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The use of the ISO/TC92 test for ignitability assessment
Hu, X. F.; Clark, F. R. S.
TH1
N21d
National Research
Conseil national
no.
1570
1
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1
Council Canada
de recherches Canada
c. 2
-
BLDG
Institute for
lnstitut de
Research in
recherche en
Construction
construction
The Use of the ISO/TC92 Test
for
lgnitability Assessment
by XiFang Hu and F.R.S. Clark
Reprinted from
Fire and Materials
Vol.
12,No.
1,March
1988p. 1 - 5
(IRC Paper No.
1570)N R C
-
CIS*I R C
-,I
L I B R A R Y
MAR
1
1989
IINRCC
29768I
B I B L I O T H ~ Q U E
t
I R C
c . w - - r-
t c : ~ ~1
-
--.,L'inflammabilitk des solides, y compris des polystyrknes contenant des ignifuges retardateurs. est Ctudiee au moven d'un essai d'exmsition aux ravonnernents thermiaues h Cchelle ruuite (mCthode d'esiai d'inflammabiliti de I'ISO modifice). Des informations supplCmentaires pmviennent des dsultats d'exposition h un chauffage par convection et de mesures de I'indice d'oxygkne. L'utilisation d'un masque kchantillon permanent et d'Cchantillons plus petits gue ceux de la mkthode IS0 s'avkre commode. La d t h o d e IS0
s'est dvklke utile pour dktenniner le temps de dponse de l'inflammabilitt! aux changements de flux d'knergie rayonnante. La mtthode est en accord avec l'ttude de Quintiere et Harkleroad pour la plupart des tkhantillons, mais pas pour le polystyri?ne avec ou sans ignifuges aux halogknes. L'augmentation de dsistance h I'inflammabilitk avec la concentration de retardateur d'inflammabilitk suggkrde par l'indice d'oxygkne ne correspond pas toujours au dklai d'inflarnrnation sous l'effet du chauffage par convection ou par rayonnement.
I
FIRE AND MATERIALS VOL. 12,l-5 (1988)
The Use
of the ISO/TC92 Test for Ignitability
Assessment
XiFang HuThe Tianjin Fire Research Institute, Ministry of Public Security, Peoples' Republic of China
Ferrers R. S. Clark Fire Research Section,
Institute for Research in Construction, National Research Council Canada, Ottawa, Canada, KIA OR6
The ignitability of solids, 'including fire-retardant-containing polystyrene, is reported using results of a small-scale thermal radiation exposure test (a modified I S 0 ignitability test procedure). Additional information is provided from the results of exposure to convective heating and from oxygen index determinations. The use of a permanent sample mask and smaller samples than described in the I S 0 procedure proved convenient. The IS0 procedure was found useful for determining the response of ignition time to changes in radiant flux. Good agreement was found with the analysis of Quintiere and Harkleroad for most samples but not with polystyrene, with and without halogen fire retardant. The increase in ignition resistance with fire retardant concentration suggested by the oxygen index is not always consistent with the ignition delay times under radiative or convective assault.
I N T R O D U C T I O N
For several years, studies in the authors' laboratory have been directed towards seeking useful methods of assess- ment of the ignitability of materials used in the construc- tion industry. The ignition tests in common use are not expected to indicate actual fire performance, being issued with such provisos as 'for development purposes only' or 'to rank materials only'. Nevertheless, these tests are used to choose between materials in use where there is expect- ation by the engineering and design professions that the ones chosen will afford a greater degree of safety than those rejected. One such test procedure that has attracted
interest is the 'Reaction to fire-Ignitability of Building
Products' test that is currently a draft international stan- dard, issued by ISO.'
In the course of our assessment of the utility of this relatively new procedure, modifications to improve the sample handling have been devised that are reported here. This modified I S 0 procedure is assessed in this paper by a comparison of the results it affords with those from a test procedure that also uses radiant exposure and from other rather different test procedures. The first of these procedures involves exposure of a sample surface to nearly pure convective heating from a hydrogen-oxygen flat flame; the second is the oxygen index (LOI) proce- dure.
A second aim of this paper is to report some prelimin- ary investigations of fire retardant behaviour using the sensitivity of ignition delay time to the radiant flux of exposure in the I S 0 apparatus.
E X P E R I M E N T A L S E C T I O N
Radiative ignition
Samples were exposed to the radiation from an electrical- ly heated coil, following the procedure of I S 0 draft inter-
national standard 5657 (198547-18),l except as noted. Figure 1 shows the relationship between the coil and the specimen stage. A pilot flame, not shown in the figure, is presented for 1 s every 4 s to a point of 1 cm above the centre point of the sample surface. The apparatus used was constructed by Heightfield Ltd, England.* Radiant fluxes at the sample plane could be established within 3% (at 5 W cm-') and 8% (at 2 W cm-') by changing the voltage supplied to the heating coils.
As called for in the I S 0 procedure, each sample was wrapped with aluminum foil. In addition, a steel mask
(165 x 165 x 0.75 mm) was placed on top of the foil. The
mask and the wrapping foil were pierced by a circular hole 140 mm in diameter, as required in the standard. In addition, a similar plate (0.53 mm thick) with a hole of 45 mm diameter was used. Due to the smaller exposure area, less material was used in each test and the amount of toxic fumes released was reduced. The metal plate had the function of keeping the sample plane relatively con- stant. Most of the data reported here were obtained with use of this small mask. Without it, with some samples, heaving that occurred when samples became hot changed the distance between the sample and the radiant coil.
Convective ignition
Ignition by convective heating was studied using a hydrogen-oxygen flat flame burner (Fig. 2) used for other studies on polymer ignition.' The temperature of the flame was adjusted to 682-4°C at a distance of 7 mm below the surface of the burner, and the samples were placed at this distance. The flame was operated lean and was transparent, with a hydrogen-oxygen ratio of 0.25. The same temperature was recorded on the heater cone of the I S 0 apparatus when the radiant flux was 3 W cm-' in the sample plane.
*Mention of any particular brand of apparatus, device or product should not be construed as endorsement by the National Research Council of Canada.
Q Canadian Government
Received 19 September 1986
XIFANG HU AND F. R. S. CLARK
RADIATOR CONE
UPPER MASKING PI
UPPER MASKING PLATE
w
Figure 1. Schematic of IS0 ignitability test apparatus.
I
i
i
WATER O U T1
C O O L I N G JACKET WATER I N S P E C I M E N\
U P P E R M A S K I N G P L A T E /Figure 2. Schematic of Hz-0, flat flame burner.
Each sample was cut into a specimen 50 mm x 50 mm and exposed to the flame masked by a specimen mask with a circular hole 41 mm diameter. Each sample was mounted on a slab of Fiberfrax* 3 mm thick over a water cooled brass plate.
Commercial polymers and composites
The selection of materials was designed to cover a wide r a n g of polymers and finishing materials used commer- cially. Fire retardant polyurethane foam (FRPU), glass fibre and nylon reinforced polyester board (PEB), poly- styrene pellets, suitably formed into a sheet (PS), high- density polystyrene sheet (HPS), poly(methy1 methacryl- ate) (PMMA), hardboard
(HR),
polypropylene(PP),
poly(viny1 chloride) (PVC), high-density polyethylene ,(HPE), white low-density poIyethylene (PE) containing
3% by weight titanium dioxide and polycarbonate [poIy(bis phenol-A)] were used as supplied.
Fire-retardant-treated polystyrene
Samples were prepared from pure polystyrene beads (Aldrich Chemical Co. Ltd, Catalogue 18,242-7), two * Fiberfrax ceramic fibre insulation, The Carborundum Company, In- sulation Division, Niagara Falls, New York.
ISO/TC 92 TEST FOR IGNITABILITY ASSESSMENT
chlorinated paraffins, Cereclor 63L liquid (CER 63) and Cereclor 70 solid (CER 70) (from CIL Inc., manufactured by ICI), tetrachlorobisphenol-A (TCBPA) (Polyscience, Inc., Catalogue Number 6775, Lot 341 15) and tetrabrom- obisphenol-A (TBBPA) (Polyscience, Inc., Catalogue Number 6767, Lot 1647). Viscous mixtures of the poly- mer and the fire retardant in methylene chloride were stirred thoroughly before being spread on a thick alumin- ium foil. The solvent was then removed by storing under vacuum at 60°C for 3-4 h. Sheets 0.8 mm thick were then prepared by pressing the resultant foamy mass at a temperature just sufficient to ensure adequate flow. Slugs for LO1 analysis were similarly prepared.
large samples. Dilution of the pyrolysis phase by air entrainment is more effective with small samples.
Thermal radiation causes ignition in times that are dependent on the reflectance of the
ample.^
To probe the effect of this dependence on experiments using the I S 0 test a white PE sample was chosen that was highly reflective because of added titanium dioxide. The time to ignition for this sample was thus the longest observed (large sample: 385 s; small sample: 347 s) and the depen- dence of time to ignite on exposed area was the reverse of that found for all other samples.The effect of flux
The dependence of ignition time on irradiance has been
RESULTS and Quintiere and Harkleroad6 have sug-
gested a relationship based on conduction principles to explain such data:
The effect of exposed area
Samples of P P and PMMA were tested according to the slightly modified draft I S 0 standard.' The time to igni- tion was measured as the applied radiant flux was varied, for both exposed areas (Fig. 3). There was a linear re- lationship between the times to ignition in the two cases. Similar results were obtained with a range of commercial samples. Samples of hardboard, similarly exposed, followed the same trend until the flux used dropped below 2.98 W C ~ - ~ , when the exposure time to ignition of the small sample rose dramatically, possibly due to char protection of the sample surface (Fig. 3). These experiments indicate that smaller samples than specified in the standard may be, used when necessary, provided care is taken with interpretation of results with char- forming samples.
Samples with smaller exposed areas took longer to ignite, consistent with the results of experiments conduc- ted on smaller samples with a similar radiant s ~ u r c e . ~ Ignition occurs after a critical concentration of pyrolysis gas is reached, a condition more readily achieved with
TIME TO IGNITION ( l a r g e s a m p l e a r e a ) , s Figure 3. Time to ignition for small versus large specimens of PMMA, PP and HB with the modified I S 0 test and varying irradia- nce.
where b = 2h
z
.
p
c
)
go =critical radiant flux,
qE = actual (constant) flux, h = heat transfer coefficient,
K = conductivity,
p =density,
c = specific heat.
This relationship is obeyed in the present work for PMMA, PP, PE and HB, since a plot of go / q , versus Jt
was linear (Fig. 4).
The I S 0 method allows the measurement of the criti- cal radiant flux necessary before a sample will ignite in up to 15 min of exposure. Table 1 shows the similarity of the critical radiant fluxes for ignition recorded by the I S 0 test and by the Quintiere radiant panel flame spread test.6 0.75
-
0.50-
-
0-0 PMMA &--A p p 0-.-0 HPE-
0---0 H B 0 5 10 15 2 0Figure 4. Time to ignition as a function of radiant flux for pure polymers (large area sample).
XIFANG HU AND F. R. S. CLARK Table 1. Comparison of critical radiant heat flux at ignition by
the IS0 method with the results of Quintiere and Harkleroad6
I S 0 ignitability Duintiere flame test spread test Critical flux Critical flux Spectmen (Wcm-') ( W ~ r n - ~ )
P M M A H B PC
Correlations
Figure 5 shows the lack of correlation between the results of the modified I S 0 ignitability test (run at 3 W cmP2), the convective ignition (flame) test and L017 tests for ten materials. Thus, for example, the commercial fire re- tardant polyurethane (FRPU) performed well in the ox-
ygen index test (LO1 = 24.5), but performed poorly in the
I S 0 ignition test.
Evaluation of fire retardants
T h e ignitability of polystyrene containing chlorine- and
bromine-based fire retardants was studied using the
methods described above. The effects of halogen content
(as an equivalent weight fraction of halogen element in
the composites) on the LOI, time to ignition in the
convective flame test and the modified I S 0 test are shown in Fig. 6. (All I S 0 tests were performed with 45 mm wide samples.)
By two measures (LO1 and I S 0 test radiant exposure), the fire-retardant-containing bromine is more efficient than the fire-retardant-containing chlorine. In the hydrogen-oxygen flame this trend was not apparent, possibly as a result of flames with different flame chemis- try.
For the LO1 of all fire-retardant-containing polystyr- ene and for the I S 0 ignition test of that polymer with
TIME T O IGNITION ( I S 0 T E S T ) , s
Figure 5. Correlations of I S 0 ignitability test, the convective flame ignition test and the LO1 test; with commercial samples. 1 FRPU, 2 PS, 3 PEB, 4 HPS, 5 PMMA, 6 HB, 7 PP, 8 PVC, 9 HPE, 1 0 PE.
C
1 0 . 0 0
I
I I I1
0 6 . 2 5 1 2 . 5 0 18. 75 2 5 . 0 0
HALOGEN. %
Figure 6. Effect of halogen content on ignitability of PS.
TBBPA alone, increasing halogen content increased fire retardant activity. This is consistent with other recent
report^.^
However, in the hydrogen-oxygen flame igni- tion test, increased fire retardant concentration (TBBPA and CER 70) actually decreased the time to ignition.Figure 7 shows the effect of heat flux on the time of ignition of polystyrene containing CER 70, as displayed
after the analysis by Quintiere and H a r k l e r ~ a d . ~ Addi-
tion of chlorinated hydrocarbon (CER 70) increased the flux required to produce a given time to ignition. While linear trend lines are indicated, they may equally be curved, possibly indicating that the Quintere and Harkle-
Figure 7. Ignition delay as a function of radiant flux for polystyrene treated with CER 70.
r
ISOITC 92 TEST FOR IGNITABILITY ASSESSMENT
road analysis is not completely appropriate for pure PS (2) The response of time to ignition to flux can also be and PS containing these halogenated fire retardants. readily measured; the effect of the four fire retardants under this study on this response was, however, re- latively small;
(3) The critical radiant flux necessary for ignition is similar to that obtained from the larger NBS/Quin-
CONCLUSIONS tiere panel test. Acknowledgements
The I S 0 ignition test is a versatile tool and can be used in
conditions other than those specified in the draft stan- The authors gratefully acknowledge the contributions of dard: Miss A. BaienQ. Mr J. MacLaurin and Mr R. Flaviani to this paper. - - - - - -
One of the a"uthors (XiFang Hu) acknowledges the support of the Fire than 'pecified can be used when little Bureau of China and the National Research Council of Canada. This material is available or the toxicity of released gases is paper is a contribution from the Institute for Research in Construction,
high; National Research Council of Canada.
REFERENCES
1. Fire tests--Reaction to firelgnitability of Building Products.
Draft International Standard ISO/DIS 5657, by ISO/TC 92, Inter-
national Organization for Standardization, Secretariat-British
Standards Institution, London, 1985.
2. F. R. S. Clark, J. Polymer Science, Polymer Chemistry Edition 21,
2323 (1 983).
3. F. R. S. Clark, Fire and Materials 8, 196 (1 984).
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5. S. Martin, Tenth Symposium (International) on Combustion, The
Combustion Institute, Pittsburgh, pp. 877-96 (1 965).
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ASTM Special Technical Publication 882, ASTM. Philadelphia
(1 985). pp. 2 3 M 7 .
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tration to support candle-like combustion of plastics (oxygen
index). ASTM 0-2863-77, ASTM. Philadelphia (1 977).
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T h i s p a p e r
i s
b e i n g d i s t r i b u t e d I n r e p r i n t f o r m by t h e I n s t i t u t e Eor R e s e a r c h i n C o n s t r u c t i o n . A l i s t o f b u i l d i n g p r a c t i c e a n d r e s e a r c h p u b l i c a t i o n s a v a i l a b l e f r o m t h e I n s t i t u t e may be o b t a i n e d by w r i t i n g t o t h e Publications S e c t i o n , I n s t i t u t e f o r R e s e a r c h i n C o n s t r u c t i o n , N a t i o n a l R e s e a r c h C o u n c i l of C a n a d a , O t t a w a , O n t a r i o , K1A0R6.
Ce document e s t d i s t r i b u b -sous forme d e
t i r E - 8 - p a r t p a r
1'
L n s t i t u t d e r e c h e r c h e en c c m s t r u c t i o n . On p e u t o h t e n i r ilnel i s c e
d e s p u b l f c ~ t i o n s d e L ' I n s t i t u t p o r t s n t s u r
les t e c h n i q ~ ~ e s ou les r e c h e r c h e s e n matizre d e b 3 t i m e n t e n C c r i v a n t
