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Spread of fire in vertical concealed spaces containing foamed-plastics
insulation. Part II: expanded polystyrenes
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SPREAD OF FIRE IN VERTICAL CONCEALED SPACES CONTAINING FOAMED-PLASTICS INSULATION
PART II. EXPANDED POLYSTYRENES by W. Taylor
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Please note that this is a private internal report of the Division of Building Research and is sent to you for your personal use. The information in this report is not generally available and therefore the report is not to be cited as a reference in any publication.
DBR Internal Report 469
SPREAD OF FIRE IN VERTICAL CONCEALED SPACES CONTAINING FOAMED-PLASTICS INSULATION
PART II. EXPANDED POLYSTYRENES by
W. Taylor
PREFACE
Demands for better thermal insulation have resulted in the increased use of foam plastics in buildings, Concern has been expressed, however, that the widespread use of such combustible materials could increase the hazards from accidental fires. A test series to examine the contribution of plastic foams to fire spread in buildings was undertaken in an Industrial Fellowship Program sponsored jointly by the Society of the Plastics Industry of Canada and the National Research Council of Canada. This report describes the results of part of this investigation concerning the fire behaviour of expanded polystyrene used as insulation in cavity walls.
The author, Dr. William Taylor, held the position of DBR Plastics Research Fellow from 1979 to 1981. Other reports prepared by Dr. Taylor during his stay with the Division are:
- Evaluation of thermal barriers for foam plastics insulation (Internal Report No. 466)
- Spread of fire in vertical concealed spaces containing foamed-plastics insulation. Part I. Polyurethanes and polyisocyanurates (Internal Report No. 468)
- Evaluation of the effectiveness of fire barriers in preventing fire spread in concealed spaces (Internal Report No. 470)
- Spread of fire in residential-type wood-frame construction (Internal Report No. 471)
The Division of Building Research greatly appreciates the interest and support of the Society of the Plastics Industry in this program.
Ottawa
November 1981
C.B. Crawford Director DBR/NRC
DIVISION OF BUILDING RESEARCH
DBR INTERNAL REPORT NO. 469
SPREAD OF FIRE IN VERTICAL CONCEALED SPACES CONTAINING FOAMED-PLASTICS INSULATION. PART II. EXPANDED POLYSTYRENES
by W. Taylor
Checked by: T. Z .H. Approved by: L.W.G.
Prepared for: Record purposes
Date: November 1981
Experimental work on the fire performance of expanded-polystyrene insulation in cavity walls has evaluated primarily the effectiveness of protective thermal barriers, which many building codes, including
the National Building Code of Canada1 , require for covering all foam
plastics. Full-scale corner-wall tests have demonstrated that a
protective barrier consisting of gypsum wallboard either 9.5 mm or 12.5 mm thick, applied over expanded-polystyrene insulation, can prevent any contribution to fire growth by the insulation for more than 20 minutes when the gypsum wallboard is subjected to a fire source with a heat output of 90 kW, or to the burning of a 13.5 kg
wood crib2•3•4 •
Other tests, in which the expanded polystyrene was directly exposed to the heat of a furnace or a direct flame source, have allowed investigation of the situation likely to develop later in a
fire when there are openings in the protective barrier. Lie5 , who
used a furnace to expose the expanded polystyrene to the temperature
-2-the insulating material was installed in a vertical position between two layers of non-combustible material with no internal air space. Other tests carried out on behalf of the Expanded Polystyrene Products Manufacturers Association in England using 25 mm thick expanded polystyrene to line a 50 mm cavity brick wall showed that ignition of the polystyrene by a gas flame applied through either a hole 50 mm in diameter or an orifice 100 mm x 250 mm in the outer leaf of the wall was difficult, even when the cavity was thoroughly ventilated. Fire damage to the insulation inside the wall was not widespread and it was concluded that these conditions provided a minimal fire hazard.
These tests appear to show that expanded polystyrene, when used as
insulation in vertical assemblies between two layers of incombustible material, is unlikely to contribute to fire propagation within a wall cavity in which the air space is limited to 25 mm or less, even after the protective barrier has been penetrated by the fire. However, subsequent work carried out during the development of a test that evaluated the hazard of fire propagation by
insulation in cavities8 has indicated the following limitation to this
conclusion. The melting behaviour of expanded polystyrene may in fact present an extreme fire hazard when it flows out of the cavity and burns on the floor of the test area; this hazard is more severe when no air space is present than with an air space of 50 mm.
The series of tests described in this report was undertaken to assess further the fire performance of expanded polystyrene used as an insulation in cavity walls and in buildings of non-combustible construction, and to determine if the danger of the pool fires reported in Ref. 8 is a significant fire hazard. TEST FACILITY AND PROCEDURE
The test apparatus, capable of simulating wall designs typical in buildings
of non-combustible construction, is illustrated in Fig. 1. It was essentially
similar to the cavity test apparatus described in Ref. 8, but was scaled up by a
factor of 2.5. It comprised a vertical, rectangular duct 5 m high x 1.25 m wide,
bounded on the back side by calcium silicate boards 13 mm thick and on the front by 13 mm gypsum boards, and lined with the expanded-polystyrene insulation
materials to be tested. Three of the vertical sides were fixed rigidly to a supporting framework while the front face could be adjusted to suit the thickness of the insulation and the air gap selected for the specific test. A number of Vycor-covered viewing ports set in the front (adjustable) panel allowed
observation of the flame spread during a test. In addition, thermocouples were
located at intervals along both front and rear interior faces to monitor cavity temperatures.
ln the initial series of experiments the source flames were applied through
a 25 mm opening in the front face at the base of the test rig (Fig. 1) and
impinged on the vertical face of the insulation just above the base. In a later
series, the opening in the front face, through which the flames were applied, was located at approximately the mid-height of the test assembly.
The fire source for the tests was a natural-gas burner comprising a pipe, 25 mm O.D., with a series of 24 radial holes, 4.75 mm in diameter, set at SO mm intervals along its length. The natural-gas flow through this burner was maintained constant during a test at a level to produce a heat
output of 25 kW. This source caused the mean temperature at the inlet to
rise to 820°C in blank runs with a 25 mm air space (no insulation installed). The temperature in the upper section of the cavity (4 m above the source)
reached 220°C. These cavity conditions were similar to those established for
the tests described in Ref. 8.
During a test the source flames were applied to the cavity for a period of 10 minutes after which the burner was extinguished. Any continued burning in or around the cavity was monitored until natural extinction took place. Ten minutes was selected as the application time for the source-burner flames
because, for the range of realistic fire loads (between 20 and 40 kg/m2 ),
fully-developed compartment fires generally last no longer than 30 minutes9 ,
and during the first 20 minutes of this time ignition of the foam plastic
within the cavity wall is prevented by the required gypsum thermal barrier2•3•
TEST RESULTS
Details of the materials and tests carried out in the investigation are listed in Table I. Appendix A includes a selection of photographs illustrat-ing some of the results obtained.
FLAME ENTRY AT BASE - HORIZONTAL PLATE
a) Assemblies with no air space
The insulation near the burner flames began to melt and shrink almost at once, and after a short time molten material began to flow down onto the horizontal plate at the base of the cavity. This outflow of polystyrene from the lower regions enabled the heat from the source burner to affect the
material higher in the cavity. The melted out area continued to expand slowly. After 3 to 4 minutes, the molten material accumulating on the
baseboard was ignited by the burner flames, and the burning material began to flow onto the floor of the test area, forming a pool some 250 mm below the
cavity base. Heat from the material burning on the base and on the floor
continued to melt more polystyrene in the cavity even after the source flames
were extinguished. In the case of extruded polystyrene board, the pool fire
was moderately severe and continued to burn for about 15 minutes after the source burner was turned off. With polystyrene bead board the pool fire was less severe and went out within 7 to 8 minutes.
At the end of the test the effect on the expanded polystyrene was observed to be marginally greater for the bead board than for the extruded board. The melted zone extended to a height of between 1.25 m and 1.5 m into
the cavity and above this partial melting and shrinkage had occurred to ｡｢ｯｾｴ＠
0.5 m. Because of the difference in densities of the two materials, the
weight of the extruded polystyrene board that melted and collected at the base of the assembly was almost double that for the polystyrene board. This
-4-fact was reflected 1n the relative severity of the pool fires which developed.
All burning observed during the tests was confined to the base area and no flame spread inside the cavity ever occurred.
b) Assemblies with air spaces of 25 mm
When extruded polystyrene board was installed with a 25 mm air space, melting was again evident early in the test. Some molten material flowed
down to the base and then onto the floor. In contrast to the zero air-gap
configuration, heat fluxes from the source burner were not absorbed within a limited volume inside the assembly where the material had melted and flowed out; instead, they were dispersed throughout the total volume of the test cavity. As a result, apart from the area immediately adjacent to the burner flames and extending some 0.5 m into the cavity, the heating of the polystyrene surface was sufficient only to cause the polystyrene to soften and shrink, but not to flow down the walls of the enclosure. The surface melting and shrinkage extended to the top of the assembly, but very little molten material was able to flow down the cavity and accumulate on the base. Only very small isolated areas of burning developed at the cavity base and these died out as soon as the source burner was turned off.
Bead-board polystyrene, having only half the density of extruded polystyrene, requires less heat input to cause melting for a given volume.
In this configuration, the heat from the source burner was sufficient to melt a more extensive area and to cause the melt to flow down to the base from as
high as 2.5 minto the cavity. In addition, as the material melted away
around the screws which held the insulation in place, several pieces of unmelted bead board also fell into the base area, thus coming under the direct influence
of the burner flames. This material at the base of the cavity was eventually
ignited by the flames of the source burner. The resultant increase in heat flux inside the cavity was sufficient to raise the temperature of the
remaining polystyrene to the critical ignition point1D, and most of it was
consumed as a flame front swept up the cavity, causing heavy, sooty smoke to evolve from the top of the assembly.
c) Assemblies with an air space of 38 mm
Only the extruded polystyrene board was tested in an assembly with a 38 mm
air gap. In this configuration, the temperatures that developed in the cavity
were higher than with a 25 mm air gap, resulting in more extensive melting of the polystyrene. There was increased. accumulation at the base of molten material,
which was eventually ignited by the source-burner flames. Some of this burning
material dripped off the baseboard onto the floor, forming a small pool fire. The additional heat from the burning material on the base melted even more polystyrene. This added fuel to the fire, thereby increasing the heat flux
still further. Eventually the material inside the cavity caught fire, and a
stream of burning polymer poured out of the cavity into the pool fire on the
floor of the test area. When the test was terminated 12 minutes later, most
In the latter two tests described above the severe fire conditions
appeared to be a direct consequence of molten polystyrene accumulating on the lower horizontal surface of the test assembly (Fig. 2a) which was coincident with the location of the fire source. The burning which developed with a zero air-space configuration, although much less severe, was also due to the accumulation and burning of the melt.
In an actual compartment fire, the hot products of combustion accumulate near the ceiling and the highest gas temperatures develop in the upper half
of the room. Failure of the protective covering over expanded polystyrene in
a room containing a fire is therefore most likely to occur in this upper area, some distance above the base of the wall. As it is only at the base of the wall that a ledge in the form of a fire barrier similar to that at the base of this test assembly, is likely to be present, the condition reproduced in the test is one of low probability in a real-life fire situation. Therefore, further tests were carried out to investigate the more probable situation of fire penetrating into the cavity some distru1ce above the position of a fire barrier. For these tests the fire source was introduced through a 25 rnrn slot across the width of the front face of the test rig at approximately mid-height. In other respects, the test conditions were identical to those in the previous experiments.
FLAME ENTRY AT MID-HEIGHT
With an air space of either 25 rnrn or 38 rnrn in the cavity the results, when the fire source was introduced at the mid-height of the assembly, were
similar for both extruded and bead-board expanded polystyrene. In each case,
the polystyrene in the area close to the flame source melted and flowed down the boundary wall of the cavity, past the source-burner flames, settling on
the polystyrene board immediately below. Heat from this molten material
caused some melting and shrinkage of the polystyrene board below the flame-entry slot; the extent of this shrinkage was limited to between 75 mm and
100 rnrn. No other effect was noted below the level of flame entry.
In the upper part of the assembly, hot gases rising through the air space caused surface melting and shrinkage of the expanded polystyrene which reached to the top of the assembly. The extent of the melting was greater for the bead board than for the extruded board but in neither case did ignition of molten material occur. As a result smoke evolution during the test was negligible.
When the air space in the cavity was reduced to zero, the melting of the
expanded polystyrene was more extensive. Reducing the air space apparently
concentrated the heat output from the source flames on a limited volume of expanded polystyrene foam, which rapidly melted, thereby exposing a new surface for the flames to reach. An open space inside the wall assembly was thus created. The heat from the source continued to affect the expanded polystyrene forming the upper boundary of this open space, melting it and causing it to flow down the inner walls. The lack of ventilation within the cavity did not allow convective purging of the heat from the source burner. As the open volume increased with the melting of more polystyrene, the
-
6-conductive loss of heat through the cladding became more significant as the
area of exposed cladding increased. Eventually a point was reached where the
heat reaching the retreating front of polystyrene board was insufficient to cause any further melting, and expansion of the open volume stopped.
The height to which the polystyrene melted in these tests extended to
about 1.5 m above the point of entry of the flames. The molten material which
flowed down the cavity was sufficient to cause significant melting and shrinkage of the polystyrene below the level of the flame source and in places penetrated to a depth of about 0.5 m.
Burning of the expanded polystyrene inside the cavity was limited to a few isolated flames and conditions were such that the fire did not spread; as a result, evolution of smoke was minimal.
These results indicate that if fire penetrates a wall cavity at a position remote from a fire stop, as is likely to occur in the majority of compartment fires, severe melting of the polystyrene insulation will develop, but serious fire spread in the concealed space of the wall is unlikely to
occur. If, on the other hand, the fire stop does coincide with the location
of the fire penetration, ignition of the molten polystyrene is possible and
severe fire conditions may result. In order to counteract this possibility,
some means is required to prevent the melt accumulating on the stop and coming
under the continued influence of the flames. A simple solution is to use a
suitably inclined fire stop, which would cause the molten material to flow away from the flames penetrating the wall assembly. A series of tests with such a fire-stop configuration was therefore carried out in which the stop
(i.e., the base of the test assembly) was inclined at an angle of 40° to the horizontal (Fig. 2b).
FLAME ENTRY AT BASE - BASE INCLINED 40° TO HORIZONTAL
a) Assemblies with an air space
Air gaps of 25 mm and 38 mm were included in this series of tests. In
general, the effects of fire in these tests were much less severe than in the corresponding tests in which the assembly base was horizontal. Melting in the lower 1 m of the cavity occurred early in the test. The molten material
flowed down to the base, but did not settle near the source-burner flames. Most of it flowed slowly down the inclined base without igniting and solidified a short distance away from the high-temperature region close to the flame
source. Without the added heat which would have resulted if the burning
material had remained on the base, the effects in the upper region of the cavity were limited to surface melting and shrinkage extending in a broad plume to the top of the assembly.
The results were generally similar for both types of expanded polystyrene tested, but the extent to which melting occurred was greater for the bead board than for the extruded boards. This was similar to the pattern noted in most of the previous tests using these materials.
b) Assemblies with no air space
The larger volume of molten polystyrene produced with this configuration did not flow across the inclined base rapidly enough to completely clear the area close to the source flames before ignition occurred. Consequently, some of the melted material burned and generated black, sooty smoke as it flowed away from the heat source. The burning stopped before the molten material could reach the end of the sloping base and drip to the floor, so that no pool
fire developed. When the source burner was removed, burning continued on the
sloping base for about five minutes before all the flames died out. The extruded boards produced marginally more severe burning than did the bead board polystyrene, reflecting the greater weight of the former.
At the end of the tests, it was observed that the polystyrene had melted
to a height of about 1.5 m into the assembly. This observation was similar to
that made in tests with a horizontal base. However, the burning which
developed at the base and outside the cavity was less severe in tests in the inclined bases.
CONCLUSIONS
The test results indicate that expanded polystyrene insulation used in a vertical position between two layers of non-combustible material will melt, but will not contribute to fire propagation. Even if the fire penetrates the wall assembly immediately above a fire stop, spread of the fire in the
concealed wall space is still unlikely; however, molten polystyrene accumulat-ing on the stop may ignite and augment the heat and smoke evolution in the
fire cavity. Because of the small mass of polystyrene insulation used in the
test, this effect may be of minor importance; nevertheless, the problem can be effectively eliminated if some means to channel the molten polystyrene away
from the fire is incorporated in the structure. In this investigation it was
shown that this can be achieved by use of a fire stop which slopes at an angle of about 40° to the horizontal.
The evidence from this test suggests that the presence of an air gap in the cavity wall structure may help to reduce the probability of ignition of molten polystyrene. An open configuration allows the heat emanating from the flames to disperse over a larger area of the insulation surface and consequently reduces the amount of material which is heated sufficiently to melt and flow out of the cavity.
REFERENCES
1. National Building Code of Canada 1980, National Research Council of Canada,
Assoc. Comm. on the National Building Code (NRCC 17303), Ottawa.
2. Fact-finding report on enclosed corner testing of expanded-polystyrene
foamed plastic, ULC File NC 554, Project 74NK8683, New York, 1975.
3. Lie, T.T. Contribution of protected plastic foams to fire growth.
National Research Council of Canada, Division of Building Research, Fire Study No. 37, (NRCC 14932), Ottawa, 1975.
-8-4. Full-scale fire tests on E.P.S. exterior sheathing, South-West Research
Institute, Report 03-4907-001, San Antonio, 1977.
5 . Lie, T.T. Contribution of insulation in cavity walls to propagation of
fire, National Research Council of Canada, Division of Building Research, Fire Study No. 29, (NRCC 12878), Ottawa, 1972.
6 . Standard methods of fire tests of building construction and materials,
ANSI/ASTM Ell9-80, 1980 Annual Book of ASTM Standards, Part 18, p. 844, Philadelphia.
7 . Richardson, R.J. and Barker, H.A. Fire tests on expanded
polystyrene-lined cavity walls, Redlands Technology Ltd., Report No. 775-01, London (England), 1974.
8 . D'Souza, M.V. Fire propagation tests with foamed plastics ｾｮｳｵｬ｡ｴｩｯｮ＠
within a wall cavity, National Research Council of Canada, Division of Building Research, DBR Internal Report No. 424, Ottawa, 1976.
9. Harmathy, T.Z. Performance of building elements in spreading fires,
Vol. I, pp. 119-132, National Research Council of Canada, Division of Building Research, DBR Paper No. 752 (NRCC 16437), Ottawa, 1977.
10. Thomas, P.H. and Bullen, M.L. On the role of K p C of room-lining
materials in the growth of room fires, Fire and Materials, Vol. 3, pp. 68- 73, London (England), 1979.
MATERIALS AND TEST CONDITIONS
Air s12ace and
Material type Thickness Density FSC* test condition**
(mm) (kg/m3 ) (ULC Sl02 . 2) (0) (25 mm) (38 mm)
1. Polystyrene bead board 75 16 230 a,b,c, a,b,c, b,c
2. Extruded polystyrene board 75 32 210 a,b,c a,b a,b,c
* FSC = Flame Spread Classification
** Test Conditions
a . Flame entry at base-horizontal base
b. Flame entry at mid-height
VIEWING PORTS MARINITE BOUNDARIES I I I I
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ｾ ｉ＠ I I I I I ｾ＠ E ＺＯｾＭＭＭＭＭﾭ ｾ＠ I / 1 I I I I ｲＭＭＭＭＭｾ＠ L . -r ＭＭＭＭｾ＠ !_ ___ _l 2 5ＮＮｌＮｾ＠
- - 1-.,.C....:.=-==-==-=-....=..=-=-=i m m Tt ＭＭ ｾｾｾｾｾｾＮＣ＠ FLAME SOURCE FIGURE 1CAVITY WALL TEST RIG
INSULATION AIR SPACE (VARIABLE) in front of insulation BR 6091
GYPSUM BOARD 25
m m
0. D. FUEL LINE ｾＭｎｭ＠ FIGURE 2 SOURCE FLAMES (a) EXPANDED PO LYSTYR EN E SPECIME N MARINITE BOARD GYPSUM BOARD 25mm
0. D. FUEL ll NESCHEMATIC OF ASSEMBLY BASE CONFIGURATIONS
EXPA NDED POLYS TY RE NE SPECIM EN MARINI TE BOARD SOURCE FLAMES (b) BR 6169
A SELECTION OF PHOTOGRAPHS, WITH TEST RIG FRONT PANEL REMOVED, SHOWING APPEARANCE OF INSULATION AFTER THE CAVITY WALL TESTS
Tests with extruded polystyrene boards. Flame entry at base of assembly
(a) Air gap 0 (b) Air gap 25 mm
Figure A2
Tests with polystyrene bead board. Flame entry at base of assembly
(a) Air gap 0
Tests with flame entry at mid height
(a) Polystyrene bead board
Air gap 0
(b) Polystyrene bead board
Air gap 25 mm
(c) Extruded polystyrene board
(a) Extruded polystyrene board Air gap 0
Figure A4
Tests with base inclined at 40° angle
(b) Polystyrene bead board
Air gap 0
(c) ｐｯｬｹｾｴｹｲ･ｮ･＠ bead board Air gap 38 nun
