A111Q0 imoos

NBSIR 81-2202

Fire Tests of Stairwell-Sprinkler

Systems

Leonard Y. Cooper and John G. O'Neill

Center for Fire Research

National Engineering Laboratory

U.S. Department of Commerce

National Bureau of Standards

Washington, DC 20234

February 1981

Final Report

Issued April 1981

Prepared for: The Occupational Safety and Health Administration (OSHA)

Department of Labor

Washington, DC 20210

100

. U56

31-2202

1981

NBSIR 81-2202

FIRE TESTS OF STAIRWELL-SPRINKLER

SYSTEMS

Leonard Y. Cooper and John G. O'Neill

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Center for Fire Research

National Engineering Laboratory

U S. Department of Commerce

National Bureau of Standards

Washington, DC 20234

February 1981

Final Report

Issued April 1981

Prepared for: The Occupational Safety and Health Administration (OSHA)

Department of Labor

Washington, DC 20210

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

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

PREFACE

This report on fire tests of stairwell-sprinkler systems is one product of an ongoing joint research program of the Occupational Safety

and Health Administration (OSHA) of the Department of Labor and the

National Bureau of Standards (NBS), Center for Fire Research. The

program is entitled: Key Elements of Emergency Escape Requirements for

Employees in Workspaces Under OSHA Jurisdiction. Other areas of research

presently included in this program are: estimating available safe

egress times for workspaces subsequent to the ignition of hazardous

fires; the relation of building design and human factors to emergency

evacuation of workspaces; and studies of the smoke leakage of door

assemblies

.

iii
TABLE OF CONTENTS

Page

PREFACE iii

LIST OF TABLES vi

LIST OF FIGURES vi

NOMENCLATURE viii

Abstract 1

1. INTRODUCTION 2

2. PROJECT OBJECTIVES AND SCOPE 4

3. REVIEW OF PREVIOUS WORK 5

4. EXPERIMENTAL DETAILS 6

4.1 Test Facility . 6

4.2 Fire Protection Systems 7 4.3 Instrumentation 5. 4.4 Test Program 1U

4.5 Test Procedure IQ

5. TEST RESULTS 12

5.1 Water Curtain System Tests 12

5.2 Spray Nozzle System Tests 13

6. ANALYSIS OF THE DATA AND CONCLUSIONS 14

6.1 The Concept of a Stairwell-Sprinkler Component 14

6.2 The Physical Bounds of the Stairwell-Sprinkler

Component 16

6.3 Parameters to Describe the Component Performance

Characteristics 17

6.4 The Flow Phenomenology in the Experimental Facility. . . 19_

6.5 A Useful Operating Characteristic of the Stairtower

Facility Burn Room 22

6.6 Some Performance Characteristics of StairwellSprinkler Components: The Experimental Results

and Their Correlation 25

6.6.1 Plots of the Experimentally Obtained

Component Efficiencies 25

6.6.2 Correlation of the Reduced Data Results 27

6. 6. 2.1 Cooling Efficiency as a Function

of Water Flow Rate 27

iv
TABLE OF CONTENTS (Continued)

Page

6.6.2.1.X The 12.5 mm (1/2 in)

Water Curtain Data 27

6. 6. 2.

1.2

Correlation of the

Other Data 28

6. 6. 2.

2

Water Usage Efficiency as a Function

of Extractable Energy Flow Rate 30

6.7 Discussion of Results 31

6.7.1 Cooling Efficiency and It's Application 31

6.7.2 Water Usage Efficiency and It's Potential

Improvement 33

6.7.3 Extension of the Results to Other Geometries

and Configurations 34

7. SUMMARY OF CONCLUSIONS 38

8. ACKNOWLEDGEMENTS 40

9. REFERENCES 41

APPENDIX A. PROPERTY VALUES AND DETAILS OF DATA MANIPULATION . . 42

v
LIST OF TABLES

Page

Table 1. Water curtain and spray nozzle systems 45

Table 2. Deployment of the instrumentation 46

Table 3. A listing of the test runs 48

Table 4. Data from unsprinklered operation of the stairtower

used to estimate hA from Eq. (6) 49

LIST OF FIGURES

Page

Figure 1. Plan view of lowest level of stairtower

including the bum room 50

Figure 2. A section of the stairtower elevation 51

Figure 3. Plan views of the first and second floors of the

stairtower . 52

Figure 4. Water curtain system 53

Figure 5. Spray nozzle system 54

Figure 6. Burn room temperature profiles with two different

lower vent areas 55

Figure 7. Temperature at first floor vs nominal average flow

rate for water curtain and for a fire energy of

1.5 MW [5.5 (106

) BTU/hr ] 56

Figure 8. Nominal average water flow rate vs combustion gas

exhaust rate for the water curtain system and a fire

energy of 1.5 MW [5. 5(106 )BTU/hr] 57

Figure 9. Temperature at first floor vs nominal average water

flow rate for the water curtain system and a fire

energy of 4 MW [13.6(106

) BTU/hr] 58

Figure 10. Water flow rate vs combustion gas exhaust rate for

the water curtain system and a fire energy of

4 MW [13.6 (106

) BTU/hr] 59

vi
)

'

LIST OF FIGURES (Continued)

Page

Figure 11. Nominal average water flow rate vs combustion gas

exhaust rate for the spray nozzle system and a fire energy of 4 MW [13.6(106

) BTU/hr] 60

Figure 12. Model of ^ phenomena in the overall stairwellsprinkler system 61

Figure 13. The stair tower: an instrument used to measure

the performance characteristics of a stairwellsprinkler system component 62

Figure 14. Plot of cooling efficiency as a function of

water usage - WC, 12.5 mm (1/2 in) nozzle 63

Figure 15. Plot of cooling efficiency as a function of

water usage - WG, 10 mm (3/8 in) nozzle 64

Figure 16. Plot of cooling efficiency as a function of

water usage - SN, 12.5 mm (1/2 in) nozzle 65

Figure 17. Plot of cooling efficiency as a function of

water usage - SN, 10 mm (3/8 in) nozzle . 66

Figure 18. Plot of water usage efficiency as a function

of extractable energy flow - WC, 12.5 mm

(1/2 in) nozzle . . 67

Figure 19. Plot of water usage efficiency as a function

of extractable energy flow - WC, 10 mm

(3/8 in) nozzle 68

Figure 20. Plot of water usage efficiency as a function

of extractable energy flow - SN, 12.5 mm

(1/2 in) nozzle 69

Figure 21. Plot of water usage efficiency as a function

of extractable energy flow - SN, 10 mm

(3/8 in) nozzle 70

Figure 22. Estimate of cooling efficiency as a function

of water usage for the four tested designs - a plot of Eq. (11) 71

Figure 23. Relation between dry and saturated air

temperatures at one atmosphere 72

Figure 24. Heat of vaporization of water as a function

of saturation temperature 73

vii
NOMENCLATURE

A . riser

^well

A.

1

C

C

V

E

aE

P

•* E

P

•* ^p(WC)

G

G

evap

•* G

•** G

hA

K

K

cKw

K

c(WC)

K

w(WC)

“in

P

stairwell passage area measured normal to riser

total area of stairwell

inlet duct area

a constant in Eq. (9)

specific heat

actual rate of energy extration from stream

maximum possible rate of energy extraction

a dimensionless value of E [see Eq. (10)]

a dimensionless value of E^ [see Eq. (15)]

water flow rate

portion of G which is evaporated

a dimensionless value of G [see Eq. (9)]

•* value of G at stream saturation

a dimensionless value of G [see Eq. (15)]

heat of vaporization for water

the effective product of heat transfer coefficient and

burn room surface area [see Eq. (4)]

discharge coefficient (see table 3)

a constant in Eq. (11)

a constant in Eq. (12)

a constant in Eq. (16)

a constant in Eq. (17)

length of the water curtain

mass flow rate of air entering inlet duct

nozzle pressure

viii
P

amb pressure of the ambient air outside the stairtower

tower pressure within the stairtower

( AP pressure differential across velocity probe

•Q energy release rate of burner

•^loss

• portion of Q transferred to surfaces of burn room

T effective temperature of burn room gases [see Eq. (4)]

T , amb temperature of ambient air

T.in temperature of gases entering stairwell

T

out temperature of gases leaving stairwell

Twall effective temperature of burn room surfaces

T _ sat

saturation temperature of air

T,dry

• temperature of dry air

V velocity measured by probe

v

i

air velocity at stairtower inlet duct

W width of stairwell

zn elevation where P , = P^ amb tower

6 distance between edge of stairwell opening and water

curtain nozzles

nc cooling efficiency [see Eq. (2)]

nw

water usage efficiency [see Eq. (2)]

Pamb density of ambient air

Pw(liq) density of liquid water

lx
' j : • : : " > • 1 . • ' s 1 if • 1
)

P

amb pressure of the ambient air outside the stalrtower

P„tower pressure within the stalrtower

AP pressure differential across velocity probe

•Q energy release rate of burner

•^loss

• portion of Q transferred to surfaces of burn room

T effective temperature of burn room gases [see Eq. (A)]

Tamb temperature of ambient air

T

in temperature of gases entering stairwell

T

out temperature of gases leaving stairwell

Twall effective temperature of burn room surfaces

T „ satsaturation temperature of air

T,dry temperature of dry air

V velocity measured by probe

v

i

air velocity at stalrtower inlet duct

W width of stairwell

zn

elevation where P , = P_ amb tower

6 distance between edge of stairwell opening and water

curtain nozzles

n

c cooling efficiency [see Eq. (2)]

nw

water usage efficiency [see Eq. (2)]

Pamb density of ambient air

Pw(liq)

Jl

density of liquid water

lx
.

'

'*" 3

'

•

. :

:

' •

' :

!

. .

:

' T. V

,

'
FIRE TESTS OF STAIRWELL - SPRINKLER SYSTEMS

Leonard Y. Cooper and John G. O'Neill

Abstract

The effect of water curtain or spray nozzle

fire protection of an open stairwell was studied

experimentally. The experimental setup Includes

a three story stairtower with a contiguous first

story burn room. The instrumentation used to

measure the flow phenomenology resulting from

fire sizes up to 4MW/ [13. 6(10^)BTU/hr] with and

without sprinkler operation is described. A

model of evaporation cooling of the hot fire

gases as they pass up through the first to second

floor stairwell-sprinkler system component is

introduced. Based on this model the data are analyzed and correlated for the purpose of

identifying both a cooling and a water usage

efficiency for each of the system components that

were tested. Application of these measured performance characteristics and their extension to

stairwell-sprinkler components of different

geometries and configurations are discussed.

Key words: Automatic sprinklers, cooling efficiency,

evaporation cooling, smoke movement, spray nozzle,

stairway protection, ventilated stair.

1
1 . INTRODUCTION

A traditional method of providing fire protection in commercial

and industrial buildings is to subdivide the building into areas and

floors by means of fire rated construction. This compartmentation is

intended to confine a fire to a given floor and area and thereby limit

property damage and reduce the exposure of the occupants of buildings

to heat, smoke and toxic gases. By confining the fire to a given area,

the fire rated construction acts to retard smoke and toxic gases from

entering exit ways and other areas of the building where occupants

either are proceeding toward exits or where they must take refuge until

the fire is brought under control.

Building codes typically require fire rated closures (e.g., door

assemblies, duct dampers, etc.) for openings through the fire rated

walls and floor-ceilings to insure the integrity of compartmentation.

Openings through floor-ceilings for exit stairs must be protected not

only to limit the fire to the floor of fire origin but also to keep the

stairway safe for a given time to permit the occupants to exit from the

building. These types of stairways are usually enclosed in shafts

constructed of fire rated walls and door assemblies.

Not all stairways, however, are intended to serve as fire exits.

In mercantile buildings, for instance, escalators may be used extensively

to move occupants from one floor to another. These escalators are usually not intended to serve as fire exits; other enclosed stairways

are provided to serve this purpose and are marked as such. The fire

protection for such an opening which is not intended as an exit way

must primarily prevent smoke and heat from extending to other floors.

Some building codes permit these stairs and escalators, not

designated as fire exits for the building, to be unenclosed if alternative methods of stopping smoke and heat are provided, e.g., sprinkler

or spray nozzle systems. A survey of codes and standards by O'Neill

2
indicated that alternative methods incorporating the stairway-sprinkler

systems are generally permitted in certain occupancies only if automatic

sprinklers are installed throughout the building [1]^.

In many older buildings built prior to the development of modern

building codes the stairways are often open; that is, they are not

enclosed in fire rated construction. In many new buildings, architects

have sought to utilize open stairways and open atriums to enhance the

interior arrangement of the buildings. Many older commercial buildings

are being restored with the purpose of making these buildings useful in

terms of current living standards as well as retaining the atmosphere

created by the original classic architecture. Designers of these

restoration projects often desire to retain, for instance, open ornamental

stairways which were often the focal point in the layout of the building.

In many older buildings not undergoing extensive restoration projects

more practical reasons arise for retaining open stairways; that is, the

cost of enclosing such stairways is often prohibitive and the enclosure

of stairways may seriously interrupt the functional use of the building.

In such cases, a serious life safety hazard remains as well.

As mentioned previously, present criteria in building codes would

usually require the installation of a complete automatic sprinkler

system in all cases where open stairways are desired. Thus, the alternative to a costly construction of a fire rated enclosure for an open

stairway may then be a more costly installation of a complete automatic

sprinkler system.

The examination of technology for using sprinkler or spray nozzle

systems for protecting open stairways in buildings without a complete

automatic suppression system may provide an alternate, less costly means

of protecting these types of openings. Prompted by the need for examining

this technology the Occupational Health and Safety Administration, U.S.

Department of Labor requested the Center for Fire Research (CFR) , at the

1 Numbers in brackets indicate the literature references at the end of

this paper.

3
National Bureau of Standards (NBS) to investigate the use of sprinkler

and spray nozzle systems to protect open stairways subjected to a freely burning fire. This report provides the results of the research

program.

2. PROJECT OBJECTIVES AND SCOPE

The objective of this project was to determine the performance of

selected water curtain sprinkler systems and spray nozzle systems in

their capacities to reduce the flow of heated gases into a stairwell.

The project examined various design parameters of these systems, including flow rates and nozzle pressures and their impact on the overall

performance of the different stairwell-sprinkler system designs.

Specifically, the performance of the systems was studied in terms of

cooling efficiency, efficiency of water usage, and ability to reduce

the flow of combustion gases up through the stairway.

The project encompassed two major activities. The first activity

involved a full scale experimental program. This test program was formulated with a major objective of studying the overall effects of

deploying sprinkler or spray nozzle systems around or within open

stairwells during different fire scenarios. The tests used a particular

three story stair tower structure with the stairwell open to a freely

communicating room of fire origin on the bottom level. Two different

water delivery systems were used in the tests. The first system con- sisted of a water curtain arrangement made up of standard open-orifice

sprinklers placed between the burn room and the stairwell. The second

system consisted of spray nozzles located in the stairwell at the

second level and directed downward into the stairwell. To a lesser

extent, the impact of draft curtains placed around the stairway was

also investigated. The experimental procedure was such as to model

freely burning fire threats, i.e., there was no simulation of fire

extinguishment. This first activity of the project is described below

in sections 4 and 5.

4
The second major activity of the project involved an analysis and

generalization of the test data. The analysis was carried out with

specific reference to the effectiveness of sprinklers/spray nozzles in

cooling of flow-through fire gases. This activity was included in the

project once it became clear that the major effect of stairwell-sprinkler

systems on the migration of combustion projects is in the reduction of

fire gas buoyancy. This second activity of the project is discussed in

section 6.

This project did not investigate the performance of stairwellsprinkler systems in conjunction with fully sprinklered installations.

Most building codes which presently allow sprinkler protection of open

stairwells do so only in fully sprinklered buildings.

3. REVIEW OF PREVIOUS WORK

A review of previous experimental work is contained in the previously

mentioned report by O'Neill [1]. Experimental work reported by Thompson

at Factory Mutual Laboratories (FM) was specifically considered in the

development of the test plan reported here [2], In that work spray

nozzle systems were evaluated with regard to their capability to protect

conveyor openings through fire rated walls and ceiling assemblies. The

results of these tests indicated improved cooling of gases passing the

opening as nozzle pressures were increased for given flow rates. The

report also indicated that the position of the nozzles and the shape of

the spray cone were important design considerations to insure optimum

coverage of the opening with the water spray. A flow density of 81.5

2 2

to 163 £/min/m (2 to 4 gal/min/ft ) was recommended for protection of

openings through walls and ceilings.

5
4 . EXPERIMENTAL DETAILS

4.1 Test Facility

The experimental procedure was carried out in a 3-1/2 story structure

shown in figures 1 through 3. The structure was constructed in and

above a structure previously used as a NIKE Missile Pit located on Federal property adjacent to NBS. Figure 1 shows the layout of the

structure located in the pit itself which served as the bottom floor of

the test structure. This basement level, which is equivalent to 1-1/2

stories in height, consisted of a burn room adjacent to the base of a stairway which extended an additional two stories above grade level. A

ventilation port was provided to bring combustion air into the burn

room from the remaining unused area in the pit outside of the burn room

structure. During the test period this remaining pit area was opened

to the exterior by means of an open doorway, which provided an unlimited

2 2 air supply to the pit area. A 1.9 m (20 ft ) nominally sized vent was

located in the roof of the tower. In the basement level the test

structure consisted of concrete block walls with a cementitious fireproofing material applied to the inside to provide increased fire resistance.

The ceiling in the burn room consisted of the reinforced concrete con- struction existing in the pit with a coating of the cementitious fireproofing material applied to the area inside the burn room.

As previously mentioned, a stairway of steel construction extended

3-1/2 stories from the lowest level, adjacent to the burn room, up to

the top of the tower. Cementitious fireproofing was applied to the

columns and stringers and underside of the stair risers and landings in

the lowest level to protect the steel from the initial heat exposure

prior to the actuation of water curtain or spray nozzle systems. Fire

rated doors provided access into the test facility at the lowest level

and at the grade level and fire rated wired glass windows were installed

in the two levels above grade. The floors which were built surrounding

the stairway at grade level and at the top level, as well as the roof

structure consisted of hollow core precast concrete panels supported by

exterior bearing walls and steel I beams.

6
The heat source consisted of a large propane burner as shown in

figure 4, located in the bum room at the lowest level. The burner

consisted of 39 orifices divided into seven zones to permit operation

of the burner at varying rates of heat release. The maximum heat

• g release rate (Q) of thej burner was approximately 4 MW [13.6 (10 ) BTU/hr]. Propane was piped to the burner from a battery of propane

storage cylinders located above and outside the test area at grade

level. The burner was remotely controlled from an instrumentation

trailer located at grade level. During testing the burner was con- tinuously monitored with the video equipment.

4.2 Fire Protection Systems

The first system used in the experimental program was a water

curtain consisting of a row of open pendant sprinklers spaced 1.8 m (6

ft) on centers, located at the opening between the burn room and the

base of the stairway. This spacing is recommended for the location of

closed ordinary sprinklers around openings for escalators in the National

Fire Protection Association (NFPA) Standard No. 13, Standard for

Installation of Sprinkler Systems [3]. Sprinkler heads selected for

the tests were of the same manufacturer and model. Two different

orifice sizes were examined; 12.5 mm (1/2 in) and 10 mm (3/8 in). The

water curtain piping was supplied by a fire hose from a fire department

pumper located at grade level. Water flow was controlled and measured

by a mechanical water meter and an on/off control valve. The water

meter was equipped with a voltage output and the flow rate was con- tinuously recorded with the test data aquisition system. Figure 4

details the installation of the water curtain sprinklers.

The second system consisted of five conical shaped spray nozzles

located on the second level and directed downward into the stairway.

The two different orifice sizes used in the first system were also used

here. The conical shaped spray nozzles were used since this type of

7
nozzle directs a conical shape spray pattern which completely fills the area of protection with spray droplets. The design of the spray nozzle

system was based on engineering design information provided by the

manufacturer concerning the area of coverage versus the distance from

the spray nozzle. (This type of data is typically provided from the

manufacturers for these type of special spray nozzles.) The flow from

these nozzles was supplied and controlled in the same way as the water

curtain system. Figure 5 provides the design details for the locations

of the nozzles. It should be noted that current guidelines primarily

address straight run stairs (such as escalators) through openings in

floor/ceiling assemblies and not stairs which change directions at

landings such as the stairway in the test facility. The opening perpendicular to the landing, therefore, was included in the area of

coverage and in total water flow demand calculations.

For several tests, aluminum sheet panels were installed around the

stairway at the first floor. The purpose of the panels were to enhance

the air entrainment properties of the spray nozzles.

The baseline flow parameters from the systems were determined in

accordance with criteria contained in nationally used standards. The

NFPA No. 13 [3] recommends that sprinklers placed around escalators be

designed for a minimum flow rate of 37.2 £/min/m (3 gal/min/ft) along

the perimeter with sprinklers spaced 1.8 m (6 ft) on centers. With 12.5

mm (1/2 in) orifice size sprinklers these design criteria equate to each

sprinkler operating at a minimum 56.8 £/min (15 gal/min) with a nozzle

pressure of 51.7 kPa (7.5 psi) . The baseline flow parameter for the

2

spray nozzle system was based on a requirement of 81.5 £/min/m (2 gal/

2 min/ft ) over the area protected, ^

r -^ ser » as measured perpendicular to

the risers of the stairs. This criterion is contained in the Life

Safety Code 101 [4].

A summary of the sprinkler systems that were evaluated is presented

in table 1.

8
4.3 Ins trumcntn

The instrumentation used in the test is listed in table 2 and the

specific locations for the two series are shown in figures 1-3.

Signals from the instrumentation channels were recorded at 10 second

intervals on a magnetic tape data acquisition system.

Chromel-alumel type unsheathed thermocouples, 0.25 mm (30 gauge);

measured gas and surface temperatures throughout the test area.

Calibrated, water-cooled heat flux meters measured total heat flux

in the burn room and across the lower level on the opposite side of the

stairway from the burner. The velocity of air and gases entering the

burn room and exhausting through the roof of the stairwell were measured

with directional low velocity probes placed in the openings. This type

of probe was developed by Heskestad [5] and the description and con- struction details of these devices are provided in the reference. The

differential pressure was measured with a calibrated diaphragm-type

pressure-transducer. Calibration techniques are provided by McCaffrey

and Heskestad [6].

Oxygen was measured at three locations as shown in figures 1-3.

Gases were pumped through cold traps to remove condensable vapors

before being sampled by electrolytic oxygen cells for 0

^ concentrations.

Pressure differential measurements were made between the following

areas in the facility:

a. Burn room and exterior at the basement level.

b. Burn room and stairwell at the basement level.

c. Basement and 1st floor in the stairwell.

d. 1st and 2nd floor in the stairwell.

Water flow rate measurements were made using a vane type meter

with a frequency analog converter which permitted flow rates to be

recorded by the data acquisition system.

9
4.4 Test Program

The test program concentrated on the investigation of two selected

fire protection system technologies to reduce the flow of products of

combustion into an open stairway. Before measuring the relative performance of the systems, an investigation was needed to characterize

the flow of combustion gases in the stair tower which served as the test

facility. It was essential that the test fires and resulting flow of

products of combustion were repeatable from test to test in order to

compare the performances of various fire protection systems interms of

selected parameters. Also, an analysis of the relative efficiencies of

the different fire protection systems being examined required an initial

quantification of the test fires in this facility in the "non- sprinkler"

mode

The test program addressed these tasks:

a. Quantify the flow of products of combustion in the test

facility at the selected burning rates.

b. Measure the impact that sprinkler and spray nozzle systems

have on cooling and reducing flow of the product of combustion

gas stream.

c. Determine the impact of draft panels installed around the

stairway on the performance of the spray nozzle systems.

4.5 Test Procedure

Prior to the water curtain tests "dry" burns were conducted to

characterize the profile of the stream of hot gases passing under the

arch between the burn room and the base of the stairway. Since the

burner emitted a fairly narrow column of flame and the deep beams

10
created channels in the bum room perpendicular to the opening, tneie was a concern that the flow of heated gases would be concentrated in the

center of the opening. A series of test fires were conducted using a thermocouple tree as described in table 2 to measure the temperature

• £ profile. The tests were conducted at Q

= 1.5 MW [5.5 (10 ) BTU/hr]

and under two different ventilation conditions. The first test series

2 2 incorporated a combustion air inlet of 0,39 m (4.25 ft ) and for the

2 2

second series the inlet was increased to 1.6 m (18 ft ). The roof

2 2 (exhaust) vent remained the same, 1.75 m (18.8 ft ) for both tests.

The temperature profile was made at each of the two ventilation conditions by moving the thermocouple tree from one location to another

between tests. The temperatures were recorded after quasi-steady state

conditions were reached in the test area. The results as shown in

figure 6 gave assurance that the construction across the opening between

the burn room and the base of the stairway created a generally uniform

distribution of the flow of gases under the arch.

The initial tests of the water curtain systems were conducted at a

• £

burner setting of Q

= 1. 5 MW [5 . 5 (10 ) BTU/hr]. For each test, the

burner was fired and after three minutes, when quasi-steady conditions

were reached, the water curtain was activated at a specified total water

flow rate (G) . The water flow at the established rate was then maintained for 5 minutes by which time a quasi-steady condition was again

achieved. In several water curtain tests, the water flow rates were

increased at 5 minute increments. Intermediate test flows were repeated

and the results were found to be consistent. For example, a single test

of a water curtain system included nominal average flow rates per unit

length of water curtain (G/L^,) of 37.2, 49.6, 62.0, and 74.5 £/min/m

(3, 4, 5, and 6 gal/min/ft), where L^, is the length of the water curtain.

in these tests was fixed at 7.9 m (26 ft) (see figure 1). A repeated

test at both 62.0 and 74.5 Jl/min/m (5, 6 gal/min/ft) provided equivalent

results. Table 3 lists the tests conducted in the series.

11
5. TEST RESULTS

5.1 Water Curtain System Tests

The initial tests of the water curtain fire protection scheme were

• g conducted with the burner delivering Q = 1.5 MW [5.5 (10 ) BTU/hr].

Figure 7 provides the temperature reduction results of the tests at

nominal average flow rates varying from 37.2 to 74.5 £/min/m (3 to 6

gal/min/ft) for both the 12.5 mm (1/2 in) and 10 mm (3/8 in) sprinklers.

* £ At a Q = 1.5 MW [5.5 (10 ) BTU/hr], the quasi-steady gas stream temperature recorded in the stairway at the 1st floor was 120°C (248°F) in the

absence of a water spray protection system. When water flow was initiated

and was increased in intensity, the gas stream temperatures decreased

eventually to a low of 39°C (102°F). For both the 12.5 mm (1/2 in) and

10 mm (3/8 in) sprinklers this low temperature was reached at G/L^, =

62 £/min/m (5 gal/min/ft). The first floor temperatures did not decrease

when flows were increased beyond this to 74.5 £/min/m (6 gal/min/ft).

At a flow rate of 37.2 £/min/m (3 gal/min/ft), which is the minimum flow

rate recommended in NFPA 13 [3] for sprinklers around escalator openings,

greater cooling was achieved with the 10 mm (3/8 in) orifice sprinkler.

The volumetric flow rates of the gas stream through the roof vent

at the varying water flow rates is shown in figure 8. As expected, the

range of performance was consistent with the gas cooling data shown in

figure 7. The flow through the stairway and the flow of combustion air

were eventually reduced to the point where the burner became starved.

• g The next series of tests was conducted with Q = 4 MW [13.6 (10 ) BTU/hr]. Steady state gas temperatures in the stairwell at the 1st

floor reached 234°C (485°F) prior to operation of the water curtain.

The reduction of gas temperatures measured at this location as a function of varying water flow rates for both the 12.5 mm (1/2 in) and 10 mm

(3/8 in) orifice sprinklers is shown in figure 9. The improvement in

the cooling of the gas stream by the 10 mm (3/8 in) sprinklers was significant

12
At G/L^c = 74.5 &/min/m (6 gal/min/f t) for the 10 mm (3/8 in)

sprinkler and at G/L^ = 86.9 2,/min/m (7 gal/min/f t) for the 12.5 mm

(1/2 in) sprinkler the cooling phenomenon appeared to be approaching a maximum level where the heated gas stream became saturated by the spray

droplets. At this cooling level, temperature measured at the 1st floor was approximately 60 °C.

As shown in figure 10, the water curtain systems at the higher

water flow rates were able to substantially reduce the flow of the gas

stream. However, once the gas stream approached a saturated condition,

the flow of gases continued upward through stairwell at a constant rate

3 3 of around 102 m /min (3600 ft /min) as measured at the roof exhaust.

This situation represented the point where increased water flow rates

for the systems would not result in significant further cooling of the

gas stream. Therefore, the rate of the flow the products of combustion

at these water flow rates asymptotically reached a minimum, essentially

constant rate. In short, the flow of products of combustion could not

• £ be further reduced in these tests with Q

= 4 MW [13.6 (10 ) BTU/hr]

5.2 Spray Nozzle System Tests

The spray nozzle system tests were all conducted with Q

= 4 MW

[13.6 (10 ) BTU/hr], The initial fire test was conducted at water flow

• r rates per unit equivalent passage sectional area, G/A^, of 81.5 2,/min/m

(2 gal/min/f t^) which is the design criterion contained in NFPA 101 [4]

for spray nozzle system protecting escalator openings. Here A , the equivalent passage sectional area of the stairway as defined in [4]

At this water flow rate, the 10 mm (3/8 in) spray nozzle system substantially reduced the flow of gases up through the stairwell as indicated in figure 11. In this test the flow of incoming combustion air

was reduced to the point where the burner became starved before the test was terminated. Prior to the termination the gas stream up through the

stairwell became saturated and flow gases continued upward at a relatively constant but reduced rate. Figure 11 provides the results of

13
tests at varying water flow rates and their impact on the flow of the

gas stream. The 10 mm (3/8 in) nozzles operating at higher nozzle

pressures provided significantly better results than the 12.5 mm (1/2

in) nozzles.

In a series of non-fire tests, it was determined that the spray

nozzle systems, projecting high velocity sprays downward, created a downdraft in the stairway. The installation of draft panels surrounding

three sides of the stairwell at the first floor level was found to

slightly increase this downdraft effect.

As discussed later in the analysis of the data, a major function of

the spray nozzle system (as well as the water curtain system) in reducing

the flow of the gas stream in the stairway is to cool and reduce the

buoyancy of the heated gas stream. With regard to this function the

installation of the draft panels around the stairway did not improve the

performance of the spray nozzle systems for the few fire tests where

they were employed. It is envisaged, however, that in other stairwellsprinkler configurations draft panels or suspended draft curtains may be

effective in channeling the gas stream in a manner as to enhance gaswater mixing and improve cooling efficiency.

6. ANALYSIS OF THE DATA AND CONCLUSIONS

6.1 The Concept of a Stairwell-Sprinkler Component

As mentioned in section 2, the overall purpose of this experimental

investigation is to study the effect of water sprinkler operation on the

spread of products of combustion through open stairways. There are basically three mechanisms by which hot products of combustion migrate

through a room of fire origin and eventually throughout an entire building structure. These mechanisms are buoyancy, expansion, and forced

ventilation. The experimental part of the program indicated that the

sprinkler systems investigated had a primary effect on the buoyancy

mechanism. Such systems positioned around or within open stairway floor

14
penetrations would produce a fundamental variation in intrabuilding

migration of the products of combustion by virtue of their effect in

reducing the buoyancy of (i.e., in cooling) those gases which pass

through their region of influence.

Reducing the buoyancy of the products of combustion as they pass

from a room of fire origin to an adjacent space may be beneficial or detrimental to the overall hazard development within a building.

Indeed, the overall effect of sprinkler operation would depend on, and

must be studied in the context of the overall building design (including

active ventilation systems) and on the particular fire scenario which

generates the threat. It is outside the scope of the present investigation to consider such an overall systems problem. As such, it turns

out to be premature and, in a sense, inappropriate to address the general question: Sprinkler protection of open stairways - good or bad?

Rather, open stairway sprinkler protection should more appropriately be

studied as a potential fire protection system component. To ultimately

investigate its utility in a given application it must first be understood in terms of its separate component performance characteristics.

In view of this, the reduction and analysis of the acquired full scale

experimental data was carried out with the goal of identifying and, to

the maximum possible extent, deducing meaningful performance characteristics of these sprinkler components.

In the remaining discussion of this section we first proceed to

define the physical bounds of the open stairwell-sprinkler system

component. Following this, certain parameters which will prove useful

in describing the component performance characteristics will be defined.

A qualitative review of the principles which govern the flow phenomenology within the experimental stairtower facility will then be discussed.

In the present context this facility should be thought of as an instrument where the stairwell-sprinkler component under study is inserted,

and with which the desired component characteristics are measured.

Certain experimentally obtained and useful operating characteristics of

15
this facility instrument, in the absence of sprinkler operation, will be

presented. Data acquired during operation of the various stairwaysprinkler types and appropriately reduced in the context of defined

component performance characteristics will be presented. Finally plots

of these reduced data and their implications will be discussed.

6.2 The Physical Bounds of the Stairwell-Sprinkler Component

In order to identify performance characteristics for the system

component under investigation it is important to develop definitions

both for the physical bounds of the component and for its input and

output.

Here we are talking about an array of sprinkler heads which either

surround the perihery of, or are placed within an open stairwell. At a minimum the overall component description would require the type of

sprinkler heads, the spacing or general positioning of the heads, the area of the stairwell, and any other special devices or characteristics

of the overall configuration.

The bounds of the overall component can be usefully described by

the surfaces indicated by the dashed lines of figure 12. The input to

the stairway-sprinkler component is the hot gas which enters the imaginary vertical surface of these bounds. The output of the component is

the relatively cool gas which passes up through the imaginary horizontal

surface. This input and output is also indicated by arrows in figure

12 .

As discussed previously the present experimental program has

investigated two basic component design types and a few variations of

each of these. The component design types are summarized in table 1.

16
The designs involve a fixed floor to ceiling distance of

2 approximately 3.7 m (12 ft) and a square stairwell area of 9.3 m (100

2

ft ). As will be seen, even with the limited available data a reasonable

basis for generalization of the present experimental results to other

geometries and configurations can be formulated.

6.3 Parameters to Describe the Component Performance Characteristics

As noted in the introductory paragraph to this section the major

effect of the stairwell-sprinkler component is to reduce the temperature

or buoyancy of hot gases that pass through it. The mechanism by which

the incoming gases are cooled is primarily evaporation. Most of the

inlet gas which enters the stairwell-sprinkler component is the ambient

air which has been heated to high temperatures by mixing with the products

of combustion within the fire plume. As a result of this heating one can anticipate that the relative humidity of this inlet gas will be very

low. That is, the absolute water content of the air in its original

ambient state together with the amount of water added from the products

of combustion represents a relatively small percentage of the total

water (vapor) carrying capacity of the air in its newly heated inlet

state. Thus, as the relatively dry hot air enters the confines of the

stairwell-sprinkler component envelope, a great deal of cooling of this

stream can be potentially achieved if the sprinklers bring it anywhere

near its fully saturated state.

Of the several possible component designs that one might consider

in providing this evaporative cooling, the one which achieves a fully

saturated output gas stream with the least total water usage would

appear to have advantages over the others. In any event, one would like

to have the capability of estimating the degree of cooling which will be

achieved by a given design for given inlet stream conditions and as a function of water usage. Such a capability would represent the com- ponent design performance characteristics being sought.

17
The above discussion suggests that the following parameters would

be useful in providing a description of inlet and outlet gas stream

properties and in relating these to component performance:

Ep - Maximum possible rate at which energy can be extracted from the

inlet air stream by virtue of adiabatically bringing the stream

from an assumed zero saturation inlet state to a fully saturated

outlet "State. Additional energy extraction (temperature drop) that

may be achieved by further cooling from the fully saturated state

(by sensible cooling) is assumed to be negligible compared to the

energy extraction associated with the above evaporation cooling.

E - Actual rate at which a specific stairway-sprinkler component

cl design, assumed to be adiabatic, extracts energy from the inlet

stream.

- Actual volume rate of water flow delivered by all of the sprinklers

in a given design.

• • Gevap ~ Amount of G which is actually evaporated during the course of

extracting energy from the stream. To estimate this from the data

the assumption of a zero humidity inlet state is made. It is

further assumed that the total energy which the inlet gas stream

provides to the entire sprinkler water stream as this water goes

from its original temperature to its final temperature is negligible

compared to the heat of vaporization associated with Gevap

•

The above definitions can be expressed as follows:

E = m. C (T - T , ) p in p sat in

E = m, C (T - T. ) a in p out in

G = volume rate of water delivered by all sprinklers

( 1 )

18
G = E / [p . Ah]

evap a w(liq)

where T

Qut

is the average temperature of the flow in the outlet stream,

is the average temperature of the (assumed dry) inlet stream, T

gat

is the adiabatic saturation temperature of this inlet stream, is the

mass rate of inlet gas flow, P w (-L£q)

is the density of liquid water,

Ah is the enthalpy of vaporization of water, and is the (assumed

constant) specific heat of the inlet gas. The properties of the inlet

stream will be taken to be those of air. Also the mass rate of air

flowing through the stairtower’s lower vent and into the burn room will

be assumed to be identical to . This latter assumption is essentially

equivalent to neglecting the mass rate addition into the burn room of

fuel (propane) compared to air. Condensation on relatively cool burn

room surfaces is also neglected.

From the above assumptions and analysis it is possible to define

the following two types of efficiencies which will be useful in establishing the performance of a given stairwell-sprinkler design:

• • n c = E

a /E = cooling efficiency

( 2 ) q = G /G = water usage efficiency

w evap

6.4 The Flow Phenomenology in the Experimental Facility

A simplified sketch of the experimental stairtower facility is

presented in figure 13. As mentioned earlier, this facility should be

thought of as an instrument wherein the stairwell-sprinkler component is

inserted for its performance evaluation. Referring to figure 13, the

component under study is '’placed’' on the right side of the lower level.

The fire source is placed on the left side of this lower space. Together

with air which is brought in through the lower level vent, this source ultimately generates the high energy gas inlet stream with its associated

Ep to the insitu stairwell-sprinkler component under investigation.

19
The inlet stream passes through the stairwell-sprinkler component

and, if the sprinklers are engaged, it enters the next level of the

tower in a cooled and humid state. From there the stream passes up

through the stairwell to the third level and finally exits from the

facility through the ceiling vent. While passing through the second and

third level, complicated mixing of the stream leads to significant heat

transfer to the upper structural components of the facility. With

further cooling of the flowthrough stream, condensation of water vapor

from the warm humid gases to the cool walls could play a significant

role in this heat transfer process.

In the context of the remarks at the beginning of this section the

stair tower test facility includes a fire scenario and a very specific

building design system, one component of which is represented by the

stairwell-sprinkler system. Thus, activation of the sprinklers will

influence, but not completely determine, the overall rate of migration

of the products of combustion. In order to understand the effect of

sprinkler operation in this particular building design it is useful to

briefly describe the interfacility flow phenomenology and outline the

major physical considerations that bring it about. This can best be

accomplished by discussing the vertical pressure distributions both

inside and outside the stair tower structure.

Between the levels of the lower and upper vents of the structure

the uniform vertical outside temperature (density) distribution leads to

a linear variation of ambient pressure. This is sketched in figure 12.

Now assume an airflow into the lower vent, past the fire, up through the

stairway and out of the upper vent. Having been heated by the fire, the

temperature of the gas flowing through the facility will generally have

a high temperature compared to the ambient. This gas temperature will

be highest at the lower level. Due to heat transfer to the walls,

floors, etc. the temperature of the gases will generally decrease while

flowing upward through the tower. Depending on the specific vertical

20
temperature (density) profile (which can be significantly altered by

operation of the sprinkler system) the variation of inside pressure

between the elevations of the upper and lower facility vents would look

something like the sketch in figure 12.

Compatible with the above assumption on the basic flow direction,

and as indicated in the sketch of figure 12, it is evident that there

must be a (neutral plane) level, z^, between the two vent elevations.

At this elevation, P , (z ) = P (z ) . Thus, pressure drops exist

from outside to inside the facility at the lower vent and from inside to

outside the facility at the upper vent. The pressure drops at these two

vents are required to actually drive the flow of air and air plus products of combustion plus water (added by the sprinklers - if they are operating) through the lower and upper vents respectively. The actual

rate of flow through the two vents must of course be compatible with the

overall principles of mass and momentum conservation (for example,

smaller vent openings would require a larger pressure drop to maintain

the same mass rate of flow) . The coupled principles of energy, momentum,

and mass conservation dictate the temperature distribution that will

result from various additions and deletions of energy to the stream as

it passes through the inside of the facility. All these considerations

taken together determine the rate of which air will enter the facility,

provide oxygen for the fire and ultimately supply a particular inlet

flow condition to a stairwell sprinkler component whose performance is

under investigation.

It is clear from the above that the actual operation of the

stairwell-sprinkler component will, in and of itself, alter the state of

the flow throughout the entire facility. By varying the water flow

through the sprinklers, the inlet flow to the stairwell-sprinkler com- ponent itself will be varied. This latter inlet flow variation will

depend on performance characteristics of the overall facility design.

In particular, the state of the flow before and after sprinkler operation

21
will not be a measure solely of stairwell-sprinkler component performance

characteristics. In order to extract such characteristics it would

appear that simultaneous measurement of both inlet and outlet stream

parameters during actual operation of the component is required.

As it turns out, it is neither practical nor necessary to directly

measure bulk inlet stream parameters, say bulk temperature T^ , during

actual sprinkler operation. However, it is possible to experimentally

deduce such parameters as function of easily measureable fire size and mass rate of air flow through the lower vent and into the burn room.

A functional dependence of T . on m. and fire size has been

in xn obtained from measurements taken during nonsprinkler operation of the

facility. This will be discussed in the next section.

6.5 A Useful Operating Characteristic of the

Stair tower Facility Burn Room

This section focuses attention on the phenomenology within the burn

room. Referring again to figure 12, ambient air is drawn in through the

lower vent and is entrained within the plume above the propane burner.

For the experiments under discussion the entrained air actually supplies

(more than enough of) the oxygen required to support the combustion of

the fuel. The hot products of combustion rise in the plume to the

ceiling. Once a quasisteady state has been achieved, the flow in this

plume maintains an upper hot layer of products of combustion throughout

the burn room and, at the same time, supplies a continuous flow of hot

gases from this layer to the stairwell opening.

As has been discussed earlier, the amount of air which is brought

into the burn room, m. , is a function of the rate of fuel supply and of

in

the overall stair tower design parameters. Nonetheless, by applying

conservation principles solely to the burn room envelope an estimate of

the properties of the flow exiting the burn room (or entering the domain

of influence of the stairwell-sprinkler component) can be obtained as a function of m^, whatever its value. It is the objective of this

paragraph to develop such a functional relationship.

22
For the experiments under discussion the rate of mass flow of

propane introduced by the burner is small compared to the rate of inlet

air mass flow, Also, any mass transfer to or from the burn room

wall ceiling and floor surfaces can be assumed to be small compared to

m^

n

. Then, by continuity, the total rate of mass flow leaving the burn

room is substantially the same as m^.

Applying conservation of energy to an envelope surrounding the

gases in the burn room and in the absence of any sprinkler operation the

following results:

m. C m p

(Tout loss (3)

where C is the specific heat of the gases (assumed to be identical to

P • that of air) entering and leaving the burn room, Q is the heat addition

due to fuel combustion, and Q^oss are ei*ergy losses due to heat

transfer to internal surfaces of the burn room.

Since the rate of propane supply to the burner is controlled and

measured, and since complete combustion within the burn room is likely,

the value of Q in the above equation can be accurately estimated. Also,

m^

n

is easily computed from a velocity probe measurement in the lower

stair tower vent. T , is also measured at this lower vent location. amb

Finally, T

Qut can be estimated from measurements of two thermocouples

which are submerged in the hot outlet stream somewhat above the stairwell opening at the lower part of the first floor level.

It is convenient to express the Q^ogs

term of Eq. (3) in the

following conventional terms:

Q

lOSS

“

<T - W (4)

Here, hA represents an effective product of heat transfer coefficient and exposed burn room surface area, T represents an effective wall

temperature of this surface area, and T represents an effective temperature of the burn room gases from which the net energy Q 1qss

is being

transferred. 23
T

Qut

of Eq. (3) is clearly representative of a characteristic value

for T. Also, during the limited interval of a given test, which is

initiated with the burn room in an initial ambient temperature state,

the effective temperature of the burn room surfaces, T ,,, can be taken wall

as T . In view of all this, and since, heretofore, none of the amb

individual terms on the right hand side of Eq. (4) have been defined

precisely, it is reasonable to make the replacements T and T , for T

out amb

and respectively. By doing this, all of the complex burn room phenomenology is thrown into the coefficient hA. Thus

Q, = hA (T - T , ) loss out amb (5)

Using this in Eq. (3) leads to the following equation for hA:

hA = Q/(T

out

T , ) - m. C amb in p

( 6 )

The stairtower was exercised, without sprinkler operation, for a variety of different combinations of Q and upper vent area. The measurable variables mentioned above were averaged during that time interval

of a given test run when quasisteady behavior was exhibited. The

averaged data for these variables are presented in table 3 along with

computed values [according to Eq. (6)] for hA.

As can be seen in table 4, the measured values of hA are remarkably

uniform. For all five of the tests in the present series which were appropriate for the present hA evaluation and which are enumerated in

the table, the average value

hA = 466 BTU/ (min °F) =14.7 kW/°C (7)

is accurate to within ten percent. This exceedingly useful result must

be considered as strictly empirical, and by no means general beyond the

range of experimental parameters from which it was deduced. Thus, the

complex heat and mass transfer phenomena which dictate the value of hA

do not provide any clear basis on which to extrapolate this constant

hA result. Indeed, that hA should exhibit constant behavior at all must

be viewed as fortuitous.

24
With a known value of hA in hand, Eq. (6) can be rewritten so as to

provide an estimate for T

Qut

as a function of the measured experimental

values Q , m , , and T , . in amb

T = T

out amb + Q/(min C

P

+ hA)

As defined earlier, T

Qut

is the temperature of the mixed gas stream

as it exits from the stairwell to the second level of the stairtower.

Also, this section does not consider any sprinkler operation. It is now

reasonable to assume that the contribution to the heat loss term of Eq.

(5) which takes place at boundaries of the stairwell-sprinkler system

(i.e., at the surfaces on the right hand side of the burn room - c.f.

figure 12) is negligible compared to the heat transfered to the burn

room surfaces themselves (i.e., on the left side of the burn room).

Accordingly, T

Qut

in the above equation can then be replaced by T^, the

average temperature of the stairwell-sprinkler component inlet gas

stream. Doing so yields the following final working result of this

section

T . = T in amb + Q/(min C

P

+ hA) ( 8 )

Together with the definitions of section 6.3 and the data acquired

according to the description of earlier sections, the result of Eq. (8)

will be utilized in the next section to obtain operating characteristics

of stairwell-sprinkler components.

6.6 Some Performance Characteristics of Stairwell-Sprinkler

Components — The Experimental Results and Their Correlation

6.6.1 Plots of the Experimentally Obtained Component Efficiencies

As described in earlier sections, the stairwell-sprinkler components

identified above in section 6.2 were operated in the stairtower structure

under various water flow rates and fire sizes. With Eqs. (1), (2), and

25
(8) the data from each of these test runs were used to compute the

corresponding values of cooling efficiency, pc

, and water usage efficiency, p^. The appendix describes the property values and the details

of the data manipulation which were used in performing these computations.

For each of the component types, water curtain (WC) and spray

nozzle (SN), and for each of their two variations [12.5 mm (1/2 inch)

nozzles and 10 mm (3/8 inch) nozzles] a plot of p as a function of the

c water usage parameter

G = G/(gpm . A

wen

/ft

2

) = .0245 G/ [ (5,/min) (Awell/m

2

) ] (9)

is provided in figures 14-17, where is the planview area of the

total stairwell opening which was taken to be 9.3 m

2 (100 ft2 ). The

computed value of the extractable energy flow rate parameter

E = E / [ (10

4 BTU/hr) (A .,/ft 2 )] = .0317 E /[kW*(A . , /m

2

)

]

(10)

p p well p weii

is also included in these plots alongside each data point. In a similar

* * manner, plots of p^ as a function of E^ are presented in figures 18-21.

G is also included alongside each of the data points in these latter

plots

As indicated above, the parameters G and E^ are measures of G

and E per unit stairwell area.

P

According to the model adopted here, every data point with

corresponding computed p^ >_ 1 is assumed to represent a fully saturated

outlet flow. The letter S is therefore attached to every data point of

this category in all Figures 14-21.

26
6.6.2 Correlation of the Reduced Data Results

6. 6. 2.1 Cooling Efficiency as a Function of Water Flow Rate

6. 6. 2. 1.1 The 12.5 mm (1/2 Inch) Water Curtain Data

* &

Attention is focused on the vs G plots of figures 14-17.

Within this group the figure 14 data for the 12.5 mm (1/2 in) nozzle

water curtain will first be discussed, and an empirical correlation of

these will be developed. The same discussion and method of correlation

will then be extended to the data of figures 15-17.

According to the assumed model of the phenomena, q can exceed 1 c only by providing more than enough sprinkler water flow to saturate the

outlet stream. Further, the model assumes that (for practical systems)

increased cooling beyond the fully saturated state will not be significantly greater than the cooling that would have been achieved if the

outlet stream was exactly in a saturated state. This assumption, which

is equivalent to the expectation that q^ should never be significantly

greater than 1, is clearly consistent with the data of figure 14.

•* Following the line of reasoning of the model further, as G is

•* increased, say for a fixed, arbitrary E^, the outlet stream would be

expected to eventually reach the saturated condition and n would reach

a value of 1. Larger G s would lead to saturated outlet conditions

•* with q

' s only slightly greater than 1. At the other extreme of the G

^ * * * * spectrum it is evident that (again, independent of E ) as G goes to

•* p

zero, n must go to zero. For E in some fixed range and for outlet

c p

streams which are unsaturated (e.g. , for all data points of figure 14

without the attached S) it is therefore anticipated that reduced data

•* plotted in q , G coordinates should fall in a band. This band would

c * * originate at the q = G =0 point on the left and eventually terminate

c •* *** at some (apriori unknown) point q = 1, G = G on the right. Beyond

this latter point (i.e., for G > G ) all data points should represent

saturated outlet states and they should essentially lie on the line

n

c = 1 *

27
It is evident from the data in figure 14 that, in the entire

•* available range .39 <_ <_ 2.04, good correlation with the (five unsaturated) data points is achieved by assuming the above described band

to be a single straight line. A least squares curve fit of this figure

14 data leads to a line of slope 0.84 and an = 1 intercept at G = 1./0.84 = 1.19. This line along with the continuing n =1 line is

c included in the figure 14 plot. Together, these lines represent the

empirical correlation of the data and its logical extension.

It is anticipated that there would be a breakdown of the above,

•* narrow band (single line) correlation for s that were significantly

larger than 2.04. However, some extension of the correlation's validity

** •* beyond the strict values .39 £ E^ £ 2.04, say to the general range E^

of the order of one, e.g., from 0.2 to 5, would appear to be both valid

and of great practical use.

All of the above analysis and discussion leads to the following

conclusion:

•* For Ep of the order of one, the cooling efficiency performance

characteristic of the 12.5 mm (1/2 in) nozzle water curtain component

design which was tested in the stairtower can be estimated by

0.84 G* ; G* £ 1.19

1 ; G* > 1.19

6.6. 2.1.2 Correlation of the Other Data

The entire analysis and discussion of the last paragraph has been

applied to the 10 mm (3/8 in) nozzle WC component design (figure 15) and

to the SN component design with both 12.5 mm (1/2 in) (figure 16) and 10 mm (3/8 in) (figure 17) nozzles. The general conclusion from all of

this is as follows:

28
characteristics of the stairwell-sprinkler components which were tested

in the stairtower can generally be estimated from:

where is some constant associated with the type of stairwell-sprinkler

component used, i.e..

and where, specifically,

K

c [12.5 mm (1/2 in) nozzle WC] = 0.84

K [10 mm (3/8 in) nozzle WC] = 1.00

c

K [12.5 mm (1/2 in) nozzle SN] = 0.76

c

K [10 mm (3/8 in) nozzle SN] = 0.95

c

The above result for n

c is plotted in figure 22.

In the present test series the draft board variation to the SN

component designs do not appear to alter the efficiency in any significant way. For general comparison, the data from the draft board variation of the SN designs were included in figures 16 and 17. However,

these few data have not been taken account of in the sloped line curve

fits.

** •* KG ; G < 1/K

c — c

( 11)

• &

1 ; G > 1/K

c

K^ = K^ (stairwell-sprinkler component type)

29
It should be noted that in figures 16 and 17 (i.e,, the SN data)

the number of data points from which the sloped straight line curve fits are constructed are scarce indeed. For example, the figure 17 line is

constructed from a single available (unsaturated) data point. More data

would clearly enhance confidence in the validity of the Eq. (11) performance characteristics for these latter SN components. Nevertheless, the

SN results in hand are reasonable in that they are consistent with the

WC results which were constructed from a far firmer data base.

6. 6. 2. 2 Water Usage Efficiency as a Function of

Extractable Energy Flow Rate

Eqs. (1), (2), (9), and (10) yield the following equation for water

usage efficiency:

Using the property values

p ... 62.4 lb /ft

3 = 1.000 g/cm3

w(liq) m

Ah = 1035 BTU/lb = 575 cal/g m

in this last result yields

p = .0193 E* n /G* = K E* (12) w pc w p

/ • ^

. 1247 (10 ; E n P 9- M w(liq) Ah '

,, /f .3 BTU/lb

lb /ft m

m

11.10 E* n E—£_

• * w(liq) Ah G

g/ cm' cal/g

where

K = .0193 n /G* w c

30
= K^(G ; stairwell - sprinkler type)

and where n c is provided in Eq. (11).

The above analytic estimate for n which was derived from the Eq.

(11) correlation is plotted in figures 18-21 along with the reduced

data. For good correlation with the analytic estimate, a data point

•* •* with its associated G value should lie on an appropriate, constant G

sloping line. From all of the data of the four figures only one data

point has a water usage efficiency which is significantly below the

** predicted value, namely, the n = .026, E =2.04 point of figure 18.

w p * * For this point, the predicted value of n = .033 (at E =2.04 and

•* w p

G = .62 _< 1.19) is to be compared to the measured value of = .026.

>

6.7 Discussion of Results

6.7.1 Cooling Efficiency and Its Application

The major results of the present experimental study are the cooling

efficiency performance characteristics of the specific stairwell-sprinkler

component types which were actually tested. These are portrayed graphically in figure 22 and presented analytically in Eq. (11). Assuming

that the introduction of one of these tested stairwell-sprinkler components in a given building design would decrease the overall building

fire hazard, these results give guidance in implementing one of the

various design choices. For example:

(a) For the same total water delivery rate, the 10 mm (3/8 in) nozzle

is preferable to the 12.5 mm (1/2 in) nozzle both in the WC and SN

design.

(b) The WC design in the tested configuration may be slightly preferable

to the SN design in that approximately five percent less water

consumption would be required to provide the same cooling efficiency.

31
(c) In the WC design, use of the 10 mm (3/8 in) nozzle instead of the

12.5 mm (1/2 in) nozzle results in the same amount of cooling with

sixteen percent less water consumption. With the 10 mm (3/8 in)

2 nozzle, water consumption should be restricted to 41 i/min/m

2 (1.0 gal/min/ft ) of stairwell opening. Using more water will not

result in significantly more cooling. This consumption is equivalent

to an average flow rate of 48 £/min/m (3.8 gal/min/ft) across the

length of the opening between the stairway and the burn room.

(d) In the SN design, use of the 10 mm (3/8 in) nozzle instead of the

12.5 mm (1/2 in) nozzle results in the same amount of cooling with

twenty percent less water consumption. With the 10 mm (3/8 in)

2 nozzle, water consumption should be restricted to 43 £/min/m

2 (1.1 gal/min/ft ) of stairwell opening. Using more water will not

result in significantly more cooling. This consumption is equivalent

2 2

to an average flow rate of 67 £/min/m (1,6 gal/min/ft ) over the

protected opening as measured according to NTTA 101 [4].

(e) Draft boards do not significantly alter the cooling efficiency of

the SN design.

The analytic estimate for the cooling efficiency performance

characteristic allows a direct estimate for the component outlet stream

temperature as a function of the inlet stream temperature. Thus, from

Eq. (1) and the definition of Eq. (2) it follows that T

out can be

obtained from

T = T.

out in (1 - n ) c

n T _ c sat

(13)

where ^

is given in Eq. (11), and where T

sat > a be estimated to within 1°C (2°F) in the range 27

(80 < T. < 1000, T. in°F) by in in

function of T

< T. < 538, in

can in°C

T = 22.7 In (T. + 17.8) - 77.2, T and T. in °C sat m sat in

32
T =40.8 In (T4 ) - 131, T _ and T, in °F

sat in * sat in

Eq. (14) is an empirical curve fit of saturation air temperatures provided

in reference [7],

6.7.2 Water Usage Efficiency and Its Potential Improvement

It is clear from the plots of figures 18-21 and from the result of

Eq. (12) that for the purpose of evaporation cooling the components

under review have very poor water usage efficiencies. In particular,

for the extractable energy flow rate levels of the present experiments

the values nw

are of the order of .03 or less. This poor efficiency is

not all that surprising when one considers the purpose for which the

sprinkler nozzles were designed, namely, to extinguish deep seated

fires, or to cool hot surfaces.

Characteristics of a water delivery system that would be successful

and efficient in the extinguishment or surface cooling role are incompatible with a system that would efficiently provide gas stream cooling.

In extinguishment, for example, one delivers water droplets which are relatively large. Indeed, they should be large enough so that during

their trajectory and until they reach their intended target they will

achieve or retain enough momentum to negotiate opposing hot gas flows

without significant evaporation. Such water droplets will for example,

enter the threatening fuel bed with most of their original liquid phase

water intact and available to cool the fuel to the point of extinguishment. In direct contrast to this, when performing an evaporation cooling

role, that liquid part of a droplet which passes completely through the

hot gas stream intact is totally wasted.

In view of the above it would appear that arbitrarily small droplets

with corresponding large surface area per unit mass of water may be the

appropriate choice for efficient evaporation cooling of a hot gas stream.

This choice would, however, lead to a problem in practical systems in

that such mist-like particles would be rapidly swept away by the gas

33
stream near their point of injection thereby never actually penetrating

and cooling the stream throughout its depth. What is actually required

for effective evaporation cooling is a system that delivers droplets of

appropriate size and/or momentum so that, during the same time interval

that these droplets successfully penetrate a hot gas stream indepth,

they effectively loose all of their liquid phase to evaporation. In any

event, one would anticipate that with smaller nozzle sizes than those

used in the present component designs (which would lead to smaller

* * droplet sizes for a fixed G ) cooling efficiencies of 1.0 could he

•* achieved at water usage rates which were considerably less than the G

= 1.0 - 1.3 range required in these tests. Put another way, by using

smaller nozzles it should be possible to practically achieve maximum

stream cooling (q^ = 1.) with a tenth or less of the present water

delivery rate (i.e., at q^ _> .3).

6.7.3 Extension of the Results to Other Geometries and Configurations

The results for the performance characteristics of the actual

stairwell-sprinkler components tested in the present experimental program

have been presented above. The outstanding remaining question relative

to these results has to do with their potential extention to other

stairwell geometries and configurations. For example, if the WC or SN

design is used to provide one-sided protection of a high aspect ratio

stairwell [as compared to one-sided protection of the present square,

2 2 9.3 m (100 ft ) stairwell], can the above results be applied with any

confidence? Alternatively, can the above results be applied to a square

2 2

9.3

m (100 ft ) stairwell centered in a space of fire origin and protected around its entire periphery (as compared to the one-sided protection required in the present configuration)? Finally, can the results

be used in designing protection of stairwells that open upward from a room of fire origin and that have heights significantly higher or smaller

than the 3.9 m (12 ft) height of the present configuration?

The fact of the matter is that each of the above example variations

to the tested geometry and configuration represent a new stairwellsprinkler design in their own right. For confident knowledge of the

34
performance characteristics of these variant designs, separate experimental programs would be required. By nature of the geometry (size) and

configuration (placement of stairwell within the burn room) of the above

example components, such programs would require a much larger area burn

room than the one in the existing stairtower facility.

In spite of this last observation, and by nature of its area type

of water discharge, it would appear that the performance of the SN type

A

of stairwell-sprinkler component designs based on G or E (water usage

or extractable energy per unit stairwell area) would be relatively

insensitive to the details of total stairwell area [provided the narrow

dimension of the planview is not significantly less than 3 m (10 ft) ]

location within room of fire origin and height of room of fire origin.

It is not at all clear that the same would be true for the WC type of

design which provides cooling in the vicinity of its line of water

discharge whose effectiveness may be insensitive to the actual area of

the stairwell on which G and E are based. However, if extension of

the present WC results is valid then it would probably be more appropriate

to present and use them on a basis of water usage or extractable energy

per unit length of water curtain (as compared to per unit area of

stairwell)

In view of the latter observation, the following new water usage

and extractable energy parameters are defined for use with water curtain

designs:

•* Gwc

= G/(gpm . L

W(

,/ft) = .0805 G/[ U/min) (L^/m) ]

4. •* E

(15)

-p(WC) = E

p

/[(10 BTU/hrHL^/ft)] = .104 E

p

/[Kw . (L^/m) ]

where is the length of the water curtain.

Using a water curtain length of 7.9 m (26 ft) for the tested WC

design, a new abscissa is included at the top of the plot of figure 22

_ •* to reflect the n

c vs G^

c presentation of the WC results. Also, for the

35
present tests, the E range .39-2.04 corresponds to an E /TT„S range 1.5-

P ^ P(WC)

7.9, and the extended useful E range .2-5. (i.e., of the order of 1)

P * corresponds to an extended useful E range .8-20. Finally, the WC

results of Eqs. (11) and (12) are rewritten as follows:

•* For E /TT _. in the approximate range .8-20. , the cooling efficiency

P(WC)

performance of the two water curtain stairwell-sprinkler components

which were tested in the stairtower can generally be given as

nc

K

c(WC)

G

WC ’ SjC - 1 ^K

c(WC)

5 G

WC

> 1/K

c(WC)

(16)

where

K

c(WC)

= K

c (WC) (water curtaln type)

and where, specifically.

K /tt _ n [12.5 mm (1/2 in) nozzles on 1.8 m (6 ft) centers] = 0.22

cCWC)

K /tt„ n [10 mm (3/8 in) nozzles on 1.8 m (6 ft) centers] = 0.26

c(WC)

The water usage efficiency of these water curtain components can be

estimated from

•*

nw

= K

w(WC)

E

p(WC)

(17)

where

K = .0193 n /G* w(WC) c WC

** = K

w(wc)

(G

wc ; water curtain fc ype>

and where is provided in Eq. (16).

36
Based on all of the above remarks, the following conclusions

result:

** a. For Ep in the approximate range 0. 2-5.0 and for stairwells with

widths not significantly larger than 3 m (10 ft) but otherwise of

arbitrary area and location it is reasonable to estimate performance characteristics of SN stairwell- sprinkler components from

Eqs. (11) and (12).

•* b. For Ep^

c^ in the approximate range 0.8-20. and for stairwells of

arbitrary area and location and serving floors with heights not

significantly larger or smaller than 3.7 m (12 ft), it is reasonable to estimate performance characteristics of WC stairwellsprinkler components from Eqs. (16) and (17)

.

To implement a WC design according to the above conclusion obviously

requires protection around the entire stairwell perimeter. As in the

experimental configuration, this can involve portions of the stairwell

perimeter being protected by fixed walls and portions by the actual

water curtain. Alternatively, the entire perimeter can be protected by

the water curtain.

If the SN or WC is implemented in a given building, it would

appear reasonable to do so at the lowest water usage rate which provides

r\ =1. Of the two nozzle sizes investigated the 10 mm (3/8 in) one is

** preferable and should be implemented at water rates of G = 1/.95 = 1.05 and G = 1/.26 = 3.8 for the SN and WC designs respectively. A

choice between SN and WC in a given application is a choice between the

lowest total water usage rate, q , consistant with these latter values.

3. From the definitions of Eqs. (9) and (13) this suggests:

When implemented in the 10 mm (3/8 in) nozzle, the SN design is

more efficient than the WC design if

37
area of stairwell/m

length of water curtain/m

2

area of stairwell/ft

length of water curtaln/ft

< 1.10

< 3.6

( 18)

and the WC design should be used if Eq. (16) is not satisfied.

As noted in the above conclusion a. and b., this last result would

not necessarily be valid if the stairwell width was significantly larger

than 3 m (10 ft), or if the ceiling height was significantly different

than 3.7 m (12 ft).

Applying the last conclusion to configurations where the WC design

would completely surround the perphery of the stairwell yields the

result that the SN is preferable to the WC if the stairwell length L

satisfies

:

L/m < 2. 2 (W + 26) /m

(W/m - 2.2)

L/ft < 7. 2(W + 26) /ft

(W/ft - 7.2)

(19)

where W is the width of the stairwell and 6 is the distance between the

edge of the stairwell opening and the position of the line of water

curtain nozzles.

7. SUMMARY OF CONCLUSIONS

In this investigation the concept of sprinkler fire protection of

open stairways has been studied experimentally. In the event of a threatening fire the implementation of such stairwell-sprinkler components has previously been assumed to result in less hazardous migrations

of products of combustions throughout a building of interest. However,

this is not necessarily the case. Whether beneficial or detrimental,

the fact of the matter is that the result of implementing such components

can be determined only by taking account of the characteristics of the

38
overall building system. Besides the stairwell-sprinkl er component

itself, the significant elements of this system would generally include

all components and construction details which impact on the normal or emergency building ventilation system. The nature of most likely fire

threat scenarios would also play a key factor in determining the ultimate

utility of the stairwell-sprinkler component.

If implementation of a stairwell-sprinkler system component would

reduce the fire hazard in a given application, then it would do so by

cooling hot fire gases as they pass into or through the component's

boundaries. This cooling of the gases reduces their buoyancy and,

therefore, the nature of their ultimate spread throughout the building.

In view of the above, the present experimental program was carried

out with the objective of evaluating and generalizing the performance

characteristics of different stairwell sprinkler designs relative to

their cooling capability. Two different types of sprinkler deployment

were studied, the water curtain (WC) and the spray nozzle (SN) . For

each of these, 12.5 mm (1/2 in) and 10 mm (3/8 in) nozzle sizes were

evaluated. For the SN design, a minor variation with draft boards

surrounding most of the stairwell (above the actual opening) was inves2 tigated. A fixed, square, stairwell opening of approximately 9.3 m

2

(100 ft ) was used in all tests.

The data acquired during the tests were analyzed and correlated

within the context of an evaporation cooling model of stairwell-sprinkler

component performance. For the fire sizes and specific stairwellsprinkler components which were tested, the following conclusions

resulted:

a. The 10 mm (3/8 in) nozzles are more efficient than the 12.5 mm (1/2

in) nozzles (for a given water flow rate).

b. The WC design may be more efficient than the SN design, but not

significantly so for single side exposure.

39
c. Draft boards do not significantly alter the performance of the SN

design.

d. With the use of 10 mm (3/8 in) nozzles, total water usage greater

2 2 than 41-43 2,/min/m (1. 0-1.1 gal/min/ft ) of stairwell plan area

[i.e. , 380-400 £/min (100-110 gal/min)] will not significantly

increase the cooling.

e. Actual cooling efficiency and water usage efficiency can be estimated from Eqs, (11) and (12) and from figure 22. The temperature

of the gas stream issuing from a component can be estimated from

Eq. (13).

Further study suggested extensions to these above specific results

which could be used with some confidence on stairwell-sprinkler components

of different geometry and/or configuration. These extensions are found

at the end of section 6.7.3. They provide explicit guidance in choosing

between the SN or WC designs.

Finally, it was concluded that for the task of evaporation cooling

of hot gas streams, fire protection sprinkler or spray nozzles of the

types that were used in this study are exceedingly inefficient in their

water usage. In particular, it was estimated that with more appropriate

nozzle designs, water usage could be reduced to a tenth or less of the

tested rates without any degradation in cooling efficiency. It is

important to point out, however, that to achieve such high water usage

efficiency a significant nozzle technology development program may be

required.

8. ACKNOWLEDGEMENTS

The authors would like to express thanks to Messrs. Richard Zile

and Warren Hayes, Jr. who participated in both the planning and the

preparation of the test facility as well as in the experimental work.

40
9 . REFERENCES

[1] O'Neill, J. G., Sprinkler-Vent and Spray Nozzle Systems for Fire

Protection of Openings in Fire Resistive Walls and Ceilings - The

State of the Art and a Plan for Future Research Work, NBSIR 78-

1571, National Bureau of Standards, (1978).

[2] Thompson, N. J., New Method of Protecting Conveyor Openings, NFPA

Quarterly Vol. 41, p. 9-18, (July 1947).

[3] Installation of Automatic Sprinkler Systems, NFPA No. 13, National

Fire Protection Association, Boston, MA (1978 Edition)

[4] Life Safety Code, NFPA 101, National Fire Protection Association,

Boston, MA (1976 Edition)

[5] Heskestad, G., Bidirectional Flow Tube for Fire-Induced Vent

Flows. In: Large-Scale Bedroom Fire Test, July 11, 1973, P. A.

Croce and H. W. Emmons, eds. FMRC Serial 21011.4, pp. 140-5,

Factory Mutual Research Corporation, Norwood, MA (1974).

[6] McCaffrey, G. J. and Heskestad, G. , A Robust Bidirectional Low

Velocity Probe for Flame and Fire Application, Combustion and

Flame, Vol. 26, pp. 125-7 (1976).

[7] Threlkeld, J. L, Thermal Environmental Engineering, Second Edition,

1970.

41
APPENDIX A. PROPERTY VALUES AND DETAILS OF DATA MANIPULATION

The following equations were developed in section 6:

E = m. C (T - T ) p in p sat in

E = m, C (T - T . ) a in p out m

G = volume flow rate of water

( 1 )

G =E/[p , . Ah]

evap a w(liq)

n cap = E /E = cooling efficiency

( 2 )

n = G /G = water usage efficiency w evap

hA = 466 BTU/ (min °F) = 14.7 kW/°C (7)

T = T , + Q (A. C + hA) (8) in amb in p

It is the purpose of this appendix to explain the details of how

actual test data were used in these equations to obtain the plots of

Figures 14-21.

To begin with, the following property values were used in the

calculations

C =0.24 BTU/ (lb °F) = 0.24 cal/(g °C)

p m

P am ® 540-R = 300«K

= - 0735 lb

m

/ft3 " l-l”(10- 3)g/om2

(A-l)

pw(Uq) = 62 ' 4 lb

m

/ft3 " 1 - 000 8 /cm3

42
T /°C = 22.7 ln(T, /°C + 17.8) - 77.2

sat dry

(A- 2)

T

sat

rF = 40,8 ln(Tdry/

° F) ' 131>

for T _ and T, in the range

sat dry

16 < T /°C <54 ; 43 < /°C < 318 — sat — — dry —

60 < T / °F < 130 ; 109 < T, /°F < 604 — sat — — dry —

Ah/ (cal/ g) = 597.5 - .5821 T /°C

S al

(A- 3)

Ah/(BTU/lb ) = 1094.1 - 0.5821 T /°F

m sat

for T in the range

S aL

10 < T J°C < 93 ; 50 < T /°F < 200 — sat — ’ — sat —

The above equation for T

gat

as a function of was generated as a linear (in semilog coordinates) curve fit to T

gat , ^dry temPerature

pairs which were computed using Eq. 8.31 and tables A.l and A. 5 of

Threlkeld [7]. The approximation of Eq. (A-2) and these computed values

are plotted in figure 23.

Compatible with the ideas of section 6.3, T of the first of Eqs. Sau

(1) is the saturation temperature of the inlet air stream (to the

stairwell-sprinkler component - see figure 12) assuming that this inlet

air, at temperature T , is in a dry state. Thus, T

gat

of the first of

Eqs. (1) was computed from Eq. (A-2) where T^ was taken as T^, and

where Tin was computed from Eq. (8).

Eq. (A-3) for Ah as a function of T , which was used in the last bau

of Eqs. (1), is a linear curve fit to tabulated Ah values provided in

table A. 5 of [7]. The approximation of this equation and the tabulated

43
values for Ah are plotted in figure 24.

The value for m , used in the first two of Eqs. (1) was computed

from:

m = A V p , in i i amb (A-4)

where is the cross-section area of the circular inlet duct to the

stairtower, is the density of the incoming ambient air, and is

the average incoming air velocity. A^ and P am^ were taken as

A = .393 m

2 = 4.24 ft2

p amb

= [1-177(10" 3

) (300. )/(T

amb /°K)]g/cm3

(A-5)

= [. 0735(540. )/(T ,/°R)]lb /ft 3

amD m

where is the measured temperature of the ambient air. was taken

as the air velocity measured on the duct axis. The actual value for

used in Eq. (A-4) was an average of those ten consecutive data points

(taken at 10 second intervals) which appeared to best represent a quasisteady condition for the portion of a given test run being analyzed.

The value of Q in Eq. (8) was computed from the measured flow rate

of burner fuel.

The value for G used in the third of Eqs. (1) was the actual total

measured volume flow rate of water averaged over the above mentioned 100

second quasi-steady test interval.

The value of T used in the second of Eqs. (1) was taken to be

out

the average of the time averaged measurements of the two thermocouples

14 and 15 (see figures 2 and 3).

44
Table 1. Water curtain and spray nozzle systems

Type I: Water Curtain (WC) . Sprinklers on six foot centers surround

the portion of the periphery of the stairwell which is open to the room

of fire origin.

Variation IA : 10 mm (3/8 inch) sprinkler head opening.

Variation IB : 12.5 mm (1/2 inch) sprinkler heat opening.

Type II: Spray Nozzle (SN) . Spray nozzles located within the stairwell

opening. The spray pattern covers the entire area of the opening.

Variation IIA : 10 mm (3/8 inch) spray nozzle heat opening.

Variation IIA-DB : Same as IIA but with draft boards surrounding

the opening above the stairwell.

Variation IIB : 12.5 mm (1/2 inch) spray nozzle head opening.

Variation IIB-DB: Same as IIB but with draft boards.

45
Table 2. Instrument description

I.D. Description

TC 1 Room Tree A, 11*10" from Floor (2" down)

TC 22 Room Tree D, 2" from Ceiling

TC 23 Room Tree D, 8" from Ceiling

TC 24 Room Tree D, 14" from Ceiling

TC 5 Room Tree B, 11' 10" from Floor (2" down)

TC 6 Room Tree B, 10* from Floor

TC 7 Room Tree B, 5* from Floor

TC 8 Room Tree B, 1' from Floor

TC 9 Room Tree C, 17' 10" from Floor

TC 21 Velocity Probe, Bum Room Air Intake

TC 25 Room Tree D, 20" from Ceiling

TC 26 Room Tree D, 32" from Ceiling

TC 10 Basement, 9* from East Wall, 5' from Floor

TC 11 Basement, 3’ from West Wall, 5' from Floor

TC 12 Basement Stair, First Landing, North Rail

TC 13 Basement Stair, Second Landing

TC 14 First Floor Stair Opening

TC 15 First Floor

TC 16 Second Floor, Stair Opening

TC 17 Second Floor

TC 18 Second Floor Ceiling Gas

TC 19 Velocity Probe, Roof Vent No. 1

TC 20 Velocity Probe, Roof Vent No. 2 TC 27 Room Tree D, 44" from Ceiling

PRS 1 Air Pressure, Bum Room 10.5* Level

PRS 2 Air Pressure, Stairwell, Basement Referenced

First Floor

PRS 3 Air Pressure, First Floor, 3' Level

PRS 4 Air Pressure, Second Floor, 3' Level

VEL 1 Air Velocity, Bum Room Air Intake

VOL 1 Air Volume, Bum Room Air Intake

VEL 2 Air Velocity, Roof Vent, No. 2

VOL 2 Air Volume, Roof Vent, No. 2 VEL 3 Air Velocity, Roof Vent, No. 1

VOL 3 Air Volume, Roof Vent, No. 1

CO 1 Carbon Monoxide Concentration, Floor Level,

First Floor

46
Table 2 (continued)

I.D. Description

OXY 1

OXY 2

OXY 3

FLX 1

FLX 2

FLO 1

Oxygen Concentration, Burn Room 10' Level

Oxygen Concentration, Floor Level, First Floor

Oxygen Concentration, Roof Vent

Total Heat Flux, Burn Room East Wall, 8' Level,

Horizontal View

Total Heat Flux, Stairwell, No. Wall, 8* Level,

Horizontal View

Sprinkler Water Flow

47
Table 3. List of Fire Tests

Water Curtain System Tests

•Q (MW)

•G/L

wc

(gal/min/ft) Nd (in) K A

L (ft

2

) A

e

(ft

2

)

1.5 3, 4, 5,

6

1/2 5.6 4.2 18.8

1.5 3,4. 5.

6

3/8 2.7 4.2 18.8

4.0 4,5,6 1/2 5.6 4.2 18.8

4.0 7,8 1/2 5.6 4.2 18.8

4.0 3 1/2 5.6 4.2 18.8

4.0 3,4 3/8 2.7 4.2 18.8

4.0 5,6 3/8 2.7 4.2 18.8

4.0 4,5,6 3/8 2.7 4.2 18.8

4.0 6,7 3/8 2.7 4.2 18.8

Spray Nozzle System Tests

•Q (MW) G/Ariser (8al/mln/ft^ Nd (in) K A. (ft

2

) A

fi (ft

2

)

4.0 2.0 3/8 2.96 4.2 18.8

4.0* 1.66 3/8 2.96 4.2 18.8

4.0 1.66 3/8 2.96 4.2 18.8

4.0 1.66 3/8 2.96 4.2 18.8

4.0 2.0 1/2 4.96 4.2 18.8

4.0 2.16 1/2 4.96 4.2 18.8

4.0 2.33 1/2 4.96 4.2 18.8

4.0* 2.16 1/2 4.96 4.2 18.8

4.0 2.16 1/2 4.96 4.2 18.8

4.0* 2.16 1/2 4.96 4.2 18.8

Nd = nozzle size (nominal)

K = Discharge coefficient = — where P = nozzle pressure

* = Tests with draft panels.

48
Table

4.

Data

from

unsprinklered

operation

of

the

stairtower

used

to

estimate

hA

from

Eq.

(6) P»4 O

#-* O *H p-s C\ /~

/N

o 0 o <r 1^ CM CM O' fN m pH O' IN. SO

l-<J -n. • in • o • fN • vo • O • VO

lx: S — in <f CM Mf m <r •3- *3- vo m Ht <3- * R w rH w pH n_x rH N_^ rH w pH n^

PQ u—

a) r—

i—i f-

r—

r“> 00 ~s /N /N /"N /-N n 03 H U VO vO . vO VO vO H

< x: o O o m o O' O a> Pu vO rH Cl rH CM rH VO rH Cl rH O s p m v_x in n/ O v-4 rH v-' CM N/ <

c P • Cl • pH • O' • O • m

•H PQ O' 00 rH -3" vO i—

•0 n-/ • • •/ m 00

rH rH Cl • •

1—1 i—

'

1 UJ 1—

C /N H rH in H /-N 00 /N vO • m

II o o ci oo • CM • • Cl

1 O pH rH «—

in oo m O r- in. m

H 0 o cm <r cm <r C~ Cl 00 rH VO rH < 4-1 V-/ v-/ rH w v-/ N/

0

o H

44d ^ /—

0) 4-1 0 /-N n /N

> n O *H m ci 00 CM pH In O /-s ci rN

CJ a> 6 -3- i". Cl vO 00 CM on O oo

>4 O to ^ • o • 00 • rH • cs • rH

<U rH N^ 4J m rH Ml- W O CM co VO rH 3 0) 0 «4H pH nc o > >» a

4-1 0 n CS /N

<u CN oo n- 00 fN m oo oo in oo ^ id CM *3- vO <f vO N • <J* vO IN • a) cm 4-t CM • CM • • oo CH • • 00

V4 h 0 >44 • CM • CM pH rH • N rH pH

0)a

a

s-x v^ v-/ S_/ vy

0>

a) r—

r—

r—

>N 4-1 n /-n /-N r—

i .

t>o <d vO vO vO CN PN

M Pd M O o O vO vO

<u X3 O «H O pH O pH in o n o

0 <U • N4 • v^ • v—

• rH • rH W (0 § ^ «3- sO <}• vO sr vo rH N^ rH W cd H • • • in in

II <D PQ Cl Cl Cl • • i—

w pH pH rH in in

• O’ <0 i—i i—

j

i—i—i—

PS

UH O o o o o

o O' vO «3- O' fN a O 00 O CM m rH

92 3 <u 1 1 1 i 1 0 Pd to o o O o O *rl O' o O' O' *3- H i-n Cl pH M* pH

0 4JJ <

o Cl O o in

Pd o CM Cl

49
CM

CMO

Ot—

CM

K

CO

oc

CL, -<3

D.CO

5“ •

CM

CM o w

z*l_^ CO

CM

CM

CM o

CO o 

X

<3

a

CO o r»» o CO

oi in o»

25 o u

PQ

*— 1— • •

in

co

CM

50 I'

Figure

1.

Plan

view

of

lowest

level

of

stairtower

including

the

burn

room
I 51

Figure

2.A

section

of

the

stairtower

elevation
52

Figure

3.

Plan

views

of

the

first

and

second

floors

of

the

stairtower
V

rau

CO

a

a>

•H

53

WATER

CURTAIN

SYSTEM
STAIR

TOWER

-

54

Figure

5.

Spray

nozzle

system
BOTTOM

OF

ARCH

ii wo

</>

Oo M300o

ca

u

to

nJ

a)M

cO

4-1 c

a)>

>4a)So

4-1 c

aj

)-4 at >4-1

14-1 •H

T3O

4-1

55

Figure

6.

Burn

room

temperature

profiles

with
TEMPERATURE

AT

1st

FLOOR

vs

FLOW

RATE

O

56

Figure

7.

Temperature

at

first

floor

vs

nominal

average

flow

rate

for

water

curtain

and

fora

fire

energy

of

1.5

MW

[5.5

(10 b)

BTU/hr]
FLOW

RATE

vs

COMBUSTION

GAS

EXHAUST

RATE 3

443u

•U

CO S 3 S 3

42 IT> X • (U i—i

co 44 3 o

oo

>> E 3 oo o u

•H 3 MB U 3 ra co a) 3

to/) 40 a) '—’ g H O o O 44

co cd >

T3

<0 3

CD 4-1 3 3

>4 03 5 4-» o co rH 5n

44 CO M 3 3 *H

44 3 3 4J i—i 3

oo3 LjU J4 3 43 U "»

<U PQ

a) 4-* > 3 ^ Cd 3 lbo

a) rH 3 43 a w

in

j-i • o m

52 44 1—1

00

0)M3

00

•H

p4

a> E

57
TEMPERATURE

AT

1st

FLOOR

vs

FLOW

RATE

Figure

9.

Temperature

at

first

floor

vs

nominal

average

water

flow

rate

for

the

water

curtain

system

anda

fire

energy

of4

MW

[13.6

(10 6)

BTU/hr]
FLOW

RATE

vs

COMBUSTION

GAS

EXHAUST

RATE

WATER

CURTAIN

LQ

=4.0

MW[13.6(106)

BTU/hr]

59

Figure

10.

Water

flow

rate

vs

combustion

gas

exhaust

rate

for

the

water

curtain

system

anda

fire

energy

of4

MW

[13.6

(10 6)

BTU/hr]
FLOW

RATE

vs

COMBUSTION

GAS

EXHAUST

RATE 5 s o ° oo oo i- i—

Uu U_

<t «GC OS OS 5 5O

C3bo

09

CO

C3

09 E

60

Figure

11.

Nominal

average

water

flow

rate

vs

combustion

gas

exhaust

rate

for

the

spray

nozzle

system

anda

fire

energy

of4

MW

[13.6

(10 6)

BTU/hr)
3

N NOI1VA3H3- z

HI

cc=5

(/>

</) HI

CCCL

cN

61

Figure

12.

Model

of

phenomena

in

the

overall

stairwellsprinkler

system.
UPPER

VENT P I t—i p i-l P <D 0) S B P 3 *H P cd p p

CO CO P

•H cd p <p

cd o

.. co p o 0) -H £ p O CO P *H P P

•h a)

cd

p

p o

co cdP

aj cd Eh CJ

co

a>pp

60

ccLU5

LU>

62

INSERT”

STAIRWELL-SPRINKLER

COMPONENT

HERE
1.0

0 0.4 0.8 1.2 1.6

G* = G / [GPM A WELL /FT 2 ]=.0245G/ ^/MIN) (A WELL /

m

2 )]

Figure 14. Plot of cooling efficiency as a function of water usage - WC,

12.5 mm (1/2 in) nozzle

63
Figure 15. Plot of cooling efficiency as a function of water usage - WC, 10 mm (3/8 in) nozzle

64
COOLING

EFFICIENCY

1.20

1.0 -

.8 -

.6 -

.4 -

o

.2 -

1 . 40 = E,

• *

SPRAY NOZZLE

12.5mm(1/2 INCH) NOZZLE

( 0- DRAFT BOARD)

0 0.4 0.8 1.2 1.6

G* = G/[GPM • A WELL /FT 2 ]=.0245G /[( 6/WN) (AWELL /m2

)]

Figure 16. Plot of cooling efficiency as a function of water usage

SN, 12.5 mm (1/2 in) nozzle

65
COOLING

EFFICIENCY

SPRAY NOZZLE

10mm(3/8 INCH) NOZZLE

( i -DRAFT BOARD)

J 0.4 0.8 1.2 1.6

G / [GPM AWELL / FT2 ] =.0245 G/[( <7MIN) (

A

WELL/m2

)

]

Figure 17. Plot of cooling efficiency as a function of water usage

SN, 10 ram (3/8 in) nozzle

66
67

Figure

18.

Plot

of

water

usage

efficiency

as

a

function

of

extractable

energy

flow

-

WC,

12.5

mm

(1/2

in)

nozzle
0.04

CM

eg

Hi£

<

XL

CL Lii

CO

o

egh

LL

<

S

co

*to

Q. LU

II * CL LU

AON3IOIdd3 3DVSf1 H3±VM -

68

Figure

19.

Plot

of

water

usage

efficiency

as

a

function

of

extractable

energy

flow

-

WC,

10

mm

(3/8

in)

nozzle
0.04

— CM

o o

°

AON3IOIdd3 30VSfl H31VM -

69

Figure

20.

Plot

of

water

usage

efficiency

as

a

function

of

extractable

energy

flow

-

SN,

12.5

(1/2

in)

nozzle
90L>*0

1

©

o

CO

oa o

CM

o

6

o

o

A0N3I3ldd3 30VS0 H31VM -

"v.

Q.

• LU

II * 0-

- LU

70

Figure

21.

Plot

of

water

usage

efficiency

as

a

function

of

extractable

energy

flow

-

SN,

10

tnm

(3/8

in)

nozzle
COOLING

EFFICIENCY

G’wc^tGPM'Lwc/FT] = .0805 <3/ [(^/MIN) (L WC /M)]

1. 2. 3. 4. 5. 6.

Figure 22. Estimate of cooling efficiency as a function of water usage

for the four tested designs - a plot of Eq. (11)

71
T

sat(°C)

(Oo)^!

o o o o

o o o o

10 CO CM

o

o

(do)**!

72

Figure

23.

Relation

between

dry

and

saturated

air

temperatures

at

one

atmosphere
20 80 100

TSat(°C)

40 60

Figure 24. Heat of vaporization of water as a function of saturation

temperature

73

A

h

(cal/g)
NBS-1 i 4 A SREV. «•

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. NBSIR 81-2202

2.

I

'

4. TITLE AND SUBTITLE

FIRE TESTS OF STAIRWELL-SPRINKLER SYSTEMS

I

•

4 ' :m

5. Publication Date April 1981

..lll.M.W 7. AUTH0R( S) Leonard Y. Cooper and John G. O'Neill

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, DC 20234

11. Contract/Grant No.

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

The Occupational Safety and Health Administration (OSHA)

department of Labor

Washington , D . C . 20210

13. Type of Report & Period Covered Final

15. SUPPLEMENTARY NOTES

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

16. ABSTRACT (A 200-word or leas factual summary of most significant information. If document includes a significant bibliography or

literature survey, mention it here,) The effect of water curtain or spray nozzle fire protection of an open

stairwell was studied experimentally. The experimental setup includes a three

story stairtower with a contiguous first story burn room. The instrumentation

used to measure the flow phenomenology resulting from fire sizes up to 4MW

[13.6(10^)BTU/hr] with and without sprinkler operation is described. A model of

evaporation cooling of the hot fire gases as they pass up through the first to

second floor stairwell-sprinkler system component is introduced. Based on this

model the data are analyzed and correlated for the purpose of identifying both a cooking and a water usage efficiency for each of the system components that were

tested. Application of these measured performance characteristics and their

extension to stairwell-sprinkler components of different geometries and

configurations are discussed.

17. KEY WORDS (six to twelve entries ; alphabetical order; capitalize only the first letter of the first key word unless a proper name;

separated by semicolons)

Automatic sprinklers; cooling efficiency; evaporation cooling; smoke movement;

spray nozzle; stairway protection; ventilated stair.

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