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Small-scale fire test facilities of the National Research Council

Blanchard, J. A. C.; Harmathy, T. Z.

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NATIONAL RESEARCH COUNCIL CANADA

DIVISION OF BUILDING RESEARCH

SMALL-SCALE FIRE TEST FACILITIES OF

THE

NATIONAL RESEARCH COUNCIL by

J . A. G

.

Blanchard and T

.

Z.

Harmathy

F i r e Study No. 14 of the

Division of Building R e s e a r c h

OTTAWA November

1964

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PREFACE

The f i r s t paper in the F i r e Study s e r i e s , published in

1960,

was devoted to the description of the full-scale f i r e t e s t facilities of the National Research Council.

Since that time several new r e s e a r c h tools have been added to the facilities of the F i r e Research Section. Among manu- f a c t u r e r s of building materials a small-scale f i r e t e s t furnace aroused the most interest. F i r e t e s t s c a r r i e d out with the aid of this furnace over several y e a r s proved conclusively that, contrary to previous beliefs, small-scale t e s t facilities can be used very effectively in development work.

The F i r e Research Section has already received

several inquiries concerning certain details of the furnace operation. Because of the continuing interest, the most important technical information i s now published in this report.

The authors of this report a r e both mechanical

engineers, working in the F i r e Research Section of the Division of Building Re search, National Re s e a r c h Council.

Ottawa

November 1964

R.F. Legget, Director

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SMALL-SCALE FIRE TEST FACILITIES O F THE NATIONAL RESEARCH COUNCIL

by

J

.

A. C

.

Blanchard and T

.

Z

.

Harmathy

ABSTRACT

Small-scale f i r e t e s t s a r e constantly gaining popularity in the development work of manufacturers of building m a t e r i a l s . The m o s t important technical information concerning the small-scale f i r e t e s t unit of the National R e s e a r c h Council is presented in t h i s paper.

In modern building designs, f i r e safety is always a n important consideration. It is gene r a l l y a g r e e d that the most effective way of preventing the spread of f i r e in a l a r g e building is t o divide the

. building into a number of compartments by appropriate u s e of e l e m e n t s of satisfactory f i r e endurance.

F i r e endurance is a t e r m meaning the t i m e f o r which a building element i s capable of functioning a s a f i r e b a r r i e r in a

building f i r e . It is obviously a c h a r a c t e r i s t i c property of a construction, and a s such, can be determined by m e a n s of suitably devised f i r e t e s t s . F o r walls and f l o o r s , the f i r e t e s t methods now in common u s e a r e those specified by ASTM E l

19,

BSI 476, and CSA

B54.3.

These standard t e s t s a r e essentially simulated f i r e exposures

.

One side,

a s a r u l e , of

a

c h a r a c t e r i s t i c specimen of the building element, i s exposed to the atmosphere of a t e s t furnace, the t e m p e r a t u r e of which is

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an idealized building f i r e . These f i r e t e s t standards specify the way of evaluating the time at which the specimen fails, i. e. ceases t o function a s a f i r e b a r r i e r . (According to the above definition this time i s clearly identical with the f i r e endurance of the corresponding construction. ) The specimen can fail in three ways:

(i) by collapse,

(ii) by formation of cracks o r openings large enough t o permit passage of flames o r hot g a s e s , and

(iii) by r i s e of temperature of the surface opposite to the f i r e exposure by more than 250°F.

Owing to the incomplete understanding of the effect of the size of specimen on the f i r s t two modes of failure, whether o r not a specimen is liable t o fail by collapse o r c r a c k formation can be determined a t this time, only by means of standard f i r e t e s t s c a r r i e d out on full size specimens. The third mode of failure, on the other hand, depends very little on the size of the specimen perpendicular to the direction of heat flow, and thus can be determined f r o m t e s t s

c a r r i e d out on specimens of reduced size, o r v e r y often even by heat flow analyses (1,2,3).

The f i r e t e s t unit t o be described h e r e has been designed t o c a r r y out f i r e t e s t s on specimens of approximately 6 . 2 5 s q ft a r e a . Besides determining the t h e r m a l f i r e endurance of building elements, i . e . the time of failure by temperature r i s e , the t e s t unit can a l s o be used to study various aspects of the performance of constructions such a s the effect of moisture on the t h e r m a l f i r e endurance, the liability of component m a t e r i a l s to spall, the p r o g r e s s of their deterioration during f i r e exposure, etc.

As the relative m e r i t s o r weaknesses of different

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"small-scale" f i r e t e s t s $ , t h e r e i s an increasing i n t e r e s t by the

m a n u f a c t u r e r s of building m a t e r i a l s t o u s e such t e s t s in t h e i r develop- ment work. To a s s i s t those who wish t o install s i m i l a r t e s t facilities, some technical information concerning the s m a l l - s c a l e f i r e t e s t un'it of the National R e s e a r c h Council will be presented in this paper.

THE ELECTRIC FURNACE

The s m a l l - s c a l e f i r e t e s t unit of this laboratory c o m p r i s e s : (i) a n e l e c t r i c a l t e s t furnace,

(ii) equipment f o r controlling the a i r supply t o the heated side of the specimen in the furnace, and (iii) equipment f o r controlling the f u r n a c e t e m p e r a t u r e .

The furnace h a s been designed t o operate f r o m a 3-phase, 60 cps, 550v (phase-to-phase) power s o u r c e , a t a maximum t e m p e r a t u r e of 2300°F which i s the t e m p e r a t u r e t o be reached a t the end of a standard f i r e endurance t e s t of 8 h r duration. E l e c t r i c energy was chosen f o r heating because of the e a s e it offered

( i ) in achieving a plane heat s o u r c e of uniform

t e m p e r a t u r e (representing the s o -called "furnace temperature") and

(ii) in making the furnace movable and i t s position adjustable.

F i g u r e 1 .is a drawing of the furnace a s s e m b l y . The furnace p r o p e r is enclosed in a s t e e l f r a m e welded mainly f r o m 3 in. by 3 in. angles and plates of 1/4 in. and 3/8 in. thickness. T o this another f r a m e , made f r o m 2 in. by 2 in. angles, is bolted. The l a t t e r c a r r i e s some components of the a i r supply controlling

*

It should be emphasized that in t h e s e t e s t s nothing e l s e but the width and length of the t e s t specimen is "scaled down". F r o m the point of view of heat flow, t h e s e t e s t s a r e actually full s c a l e t e s t s .

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system which will be described l a t e r .

The furnace has been built mainly f r o m insulating f i r e brick, group 23, and high temperature m o r t a r . It has an opening of

29 1/4 in. by 3 1 in.

,

and thus can accommodate approximately square specimens of 31 in. by 33 in. s i z e s . The edges of the opening a r e lined with hard f i r e clay bricks which provide sufficient protection against damage during the handling of the specimen.

On two sides the furnace walls extend about 8 in. beyond the ledges to provide a shield to the speci'men. On the other two sides removable shields (also made f r o m insulating f i r e bricks) a r e used to facilitate the installation and removal of the specimen.

Six ports cut into two opposite side walls of the furnace make possible the observation of the whole exposed surface of the specimen during the t e s t . The outer (narrower) ends of the ports a r e closed with mica sheets.

The heat i s supplied to the furnace chamber through twelve "Globar" silicon carbide heating elements (4) of 3/4 in. diameter, 34 in. effective length and 54 in. over -all length. The nominal resistance of these elements i s 3 ohms a t 2000°F. When they a r e connected according to the diagram shown in Figure 2, a maximum heat input of 100 kw

(340,000 ~ t u f h r ) can be achieved. With conventional wall o r floor assemblies the maximum heat input requirement during a f i r e t e s t i s generally half of the above value.

The heating elements a r e r a t h e r brittle, and therefore must be protected f r o m possible shocks caused by spalling of the spec2men.

An

Inconel plate of 29 in. by 30 in. by

5/8

in. over -all s i z e , provides this protection, but a t the same time a l s o s e r v e s a s a heat exchanger. The role of the plate a s a heat exchanger will be further discussed in the next section.

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To eliminate the build-up of high t h e r m a l s t r e s s e s during the t e s t , the plate h a s been made a flexible device. It consists of s i x

s e p a r a t e rectangular ducts of 1/2 in. by 4 in. c r o s s section and 29 in. length which a r e fastened together n e a r their ends by two parallel s t r i p s . Each channel i s closed a t one end and the closed ends a r e arranged alternately a t the top o r bottom of the plate. Near the closed end a tube i s introduced into each channel. When the plate i s installed, these tubes p a s s between the heating elements and through the r e a r wall of the furnace. Besides supporting the plate these tubes introduce a i r into the furnace when combustible constructions a r e tested.

The plate i s a welded device, made f r o m 1/16-in. Inconel sheets and 13/16-in. 0 . D. Inconel tubes of 0 . 0 3 5 - i r ~ t h i c k n e s s . It can be installed and rem'oved f r o m the furnace a s a unit through the furnace opening.

Twelve c e r a m i c rods, 3/4 in. in diameter and

6

in. long, a r e partially embedded into the r e a r wall between the heating elements. These r o d s e n s u r e a distance of 3/4 in. between the elements and the plate and thus prevent the development of s h o r t c i r c u i t s .

AIR SUPPLY CONTROL

To maintain the oxygen concentration of the furnace atmosphere a t a proper level when combustible m a t e r i a l s a r e tested, a i r has to be introduced into the furnace and the combustion products must be continuously withdrawn.

A regulated amount of a i r can be introduced into the furnace through two 2 -in. s t e e l pipe h e a d e r s and the joining s i x Inconel tubes

and ducts of the plate described previously. Because of i t s passage through the ducts, the a i r entering the furnace i s slightly preheated.

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provided by filling the ducts with crushed silicon carbide particles between 1/4 and 3/8 in. in size.

There i s a shielded opening a t the centre of the plate. The combustion products a r e withdrawn through this opening and a

slightly sloping 1 1/4-in. Inconel tube (see Figure 1). This tube is connected to the inlet nozzle of an ejector (5) operated f r o m a

compressed a i r line capable of supplying 120 lb/hr a i r a t 60 psig. The ejector i s capable of removing 374 lb/hr combustion products f r o m the furnace if the total p r e s s u r e drop along the a i r inlet and exhaust line is not l a r g e r than 15 in. of water. The combustion products a r e discharged through a

3-in.

flexible pipe outside the building.

In

Figure 1, one can see

a

s m a l l nozzle welded t o the Inconel exhaust tube. When testing combustible specimens, this nozzle is connected to the inlet hose of an oxygen analyzer assembly,

consisting of a pump, a filter, a flowmeter, and

an

indicating analyzer (6). A small amount of the combustion products i s continuously withdrawn f r o m the exhaust tube and put through the analyzer. The oxygen

content of these gases is read f r o m the instrument a t 1

-

to 2-min intervals, and, if necessary, the p r e s s u r e of the compressed a i r at the ejector inlet, o r the valves of the 2-in. f r e s h a i r headers a r e adjusted to keep the oxygen content in the furnace a t the desired level.

To prevent the temperature of the ejector and flexible pipe f r o m rising higher than 500°F, f r e s h a i r and water spray can be mixed with the combustion products prior t o entering the ejector. As Figure 1 shows, valves a r e provided on the inlet side of the ejector for the introduction of these cooling media. By means of a conveniently located thermocouple and a potentiometric r e c o r d e r , a continuous

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The flow of f r e s h a i r o r water i s adjusted manually whenever this temperature exceeds the allowable maximum.

CONTROL OF FURNACE TEMPERATURE

The temperature of the furnace i s measured by five

B

8t S

gauge 16, Chromel-Alumel Cerarno-type thermocouples with Inconel sheath (7). The hot junction of the thermocouples is kept in contact with the Inconel protecting plate on the specimen side by clips welded to the plate. All of the five temperatures, a s well a s . t h e i r average a r e recorded on a potentiometric multipoint temperature recorder (8). This same instrument i s used for recording the temperature of the specimen a t the unexposed surface, a s well a s a t some other locations.

An additional thermocouple, attached to the Inconel plate, supplies signal to an ElectroniK

-

1 5 circular -chart potentiometric

temperature -controller -recorde r (9). The output f r o m this instrument (0.2 t o

5

milliamperes d. c. ) drives a Fincor Model FNA98, 3 -phase, 100-kw magnetic amplifier

-

saturable c o r e reactor system (10) which supplies energy to the furnace. . Owing to a properly cut c a m installed in the controller-recorder, the output signal is such a s t o cause the saturable core reactor to supply the right amount of energy necessary t o produce temperatures in close agreement with the standard temperature v e r s u s time curve.

The wiring diagram of the furnace heating, and temper.ature recording and controlling system i s given in Figure 2. It a l s o shows how the signals f r o m the five furnace thermocouples a r e averaged to obtain a record of the average furnace temperature.

Figure 3 shows all of the important components of the testing assembly. In the photograph the furnace i s in an e r e c t position, ready to receive the wall specimens. When t e s t s on floor assemblies a r e contemplated, the furnace is laid down to have i t s opening facing upward.

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REFERENCES

1. Harmathy, T. Z. A t r e a t i s e on theoretical f i r e endurance rating, ASTM Special Technical Publication, No. 301, 1961, p. 10. 2. Harmathy, T. Z. T e m p e r a t u r e distribution in homogeneous s l a b s

during f i r e t e s t , T r a n s . Eng. Inst. Can., Vol. 6, No. B-6, October 1963, P a p e r No. E I C - 6 3 - m C H 6.

3. Harmathy, T

.

Z. Effect of moisture on the f i r e endurance of building elements, presented a t the 67th Annual Meeting of ASTM, Chicago, 111. 21-26 June 1964. ( P a p e r No. 94-G). 4. Globar silicon carbide heating elements. Carborundum Co.

,

Niagara F a l l s , N. Y .

,

Technical Bulletin H, 1957.

5. Single stage a i r ejector. G r a h a m Manufacturing Co.

,

Inc.

,

G r e a t Neck, N.Y., Dwg. No. A-12549-1, 1963.

6, C2 Oxygen analyzer. Beckman Instruments, Inc., Instructions NO. 1032-B, 1964.

7. C e r a m o thermocouple w i r e s and thermocouple extension w i r e s . T h e r m o E l e c t r i c (Canada) L t d . , S r a m p t o n , Ont.

Bulletin "Wire Section 31 -300", 1958.

8. Daystrom-Weston s t r i p c h a r t multiple point r e c o r d e r . Weston Instruments, Division of Daystrom, h c . , Newark 12, N. J . , C i r c u l a r 08-202-A, 1959.

9. ElectroniK e l e c t r i c controllers. Minneapolis -Honeywell Regulator Co.

,

Philadelphia 44, P a . Specification S150- 1, 1961. 10. F i n c o r power package. Fidelity Instrument Gorp.

,

York, P a .

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@

T E S T FURNACE

@

MULTIPOINT POTENTIOMETRIC TEMPERATURE RECORDER

@

CIRCULAR CHART CAM TYPE PROGRAM CONTROLLER

-

RECORDER

@

3 PHASE SATURABLE CORE REACTOR

-

FIGURE 2 TEMPERATURE RECORDING AND CONTROLLING SYSTEM ' 1 ) 1 2 0 8 - 2

-- -

-

-

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F i g u r e 3 . S m a l l - s c a l e F i r e T e s t Assembly.

1 . E l e c t r i c t e s t f u r n a c e . 2. Inconel plate.

3 . Equipment f o r

a-ir

supply control.

4. Oxygen a n a l y z e r .

5. Multipoint t e m p e r a t u r e r e c o r d e r .

6.

T e m p e r a t u r e c o n t r o l l e r - r e c o r d e r .

Figure

FIGURE  2  TEMPERATURE  RECORDING  AND  CONTROLLING  SYSTEM

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