heat responsive devices between the baffles to

react faster than predicted.

5. Fire protection improvements will be made in the areas not open

to the public and in the souvenir and book sales area to prevent fire

intrusion from such spaces into visitor spaces. The most likely means

of providing this assurance is through the installation of automatic

sprinkler protection through these areas, though other methods such as installation of fire resistive compartmentation can also be effective.

6. The smoke control system which now draws supply air from locations

near the celling can be converted to provide only floor level supply air

from outside the building, when operating in the smoke control mode.

The cost of the fire protection improvements and the modifications to the

smoke control system have not been appraised. The potential effectiveness

of the modified smoke control system is examined in the analysis.

The impact of a fire developing in a non-public space and entering the museum

or lobby area is beyond the scope of this analysis. Experience would indicate

that there is sufficient combustible material in these spaces to support a "large" fire. If such a fire were to develop in a non public space and then

enter the public space at an advanced stage the time available for safe egress

would be very short. This assumes that effective egress does not begin until

the fire enters the public space. Experience from other fires indicates that

this may well occur.

Procedure

The following seven step process was undertaken:

a. Prediction of the growth of hazardous conditions in the public

spaces of the museum and the adjacent lobby.

3
b. Prediction of the impact of emergency smoke removal if the system were made effective.

c. Prediction of the response of smoke detectors in the public spaces,

if provided.

d. Prediction of the response of automatic fire sprinklers in the

public spaces, if provided.

e. The predicted egress capabilities if normally expected egress occurs.

f. The predicted egress capabilities if optimum egress management could

be obtained.

g. Evaluation of egress potentials for persons in the arch.

In addition to the above analyses a table has been prepared relating

the fire protection system as it now exists and as it might be modified

to its impact on the ability of visitors to exit before the onset of

a hazardous condition.

Hazard Growth

In this analysis hazard growth is considered to be the increase in the

hot gas temperatures in the smoke layer and the descent of this hot, obscuring,

toxic layer from the celling towards the occupied spaces of the building. The

assumptions considered critical for this analysis were:

a. The ceiling lighting system can be obscured when the smoke layer

depth is about one foot.

b. Egress through the main doors at the top of the ramps will become

difficult when the smoke layer descends approximately four feet below

the ceiling.

c. Egress from the rear doors will become difficult when the smoke layer

descends approximately 10 feet below the ceiling.

4
d. The evacuating occupants will sense objectionable heat from thermal

radiation when the smoke layer reaches approximately 200 °F, provided it

is still above their heads.

e. Anyone left in the building will be physically harmed by heat radiation

from the smoke layer if its temperature reaches about 400°F, even if it is

still above their heads.

The semi-universal fire described in Figure 2 was used as the input to

the Available Safe Egress Time fire growth model (ASET) [2] developed by

NBS. In applying this model it was assumed that 35% of the fire energy

would be directly radiated from the flame and 90% of the total energy

would be transferred to walls, floors and ceilings. These figures are considered reasonable and conservative based on limited experimentation

that has been conducted bv NBS. The results of these calculations are plotted in Figure 4. This model predicts one-foot smoke layer depth

that could obscure light in 5 minutes, a four-foot layer making

exit from the main doors difficult in 11 minutes, and a smoke layer that had

a depth of 10 feet in approximately 17 minutes. It also indicates that the

temperature in the hot gases would rise to 200°F in about 13 minutes and

to 400°F in 17 minutes. The basic heat transfer calculations involved

are shown in Appendix A.

Impact of Emergency Smoke Removal

A second series of calculations also plotted in Figure 4 were made to

determine the impact of a smoke removal system brought into service

at approximately the time smoke descended to 1 foot level. Two separate

calculations were made. The first based on effective smoke removal of

20,000 cfm (cubic feet per minute); the second on the basis of effective smoke

removal of 40,000 cfm. It is expected that the removal of these gases would

have a minor effect on the gas temperature but would significantly effect the

rate of smoke layer descent. Using the ASET model the descent of the smoke

layer Indicates that it would reach a 4 foot depth (impacting on the main door

egress) at approximately 15 minutes with the 20,000 cfm smoke removal capability

and 17 minutes with the 40,000 cfm removal. Similarly a 10 foot depth would b*- reached at approximately 19 minutes given 20,000 cfm smoke removal and 22

minutes given 40,000 cfm.

5
Response of Automatic Fire Sprinklers

Recently developed methods of calculating the potential thermal ceiling

jet of a fire and the response of sprinkler heads to such a jet were used

to determine the impact of several different arrangements and styles of

sprinklers. Also within the past several years an Important hardware advance

has been made in sprinkler heads. Sprinklers are now available in different

ranges of responsiveness to their rated temperature. This difference is

included in a factor called "Response Time Index" (RTI) . Those sprinkler

heads with low thermal heat sinks (and therefore rapid response) have low

response time indices. Some have reached the market with indicies in the

range of approximately 20. The traditional sprinkler heads have Indicies

that range from about 100 to 300. Figure 5 shows the results of calculations

based on the same fire conditions used to predict hazard growth. Calculations

show that the range of sprinkler response can vary from approximately 3 minutes

to as high as 6 minutes depending on the sprinkler head and the spacing selected.

Sprinkler response is used here to indicate the time elapsed between the

beginning of the fire and the opening of the first sprinkler head. The hazard

development curves shown in Figure 4 are marked to show the range of hazardous

conditions that would be predicted at the time of the operation of the sprinkler

heads. The sprinklers are predicted to operate before the average upper layer

temperature reaches the sprinkler head setting. This is because the sprinkler

will be heated by a hot ceiling jet. See Figure 3. In view of the openness

of the museum and the low probability that a fire would involve concealed

spaces, sprinklers would be highly effective. It can be expected that the

fire would be promptly terminated or brought to a very low energy production

level upon the operation of one or more sprinkler heads. The action of the

flow from the sprinkler heads would however, pull some of the smoke from the

ceiling level to the floor level. This recirculation would take place in some unpredictable but relatively brief period of time. Calculation of the

potential toxic level and obscuration from such recirculation (See Appendix

B) indicate that the recirculated smoke would be well below toxic hazard

levels but would decrease occupant visibility. If the sprinklers used were

of the fast response type the reduction in vision would be very modest. If the

sprinklers were of the conventional operating type the obscuration would

eventually reduce visibility to less than 30 ft., even if lighting were provided

below the smoke levels.

6
Operation of Smoke Detectors

The estimate of the operation of smoke detectors is based on the calculation

procedure used for the sprinkler heads. The smoke detectors were treated as

a response device having a zero response time index and a temperature rating

of about 85°F. On this basis a smoke detector on a reasonable spacing near

the ceiling would be expected to operate in approximately 1 minute from the

initiation of the fire. (See Appendix B for calculations and references)

Emergency Egress of Visitors

Egress capabilities were based on data developed by Fruln[3] and

Predtechenski [4 ] . Appendix B provides the basic calculation data used.

Two different calculations were made as follows:

a. Figure 6 shows the evacuation time based on the exits available if

it is assumed that many persons will move from the museum through the

large passageway into the lobby and will not return to the museum even

if the rear doors of the museum are opened. This is the type of evacuation

that would be expected if no special evacuation procedures were implemented

by Park Service personnel.

b. The second arrangement, shown in Figure 7, plots the improvement in egress

capability that would occur if all exits were used in an optimum manner. This

would possibly involve ushering persons who had moved from the museum to the

lobby back into the museum to use the rear exits. If all exits were used

there would be approximately a 20% decrease in time required for all persons

to leave the building. If some of the exits become blocked or otherwise unused,

the egress time advantage will be less significant.

Emergency Egress from the Memorial Arch

In case of fire, emergency egress from the arch can be accomplished by

either transporting the persons at the top of the arch using the tram or bv

descending the stairs located in each arm of the arch. In view of the ever present possibility of electrical interruption, it is expected that normal

7
precaution would lead towards walking from the arch using the stairs. The

author descended these stairways at a comfortable pace. In this single

exercise the descent time was 15 minutes. Given the possibility of as many as 200 persons at the top of the arch and the varying conditions and

capabilities of such persons a descent time of 15 to 30 minutes is probably

the best estimate that can be made. Estimates made on evacuating as many

as 200 persons using the tram result in approximately the same amount of time.

It can be seen from examining Figure 4 and Table 1, a way in which the lobby

portion can be safeguarded for a sufficient period of time to allow emergency

egress through the lobby is through the use of automatic sprinklers.

An alternative however is available. This alternative is based on using

the existing arch ventilation system to develop a smoke proofed arrangement

for each of the legs of the arch and the emergency egress path from the

arch to the outside. Architecturally this would require providing at least one additional set of doors near the base of the ramp sections descending

on each side of the lobby to the tram loading areas. The apparent best

location for such doors is near the point where the slope of the ramp is

interrupted and a flat section occurs on the lobby side of the present

doors. This will effectively separate the lobby from the ramp discharge

arrangements using the emergency exit passageway and stairs located east

of this position.

The second item necessary to achieve smoke proofing of the arch exit

arrangement involves adjusting the controls on the present HVAC system

for the arch. It will also involve the installation of dampers or other

means to cut off the final section of the HVAC system that provides supply

air into the observation platform and machine room at the top of the arch.

The emergency system needs to be controlled to provide a positive pressure

(preferably in the range of approximately 0.1 inches of water) at the dividing

lines between the exit path and the lobby and between the observation platform

and the top of each of the legs. In addition, it is important that smoke

detection arrangements be provided in the fan plenums to assure that any fire

in the filters or machinery within the plenums will cause the fans to shut

down and not pump smoke into the arch. Most if not all of the control equipment

necessary to accomplish this is incorporated in the existing fan control system.

8
Analysis

An analysis of the preceeding predictions is made in Tables 1 and 2.

Table 1 relates the predicted available egress time from initial flame to

selected critical conditions as the facility now exists and the predicted

available egress time that would occur if certain fire protection features

were added to the facility.

Table 2 shows the predicted number of persons that can egress through all

or a portion of the facility exits in the time available as shown in Table

1. In preparing Table 2 it has been assumed that a fire of the severity

shown in Figure 3 would be fully self announcing within 3 minutes of ignition.

By that time, the fire would be burning at the rate of 500 kilowatts and

would produce a flame threatening to everyone in the building. Therefore,

the calculation of egress capacity assumes a 3 minute start-up delay in all

situations where the fire safety arrangement does not involve a general smoke

detection system. Where the fire safety arrangement involves general coverage

of the museum and lobby area with a smoke detection system, the calculation

of egress capacity assumes a 1 minute start-up delay in recognition of the

early warning provided by detectors.

References

[1]

. L.Y. Cooper, "A Mathematical Model for Estimating Available Safe

Egress Time in Fires," Fire and Materials, Vol. 6, Nos. 3 and 4, 1982,

pp . 135-144.

[2]

. L.Y. Cooper and D.W. Stroup, Calculating Available Safe Egress Time

(ASET) - A Computer Program and User's Guide, NBSIR 82-2478, Nat'l

Bureau of Standards (September 1982)

.

[3]

. J.J. Fruin, Pedestrian Planning and Design; Metropolitian Association

of Urban Designers and Environmental Planners, Inc., New York, N.Y., 1971.

[4]

. V.M. Predtechenskii and A. I. Millnskii; Planning for Foot Traffic Flow

in Buildings; Stroiiat Publishers, Moscow, 1969 (Translated from Russian

by Amerind Publishing Co. Put. Ltd. New Delhi for the National Bureau of

Standards and National Science Foundation, 1978).

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18
Appendix A

Heat Transfer Related Calculations for the Jefferson National Memorial

Historical Site

I. Methodologies

A. Hazard Growth

The Available Safe Egress Time (ASET) computer code was used to

calculate fire environment conditions in the Jefferson National

Memorial Historical Site. This computer program solves equations,

developed by Cooper^, to determine the time dependent upper layer

thickness and temperature histories. The equations for the dimensionless

interface position, C, and the upper layer temperature, 4>, are

J

2-

C,^ O G < C

^ C , ae. ^ ^ ^ ^

- ^ ^ ^ i ^

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0.2 10 f O - Ar ) ^

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(2)

The model requires data describing the fire's elevation and energy

generation rate along with a description of the enclosure geometry

(height and area). The percentage of fire energy radiated from

the flame and the percentage of fire energy lost to the walls,

floor, and ceiling must also be estimated.

A-1
The semi-universal fire, used as input to the model, is the result of

a fit of data, from burn tests on a variety of different types of

commodities, to a three-segment, multi-exponential fire growth curve. The fire is initiated from a 10 kW (9.8 BTU/s) Ignition source. It

grows exponentially at a rate characteristic of a fire initiated in

a polyurethane mattress with bedding. This early growth rate would be

appropriate for use in characterizing the early growth of fire's in

upholstered polyurethane cushioning or large assemblies of commodities

stacked on pallets. The fire growth rate beyond 400 kW (379 BTU/s),

described in two segments, is similar to that observed for fires

initiated in a variety of different types of commodities stacked

2 on pallets. The fire is assumed to be located one foot above the

floor. The percentage of fire energy lost by radiation from the flame

and the percentage of fire energy transferred to walls, floors and

ceilings were assumed to be 35% and 90% respectively. The room height

2

and area were 16 ft. and 50,516 ft respectively.

B. Impact of Emergency Smoke Removal

In order to examine the impact of emergency smoke removal, the ASET

computer code was adjusted to Include a venting term. Since it was

expected that the removal of smoke from the upper layer would have

minimal affect on the upper layer gas temperature, the venting term

was only applied to the interface position equation. The adjusted

equations for the dimensionless interface position, C» and the upper

layer temperature, ()>, are

-<T < SO (3)

ax pic.j /«?.-<?) , s s <; So

ujk I ^ o

~

^ ‘ ^ ^ * > f. ~ 4 /Qo ,
This change, while not a true representation of the venting phenomenon,

was considered accurate enough for the purpose Intended here. The altered

model required the same inputs as the standard ASET version with the

addition of a ventilation rate specified in cubic feet per minute (cfm)

.

C. Response of Automatic Fire Sprinklers

The response of automatic fire sprinklers to fire conditions, in an enclosure, is a function of the ceiling jet temperature and velocity

histories and the thermal response characteristics of the sensing element.

Correlations of ceiling jet temperatures and velocities, obtained

3

from the study of steady fires by Alpert , were used to predict the

temperature and velocity histories in the ceiling jet flow. The

dimensionless forms of the equations for maximum temperature rise,

AT*, and velocity, U*, are m m

-

[/. »7

r/iA <

r/ H >

0

0

(S)

lo.iS

r/H £.

r/H >

O . IS

o. /s

(6)

to;,...- ; AT* -- AT„ Cc; ^

h^/t^

Once the ceiling jet temperature and velocity profiles were calculated,

the response of a sprinkler, at a given radial location, was calculated

using the equation

J fATl)

d -i R T-X An) ( 7)

A3
where AT is the excess temperature of the link above its initial

Li temperature, AT is the excess temperature of the gas surrounding

S 4 the link, and RTI is the response time index for the sprinkler.

D. Celling Jet Temperatures

Ceiling jet temperatures calculated by the methods proposed by

3 Alpert vary with the time into the fire and the radial distance

from the fire axis. The calculated ceiling jet temperatures for

the museum or lobby areas in case of a fire following the course plotted in Figure 2 are:

Time

into

Fire

Burning

Rate

Btu/sec)

Ceiling Jet Temperatures

Radial Distance From Fire Axis

1 ft. 7.5 ft. 15 ft. 30 ft.

1 min. 50 115°F 90®F 83°F 78°F

3 min. 800 350°F 210“F 157°F

6 min. 9000 1500®F 700"F 500°F

A-4
E. Estimation of Detector Operating Time

Correlations developed by Heskestad and Evans have

demonstrated that a reasonable relationship can be drawn

between the ceiling jet temperature from an open flaming

fire and the response of a smoke detector to the particles

in that hot jet. For modern smoke detectors the operation

can be expected when the jet temperature rises 3°F to 13°F.

For these calculations a conservative value of 15°F rise

over a 70°F room temperature was used.

F. Constituency of the Smoke

The constituency of the smoke is derived from the amount of

material burned (from Figure 2 and the level of the smoke

layer (from Figure 4). The procedure is as follows:

a. The fuel is assumed to be 80 percent wood or similar

natural materials and 20 percent synthetic materials.

b. The products produced by burning the fuel will develop

a toxic level equivalent to one that is lethal to 50

percent of test animals exposed to that concentration

for 30 minutes when the mass burned divided by the volume

involved is approximately 40 grams per cubic meter.

(0.0025 lbs. per cubic feet)

c. Approximately 3 percent of the burned material will be

distributed through the smoke as light obscuring aerosols.

d. Toxicity is determined from the formula:

M

\ d.A.LC

50
where

:

Toxicity factor Multiples of LC^q

M = Mass burned (g)

d = Depth of smoke layer (m)

2 A = Area of space (m )

LC^q = Toxic concentration to produce a lethal

dose to 50 percent of the exposed animals

exposed for that concentration for 30

3 minutes (g/m )

Visibility through the smoke layer is evaluated by the formula

from Rasbash^.

V = 1.4

s D

o-0.767

where:

V = Distance of sight (m)

s

D^ = Optical density per meter

and D = 3.5 Y M

o sV

where

;

Y = Percent of burned material becoming aerosol

s

M = Mass burned (g)

V = Volume of smoke layer (dA)
f. For this analysis the fuel involved in the fire is considered

to be 80% natural materials (wood, paper, and similar materials)

and 20% synthetic (primarily plastics.) The is (0.4 g per

cubic meter (0.0017 lbs per cubic feet). The Y is 3 percent.

s

g. Using the preceding data and formulae the constituency of the

smoke layer at various times into the fire is:

time Yt(xLC5o) Vision in smoke

1 min 0.0125 44 feet

3 min 0.05 17 feet

5 min 0.21 6 feet

6 min 0.35 3 feet

11 min 0.75 2 feet

h. If the operation of a sprinkler head promptly extinguishes the

fire but also churns the smoke through the volume of the museum

and lobby the value of would be 0.0014 (ie less than 1% of the

LC^q) if the fire is terminated at 3 mins or 0.02 (2% of LC^g)

if the fire is terminated at 6 mins.

1. When a sprinkler head operates it adds water vapor to the

atmosphere. Currently we have no way to calculate the impact

of the water vapor fog on visibility. The portion of the

obscuration presented by the smoke can however be estimated

as 90 ft. for the matter released in the first 3 mins, of the

fire and 28 ft for the matter released in the first 6 mins.

Actual visibility would be something less due to the added

water vapor.
II. References

[1]

. L.Y. Cooper, "A Mathematical Model for Estimating Available Safe

Egress Time In Fires," Fire and Materials, Vol. 6, Nos. 3 and 4,

[2] 1982, pp. 135-144.

. L.Y. Cooper, and D.W. Stroup, Calculating Available Safe Egress

Time (ASET) - A Computer Program and User’s Guide, NBSIR 82-2478,

Nat'l Bureau of Standards (September 1982).

[3]

. R.L. Alpert, "Calculation of Response Time of Ceiling - Mounted

Fire Detectors," Fire Technology, 8, 1972, pp. 181-195.

[4]

. D.D. Evans, Thermal Actuation of Extinguishing Systems, NBSIR

in process.

[5]

. G. Heskestad and M.A. Delichatsios , Environment of Fire DetectorsPhase I: Effect of Fire Size, Ceiling Height and Material, Volume IIAnalysls, FMRC Serial No. 22427, Factory Mutual Research Corporation,

1977.

[6]

. D.J. Rasbash, "Smoke and Toxic Products Produced at Fires", Trans.

J. Plastic Inst., Jan. 1967, p. 55.

A-8
III. Nomenclature

A

C

P

g

H

L

c

•q

Q

•%

%

r

t c T

T

am

RTI

U

U*

m

V

V*

A

6AT

C

X c

Xr

T

•t- Subscripts

a

g

area

constants defined below Eqn (1)

specific heat

acceleration of gravity

heat source to ceiling distance

a characteristic length

a dimensionless value of Q

rate of fire's energy release

initial energy release rate

convective fraction of heat released from flame

radius

a characteristic time

temperature

ambient temperature

dimensionless temperature

Response Time Index

radial velocity

dimensionless velocity

ventilation rate

dimensionless ventilation rate

height of fire above floor

dimensionless value of A

T-T

a dimensionless elevation above fire

C at T = o effective fraction of Q lost to bounding surfaces of the room effective fraction of Q radiated from combustion zone ambient density

dimensionless t dimensionless temperature

ambient conditions

gas

A9
L sensing element, link

m maximum value at given radius for celling Jet

o Initial value

p constant pressure

A-10
Appendix B

Egress Calculations for the Jefferson National Memorial Historical Site

The egress capabilities of the Jefferson National Memorial Historical Site

were analyzed using two different scenarios. The first would be the result

of normally expected egress from the structure. The other would require

optimum use of the egress facilities possibly involving redirection of

people movement by NFS personnel.

The basic formula used to calculate the required egress time is:

E =1= LR N X B (1)

where: P = Population of Structure

R = Pedestrian Flow Rate out of Structure

N = Number of exit doors

B = Capacity of each Door

The data used in the calculations is presented in Table lb.

I. Normally Expected Egress

In this scenario, it is assumed that many persons will move from the museum

through the large passageway into the lobby and will not return even if the rear doors of the museum are opened. Furthermore, the last people exiting the museum

portion of the structure leave the various openings at the same time. The flow

would be unevenly divided, and a backup would develop at the lobby exits. As a result, people would still be waiting, in the lobby, to exit the structure while

the back exits, from the museum, were empty. The procedure used to calculate the

required egress time for this situation is presented below:

B-1
1. Calculate the flow rate of people through the passageway using the formula:

W

R =

p A ( 2 )

where: Rp = Flow rate for passageway

= Width of passageway opening

A = Required exit width for openings with no doors

2. Using Rp from equation (2), calculate the flow rate of persons through all

openings in the museum

R = (N X B) + R

r m p

(3)

where

:

R^ = Total flow rate of persons leaving museum

= Number of exits from museum (excluding passageway)

B = Capacity of an exit with free swinging door

3. The time required to empty the museum is determined using the basic formula

P

E = — m R

r

(4)

where

:

E = Required egress time for museum

ID

P = Population of museum

m

4. Use the egress time for the museum to determine the number of people who

move from the museum to the lobby

W

P = E X 7^

m A

(5)

where: P = Number of people who move from museum to lobby

B-2
5. Finally, calculate the time required to empty the lobby

+ P

\ “ N, X B

( 6 )

where; = Required egress time for lobby

P = Population of lobby

1j

N = Number of exits from lobby

The results of these calculations are shown in Figure 6,

II. Optimum Egress Capacity

In this scenario, it is assumed the people exit the structure in a manner such

that the flow is evenly divided among doors. This would require an exit with

five doors to carry five times as many people as an exit with one door.

Consequently, it is assumed that the last people moving through the various

exits leave the building at the same time. This could only be the result of

a planned exit system where people are directed to the exit which would release

them to the outside in the optimum amount of time. While this may be difficult

to achieve in practice, the required egress time for the entire structure may

be calculated simply from equation (1)

.

E

(7)

s N X B

s

where; = Required egress time for the entire structure

P^ = Population of the entire structure

N = Number of exits from the structure

s

B = Capacity of an exit with free swinging door

The results of this calculation for various combinations of open and closed

exits are shown in Figure 7.

B-3
III. Minimum Exit Time

The required egress time, for the building, cannot be less than the time

required for the person farthest from an exit to exit the building. The

distance farthest from an exit Is determined for each case, and a travel

time is calculated using the appropriate walking speed. This Is shown as the minimum exit time in Figures 6 and 7

.

B-4
TABLE 1 of Appendix B

EGRESS DATA

B = Capacity of each door = 60 persons per minute

R = Flow rate for passageway = 30 persons per minute per

^ foot of width

B-5
NBS-114A (REV. 2-BO)

3. Publication Date

March I985

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET (See Instructions)

1. PUBLICATION OR

REPORT NO.

NBSIR M-:?897

2. Performinf Orfan. Report No,

4. TITLE AND SUBTITLE

Jefferson National Memorial Historical Site

Analysis of Impact of Fire Safety Features

5. AUTHOR(S)

Harold E. Nelson

6. PERFORMING ORGANIZATION (If joint or other than NBS. see instructions)

national bureau of standards

DEPARTMENT OF COMMERCE

Gaithersburg, MD 20899

7. Contract/Grant No.

8. Type of Report & Period Covered

9.

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

National Park Service

Department of Interior

Washington, D.C.

10.

SUPPLEMENTARY NOTES

Document describes a computer program; SF-185, FlPS 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)

An analysis is made of the rate of the potential intrusion of hazardous environments

in a museum facility as compared to the capacity of the exit system to evacuate

the occupants.

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

egress; evacuation; fire models; fire safety; historic buildings; musei’ms ; smoke; smoke detectors; sprinkler systems

13. AVAILABILITY

Unlimited

I I For Official Distribution. Do Not Release to NTIS

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

20402.

[_5 Order From National Technical Information Service (NTIS), Springfield, VA. 22161

14. NO. OF

PRINTED PAGES

40

IS. Price

$8.50

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