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Investigating the contribution to fire growth of combustible materials used in building components
Investigating the contribution to fire growth of combustible materials used in building components* B F W Rogowski Fire Research Station, Borehamwood, UK.
* First Published in Cellular Polymers 198 7
Abstract Recent work at the UK Fire Research Station has provided a measure of the possible contribution to fire growth from the combustion of such components as wall or ceiling panels rather than the well- known contribution from surface spread of flame on wall and ceiling linings. The oxygen depletion technique is used to assess the rate of heat release from wall panels with a range of facing materials and different cellular polymer cores. The paper discusses how such an experimental approach may be adapted to direct validating modelling techniques with certain components but must take account of the variability in existing building practices.
lntroducldon Safety of life in the event of fire is initially governed by the individual's response to indications of danger. Speed of awareness and reaction vary widely but the chance of escape once the hazard is recognised can be improved if the time during which escape is possible is, by design, made commensurate with life risk in a given occupancy. To achieve this aim, a degree of control is applied to features of building design and construction with particular emphasis on the protection of escape routes. To maintain the routes in a safe condition it is necessary to restrict the initial rate of fire growth; control over wall and ceiling linings in corridors or rooms is exercised to limit flame spread over extended areas of surface, with the consequent risk of involvement of additional combustibles. Such measures reduce the risk of contamination of escape routes by the fire effluent. In the absence of such control over the contents of buildings, this restriction may, in certain occupancies, be of dubious advantage particularly where highly flammable products (eg modern upholstered furniture) are involved. Evidence of the advantages
of controlling linings has been difficult Background to demonstrate since until recently no The use of combustible cellular test method has assessed effectively polymers as lightweight cores for the rate of burning of the contents or panel constructions or as insulants in elements of building construction the external shell of buildings has under a variety of exposure conditions been limited in the UK, not because nor of measuring the life hazard the products fail to meet fire standards, generated by the emission from them but because of doubts about their of smoke and toxic decomposition possible effects on life safety if they products. b e c o m e involved in fire. The extent of involvement of the Industrial concerns involved in linings when exposed to a primary fire their manufacture requested the Fire is controlled in the UK by requiring Research Station to investigate the specific performance limits on BS performance in fire of two types of 476: Part 7 'Surface spread of flame' products, the first being infill panels test according to the occupancy and comprising a structural extruded the location of the lining. Additionally, polystyrene core with a range of restriction of the combustible content different facing materials, designed of the linings may be applied by primarily as replacement fenestration specifying limits to BS 476: Part 6 units. The second comprised a range 'Fire propagation' test, a procedure of laminates, incorporating plasterintroduced to measure and ultimately board facings over different cellular to limit the rate and extent of heat polymer insulants, designed to imrelease from a wall lining product. prove the insulation of solid masonry This characteristic has long been external walls by retrofitting to their known to be critical in determining interior surfaces. In both cases, inthe hazard to life in a building fire, and formation was required which could its investigation, together with that of help to quantify the possible increase the release of smoke and decompos- in life risk that might result from ition products, either from the structure exposure of the insulant to fire condior from the contents of a building, tions representing those most prejuprovides a basis for assessing the dicial to their performance. comparative effect on life safety. A s s e s s i n g the decomposition rate of
CONSTRUCTION & B U I L D I N G MATERIALS Vol. 1 No. 4 D E C E M B E R 1987
177
Aluminium profile framework
Masonry restraint for aluminium frames
l
S I
I I I I I
0
I
I
1800
2400
I I
2400
/JJ ~
-q... / / - Crib
I f
J
f
/
-"L/l/ /
/
/ Load Cells
Fig l a Comer rig- elevation insulating lining products Exposure conditions represented in wall lining tests simulating a developing fire* will rarely cause significant mechanical d a m a g e to a non-combustible facing. Provided the surface maintains its integrity a satisfactory performance will be recorded because the rate of emission of any volatiles from the underlying insulant will be low even if the facings have a high heat conductivity and permit pyrolysis. Combustible facings exposed in such a test will, unless very thin, be assessed solely according to their surface properties and no account will be taken of the secondary contribution from the flammable core. At the other extreme, the uniformly high severity exposure ( ~ 1 0 W / c m 2) over a wide area such as is provided by the fire resistance test, will almost inevitably cause failure of non-combustible facing materials, or distortion of
bustion of the underlying foam. However, even total decomposition of the insulant contributes only a small fraction of the heat and decomposition products comprising the total fire effluent that is generated by this type of exposure. In any case, the fire resistance test furnace is constructed in such a way that no measure can be m a d e to quantify in isolation the contribution from the product under test. An a d hoc experimental approach had therefore to be adopted which could simulate localised exposure to a high intensity fire source.
Experimental programme Experimental construction
Ideally the performance of the products should be investigated on full scale under a range of ventilaUon conditions, both in r o o m s and in free air. The first joints and junctions and allow corn- condition imposes a restricted air supply specific to that scenario. In the *In terms of most national flame spread latter a high burning rate m a y be tests, the maximum exposure level is little maintained long enough to cause failure of the facings and the situation in excess of 3 W/cm 2.
178
is m o r e representative of a freely ventilated room or of an open plan occupancy. The second system was adopted, with an open corner configuration which provided for an area of wall 2.4 m high x |.2 m and 2.4 m high x 2.4 m (Figure 1aj. By channelling the combustion products into a canopy and thence through a convection controlled chimney, it was possible to obtain a continuous record of gas flow and composition. Tests on the infill panels introduced the risk of integrity failure and to ensure that all e n e r g y / s m o k e release was monitored, an additional canopy and stack were installed at the rear of the corner wall rig. Gas temperatures within the corner assembly were m e a s u r e d and heat flux meters were installed during calibration runs to monitor the exposure severity of the ignition source; others provided comparative data on secondary flaming emitted from the burning panels.
Ignition source The choice of ignition source was governed by the need to cause
CONSTRUCTION & B U I L D I N G MATERIALS Vol. 1 No. 4 D E C E M B E R 1987
Iocalised mechanical failure of the protective facings and enable comparative assessments of different products to be m a d e with minimal excess severity. Furthermore, the initiating fire had to be representative of a fire source typical of the occupancy under consideration. An upholstered seat of modern design and construction, sited directly in front of the panels was selected but to compare effectively the rates of emission of heat, smoke and decomposition products from the experimental panels, a wood crib was designed, shown to provide essentially similar exposure conditions. This confirmed the repeatability of the fire source in each test and furthermore, under the free ventilation conditions, the smoke generated by the wood crib fire was not high enough to mask that emitted from the panels under test.
L
Positionof Rear Canopy& Stack
/
I
/l / /. Mid-way over Opening in Rear Wall
Tests on insulated panels Details of the installation of the panels in both series of tests are given in Figures l a and l b, and selected data on rates of release of heat, smoke and decomposition products from each system are listed in Table 1. Full details are published elsewhere. *The expression of flow rates of smoke and CO in terms of standard "critical" concentrations (1.4 m visibilityand 5000 ppm respectively) provides a basis for calculating the extent of life risk; the actual maximum and minimum values recorded in the tests can vary significantly from these limits but are dependent on the siting of the sampling instruments
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Calibration test Using a panel with a non-combustible facing and insulant the heat flux incident on the surface was recorded and the rate of mass loss of the crib was monitored to check repeatability of exposure throughout the tests series. The rate of heat release from the crib alone was measured using the oxygen depletion technique and flow rates of effluent were used to calculate the emission of smoke (in terms of m3/s at S.T.P. of smoke of OD/m = 1") and of the generation of CO (m3/min at S.T.P. of CO of concentration 5000 ppm*). The heat flux incident on the panels was recorded (Figure 2) and is assumed to be identical for each test since it was not possible to insert the meters into the insulated panels without generating a point of weakness.
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500
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Positionof FrontCanopy&Stack Fig l b Comer rig - plan and may thus be misleading. Discussion of results
Effect of free ventilation It is appreciated that the free ventilation conditions under which the two series of tests were carried out affected not only the rate of combustion but also the chemical processes involved. This is illustrated by the insignificant quantities of carbon monoxide measured in the calibration tests and where the insulants were faced with
noncombustibleboardswhich~tained their inteqrity.Under such conditions a maximum heat output can be achievedbut the peakconcentrations of CO and, with burning cellulosics,
the peak densities of smoke generated are likely to be lower than for a ventilation controlled fire.
Performance of facings The initial involvement in fire of the surfaces of the panels during the initial three-minute period is representative of fire growth in most well-
CONSTRUCTION & BUILDING MATERIALS Vol. 1 No. 4 DECEMBER 1987
ventilated domestic or office occupancies and comparison of their performance under these conditions with that in standard tests does indicate significant differences, due to direct fire exposure. Typical standard test results for the range of facings investigated are given in
Table 2. Heat release from burning facings Reference to Figure 2, indicating the heat flux incident on the surface of the facings, shows to what extent the exposure intensity exceeds that of the standard test. The additional energy derived from combustion of the facings (Figure 3) largely dictates the extent to which vertical flame spread can occur and, for the rig height used, lateral spread under the ceiling for the design of rig used. l'he rate of heat released from the facings is shown in Figures 4- 7 and the maximum values are listed in Table2 (together with the heat output of the initiating fire). The importance
179
Exposed facing
rain
Maximum rate of heat release kW Time rain
Calibration (non-combustible)
NA
1000
1.00
900
2.00
3.2
3.00
PVC-faced 0.6 mm steel
1.30 (distorted)
1500
2.00
900
2.00
7.0
2.00
0.6 mm steel (timber frame)
No obvious failure
1000
2.00
820
2.00
1.5
2.00
Abestos cement -6mm
1.52 (spalling)
900
2.00
800
2.00
3.2
2.00
Particle board -10mm
5.55 (burned out)
6500
7.00
1200
8.00
14.5
7.20
5.10 (burned out)
2250
7.00
1100
7.00
13.8
5.00
Plasterboard 9.5 mm/plywood -4mm
9.15 (partialfall)
1050
2.00
900
35.00
6.8
35.00
Cellulose fibre/ cement board -4mm
6.15 (massivefall)
1600
6.30
1000
6.00
12.0
6.00
Cellulose fibre reinforced plasterboard -lOmm
21.29 (partialfall)
900
2.00
780
2.00
Plywood - 10 mm
Underlying polymer
50 mm extruded polystyrene
Time to failure of facing
Maximum gas temperature °C Time min
Plasterboard
Phenolic
11.00 (partial fall)
1325
2.00
850
2.00
9.5 mm
EPS
14.00 (partialfall)
1450
2.00
850
2.00
PI R (with aluminium foil) XPS
12.20 (partial fall)
1300
2.00
870
2.00
13.30 (partial fall)
1450
2.00
880
3.00
"
"
Maximum heat flux from flames* W/cm 2 Time min
Not recorded
Not recorded
*Meters installed parallel to panels at 50 mm distance
Table 1. Fire performance of faced cellular polymers in an open corner test of these heat release rates lies primarily in their effect on the rapidity of initial flame spread; life hazard is affected more directly by smoke and CO emission rates.
Emission of smoke from burning facings During the initial three-minute fire period the measured rates of flow of effluent gases from all the burning
180
panels (1.3-1.5 m3/s) did not differ significantly but the optical density of the smoke varied enormously from test to test. The results have therefore been adjusted to express the rates of smoke production in terms of m3/s flow of smoke of OD/m = 1. Standardisation in this way indicates the effect of dilution of the smoke and permits the data to be used in
mathematical modelling of smoke flow.
Combustible facings and finishes: The initial contribution to the smoke emission from the paper of the unfinished plasterboard (Figure 8) and from the timber products (Figure 9) was low, as was the case for the timber crib in free ventilation conditions. Significant amounts of smoke
CONSTRUCTION& BUILDING MATERIALSVol. 1 No. 4 DECEMBER1987
Plywood
8f
v
~,
6 0 0 m m a b o v e crib
o
o
1.2m a b o v e crib
O
O
PVC Plaster b o a r d Particle b o a r d
O . . . . . . . . . .
[]
Non-combustible
board
I "r
m
oJ
1-
J 8
I
I 16
L
I 24
Time -- min
Fig 2
Time -- min
Heat flux on panel surface from crib fire (non.combustible panel)
Lining
Peak heat Time of Duration release peak after of peak from lining ignition kW
Fig 3
Heat flux from burning facings parallel to panel (at 1.50 m above crib)
Flame spread rating France (NF P92-501) Maximum intensity 3.0 W/cm 2
UK
W Germany
(BS 4 7 6 Pt.7) (DIN 4 1 0 2 : Blatt 2) Maximum Maximum intensity intensity 3.1 W/cm 2 4.8 W/cm ~ for Class 1
Plasterboard
400
2 min
> 1 rain
M1
1
B1
Painted plasterboard
125
2 min
Continuous to 15 min
M1
1
B1
PVConsteel
750
1 min30s
> 1 min
M2
1/2
B1
Particle board
1600
1 min 30 s
3 min
M3
3
B3
Plywood
1600
1 min 30 s
2 min
M3
3
B2/B3
Table 2. Heat release from surface linings or finish
C O N S T R U C T I O N & B U I L D I N G M A T E R I A L S Vol. 1 No. 4 D E C E M B E R 1 9 8 7
181
were, however, recorded in the case of the pvc finish over the steel facing* (Figure I 0) and, at a later stage, in excessive amounts from the particle board.
1500[-
Boards and facings of limited combustibility: Reference to Figure 8 indicates that the contribution to the overall smoke emission from such facings is negligible because no integrity failure occurred during the initial three-minute period.
Emission of CO from burning facings Investigation of the emission of CO from the panels during the initial three-minutes of test indicates shortlived changes in the combustion processes once the facings became involved in fire. To provide a comparative basis for assessment of life hazard, the rates of emission in m3/min are adjusted to concentrations of 5000 ppm (equivalent to atmospheres likely to cause rapid disorientation and death).
g
o. . . . . . . .
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o Facings without perimeter timber fixings [] Non-combustible • • Facings with perimeter timber fixings • . . . . . . . . . . . • Facings without perimeter timber fixings (at rear)
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2
4
6 Time8min
10
12
14
16"
Combustible facings and finishes: Emissions of CO from the purely cellulosic based finishes (eg plywood (Figure 11) and paper of plaster-
Fig 4
Heat release from insulant
Boards and facings of limited combustibility: Reference to Figure 8 free ventilation conditions. Only the pvc finish (Figure 13) during the short period of initial rapid flame spread generates an unacceptably high concentration (0.23%). A similar maximum (0.27%) was recorded from the particle board facing during the 30 s period of rapid flame spread. It is interesting to note the difference in output between this and the plywood finish.
-
steel facings
•
•
Asbestos cement board
•
•
Ditto (rear)
•
•
Cellulose f i b r e / c e m e n t
•
•
Ditto (rear)
o
o Non-combustible
board
1500 1
Boards and facings of limited combustibility: No significant increase over the crib output of CO was recorded, again indicating that joints and junctions maintained their integrity over this period of test (Figure
1000 I
12). Contribution to Fee effluent from polymeric insulants
-1-
Failure, due to fracture, distortion or disintegration of the protective fadngs over the polymeric insulations, results in their involvement in fire. The extent of their exposure to free air conditions, the oxygen content of the combustion air and the severity of the exposure *The design of the pvc/steel-faced panel was such that rapid distortion of the steel may have permitted Iocalised emission of polystyrene volatiles which would have increased the obscuration.
182
500
l\ I \
3 Fig 5
L ~ - 2
__w4
6 Time
--
i. . . . . . . . . . . 8 10 12 rain
14
Graphs showing heat release from insulant - board facings of limited combustibility CONSTRUCTION & BUILDING MATERIALS Vol. 1 No. 4 DECEMBER 1987
•
o Ditto (rear)
•
• Plaster board
o
o Cellulose~cement board
o. . . .
o Ditto (rear)
3600 I
I n s t r u m e n t failure
v------v
• Asbestos/cement board
D. . . . . . . .
• ......
• Non-combustible
L
~ Plaster board/plywood
Plywood
I I
z~
~ Particle b o a r d
o
a Non-combustible
lI
• ........
• Particle board (at rear)
I
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0
II
,
"11
\
I
2
6
8 tO Time - - min
12 18
24
30
36
F~g8 Smoke emission from panels - board facings of
.
'-'\,- ....
5
.
limited combustibility
10
,,
Particle board facings
o
o
Ditto (rear)
•
•
Plywood
•
•
Ditto (rear)
15
T i m e - - min
Fig6
4
Heat release from i n s u l a n t facings
combustible
•
Plaster board
•
Plaster board/plywood (painted) Non-combustible
facings
Instrument
failure
1500
v
'1000 ."~.\
I
500
/ / /
vf v
/
/ /
01
,
L
2
,
I
4
i
6I ~ /
2JO
= 28
30
32
314
2
36
Time - - rain
F~g7
& BUILDING
MATERIALS
6
8
10
Time -- min
Heat release from insulant - plaster board facings
CONSTRUCTION
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Vol. 1 N o . 4 D E C E M B E R
1987
Fig 9
Smoke emission from panels - combustible facings
183
Facing Type
Release of
Composition
Heat Maximum rate- kW
Smoke
Duration of peak rain
Maximum rate - m3/s ( O D = 1 m)
CO
Peak Duration Time min min
Peak Duration Time rain min
Maximum rate- m3/min (CO = 5000 ppm)
Non-combustible (a) spalling
Absestos/cement
160
> 6
4.3
4
5
(b) disintegrating
Plasterboard
150
> 25
1.0
~10
25
9
15
24
900
6 min at 35 min
7.4
~1
36
36
~1
35
1050
~ 6 min
9.0
4
7
26
2
11
> 10
5.75
4
4
> 6
1.0
Negligible
12
"
with plywood
Cellulose/ c e m e n t board (c) distorting
Steel Steel with timber frame
275
Negligible
CO escaped (spalled)
CO escaped (distortion) 4
5
Combustible (a)
Particle board
5700* failed rising
8.5
Plywood
1580*
4.8
disintegration
- 4
rising
failed 7.5
60
rising
200
failed
4
7
*Value includes s o m e heat from residual facings
Table 3. Emission of heat and decomposition products from extruded polystyrene
o
conditions all affect the mode of combustion. The failure pattern of the protective facings is thus very important in determining any additional life hazard introduced because of the presence of the polymeric insulants.
4-
PVC faced steel without timber frame
•
•
Ditto (rear)
•
•
Steel with timber frame
v
v
Ditto (rear) Non-combustible
Rate of heat release from insulants
14
The rate of heat release from the underlying insulants must, of course, be considered in relation to the severity of the fire which has succeeded in causing failure of the protective facings. Design factors should ensure that the time to, and extent of failure of the protection is commensurate with the need to maintain life safety in the particular environment under consideration ie, escape times, occupancy and fire source severity must be considered. Failure to prevent the rapid decomposition of an insulating polymeric lining may result in the generation, under the ceiling, of a hot gas layer comprising products of incomplete combustion. Combined with a high temperature, the spread of such a layer can be excessively hazardous, mixing with air at the base and generating an active flaming interface;
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184
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~E I O
O
E
co
//" O
2
4
6 Time-
8 min
10
12
14
Fig 10 Smoke emission from panels - steel facings CONSTRUCTION & BUILDING MATERIALS Vol. 1 No. 4 DECEMBER 1987
downward radiation may be very intense. Formation of such a layer must be avoided if the risk to life is to be kept low.
5O
200 l 7=I/
Polymers protected with non-combustible facings: Failure of these facings can occur due to fracture (plaster-based products (Figure 7), cement-based boards (Figure 5)) or to distortion resulting in integrity failure at joints and junctions (steel (Figure 4)). Table 3 indicates the contribution to overall heat emission provided by the different panel types, in excess of the output from the initiating fire in isolation. Generation of additional energy adequate to cause failure of any adjacent facing is indicative of a risk of developing a selfipropagating or even of an accelerating fire growth pattern. The values of energy release recorded during tests involving the full range of polymeric cores and different facings of this category are quoted in Tables 1 and3 and indicate the respective risks of such development. Of lower risk to life, but nevertheless of interest, is the continued burning of insulation still partially protected by the fractured facings; this problem applies primarily where thermoplastic foams have melted and is found to occur, albeit slowly, where flow of hot combustion air is possible behind the facings, unrestricted by adhesive or batten flyings, cavity barriers etc.
I
/ Instrument failure
4O
• ....
30
i
I/
-I "/II I o
z~ Particle board facing • Plywood facing • Calibration
/
\o
Polymers protected with combustible facings: The rapidly accelerating growth of fire over and through the plywood and particle board facings masks the point at which significant involvement of the underlying polymer occurs; the rate of heat release in the latter case (which involved also a rear facing particle board) was so high that it caused failure of the instrumention (Figure 6).
Smoke emission from polymeric insulants Products with metallic facings: Two fLxing systems for the steel faced panels were investigated; those without perimeter timber frames suffered rapid distortion and escaping volatiles from the decomposing core ignited and burned. The maximum smoke obscuration was recorded at 4 min 30 s when a rate of emission of 5-9 m3/s (OD/m = 1) was reached; emission persisted for 10 min giving a total
12
Fig 11 CO emission from insulants - combustible facings
output of about 600 m 3 of smoke of OD/m = 1. Panels with perimeter timber frames, to which the facings were attached exhibited significantly reduced smoke emission, the peak output rate recorded failing to exceed 1.2 m3/s (OD/m = 1) (Figure 10).
Products with non.combustible board facings: Smoke emission from the underlying extruded polystyrene was very low until after cracking or local spalling of the board when short lived peak values were recorded. In one instance a peak of 6.9 m3/s (OD/m = 1) was reached following major disintegration but where the fractured facings
CONSTRUCTION & BUILDING MATERIALS Vol. 1 No. 4 DECEMBER 1987
were retained in position protecting the insulant, emission of volatiles was strictly limited until a subsequent fracture occurred (Figure 8).
Products with combustible facings: It was not possible to isolate with precision the smoke contributions from the insulants from those from the cellulosic facings but distinct peaks in the smoke flow from the plywood faced panel indicated a maximum rate of smoke generation of > 8.0 m3/s (OD/m = 1) once the plywood had disintegrated. The smoke emission from the particle boardfaced product rapidly exceeded this
185
value at which time the instrumentation failed with the rate still rising
40
(Figure 9). Products with plasterboard facings: Smoke emission from products with a range of different polymeric insulants protected by plasterboard fadngs (Figure 14) differed very little and was negligible during the initial growth/ spread period in comparison with the output from the crib fire and paper facings. Following cracking and fall of the plasterboard on the panels adjacent to the initiating fire and burnout of the crib ( ~ 20 min) the polystyrene foams continued to support combustion albeit slowly and spread was limited only by the provision of cavity barriers formed by the supporting framework of the panel. Such a pattern was not recorded with the non-thermoplastic insulants and smoke emission rapidly ceased. Combustion could not be sustained in the vitiated air conditions between the facings because no cavity was formed by melting as was the case with the thermoplastics. The overall fire performance of these rigid non-thermoplastic polymers, laminated to the range of facings examined over extruded polystyrene cores is, on the basis of the experimental results, confidently expected to be superior to that of the thermoplastic products.
• Cellulose f i b r e / c e m e n t board facings • Plaster b o a r d / p l y w o o d facings o Calibration
3O
o~ o v
20
8 10
A
)k
,' " T ' '
1'0
1'4 '3 '
35
Time - - rain
Fig 12 CO emissions from insulants - board facings of limited combustibility
Emission of carbon monoxide from the polymeric insulants Emission of carbon monoxide is highly dependent on the combustion reactions occurring at any given time; these are signficantly affected both by the exposure intensity and the oxygen content of the atmosphere adjacent to the burning zone. Products with steel facings: Following the initial peak values, the emission of CO from the insulant in the panels with and without* perimeter timber frames (Figure I3) is not unacceptably high, and may be negligible in comparison with overall CO generation in a practical fire. Nevertheless, the higher values recorded for these facings than for other non-combustible facings may be accounted for by the high heat transfer to the core, initiating pyrolysis in advance of flaming combustion after distortion of the joints occurred. *This value was underestimated because no record was taken of CO lost due to integrity failure of the panel.
186
Products with board facings of limited combustibility (Figure 12): The total quantities of CO emitted indicate a very low life hazard with all boards which fracture only locally where directly affected by high intensity flames. Extensive disintegration permits an overall increase.
Products with plasterboard facings (Figure 12): As with smoke production, no life hazard is introduced during the active fire period but a high CO emission is recorded once cavity burning is established behind the protective facings.
Products with combustible facings (Figure 11): Following the high CO emission during the growth period a char-protected phase reduces the rate. Degradation of the cellulosic based board gradually permits decomposition of the core and a dangerously high rate of emission is recorded, particularly with the particle board-faced product.
Conclusions 1 ) The hazard to life resulting from a localised, but intense, source of ignition may be significantly increased by the rapid involvement of, and spread of flame over elements of building construction incorporating combustible materials. 2) Ease of ignition and rapid emission of heat from the surfaces may produce peak rates of burning which, although short-lived, may progressively involve further areas of lining. 3) The rate of emission of smoke and decomposition products, particularly carbon monoxide, during this initial period of flame spread can introduce a life hazard in its own right. 4) The 'reaction to fire' tests used in Europe to assess the fire performance of lining materials do not take into account a localised flame attack (in excess of 5 W/cm2), an intensity only too c o m m o n in domestic and other fire incidents.
CONSTRUCTION & B U I L D I N G MATERIALS Vol. 1 No. 4 D E C E M B E R 1987
5) The rate at which any polymeric insulant incorporated in the lining can subsequently contribute to the fire can be delayed and significantly reduced by careful selection of protective facings. 6) With good design, the additional risk to life which may be introduced by inclusion of the polymers is small in comparison with that from the initiating source and the probable involvement of other building components and contents. 7) Rapid and complete disintegration of unsatisfactory facing materials under this type of exposure in~'oduces a risk of rapid fire spread because of involvement of the cellular insulants. A serious life risk may be produced by the formation of a hot layer of partially burned gases flowing under the ceiling; a high carbon monoxide concentration is likely in this layer and escape may be further impeded due to reduction of visibility by smoke. Acknowledgement © Crown Copyright 198Z This paper forms part of the work of the Fire Research Station, Building Research Establishment. It is contributed by cour. tesy of the Director, BRE and reproduced by permission of the Controller, HMSO. First published in CeluUar Polymers 1987 6 (5).
-
-
o
PVC finished steel facings
•
Steel facings w i t h perimeter timber frame
-
-
o Calibration
30
CO f l o w - cores
Q. r~ O O O
I
O r-
20 E
I O
O (J
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10
I
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2
4
6
8
12
14
Time - - min
Fig 13 CO emission from insulants - steel facings
CONSTRUCTION & BUILDING MATERIALS Vol. 1 No. 4 DECEMBER 1987
187
* First Published in Cellular Polymers 198 7
Abstract Recent work at the UK Fire Research Station has provided a measure of the possible contribution to fire growth from the combustion of such components as wall or ceiling panels rather than the well- known contribution from surface spread of flame on wall and ceiling linings. The oxygen depletion technique is used to assess the rate of heat release from wall panels with a range of facing materials and different cellular polymer cores. The paper discusses how such an experimental approach may be adapted to direct validating modelling techniques with certain components but must take account of the variability in existing building practices.
lntroducldon Safety of life in the event of fire is initially governed by the individual's response to indications of danger. Speed of awareness and reaction vary widely but the chance of escape once the hazard is recognised can be improved if the time during which escape is possible is, by design, made commensurate with life risk in a given occupancy. To achieve this aim, a degree of control is applied to features of building design and construction with particular emphasis on the protection of escape routes. To maintain the routes in a safe condition it is necessary to restrict the initial rate of fire growth; control over wall and ceiling linings in corridors or rooms is exercised to limit flame spread over extended areas of surface, with the consequent risk of involvement of additional combustibles. Such measures reduce the risk of contamination of escape routes by the fire effluent. In the absence of such control over the contents of buildings, this restriction may, in certain occupancies, be of dubious advantage particularly where highly flammable products (eg modern upholstered furniture) are involved. Evidence of the advantages
of controlling linings has been difficult Background to demonstrate since until recently no The use of combustible cellular test method has assessed effectively polymers as lightweight cores for the rate of burning of the contents or panel constructions or as insulants in elements of building construction the external shell of buildings has under a variety of exposure conditions been limited in the UK, not because nor of measuring the life hazard the products fail to meet fire standards, generated by the emission from them but because of doubts about their of smoke and toxic decomposition possible effects on life safety if they products. b e c o m e involved in fire. The extent of involvement of the Industrial concerns involved in linings when exposed to a primary fire their manufacture requested the Fire is controlled in the UK by requiring Research Station to investigate the specific performance limits on BS performance in fire of two types of 476: Part 7 'Surface spread of flame' products, the first being infill panels test according to the occupancy and comprising a structural extruded the location of the lining. Additionally, polystyrene core with a range of restriction of the combustible content different facing materials, designed of the linings may be applied by primarily as replacement fenestration specifying limits to BS 476: Part 6 units. The second comprised a range 'Fire propagation' test, a procedure of laminates, incorporating plasterintroduced to measure and ultimately board facings over different cellular to limit the rate and extent of heat polymer insulants, designed to imrelease from a wall lining product. prove the insulation of solid masonry This characteristic has long been external walls by retrofitting to their known to be critical in determining interior surfaces. In both cases, inthe hazard to life in a building fire, and formation was required which could its investigation, together with that of help to quantify the possible increase the release of smoke and decompos- in life risk that might result from ition products, either from the structure exposure of the insulant to fire condior from the contents of a building, tions representing those most prejuprovides a basis for assessing the dicial to their performance. comparative effect on life safety. A s s e s s i n g the decomposition rate of
CONSTRUCTION & B U I L D I N G MATERIALS Vol. 1 No. 4 D E C E M B E R 1987
177
Aluminium profile framework
Masonry restraint for aluminium frames
l
S I
I I I I I
0
I
I
1800
2400
I I
2400
/JJ ~
-q... / / - Crib
I f
J
f
/
-"L/l/ /
/
/ Load Cells
Fig l a Comer rig- elevation insulating lining products Exposure conditions represented in wall lining tests simulating a developing fire* will rarely cause significant mechanical d a m a g e to a non-combustible facing. Provided the surface maintains its integrity a satisfactory performance will be recorded because the rate of emission of any volatiles from the underlying insulant will be low even if the facings have a high heat conductivity and permit pyrolysis. Combustible facings exposed in such a test will, unless very thin, be assessed solely according to their surface properties and no account will be taken of the secondary contribution from the flammable core. At the other extreme, the uniformly high severity exposure ( ~ 1 0 W / c m 2) over a wide area such as is provided by the fire resistance test, will almost inevitably cause failure of non-combustible facing materials, or distortion of
bustion of the underlying foam. However, even total decomposition of the insulant contributes only a small fraction of the heat and decomposition products comprising the total fire effluent that is generated by this type of exposure. In any case, the fire resistance test furnace is constructed in such a way that no measure can be m a d e to quantify in isolation the contribution from the product under test. An a d hoc experimental approach had therefore to be adopted which could simulate localised exposure to a high intensity fire source.
Experimental programme Experimental construction
Ideally the performance of the products should be investigated on full scale under a range of ventilaUon conditions, both in r o o m s and in free air. The first joints and junctions and allow corn- condition imposes a restricted air supply specific to that scenario. In the *In terms of most national flame spread latter a high burning rate m a y be tests, the maximum exposure level is little maintained long enough to cause failure of the facings and the situation in excess of 3 W/cm 2.
178
is m o r e representative of a freely ventilated room or of an open plan occupancy. The second system was adopted, with an open corner configuration which provided for an area of wall 2.4 m high x |.2 m and 2.4 m high x 2.4 m (Figure 1aj. By channelling the combustion products into a canopy and thence through a convection controlled chimney, it was possible to obtain a continuous record of gas flow and composition. Tests on the infill panels introduced the risk of integrity failure and to ensure that all e n e r g y / s m o k e release was monitored, an additional canopy and stack were installed at the rear of the corner wall rig. Gas temperatures within the corner assembly were m e a s u r e d and heat flux meters were installed during calibration runs to monitor the exposure severity of the ignition source; others provided comparative data on secondary flaming emitted from the burning panels.
Ignition source The choice of ignition source was governed by the need to cause
CONSTRUCTION & B U I L D I N G MATERIALS Vol. 1 No. 4 D E C E M B E R 1987
Iocalised mechanical failure of the protective facings and enable comparative assessments of different products to be m a d e with minimal excess severity. Furthermore, the initiating fire had to be representative of a fire source typical of the occupancy under consideration. An upholstered seat of modern design and construction, sited directly in front of the panels was selected but to compare effectively the rates of emission of heat, smoke and decomposition products from the experimental panels, a wood crib was designed, shown to provide essentially similar exposure conditions. This confirmed the repeatability of the fire source in each test and furthermore, under the free ventilation conditions, the smoke generated by the wood crib fire was not high enough to mask that emitted from the panels under test.
L
Positionof Rear Canopy& Stack
/
I
/l / /. Mid-way over Opening in Rear Wall
Tests on insulated panels Details of the installation of the panels in both series of tests are given in Figures l a and l b, and selected data on rates of release of heat, smoke and decomposition products from each system are listed in Table 1. Full details are published elsewhere. *The expression of flow rates of smoke and CO in terms of standard "critical" concentrations (1.4 m visibilityand 5000 ppm respectively) provides a basis for calculating the extent of life risk; the actual maximum and minimum values recorded in the tests can vary significantly from these limits but are dependent on the siting of the sampling instruments
~
'
~ /
/ / /
/~ / oXfP, a°rsiti°n ~_~/~ Thermocouples_,~.
Calibration test Using a panel with a non-combustible facing and insulant the heat flux incident on the surface was recorded and the rate of mass loss of the crib was monitored to check repeatability of exposure throughout the tests series. The rate of heat release from the crib alone was measured using the oxygen depletion technique and flow rates of effluent were used to calculate the emission of smoke (in terms of m3/s at S.T.P. of smoke of OD/m = 1") and of the generation of CO (m3/min at S.T.P. of CO of concentration 5000 ppm*). The heat flux incident on the panels was recorded (Figure 2) and is assumed to be identical for each test since it was not possible to insert the meters into the insulated panels without generating a point of weakness.
/
500
/
I
-/
Positionof FrontCanopy&Stack Fig l b Comer rig - plan and may thus be misleading. Discussion of results
Effect of free ventilation It is appreciated that the free ventilation conditions under which the two series of tests were carried out affected not only the rate of combustion but also the chemical processes involved. This is illustrated by the insignificant quantities of carbon monoxide measured in the calibration tests and where the insulants were faced with
noncombustibleboardswhich~tained their inteqrity.Under such conditions a maximum heat output can be achievedbut the peakconcentrations of CO and, with burning cellulosics,
the peak densities of smoke generated are likely to be lower than for a ventilation controlled fire.
Performance of facings The initial involvement in fire of the surfaces of the panels during the initial three-minute period is representative of fire growth in most well-
CONSTRUCTION & BUILDING MATERIALS Vol. 1 No. 4 DECEMBER 1987
ventilated domestic or office occupancies and comparison of their performance under these conditions with that in standard tests does indicate significant differences, due to direct fire exposure. Typical standard test results for the range of facings investigated are given in
Table 2. Heat release from burning facings Reference to Figure 2, indicating the heat flux incident on the surface of the facings, shows to what extent the exposure intensity exceeds that of the standard test. The additional energy derived from combustion of the facings (Figure 3) largely dictates the extent to which vertical flame spread can occur and, for the rig height used, lateral spread under the ceiling for the design of rig used. l'he rate of heat released from the facings is shown in Figures 4- 7 and the maximum values are listed in Table2 (together with the heat output of the initiating fire). The importance
179
Exposed facing
rain
Maximum rate of heat release kW Time rain
Calibration (non-combustible)
NA
1000
1.00
900
2.00
3.2
3.00
PVC-faced 0.6 mm steel
1.30 (distorted)
1500
2.00
900
2.00
7.0
2.00
0.6 mm steel (timber frame)
No obvious failure
1000
2.00
820
2.00
1.5
2.00
Abestos cement -6mm
1.52 (spalling)
900
2.00
800
2.00
3.2
2.00
Particle board -10mm
5.55 (burned out)
6500
7.00
1200
8.00
14.5
7.20
5.10 (burned out)
2250
7.00
1100
7.00
13.8
5.00
Plasterboard 9.5 mm/plywood -4mm
9.15 (partialfall)
1050
2.00
900
35.00
6.8
35.00
Cellulose fibre/ cement board -4mm
6.15 (massivefall)
1600
6.30
1000
6.00
12.0
6.00
Cellulose fibre reinforced plasterboard -lOmm
21.29 (partialfall)
900
2.00
780
2.00
Plywood - 10 mm
Underlying polymer
50 mm extruded polystyrene
Time to failure of facing
Maximum gas temperature °C Time min
Plasterboard
Phenolic
11.00 (partial fall)
1325
2.00
850
2.00
9.5 mm
EPS
14.00 (partialfall)
1450
2.00
850
2.00
PI R (with aluminium foil) XPS
12.20 (partial fall)
1300
2.00
870
2.00
13.30 (partial fall)
1450
2.00
880
3.00
"
"
Maximum heat flux from flames* W/cm 2 Time min
Not recorded
Not recorded
*Meters installed parallel to panels at 50 mm distance
Table 1. Fire performance of faced cellular polymers in an open corner test of these heat release rates lies primarily in their effect on the rapidity of initial flame spread; life hazard is affected more directly by smoke and CO emission rates.
Emission of smoke from burning facings During the initial three-minute fire period the measured rates of flow of effluent gases from all the burning
180
panels (1.3-1.5 m3/s) did not differ significantly but the optical density of the smoke varied enormously from test to test. The results have therefore been adjusted to express the rates of smoke production in terms of m3/s flow of smoke of OD/m = 1. Standardisation in this way indicates the effect of dilution of the smoke and permits the data to be used in
mathematical modelling of smoke flow.
Combustible facings and finishes: The initial contribution to the smoke emission from the paper of the unfinished plasterboard (Figure 8) and from the timber products (Figure 9) was low, as was the case for the timber crib in free ventilation conditions. Significant amounts of smoke
CONSTRUCTION& BUILDING MATERIALSVol. 1 No. 4 DECEMBER1987
Plywood
8f
v
~,
6 0 0 m m a b o v e crib
o
o
1.2m a b o v e crib
O
O
PVC Plaster b o a r d Particle b o a r d
O . . . . . . . . . .
[]
Non-combustible
board
I "r
m
oJ
1-
J 8
I
I 16
L
I 24
Time -- min
Fig 2
Time -- min
Heat flux on panel surface from crib fire (non.combustible panel)
Lining
Peak heat Time of Duration release peak after of peak from lining ignition kW
Fig 3
Heat flux from burning facings parallel to panel (at 1.50 m above crib)
Flame spread rating France (NF P92-501) Maximum intensity 3.0 W/cm 2
UK
W Germany
(BS 4 7 6 Pt.7) (DIN 4 1 0 2 : Blatt 2) Maximum Maximum intensity intensity 3.1 W/cm 2 4.8 W/cm ~ for Class 1
Plasterboard
400
2 min
> 1 rain
M1
1
B1
Painted plasterboard
125
2 min
Continuous to 15 min
M1
1
B1
PVConsteel
750
1 min30s
> 1 min
M2
1/2
B1
Particle board
1600
1 min 30 s
3 min
M3
3
B3
Plywood
1600
1 min 30 s
2 min
M3
3
B2/B3
Table 2. Heat release from surface linings or finish
C O N S T R U C T I O N & B U I L D I N G M A T E R I A L S Vol. 1 No. 4 D E C E M B E R 1 9 8 7
181
were, however, recorded in the case of the pvc finish over the steel facing* (Figure I 0) and, at a later stage, in excessive amounts from the particle board.
1500[-
Boards and facings of limited combustibility: Reference to Figure 8 indicates that the contribution to the overall smoke emission from such facings is negligible because no integrity failure occurred during the initial three-minute period.
Emission of CO from burning facings Investigation of the emission of CO from the panels during the initial three-minutes of test indicates shortlived changes in the combustion processes once the facings became involved in fire. To provide a comparative basis for assessment of life hazard, the rates of emission in m3/min are adjusted to concentrations of 5000 ppm (equivalent to atmospheres likely to cause rapid disorientation and death).
g
o. . . . . . . .
|
I~
[]
o Facings without perimeter timber fixings [] Non-combustible • • Facings with perimeter timber fixings • . . . . . . . . . . . • Facings without perimeter timber fixings (at rear)
!I" L
!I II ii
l
l',
/
it
/
kl/ t ,/I
0
/ / /
/
1oool- .! ',, _
]
/ C,,bratio° /
2
4
6 Time8min
10
12
14
16"
Combustible facings and finishes: Emissions of CO from the purely cellulosic based finishes (eg plywood (Figure 11) and paper of plaster-
Fig 4
Heat release from insulant
Boards and facings of limited combustibility: Reference to Figure 8 free ventilation conditions. Only the pvc finish (Figure 13) during the short period of initial rapid flame spread generates an unacceptably high concentration (0.23%). A similar maximum (0.27%) was recorded from the particle board facing during the 30 s period of rapid flame spread. It is interesting to note the difference in output between this and the plywood finish.
-
steel facings
•
•
Asbestos cement board
•
•
Ditto (rear)
•
•
Cellulose f i b r e / c e m e n t
•
•
Ditto (rear)
o
o Non-combustible
board
1500 1
Boards and facings of limited combustibility: No significant increase over the crib output of CO was recorded, again indicating that joints and junctions maintained their integrity over this period of test (Figure
1000 I
12). Contribution to Fee effluent from polymeric insulants
-1-
Failure, due to fracture, distortion or disintegration of the protective fadngs over the polymeric insulations, results in their involvement in fire. The extent of their exposure to free air conditions, the oxygen content of the combustion air and the severity of the exposure *The design of the pvc/steel-faced panel was such that rapid distortion of the steel may have permitted Iocalised emission of polystyrene volatiles which would have increased the obscuration.
182
500
l\ I \
3 Fig 5
L ~ - 2
__w4
6 Time
--
i. . . . . . . . . . . 8 10 12 rain
14
Graphs showing heat release from insulant - board facings of limited combustibility CONSTRUCTION & BUILDING MATERIALS Vol. 1 No. 4 DECEMBER 1987
•
o Ditto (rear)
•
• Plaster board
o
o Cellulose~cement board
o. . . .
o Ditto (rear)
3600 I
I n s t r u m e n t failure
v------v
• Asbestos/cement board
D. . . . . . . .
• ......
• Non-combustible
L
~ Plaster board/plywood
Plywood
I I
z~
~ Particle b o a r d
o
a Non-combustible
lI
• ........
• Particle board (at rear)
I
\
\
\ k
0
II
,
"11
\
I
2
6
8 tO Time - - min
12 18
24
30
36
F~g8 Smoke emission from panels - board facings of
.
'-'\,- ....
5
.
limited combustibility
10
,,
Particle board facings
o
o
Ditto (rear)
•
•
Plywood
•
•
Ditto (rear)
15
T i m e - - min
Fig6
4
Heat release from i n s u l a n t facings
combustible
•
Plaster board
•
Plaster board/plywood (painted) Non-combustible
facings
Instrument
failure
1500
v
'1000 ."~.\
I
500
/ / /
vf v
/
/ /
01
,
L
2
,
I
4
i
6I ~ /
2JO
= 28
30
32
314
2
36
Time - - rain
F~g7
& BUILDING
MATERIALS
6
8
10
Time -- min
Heat release from insulant - plaster board facings
CONSTRUCTION
4
Vol. 1 N o . 4 D E C E M B E R
1987
Fig 9
Smoke emission from panels - combustible facings
183
Facing Type
Release of
Composition
Heat Maximum rate- kW
Smoke
Duration of peak rain
Maximum rate - m3/s ( O D = 1 m)
CO
Peak Duration Time min min
Peak Duration Time rain min
Maximum rate- m3/min (CO = 5000 ppm)
Non-combustible (a) spalling
Absestos/cement
160
> 6
4.3
4
5
(b) disintegrating
Plasterboard
150
> 25
1.0
~10
25
9
15
24
900
6 min at 35 min
7.4
~1
36
36
~1
35
1050
~ 6 min
9.0
4
7
26
2
11
> 10
5.75
4
4
> 6
1.0
Negligible
12
"
with plywood
Cellulose/ c e m e n t board (c) distorting
Steel Steel with timber frame
275
Negligible
CO escaped (spalled)
CO escaped (distortion) 4
5
Combustible (a)
Particle board
5700* failed rising
8.5
Plywood
1580*
4.8
disintegration
- 4
rising
failed 7.5
60
rising
200
failed
4
7
*Value includes s o m e heat from residual facings
Table 3. Emission of heat and decomposition products from extruded polystyrene
o
conditions all affect the mode of combustion. The failure pattern of the protective facings is thus very important in determining any additional life hazard introduced because of the presence of the polymeric insulants.
4-
PVC faced steel without timber frame
•
•
Ditto (rear)
•
•
Steel with timber frame
v
v
Ditto (rear) Non-combustible
Rate of heat release from insulants
14
The rate of heat release from the underlying insulants must, of course, be considered in relation to the severity of the fire which has succeeded in causing failure of the protective facings. Design factors should ensure that the time to, and extent of failure of the protection is commensurate with the need to maintain life safety in the particular environment under consideration ie, escape times, occupancy and fire source severity must be considered. Failure to prevent the rapid decomposition of an insulating polymeric lining may result in the generation, under the ceiling, of a hot gas layer comprising products of incomplete combustion. Combined with a high temperature, the spread of such a layer can be excessively hazardous, mixing with air at the base and generating an active flaming interface;
r~
184
o
~E I O
O
E
co
//" O
2
4
6 Time-
8 min
10
12
14
Fig 10 Smoke emission from panels - steel facings CONSTRUCTION & BUILDING MATERIALS Vol. 1 No. 4 DECEMBER 1987
downward radiation may be very intense. Formation of such a layer must be avoided if the risk to life is to be kept low.
5O
200 l 7=I/
Polymers protected with non-combustible facings: Failure of these facings can occur due to fracture (plaster-based products (Figure 7), cement-based boards (Figure 5)) or to distortion resulting in integrity failure at joints and junctions (steel (Figure 4)). Table 3 indicates the contribution to overall heat emission provided by the different panel types, in excess of the output from the initiating fire in isolation. Generation of additional energy adequate to cause failure of any adjacent facing is indicative of a risk of developing a selfipropagating or even of an accelerating fire growth pattern. The values of energy release recorded during tests involving the full range of polymeric cores and different facings of this category are quoted in Tables 1 and3 and indicate the respective risks of such development. Of lower risk to life, but nevertheless of interest, is the continued burning of insulation still partially protected by the fractured facings; this problem applies primarily where thermoplastic foams have melted and is found to occur, albeit slowly, where flow of hot combustion air is possible behind the facings, unrestricted by adhesive or batten flyings, cavity barriers etc.
I
/ Instrument failure
4O
• ....
30
i
I/
-I "/II I o
z~ Particle board facing • Plywood facing • Calibration
/
\o
Polymers protected with combustible facings: The rapidly accelerating growth of fire over and through the plywood and particle board facings masks the point at which significant involvement of the underlying polymer occurs; the rate of heat release in the latter case (which involved also a rear facing particle board) was so high that it caused failure of the instrumention (Figure 6).
Smoke emission from polymeric insulants Products with metallic facings: Two fLxing systems for the steel faced panels were investigated; those without perimeter timber frames suffered rapid distortion and escaping volatiles from the decomposing core ignited and burned. The maximum smoke obscuration was recorded at 4 min 30 s when a rate of emission of 5-9 m3/s (OD/m = 1) was reached; emission persisted for 10 min giving a total
12
Fig 11 CO emission from insulants - combustible facings
output of about 600 m 3 of smoke of OD/m = 1. Panels with perimeter timber frames, to which the facings were attached exhibited significantly reduced smoke emission, the peak output rate recorded failing to exceed 1.2 m3/s (OD/m = 1) (Figure 10).
Products with non.combustible board facings: Smoke emission from the underlying extruded polystyrene was very low until after cracking or local spalling of the board when short lived peak values were recorded. In one instance a peak of 6.9 m3/s (OD/m = 1) was reached following major disintegration but where the fractured facings
CONSTRUCTION & BUILDING MATERIALS Vol. 1 No. 4 DECEMBER 1987
were retained in position protecting the insulant, emission of volatiles was strictly limited until a subsequent fracture occurred (Figure 8).
Products with combustible facings: It was not possible to isolate with precision the smoke contributions from the insulants from those from the cellulosic facings but distinct peaks in the smoke flow from the plywood faced panel indicated a maximum rate of smoke generation of > 8.0 m3/s (OD/m = 1) once the plywood had disintegrated. The smoke emission from the particle boardfaced product rapidly exceeded this
185
value at which time the instrumentation failed with the rate still rising
40
(Figure 9). Products with plasterboard facings: Smoke emission from products with a range of different polymeric insulants protected by plasterboard fadngs (Figure 14) differed very little and was negligible during the initial growth/ spread period in comparison with the output from the crib fire and paper facings. Following cracking and fall of the plasterboard on the panels adjacent to the initiating fire and burnout of the crib ( ~ 20 min) the polystyrene foams continued to support combustion albeit slowly and spread was limited only by the provision of cavity barriers formed by the supporting framework of the panel. Such a pattern was not recorded with the non-thermoplastic insulants and smoke emission rapidly ceased. Combustion could not be sustained in the vitiated air conditions between the facings because no cavity was formed by melting as was the case with the thermoplastics. The overall fire performance of these rigid non-thermoplastic polymers, laminated to the range of facings examined over extruded polystyrene cores is, on the basis of the experimental results, confidently expected to be superior to that of the thermoplastic products.
• Cellulose f i b r e / c e m e n t board facings • Plaster b o a r d / p l y w o o d facings o Calibration
3O
o~ o v
20
8 10
A
)k
,' " T ' '
1'0
1'4 '3 '
35
Time - - rain
Fig 12 CO emissions from insulants - board facings of limited combustibility
Emission of carbon monoxide from the polymeric insulants Emission of carbon monoxide is highly dependent on the combustion reactions occurring at any given time; these are signficantly affected both by the exposure intensity and the oxygen content of the atmosphere adjacent to the burning zone. Products with steel facings: Following the initial peak values, the emission of CO from the insulant in the panels with and without* perimeter timber frames (Figure I3) is not unacceptably high, and may be negligible in comparison with overall CO generation in a practical fire. Nevertheless, the higher values recorded for these facings than for other non-combustible facings may be accounted for by the high heat transfer to the core, initiating pyrolysis in advance of flaming combustion after distortion of the joints occurred. *This value was underestimated because no record was taken of CO lost due to integrity failure of the panel.
186
Products with board facings of limited combustibility (Figure 12): The total quantities of CO emitted indicate a very low life hazard with all boards which fracture only locally where directly affected by high intensity flames. Extensive disintegration permits an overall increase.
Products with plasterboard facings (Figure 12): As with smoke production, no life hazard is introduced during the active fire period but a high CO emission is recorded once cavity burning is established behind the protective facings.
Products with combustible facings (Figure 11): Following the high CO emission during the growth period a char-protected phase reduces the rate. Degradation of the cellulosic based board gradually permits decomposition of the core and a dangerously high rate of emission is recorded, particularly with the particle board-faced product.
Conclusions 1 ) The hazard to life resulting from a localised, but intense, source of ignition may be significantly increased by the rapid involvement of, and spread of flame over elements of building construction incorporating combustible materials. 2) Ease of ignition and rapid emission of heat from the surfaces may produce peak rates of burning which, although short-lived, may progressively involve further areas of lining. 3) The rate of emission of smoke and decomposition products, particularly carbon monoxide, during this initial period of flame spread can introduce a life hazard in its own right. 4) The 'reaction to fire' tests used in Europe to assess the fire performance of lining materials do not take into account a localised flame attack (in excess of 5 W/cm2), an intensity only too c o m m o n in domestic and other fire incidents.
CONSTRUCTION & B U I L D I N G MATERIALS Vol. 1 No. 4 D E C E M B E R 1987
5) The rate at which any polymeric insulant incorporated in the lining can subsequently contribute to the fire can be delayed and significantly reduced by careful selection of protective facings. 6) With good design, the additional risk to life which may be introduced by inclusion of the polymers is small in comparison with that from the initiating source and the probable involvement of other building components and contents. 7) Rapid and complete disintegration of unsatisfactory facing materials under this type of exposure in~'oduces a risk of rapid fire spread because of involvement of the cellular insulants. A serious life risk may be produced by the formation of a hot layer of partially burned gases flowing under the ceiling; a high carbon monoxide concentration is likely in this layer and escape may be further impeded due to reduction of visibility by smoke. Acknowledgement © Crown Copyright 198Z This paper forms part of the work of the Fire Research Station, Building Research Establishment. It is contributed by cour. tesy of the Director, BRE and reproduced by permission of the Controller, HMSO. First published in CeluUar Polymers 1987 6 (5).
-
-
o
PVC finished steel facings
•
Steel facings w i t h perimeter timber frame
-
-
o Calibration
30
CO f l o w - cores
Q. r~ O O O
I
O r-
20 E
I O
O (J
?, iI \\
10
I
\
/
2
4
6
8
12
14
Time - - min
Fig 13 CO emission from insulants - steel facings
CONSTRUCTION & BUILDING MATERIALS Vol. 1 No. 4 DECEMBER 1987
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