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Technical Note (National Research Council of Canada. Division of Building Research), 1971-01-01
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Fire Tests Concerning the Penetration of Walls by Horizontal Plastic
DWV Pipes
McGuire, J. H.; Huot, P.
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DIVISION OF BUILDING RESEARCH
NATIONAL RESEARCH COUNCIL OF CANADA
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No .
557 PREPARED BY J. H. McGuire and P. Huot CHECKED BY G. W. S. APPROVED BY A. G. W. DATE January 1971. PREPARED FOR SUBJECTCSA Fire Test Committee and the Associate Committee on the National Building Code.
FIRE TESTS CONCERNING THE PENETRATION OF WALLS BY HORIZONTAL PLASTIC DWV PIPES
The National Building Code of Canada 1970 is very restrictive in its recommendations regarding the use of plastic DWV (drain, waste and vent) pipe. Reference is only made to PVC and ABS pipes and Sentence 7.2. 5.8. (3), for example, states that such pipes shall "not be used in a piping system where such system or part thereof passes
through or is enclosed in a required fire separation" and shall "not be used in buildings required to be of noncombustible construction. "
The object of the study reported here was to develop a test method to permit investigation of the extent of the fire hazard associated with the penetration of walls by horizontal DWV pipes.
The scope of the study was confined to the influence of pipe penetration on the fire resistance of a partition. Substitution of plastic for metallic pipe would, in fact, involve other considerations not least of which would be the significance of the smoke generating potentialities of plastic pipe.
CONDITIONS TO BE REPRESENTED
As the subject under discussion concerned fire resistance it was assumed on these grounds alone that the heating conditions should be based on the ASTM El19 fire-resistance furnace time-temperature curve.
The next important factor to discuss was the magnitude of an adverse pressure differential across the partition in question. Regard-less of the height of the building involved, expansion of gases in a fire area can give differentials of up to 0.1 in. water gauge (W. G.) for periods of many minutes.
When high buildings are involved, in the depths of a Canadian winter, similar pressures can be sustained continuously as a result of stack action created by building heating. During the normal use of the building, these pressure differentials appear largely across the
exterior skin of the building. It is during a fire, when windows in the exterior skin are likely to be broken. that a large pressure differential can appear across a critical partition instead of across an exterior wall.
Tamura(1), in applying a computer to the solution of the pressure pattern within a 20-storey building with an interior-exterior temperature differential of 75°F, qerived results which can be extended to cover the conditions under discussion. For the hypothetical building he considered, it was shown that the floor area at grade level was at a pressure 0.212 in. W. G. lower than that outside, while the shaft at that level was at a
pressure 0.048 in. W. G. lower still. Ifthe ground floor area were brought up to exterior pressure by window breakage. the over -all
influence on the pattern of pressures and flows within the building would not be great. The shaft pressure would not change greatly but the whole of the pressure difference between the exterior and the shaft would then appear across the shaft wall. In the case cited it would be about 0.2 in. W. G.; for buildings of different heights it would be proportionally
greater or smaller.
Such pressure differentials appearing across a partition can
influence its fire resistance time and thus need to be taken into consider-ation in the present study. It was therefore decided that any test'l<
apparatus constructed should operate at some positive pressure. The performance of pipes penetrating walls might be highly dependent on the nature of the wall and such a dependency could greatly
'l< 1.S. O. Recommendation R834 ("Fire Resistance Tests of Structures, " Sept. 1968) suggests in para. 5. 2. 2. 2. that. where the significance of a crack etc. is in doubt, a pressure difference of O. 06
±
O. 02 in. W. G. should be sustained and a pad of cotton wool held about an inch from the opening.multiply the range of conditions to be investigated. The type of material in the wall itself. however. might be considered as not very significant on the grounds that the material immediately adjacent to the pipe would generally be some packing material. The thickness of the wall might then be its most important feature.
Having made this assessment of the conditions to be represented. the relevance of previously published information was considered.
PREVIOUS WORK
The only fairly comprehensive. well-known study of the hazard associated with the penetration of walls by horizontal plastic pipes was carried out in Sweden in 1963 and reported in 1966 (2). Only 6 -in. and 2-in. diameter pipes were used and of numerous tests only six gave a satisfactory performance for periods in excess of 60 min (up to a maxi-mum of 110 min). In each of these cases the pipe was sleeved where it passed through the wall and to an extent of almost 20 in. (50 cm) on either side. The temperatures prevailing in the fire chamber were appreciably lower than the time-temperature curve prescribed for an ASTM fire-resistance test and no attempt was made to establish a definite positive pressure differential between the fire chamber and the unexposed region.
Since this previous work did not consider all the conditions discussed in the preceding section. it was decided that further study of the problem was needed.
FURNACE DESIGN
At first it was hoped that an existing small-scale fire-resistance furnace (3) would serve for the investigation. The last of four exploratory tests had to be prematurely terminated. however. because of arcing and general disturbance associated with the silicon carbide electric elements constituting the heat source. On closer examination it was found that products of combustion from a plastic pipe sample. deposited on insula-tion associated with the elements. had provided an unwanted conductive path.
To avoid further problems of this nature a furnace was designed specifically to fire test small wall elements penetrated by plastic pipes. Regardless of whether gas or electricity were to be used as a fuel it
was thought desirable for the furnace to be a two-chamber device, the plas-tic pipe sample being confined to one chamber, and the heat source to the
other. By a judicious arrangement of air flows it could then be ensured that none of the products of combustion from a plastic pipe would enter the chamber including the heat source. Such a measure is required to combat the problem just described regarding electric heating. but may also be desirable with gas heating lest plastics pyrolysis products
include inhibitors that could interfere with the combustion of the furnace fuel.
A general view of the furnace is shown in Figure 1, and further detail in Figures 2 and 3. The exterior chamber is directly heated by eight gas burners and a cylindrical inner chamber constitutes the portion directly involved in a pipe -wall fire resistance test. The walls in
question consist of blocks of refractory castable, of density 57 lb/cu ft, which form the closure of the cylindrical inner chamber (Figure 2). The opening through which the pipe specimen passed is effectively circular. of 5 -in. diameter. For both 4-in. and 3 -in. diameter pipes the resulting annular space was packed with a soft asbestos material. Where 2-in. pipes were tested, a concrete annulus, of internal diam-eter 3 in., was inserted in the opening and again the remaining space was packed with soft asbestos.
Four burners. of the type illustrated in Figure 4, were installed in the two end walls of the furnace. Continuous spark ignition was provid-ed at each burner by the use of an automobile ignition coil and conventional V8 distributor rotated by an electric motor. As a further safety measure three blowout panels of dimensions 8 in. by 8 in., consisting of asbestos paper covered with soft asbestos. were installed at the bottom of the furnace. Two were in the floor of the outer chamber and one was in the bottom of the flue. hence virtually in the inner chamber.
A feature of the furnace is that the flue leads from the bottom of the furnace rather than from the top. The vertical separation between the level of the specimen and the centre of the flue is 2 ft and, when high temperatures are attained. stack action alone should give a posi-tive pressure of O. 02 in. W. G. within the furnace. In addition. fuel and air £lows were intended to give even greater pressure differentials. A simple circular damper was included in the flue and was kept partly closed, at the angle indicated in Figure 3.
OPERATION OF THE FURNACE
Because of the design of the furnace it was expected that the temperature within the inner chamber at any time would be quite uniform
almost regardless of the distribution of fuel between the burners. This being so it was thought convenient to control the heat input to the furnace by varying the number of burners operating at full capacity rather than by offering continuous adjustment of the fuel flow.
Following the above concept air. at a rate of 18 cfm per burner. was supplied to every burner at all times during test. Gas flow (at a rate of about 0.8 dm per burner) was controlled by eight individual solenoids. as many as necessary being operated to maintain the desired temperature. The temperature -time curve followed was the ASTM El19 curve. During the first 10 min of a test all the burners were operated. but after this initial period it was not uncommon to have to shut them all down again. the combustion of the pipe supplying the necessary heat. Subsequently between five and six burners were required.
The fuel was natural gas, with a heating value of a little over
1, 000 Btu/cu ft. so that the maximum heat input to the furnace was al-most 400. 000 Btu/hr.
As was expected the temperature in the inner chamber was
remarkably uniform and only one thermocouple was permanently installed in the chamber.
Trouble was experienced in determining the pressure within the inner chamber and a record was not kept of the pressure maintained during the tests. The exploratory tests carried out with the previous furnace had. in fact, indicated that the essential feature was to create a definite positive pressure to establish a flow of hot gas through any opening that appeared. thus producing very unfavourable conditions. The magnitude of the pressure differential within a range of 0.05 in.
to 0.5 in. W. G. did not appear to be very significant. When the problems associated with the pressure sensing were cleared it was found that the pressure difference established ranged between 0.1 in. W. G. early in the test and 0.2 in. W. G. when very high temperatures were reached. The pressure difference created by flow would, in fact, be expected to increase linearly with absolute temperature. for constant mass flow.
At an early stage in each test the 3- to 4-ft length of pipe within the furnace was destroyed and occasionally this gave rise to a substantial output of smoke. Early in the program. permission to continue testing was made subject to the installation of a pollution control system. Such a system was fortunately developed quite quickly by modifying a piece of equipment that had previously been used as an inert gas generator (4) .
It consisted essentially of a compact six million Btu/hr burner oper-ating on high pressure propane. It was converted to permit it to oper-ate on low pressure natural gas at a level of about one million Btu/hr and, despite the possibility of corrosion damage to the fan blades, the effluent from the pipe furnace was discharged into the air intake. The output of the pollution control burner remained transparent and invisi-ble under these conditions.
RESULTS
Four-inch. three-inch, and two-inch diameter samples of the following materials were tested.
(1) PVC type 2, grade 1, DWV Pipe (2) ABS type 1, grade 2, DWV Pipe
(3) Polyethylene. type L schedule 40, lab drainage pipe ( 4) Polyethylene, type 3, schedule 40, lab drainage pipe (5) Polypropylene, type L schedule 40, lab drainage pipe
(6)
Proxylene FR lab drainage pipe.Each test involved a 10 -ft length of pipe which left 3 ft projecting from each end of the furnace. On one side the pipe was sleeved as it passed through the test "wall", on the other side it was not. except for one test designated No.8. The sleeve material was 22 mil galvanized steel sheet and it was rolled to form a sleeve with an overlap of about 1
i
in. It projected either side of the test "wall" by the amount indicated in Table I and was secured in the centre and near each end by haywire. Both ends of the pipe were supported a few inches from the end, and except for one test which will be individually reported, both ends were closed off with a metal cap and tape.During a test it was usual for the unsleeved pipe to "fail" within about 30 min; this end of the pipe would then be removed and the resulting opening plugged with soft asbestos. The test continued until either two hours had elapsed or until the other end had "failed." A wall penetration was said to have "failed" when hot gases or flame issued freely around a pipe. The onset of these conditions was invariably quite rapid so that an accurate definition of the criteria was not called for. Except when a pipe melted and sheared off, failure was a result of progressive
destruction of the top wall of the pipe out to the end of the sleeve (or. in the case of the unsleeved penetration, to the boundary of the wall).
Table I lists the principal results of the main body of the test program. To avoid distracting detail, temperature records have not been included in the table. At the cooler end of the sleeve they ranged as high as 5400
F, whereas near the furnace the sleeve in one case attained a temperature of over 11000
F. These temperature records indicate that the type of sleeves used in this test program should be regarded as capable of igniting combustible material in contact with them.
The dimension referred to in column 6 as "length of pipe within sleeve at test termination" relates to the dimension at the top of the pipe. The end of the pipe at this stage of the test did not generally present a vertical face, the rate of destruction usually having been less towards the bottom of the pipe.
The test program reported up to this point represents only conditions involving pipes leading to trapped fixtures on the unexposed sides of fire partitions. The following is a report on a test in which the ends of the test pipe were left open. In other respects the test conditions were as in the main program. The test pipe chosen was 4-in. PVC as it had given the best results until then. from the fire propagation point of view, and because it was the only pipe in which an intumescence effect had given some appreciable measure of
blockage in the pipe. The sleeve projection, as for all the 4-in. pipe tests, was 9 in.
During the first few minutes of the test it was possible to look through the length of the pipe along the axis. After 5 min deformation at top centre could be seen and at 6! min smoke began to flow into the pipe and visibility fell to little more than an inch. Shortly after-wards the flow terminated at both ends, indicating that seals had been created. After 13 min the unsleeved end began issuing smoke again and at 16 min the sleeved end followed suit. After 18 min the unsleeved end began deforming and at 20! min it fell away from the furnace. It was then seen that the pipe had been destroyed out to the fac e of the wall.
After 35 min the sleeved end of the pipe began to deform and after 40 min a gap appeared between the sleeve and the pipe. At this stage the test could have been declared over but the furnace was kept operating for a further 7 min. At this time (at 45 min to be precise) it was found, looking down the axis of the pipe, that a red hot region (probably the furnace) could be seen. The furnace was shut down at 47 min and a minute later the pipe in the region of the sleeve caught
fire and almost immediately fell out. Examination of the remains showed the pipe to have been destroyed right out to the edge of the sleeve (even the bottom of the pipe in this case).
INTERPRETATION OF THE RESULTS
The result of the test with the open ended pipe suggests that, where appreciable adverse pressure differentials are involved, it is unlikely that the integrity of a fire partition, penetrated by a
horizontal plastic DWV pipe, can be maintained by the use of a short sleeve. The length of sleeve required to maintain integrity, which might prove practical for small diameter pipe, has not been investi-gated.
The results indicate that, with the wall and sleeve arrangements used and with the pipe closed (e. g. by a trapped fixture on the side not
exposed to fire), integrity can be maintained for the periods listed.
As suggested previously, the nature of the wall is probably not important provided it keeps in place the soft asbestos packing that should normal-ly be around the pipe. It is therefore reasonable to expect the closed pipe to perform satisfactorily with thicker walls of other materials.
Preliminary experiments and a consideration of the pressure effects involved also suggest that the performances tabulated would not be greatly dependent on the magnitude of the pressure differential involved, within the range 0.05 in. to 0.5 in. W. G.
In many constructions fire resistance times of two hours are called for and several of the pipe/sleeve combinations tested maintained their integrity for this period. Where a combination did not prove
satisfactory, a longer sleeve would be required. In several cases it is. in fact, apparent that an additional inch or so of sleeve would have extended the time to two hours. Development of this further test information has for the moment been deferred pending investigation of other aspects of the influence of plastic pipes on fire resistance.
CONCLUSION
This report describes experiments on the effect on the integrity of a fire-resistant wall of its being penetrated by a horizontal plastic DWV pipe. It would appear, for most pipe/wall combinations, that fire
propagation is unlikely provided the pipe is adequately sleeved and is closed (for example by a trapped fixture) at some location beyond the unexposed surface of the wall.
In discussing the application of the information contained in this study, its very limited context should be borne in mind. A number of other factors would deserve consideration, among them the smoke generating potentialities of certain plastics and the difficulties associated with venting a shaft involved in fire (5) .
At present an examination is being made of the effect on the integrity of floors of their being penetrated by vertical plastic DWV pipes. A report on this work should appear soon.
ACKNOW LEDGEMENT
Acknowledgement is due to R. Lamirande for carrying out much of the test work described in this report.
REFERENCES
(1) Tamura, G. T. Computer Analysis of Smoke Movement in Tall Buildings. ASHRAE Trans •• Vol. 75, Part II, 1969, p. 81-93 (NRCC 11542).
(2) Fire Tests with Plastic Tubes Carried out at the Research StationinStudsvik. Spring 1963. Report 18:1966.
(3) Blanchard. J. A. C. and T. Z. Harmathy. Small-scale Fire Test Facilities of the National Research Council. Fire Study No. 14, Division of Building Research, NRC, Ottawa. 1964.
( 4) McGuire. J. H. Building Fires. March 1965. p.
Large-scale Use of Inert gas to Extinguish The Engineering Jour. Vol. 48, No.3, 29-33.
(5) Tamura. G. T. and A. G. Wilson. Natural Venting to Control Smoke Movement in Buildings via Vertical Shafts. Prepared for presentation at the ASHRAE Annual Meeting. Kansas City, Missouri, June 28-July 1. 1970.
RESULTS OF TESTS
d
lPipe Material Pipe Sleeve Duration Length of Self Time of
.
Diameter, Length, of Test, Pipe with- Extin- Failure• 'H
o Q) in. in. min. in Sleeve guishing of
ｚｾ at Test on Remov- Unsleeve
"'u
Terminat- al End, minｾｾ
ion, in. 1 PVC 4 9 120 7 Y 48 7 3 9 120 8 Y 45 9 3 6 120 5i Y 55 23 2 4 120 3 Y 45 6 ABS 4 9 120 4 N 23 12 3 6 1203i
N 29.6
2 6 120 5 N36i
28 Polyethylene 4 18':<':< 126 0 N 20 10 type 1 4 9 31 N.A. N 19 11 3 6 41 N.A. N 17 19 2 6 102 0 N18i
4 Polyethylene 4 9 120 1/2 N19i
13 type 3 3 6 120 1-
16.!.a 21 2 4 89 N.A. N31i
5 Polypropylene 4 9 79 0 N 19 8 3 9 120 2.!.a-
N. A.*
8 3 6 79 0 N N. A. ':< 17 2 4 118 N.A. N 19 3 Proxylene FR 4 9 87 0 y16i
14 3 6 120 1/4 Y 22 20 2 4 114 0 N 19-&.
== no information available.not applicable. Pipe sheared away, leaving some in the sleeve. N. A.':< = not applicable. Both ends were sleeved in test No.8.**
Nine in. within the furnac e. In addition, this particular sleeve was secured by haywire in four places.AIR INTAKE FROM OUTER CHAMBER
--0 SOFT ASBESTOS PACKING TEST WALL 10' PlASTIC PIPE (TEST SPECIMEN) 36"FIGURE
2
HORIZONTAL SECTION THROUGH FURNACE
16 GAUGE I NCONEL
FIGURE 3 DETAIL OF INNER CHAMBER AND AIR FLOWS
1" DIA. AIR SUPPLY
-..."" Nｾｉ
6"
REFRACTORY BURNER BLOCK
