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Measurement of smoke in large scale fire tests
Fire Safety Journal, 5 (1983) 89 - 102
89
Measurement of Smoke in Large Scale Fire Tests* K. T. PAUL
Rubber and Plastics Research Association of GB, Shawbury, Shrewsbury, Shropshire SY4 4NR (Gt. Britain) (Received July 28, 1982)
SUMMARY
Large scale fire tests involving actual products and prototypes are o f major importance in that they enable the interactions o f various materials, prototypes and design features to be evaluated. The fire regime can be selected to reproduce the anticipated end-use hazard. This paper discusses the various approaches used to measure s m o k e in large scale fire tests, and their requirement and their limitations, as well as correlations between full scale test rigs.
1. INTRODUCTION
Large scale fire tests and fire tests involving actual products and prototypes are of major importance in that they enable the interactions of various materials, components, and design features to be evaluated. The fire regime can be selected to reproduce a likely or anticipated real life situation. For example, prototypes may be ignited with a cigarette, match or by a larger source, often a timber crib, designed to represent a major item such as a chip-pan fire, a fuel heater, an item of furniture, etc. Many items of the contents of buildings are sufficiently small to permit full scale testing and this, coupled with the difficulty of modelling such highly complex designs as upholstered furniture, has led to the suggestion that small scale tests are not needed for such items. However, the cost, in terms of time, manpower and complex facilities acts against this and, in practice, full scale
tests tend to be limited to product developm e n t or type approval tests. By contrast, the more simple constructions such as large surfaces and rooms cannot be tested full scale except in very isolated cases, and fire data are then frequently obtained by a combination of measuring fire properties, e.g., spread of flame, heat release, etc., by standard tests and combining these with mathematical modelling. An important observation arising from full scale or product based smoke tests is that the smoke density is directly related to a number of factors including the materials involved, the rate of burning, and the fire environment. Smoke (and incidentally heat and toxic gases) is directly related to the rate of burning, a fact which is often not apparent from, and frequently overlooked with, small scale standard tests. The measurement of smoke is important because in real life fires, smoke restricts visibility causing people to become trapped when they may then be overcome by heat and toxic gases.
2. MEASUREMENT OF SMOKE
2.1. Theoretical aspects The a m o u n t of smoke produced in a fire is frequently determined by measuring the a m o u n t of light passing through the smoke or as the obscuration of the smoke. These tests may be directly related to the optical density of the smoke using Bouguer's or Beer's Law where T = T O exp(--oL)
*Paper presented at Conference organised by QMC Industrial Research Ltd., and the Fire Research Station, at The Royal Garden Hotel, London, January, 1982. 0379-7112/83/$3.00
where T = light flux transmission, T o = initial light flux, o = attenuation coefficient, L = length of optical path, I -- T = obscuration. © Elsevier Sequoia/Printed in The Netherlands
90 The optical density per unit path length (D) can be obtained by rearranging the above equation to give D =~
1
To log -~-.
The importance of this value (D) is that it can be factored for the purposes of calculation, and it can be related to visibility [1 - 3]. It has been used to define escape paths, etc. In practice, smoke does n o t conform exactly to this relationship but it can be considered to do so for most purposes. Smoke density is not the sole factor affecting visibility, as lacrimatory and irritant effects have a direct influence on limiting visibility and walking speed [ 2, 3 ] while "panic" also plays an important role [3]. Other ways of measuring smoke include light reflection and gravimetric measurements to determine the mass of smoke particles produced. The relationship between obscuration and optical density is given in Fig. 1 which shows that the resolution and accuracy of smoke measurement decreases markedly above a b o u t 8 5 - 90% obscuration. Even with sensitive measuring instruments, the relationship becomes critical at 99% obscuration where even a small error in measurement gives a large error in smoke density (Table 1). 100,
~
9o
of poor re~olution
8O 7O ~o
= 50 4o 3o
2O I0
0'1
0'2 013 014 015 0'6 017 08 Optical density
019 /0
/1
112
Fig. 1. Relationship between percentage obscuration and optical density.
2.2. Data required The density of the smoke produced by a fire depends on a number of factors including the materials involved (design and materials interaction), the rate of burning, and the dilu-
TABLE 1 Relationship between optical density and light transmittance and obscuration Optical density
Transmittance (%)
Obscuration (%)
1 2 3 4 5
10.0 1.0 0.10 0.01 0.001
90.0 99.0 99.9 99.99 99.999
tion of the smoke. Both the rate of burning and the dilution of the smoke can depend on the air supply and, depending on the size of the fire, on the geometry of the test rig. The need to ensure an adequate supply of air is discussed later, but the dilution of the smoke has an important effect on the smoke density measured. A more absolute measure of the smoke produced is to determine the total volume of smoke produced at a specified optical density. This is essentially the parameter measured in the majority of standard smoke tests. It is usual to determine three smoke parameters during full scale tests: (a) smoke density -- which is related to visibility (see refs. 2 and 3); (b) rate of smoke p r o d u c t i o n - which is related to the rate of smoke spread in a building and the escape time; (c) total volume of smoke produced. Both smoke density and the rate of s m o k e production are determined as a function of time and will vary considerably during the fire and with the fire temperature and radiant heat levels [4]. The effect of humidity on smoke production has been calculated [14] for combustion nuclei. An increase in relative humidity from 30% to 90% will increase the particle radius by a factor of 2 for small particles (10 -6 cm), b u t the factor decreases with increasing size. Smoke measurements during fire propagation box tests (BS 476 Pt. 6/BS DD36) led to conclusions that the measured optical density could be increased by from zero to 34% by increasing the relative humidity from 30% to 90% depending on the material tested [15]. In this test, the s m o k e was collected in a large room and was at a relatively low temperature. Measurements of smoke density during large
91
scale tests are usually made at higher temperatures where condensation of water vapour, HC1, etc., are less likely to affect results.
/
/t / /
2.3. Practical considerations In order to determine the smoke produced from an article, it is necessary to burn the article c o m p l e t e l y Thus, to obtain meaningful smoke measurements, the test needs to be carried out with an adequate supply of air (oxygen). It is a relatively simple matter to calculate the oxygen demand of a material based on complete or partial combustion. In practical terms, the actual oxygen demand lies between these two results, but since burning ceases once the oxygen becomes seriously depleted, it is desirable to maintain the oxygen level above 15 - 16%. The theoretical relationship between the size of test chamber and the mass of material needed to deplete the oxygen level to 15% is shown in Fig. 2. When these figures are related to actual products, it will be seen that exceptionally larger rooms are necessary to burn items such as armchairs, storage units, etc. In these cases the smoke density is simply measured, using a vertical light path, as the smoke stratified at ceiling level, Fig. 3(a).
I I
Complete combustion / " J l ( c o ~ H~O) /
I
-C'] CO H20
J
/
/ ' 1 Cellulose
/ / 2
~
/
J
/
~
~
I I
Polyester I Polymethyl methacrylat, EuPVC
'
IPolyure,ho..
, 10
20 30 Volume oF test chamber m3
, 40
Fig. 2. Mass of material needed to deplete o x y g e n to 15% in 35 m 3 r o o m .
(a)
(b) 2.4. Ventilated room corridor facility The alternative is to carry out the fire test in a ventilated room. Many variations exist because these test facilities were often built to individual research requirements, but a typical unit will comprise a room of 20 - 35 cubic metres combined with a corridor about 2 m wide and 15 - 20 m long (Fig. 3(b)). Air flows along the corridor and enters the test room where it is consumed in the fire. The b u o y a n t smoke then passes from the room, along the corridor, and finally to the atmosphere. Alternatively, the test room and corridor may be built inside a hanger or warehouse type of building to minimize the effects of weather (on both test and operators) and of smoke pollution. UK examples of the former rig are the QMC test facility, and of the latter, the FRS rigs at Borehamwood and Cardington [5]. The measurement of smoke with this type of facility involves determining the air flowing into the test room by measuring its velocity and the cross-sectional area of flow. The latter depends on the corridor geometry and on the depth of the escaping smoke layer,
(e) Fig. 3. Measurement of smoke in large scale fire tests. (a) Large r o o m test, s m o k e m e a s u r e m e n t by vertical light path or a series of horizontal systems. Fan dispersed s m o k e is not acceptable because of effect on fire. (b) Ventilated r o o m , air entry and s m o k e exit via corridor. S m o k e m e a s u r e m e n t by angled light/path, and air flow measurements. (e) Modified ventilated r o o m ( R A P R A ) air e n t r y via duet, smoke exit via corridor/after burner (Schematic).
this being determined visually. The density of the escaping smoke and its temperature are determined and the results integrated with respect to time. See Fig. 3(b).
3. SMOKE M E A S U R E M E N T IN R A P R A F U L L SCALE FACILITY
The RAPRA test facility is essentially the same as that described above but because of
92 local building restrictions and its location in a smokeless zone, it was necessary to destroy any smoke produced using an after burner and water curtain system, Fig. 3(c). This prevents the use of the corridor for air supply. The original facility was designed such that the fire room was ventilated directly, but the building of a second chamber and the desirability of burning single products in a typical domestic type situation has led to the supply of air via the second test chamber (Fig. 4). Air now enters the building and passes into the fire room via a duct. This duct, which is of similar width to a domestic doorway, physically separates the incoming air from the outgoing smoke and essentially corresponds to the neutral plane of the open-ended type of rig. The duct contains an anemometer and provides a reasonable measure of air flow into the fire room. The smoke passes above the duct into the corridor and thence to the after burner. The smoke density and temperature are measured in the corridor. In practice vane anemometers tend to be unreliable at very low air speeds, and during the very early stages of a test the smoke is contained in an enclosed environment (100 m 3) and its density is measured using a vertical photocell/lamp system. This is facilitated by layering of the smoke along the upper part of the corridor. As the fire grows
F XDC
D E I
>~
%0
.o
Tesl pfodu(~
i
.
room
Fig. 4. L a y o u t of fire chamber showing furniture and position of temperature, smoke, and gas determining points. A, Thermocouple on ceiling; B, thermocouple on lintel; C, thermocouples positioned on test product; D, smoke measuring apparatus (knee level) horizontal beam; F, smoke measuring apparatus vertical beam; G, toxic gas probe (for CO, CO2, O2, NOx, HCs etc.); H, air flow anemometer; J, crib ignition source; K, afterburner and extractor fan; O, observation room.
the anemometer air flow readings become more reliable and a dynamic smoke measurem e n t is made by a horizontal photocell/lamp system positioned in the smoke path. Airpurged tubes are used to reduce the path length of the smoke measuring system and to increase its sensitivity. In practice, the existence of the two alternative systems as a semipermanent installation offers considerable flexibility for burning tests under dynamic or static conditions and in various sized rigs. 3.1. Measurements o f s m o k e - - a c t u a l measuremen ts In fire tests involving a ventilated fire room, all smoke parameters are calculated from measurements of the following: air inlet velocity; air inlet width and breadth; air inlet temperature; smoke path length; smoke obscuration based on zero deflection, full scale deflection, actual reading of photocell/lamp system. 3.2. S m o k e temperature The air inlet width and breadth and the smoke path length are constant. For the majority of tests, the temperature of the inlet air and the zero- and full scale deflections of the smoke recording equipment are essentially constant. The actual air inlet velocity, the smoke density, and temperature vary during each fire test and are recorded as a function of time using potentiometric recorders. The effect of errors in each measurement can be calculated theoretically by deliberately introducing errors into a single set of experimental data. Typical results are given in Table 2 for the total volume of smoke produced in a small/medium fire test. It can be seen that potentially large errors arise from measurements of the volume of the air entering the fire room, where errors in any one of three measurements have a directly proportional effect on the calculated smoke volume. The importance of accurately determining this figure is obvious if the results are to relate to tests carried out in other facilities or by other methods. Ensuring the smoke path length is constant is also very important, but this is primarily a matter of good equipment design and maintenance. Errors in the actual smoke readings
93 TABLE 2 Significance of potential errors in full scale fire smoke determinations Parameters
Typical value
Induced error
Effect on smoke volume
(%) Air entry Airflow rate
0.14
+50%
+50
0.8
+20%
+20
15
--5
+2
+20% + 40% + 4%
--20 + 0.5 --48
+50 + 100
+14 + 27
(m/s) Air inlet area (m2) Ambient temp.
(°c) Smoke measurement Path l e n g t h ( m ) 2/3 Zero reading 5 Full scale 85 reading Smoke 20 - 300 temperature
(°C)
only become important as the full scale value is approached. To minimize gross errors that can arise in transposing data from recorders to the computer, a limit has been placed in the calculation such that all readings greater than 99.3% are held at that value and the data identified as such. This is because of the relationship between optical density and per cent. obscuration where major errors in optical density result from minor errors in per cent. obscuration (see Fig. 1, Table 1).
3.3. Position of instruments Air enters the fire chamber via a duct approximately 0.9 m square and 2 m long. The air flow profile has been established for a series of steady state flows created with after burner and extraction fans. The velocity profile of air entering the duct is essentially planar but becomes curved as the air passes along the duct, with greater distortion in the upper part of the duct. The position of the anemometer in the duct is important, and it is necessary to use a duct ratio of at least 1 2 lengths:height to obtain a satisfactory measure of air flow. It is usual to record the linear air flow through a duct and calculate the volumetric air flow using an experimental factor reflecting the flow profile in the duct. The
actual factor varies with the air velocity, and with whether the air flow is assumed to be essentially square or circular in section. Calculated factors relating the linear velocity to the volumetric flow rate are 0.54 - 0.76 for square section flow and 0 . 4 6 - 0 . 6 for circular flow. For single product tests a figure of approximately 0.6 may be used. The velocity profile of smoke in the corridor varies with the type of fire and also with the position at which measurements are made. The maximum velocity is, as expected, near the ceiling, and for many fires the velocity is effectively zero below the mid-height position. The velocity profile also varies across the corridor, with smoke from the burn room moving across to the far corridor wall before moving to a more central flow. The optimum position of the smoke measurement position will vary with different fires and the position normally chosen represents a compromise for the medium scale, single product type of test. The position is approximately 5 m from the smoke exit and has a light path length of 2/3 m. The instruments are m o u n t e d outside the corridor and the path length reduced by using air-purged tubes. Typical smoke velocity profiles for medium scale crib tests are shown in Fig. 5. Ceillng~
2/2
1 / 2 ~ 1/3 - - [ Test
Floor
1
0
Test
10 m/s
3
m/s
Ceiling
est
Floor
l
1
3 i
i
10 m/s
10 m/s
i O
i 10
Fig. 5. Typical velocity profiles in corridor. A, Fire chamber end; B, afterburner end; 1, nearside of corridor; 2, centre of corridor; 3, far side of corridor; X, smoke monitoring position horizontal light beam.
94 Smoke densities are measured using a selenium barrier photocell/light path system which produces signals of 200 - 300 mV for zero obscuration and microvolts for optical densities of 5 - 6. The signals are recorded using potentiometric recorders and an upper limit is introduced to avoid gross inaccuracies due to measurement of very small voltages. The upper limit coupled with the short path length limits the m a x i m u m optical density of 4.5 o.d./m. Although certain fires exceed this value, it is n o t a major restriction on the rig. Temperature measurements are made using chromel/alumel thermocouples connected to potentiometric recorders.
3.4. Calculation o f results Recorded data are transcribed to the RAPRA computer and the following data c o m p u t e d and printed. Optical density: OD/m Rate of smoke production: m 3 of OD/m = 1 per min at selected time periods, typical 1/2 min intervals Volume of smoke: m 3 of OD/m = 1 {running total). The c o m p u t e r programme is arranged such that the input data can be varied to suit different sized test rigs and different instrument arrangements, e.g., horizontal or vertical light paths.
3.5. Reproducibility of results The reproducibility of results is given in Table 3 for small to medium scale fires using single materials. The rate of burning of these fires is quite good with coefficients of variance of 8 - 15% of the mean. The coefficients of variance for the smoke data range from 20 - 30% with that of certain tests being as low as 6.5%. When the complications of the smoke measuring process and the size of the test room (34 m 3) and corridor (66 m 3) are considered, the results do not compare unfavourably with those of the standard smoke tests. The effect of different smoke measuring positions has been studied. Within the limits of experimental error and scatter of results, it is surprising that major positional changes have relatively small effects on the results.
4. C O M P A R I S O N O F S M O K E T E S T D A T A
4.1. Large scale test results It has previously been pointed out that full scale fire test facilities differ considerably in their geometry, size, and methods of construction. However, as the recent Home Office technical paper [6] pointed out, it is necessary to be able to correlate the results of large scale tests, and two series of tests have
TABLE 3 R e p r o d u c i b i l i t y o f s m o k e d a t a , large scale t e s t s Parameter
R u b b e r latex f o a m block Mean value Range of values No. of values C o e f f . o f v a r i a n c e (%)
Time to max. OD(min)
Max. optical density (OD/m)
Vol. u p t o max. OD (m 3 )
Vol. ( O D / m = 1) up to OD/m = 2 m 3
T o t a l vol, ( O D / m = 1) ( m 3)
-----
2.10D/m 1.97 - 2.28 5 6.1
16.3 m 3 15,1 - 17.8 4 6.5
45 m 3 30 - 57 4 24
104 m 3 70 - 113 4 26
S i m u l a t e d chair s t a c k - - p o l y p r o p y l e n e Mean value 7.2 Range of values 7 -8 No. of values 5 C o e f f . o f v a r i a n c e (%) 6.2
0.94 OD/m 0.7 - 1.3 m 5 23.5
S i m u l a t e d chair s t a c k - - cellulosic boards Mean value 6.7 Range of values 6 - 7.5 No. of values 6.8 C o e f f . o f v a r i a n c e (%) 10.8
0.23 OD/m 0.2 - 0 . 2 5 3 15.7
93 m 3
54 - 118 5 29.8
m
-
-
4
22 m 3 19 - 25 3 19.3
95 b e e n carried o u t to c o m p a r e results f r o m R A P R A a n d F R S t e s t rigs. T h e c u r r e n t c o n cern over u p h o l s t e r e d f u r n i t u r e is directly r e f l e c t e d in t h e R A P R A p r o g r a m m e a n d in r u n n i n g o f t h e following tests. T h e first c o m p a r i s o n involved h a l f scale tests [7] w i t h the BS D D 58 f u r n i t u r e rig [8]. T h e m a j o r d i f f e r e n c e s which existed b e t w e e n t h e t e s t rigs f o r these tests a n d f o r a later series o f full scale m o c k - u p u p h o l s t e r e d chairs is s h o w n in T a b l e 4. D a t a f o r the full scale F R S b u r n s are r e p o r t e d in B R E CP 3 0 / 7 8 [9] a n d in all tests, the s p e c i m e n was ignited b y a No. 7 crib t o BS D D 58. A c o m p a r i s o n o f d a t a o b t a i n e d f o r t h e halfscale tests s h o w s t h a t m a x i m u m s m o k e densities r e c o r d e d at R A P R A are l o w e r t h a n t h o s e o f F R S , w h e r e a s the t o t a l v o l u m e o f s m o k e is greater. T h e v e r y great d i f f e r e n c e s b e t w e e n t h e t e s t rigs, especially in t h e m a t e r i a l s o f c o n s t r u c t i o n (which significantly a f f e c t s fire
TABLE 4 Comparison of full and half-scale fire test
facilities
Parameter
Half scale
Units
t e m p e r a t u r e s ) , o f v e n t i l a t i o n (which a f f e c t s b u r n r a t e , s m o k e d i l u t i o n ) and, p e r h a p s , most important, the destruction of smoke by burning, m a d e direct c o m p a r i s o n o f t h e results u n l i k e l y , b u t t h e c o r r e l a t i o n s s h o w n in Fig. 6(a), (b), (c) are n o t as p o o r as t h e y c o u l d be, P e r h a p s b e c a u s e o f t h e greater similarity in materials o f c o n s t r u c t i o n and g e o m e t r y , b e t t e r c o r r e l a t i o n is o b t a i n e d w i t h the full scale tests (Fig. 7). In this case, p e a k t e m p e r a tures a n d t i m e to p e a k t e m p e r a t u r e s are similar, indicating m o r e c o n s t a n t fire c o n ditions. T h e d i f f e r e n t s m o k e m e a s u r i n g positions and techniques and ventilation a i r / s m o k e m i x i n g w o u l d indicate t h e likely cause o f t h e a b s o l u t e d i f f e r e n c e s in s m o k e d e n s i t y a n d v o l u m e . T h e a p p r o x i m a t e straight line r e l a t i o n s h i p b e t w e e n the results f r o m t h e t w o t e s t rigs at least f o r m s t h e basis f o r c o m parisons a n d f o r f u t u r e investigations.
Full scale
RAPRA
FRS
RAPRA
FRS
Fire room width depth height
m m m
0.9 0.9 0.9/1.2
0.94 0.92 0.92
4.5 3.0 2.4
3.0 3.0 2.4
Corridor width length height
m m m
0.9 0.9 0.9
0.45 5.96 0.92
1.8 15.0 2.4
1.3 12.6 2.4
Smoke exit width height
m m
0.9 0.2
0.92 0.23
0.9 2.4
0.6 2.4
corridor
corridor
corridor
Air entry Air entry width height
m m
chamber top Duct 0.9 0.9
corridor 0.23 0.92
duct afterburner 0.9 0.9
corridor 1.3 2.4
Materials of construction
--
sheet
denoted
metal
concrete
brickwalls reinforced concrete ceiling
reinforced concrete
smoke
corridor
corridor
corridor
corridor
corridor
corridor
corridor
duct
corridor
Smoke exit
Position of measurement Smoke temp.
--
exit
Smoke
density
--
smoke exit
Air entry Flow rate
--
duct
96
OD/m
(a)
I 2
I
i 3
i 4
i 5
L 6
(b)
i OD/m
.........
I d ......
600
/ 50O
/ / /
E
// O
//
% v % 3oo
/ ,/
E
• 200
100
/f /
/ 20
/
•
40'
60 '
80 '
1O0 '
FRS
'
-
'
Toto~ smokq volume m
of O 0 / m
R 1
(e)
.J
20
~15 2
o ~i0 E I
i
L
L
5
10
15
.
20
Temperature
i
,
25
30
i
35
,
40
~ndex FRS
Fig. 6. (a) M a x i m u m s m o k e d e n s i t y ; ( b ) t o t a l s m o k e v o l u m e m 3 o f O D / m = 1 ; (c) t e m p e r a t u r e i n d e x [7 ].
4.2. Dynamic and static s m o k e measurements, large scale tests In small, standard smoke tests, the smoke density is frequently measured after the smoke has been stored and distributed around the test chamber, i.e., a static system. Whereas,
large scale tests usually determine the smoke as it is produced using a dynamic system. A recent paper [9] discusses the use of static and dynamic small scale smoke tests and shows that for PVC compounds and for polyacrylonitrile, a significant difference occurs between unaged and aged smoke at high temperatures. This is because the latter permits deposition and condensation of smoke particles, aerosols, and vapours as the smoke cools. To assess this effect, which is obviously important when comparing the results of full scale tests with those of half-scale standard tests a series of tests were carried out using a half-scale rig, similar to that used in full scale tests, but with a similar sized entry. Smoke from the fire passed from the rig exit and was quantified using the procedures described above. The smoke was then collected in an enclosed chamber of 100 m ~ volume and determined using a vertical light path. Two series of upholstered cushions were burned. The first series was ignited with a small gas flame and the second series with a 126 g wooden crib. The fire load was typically 6800 Kcal. Results for a series of half-scale upholstered chair tests {using a BS DD 58 rig) are shown in Fig. 8. Assuming an air flow entry correction factor of 0.6 (see above), the ratio between the volume of smoke determined by the static accumulation and the dynamic flow methods is about 1:2.8. This figure is similar to that reported for static and dynamic flow measurements in bench scale tests for PVC (9 compounds) and polyacrylonitrite. The range of figures quoted for tests at 750 °C is 1:2.5 1:6, but most values typically lie between 1:3.5 and 1:4.5. Figures quoted for low temperature (470 °C) smoke tests are 1:0.75 1:1.1 [10]. Another important factor is that the dynamic results are expressed as the volume of smoke leaving the test chamber and wilt depend directly on the smoke and fire temperature which will vary continuously throughout the fire test. An alternative m e t h o d which is not generally used would be to normalize the smoke volume to a specific temperature, e.g. STP. The smoke volume ratios referred to above for the bench tests reduce to 1:1.75 - 1:4.5 for the overall range
97
M a x OD 3
./ / / / 500
/ / /
400
/
Max smoke density OO/m
•
II
/
a 0
/
300
"'6
/
E
2OO
/ / /
tO0
/
I 1O0
/
I 200
Totol volume of smoke m3 of O D / m = 1
/ Max
(a)
I 1 optical density FRS
(b) OD/m
Comparison of full scale fire test data
300
/
/
2
/ / / / E
/ / ~0
/ /
100
./. / / I 10
I 20
I 100
Time mins FRS
(c)
I 200 FRS Temp °C
i 300
(d)
Fig. 7. (a) Maximum smoke density; (b) total volume of smoke; (c) time to maximum temperature; (d) maximum fire temperature.
and 1 : 2 . 5 - 1:3.25 for the central portion when the temperature correction is applied to reduce all values to 470 °C. These figures suggest that there was a major reduction of smoke due to ageing, the static measurement being carried out at the end of the test {i.e., 15 - 20 min after the fire was controlled). There were also small leaks of smoke through the sampling holes but these were unlikely
to have affected the final smoke volume significantly.
4.3. Comparison of products A comparison of the smoke produced and the effect of the composition of upholstered composites is shown in Table 5. When considering the results of actual product tests, it is important to realize that
98 t h e y can be directly a f f e c t e d b y the experim e n t a l c o n d i t i o n s . T h e e f f e c t o f air flow has already been discussed. T h e ignition s o u r c e used can directly a f f e c t t h e m a n n e r in w h i c h a p r o d u c t b u r n s and, c o n s e q u e n t l y , the rate at w h i c h s m o k e is prod u c e d . Where a m a j o r d i f f e r e n c e exists, e.g., flaming or s m o u l d e r i n g f o l l o w e d b y flaming,
1O0 E%.-~E
g~E Eo~ EO "~- ~ O x
x
o
o
517 tch i g m h o n ~ource ,~
10
~
I O0
Dynamic measurement
0
I 200
Crlb i g n i t i o n source
i 300
V o l u m e of smoke of O D / m
I 400 =
500 1, m3
Fig. 8. Correlation of static and d y n a m i c determinations of volume of smoke produced by burning u p h o l s t e r e d p o l y e t h e r foam cushions.
the t o t a l a m o u n t o f s m o k e p r o d u c e d can be very different, see Fig. 9. With h i g h l y - c o m p l e x p r o d u c t s such as u p h o l s t e r e d f u r n i t u r e , the rate of s m o k e prod u c t i o n can be significantly altered by changing t h e p o i n t o f ignition, even t h o u g h a c o n s t a n t ignition s o u r c e m a y be used. The total v o l u m e o f s m o k e m a y n o t be altered. S t a n d a r d s m o k e test data (NBS test) o f t w o wall signs i n d i c a t e d t h a t a s t a n d a r d grade o f polyester/glass l a m i n a t e w o u l d be e x p e c t e d to p r o d u c e less, or at least as m u c h , s m o k e as the fire r e t a r d e d equivalent. The a n t i c i p a t e d fire scenario c o m p r i s e d a large rubbish fire. Full scale tests were carried o u t using a 14 kg t i m b e r crib to simulate a large b u r n i n g rubbish fire. The signs were fixed t o brick walls as i n t e n d e d in the p r o t o t y p e installation a n d the " r u b b i s h " p l a c e d b e n e a t h the sign. In the resulting fires the s m o k e levels p r o d u c e d b y the fire-retarded sign were very m u c h less t h a n t h o s e f r o m the s t a n d a r d sign. This difference was entirely due to the relatively small a m o u n t t h a t the fire r e t a r d e d sign b u r n e d (9% as against 44% f o r the s t a n d a r d sign) (Table 6) [ 1 0 ] .
TABLE 5 Comparison of upholstered composites BS DD 58 rig No. 5 crib ignition Material
Ignitability*
Max. temp.
(°C)
1 2 3 4 5 6
Acrylic/cotton/SPE Polypropylene/SPE Viscose/SPE Wool/SPE Wool/cotton wad/SPE PVC/cotton/SPE
1P 1P 1P 2P 3/4P 6P
Viscose fabric, with alternative fillings 7 SPE foam 1F 8 FR PE foam 1F 9 H R P E foam*** 1P 10 Polyester fibre 1P 11 Latex foam*** 1F 12 Cotton wad/SPE 1F 13 FR cotton int/SPE 1F
Time to max. temp. (min)
Max. smoke (OD/m)
Time to max. smoke (rain)
Vol. smoke m 3 of OD/m = 1
Initial** mass of sample (kg)
180 283 190 125 38 280
4 3 8 4 3.5 9
0.7 0.9 0.3 0.4 0.1 1.9
4 2.5 8.5 6.5 3.5 15
307 114 71 132 4 500
1.2 1.1 1.1 1.1 1.5 1.4
190 172 170 250 170 324 280
8 8 7 4.5 12 11.5 6.5
0.3 0.5 0.3 1.2 > 1.3 1.1 0.3
8.5 11 9 3.5 10 10.5 6.5
71 141 56 177 > 300 314 75
1.1 1.5 1.5 2.0 3.1 1.5 1.2
* T o BS D D 5 8 . * * A m o u n t burned in test was approx. 8 0 - 90% o f initial mass. ***Estimated. P, Pass cigarette test. F, Fail cigarette test.
99 The importance of this comparison is that the way a product burns can directly affect the smoke measurements made and the smoke hazard generated. The limitation of these
results is that they refer to the test conditions, i.e., a simulated rubbish fire, and do not show what could occur in another fire scenario, e.g., a major fire could destroy each type of sign.
IJ
o 0
E
0 O. 0
E
2
4
6
8
10
12
14
1~
18
Time
mins Specimen Acrylic velour Polyether foam Acrylic velour Polyether foam
Ignition source Small flame
Mode of combustion Flame
Total vol. m 3 184
No. 7 c r i b
Flame
177
Smoulder flame
188
Flame
70
Cotton velour. Small wadding polyether flame foam Cotton velour. No. 7crib wadding polyether foam
Fig. 9. E f f e c t o f using d i f f e r e n t i g n i t i o n sources o n
smoke p r o d u c t i o n of u p h o l s t e r e d c o m p o s i t e s .
4.4. Correlation of full scale and standard smoke test data The correlation of smoke procedures from full scales fires with the results of standard tests is important, as smoke tests are used to quantify the smoke producing properties of materials, and thence to control the use of materials. Fire research work at RAPRA has involved a number of "full scale" tests and the results of these tests are being correlated with the results of standard smoke tests in order to provide an improved basis for test selection and application. The correlation of the smoke produced from simulated chair stack tests (see R A P R A work on the role of softening in fire growth [10]) shows that the results of the XP2 test may be used to indicate high and low smoke producing materials but that the correlation is uncertain for intermediate measurements. The rate of smoke generation during the stack tests was directly related to the rate of fire growth (and thence to the softening point of the material) and could not be predicted from the XP2 test results (Table 7).
TABLE 6 C o m p a r i s o n of s m o k e p r o d u c e d f r o m G R P signs
Parameter
S t a n d a r d grade
Fire retarded grade
690 625
L a b o r a t o r y tests Smoke density Flaming ASTM E 6 6 2 Non-Flaming
(Din) (Dm)
630 435
Max. c a r b o n m o n o x i d e c o n c n .
(ppm)*
3000 - 4000
3000 - 4000
Max. c a r b o n d i o x i d e c o n c n .
(ppm)*
5000 - 9000
6000 - 8000
Max. h y d r o g e n c h l o r i d e c o n c n .
(ppm)*
0
94
Full scale t e s t Max. ceiling t e m p Max. s m o k e d e n s i t y Typical s m o k e d e n s i t y 1 - 10 rain Max. c a r b o n m o n o x i d e Max. c a r b o n d i o x i d e Max. h y d r o g e n c h l o r i d e
(°C) (OD/m) (OD/m) (ppm) (ppm) (ppm)
800 >3.0 > 3.0 500 15 0 0 0 0
460 0.75 0.3 - 0.6 250 13 0 0 0 6
44%
9%
14 k g w o o d crib source
Weight loss * C a l c u l a t e d f r o m b e n c h test d a t a for 35 m 3 r o o m .
100 TABLE 7 Correlation of XP2 smoke test results with results of full scale simulated chair stack tests Material
XP2 Test**
Full scale simulated
Chair stack
Max. OD (OD/m)
Total vol. (m 3) 0D/m = I
0.9 0.47 1.0 0.03 0.01 0.1 0.3 0.1 0.1 0.03 0.1
0.077 0.04 0.085 0.003 0.001 0.009 0.03 0.009 0.009 0.003 0.009
0.95 0.82 0.75 0.7 0.6 0.3 0.47 0.35 0.2 0.45 0.5
87 68 63 91 110 43 29 26 22 57 96
2.9 2.9 1.6 1.8 1.5 2.9
0.25 0.25 0.14 0.15 0.13 0.25
2.2 4.5 3.3 1.9 4.5 4.5
]07 590 265 1100 > 500
4.2 9.8"* 8.9** 9.8** 6.2 4.5 9.8** 8.2**
0.36 0.83 0.76 0.83 0.53 0.38 0.83 0.70
>4.5 >4.5 >4.5 >4.5 >4.5 >4.5 >4.5 >4.5
1100 > 400 >475 > 400 >450 > 400 > 400 :>210
Max. OD/m
Total smoke vol. (m '~) OD/m = !
L o w s m o k e levels* O D / m < 1.0
Polypropylene Polypropylene/glass spheres Polypropylene/glass laminate Polypropylene/CaCO3 Polypropylene/MgCO3 Polypropylene/hydrated alumina Polyethylene Acrylic (PMMA) Hardboard Plywood (6 mm) Plywood (12 mm)
M e d i u m s m o k e levels* O D / m > 1.0 < 3.5
Cellulose acetate Polypropylene FR Polypropylene FR Polypropylene FR Polypropylene FR PPO modified
V2 (1) V2 (2) filled (1) filled (2)
High s m o k e levels* O D / m > 3.5
Polycarbonate uPVC Polystyrene (HI) ABS Polypropylene FR VO Polypropylene FR asbestos GRP (Std) GRP FR (Class BS 476 Pt. 7)
*XP2 Test, method based on ASTM D2843. **Specimen size 25 x 25 × 3 mm.
Correlations b e t w e e n the XP2 tests a n d smoke measurements of upholstered composites s h o w p r o m i s e and w o r k is c o n t i n u i n g o n this topic. F u t u r e w o r k will include correlations b e t w e e n the NBS s m o k e test, M e t h o d A S T M E 6 6 2 a n d N E S 7 1 1 a n d full scale fire test data. It is i n t e n d e d to include results f r o m the ISO (Munich) a n d A r a p a h o e tests at a f u t u r e date.
5. FULL SCALE STANDARDIZED SMOKE TESTS It has already been p o i n t e d o u t t h a t standard full scale fire tests are relatively rare a n d are usually o n l y carried o u t f o r p r o d u c t d e v e l o p m e n t , c o m p a r i s o n , or t y p e approval
purposes. Perhaps the best k n o w n full scale s t a n d a r d tests are t h o s e issued by D O E / P S A . These were originally issued in 1 9 7 5 a n d have been progressively d e v e l o p e d a n d e x t e n d e d to provide a c o m p r e h e n s i v e range o f test and c o n t r o l p r o c e d u r e s . The full scale tests include: D O E / P S A F R 5 f o r mattresses and b e d d i n g D O E / P S A F R 6 f o r seating DOE/PSA FR7 for curtaining D O E / P S A F R 1 4 f o r archival a n d o t h e r containers a n d f o r carcase f u r n i t u r e in general. T h e tests are primarily ignition tests a n d require resistance t o specified sources (listed in D O E / P S A F R 1 0 ) . Ignition tests are f o l l o w e d b y b u r n i n g tests in w h i c h t e m p e r a t u r e / t i m e , smoke density/time and carbon monoxide/
1 0 1
time curves are determined (DOE PSA FR6). The following information (Table 8) is also tabulated. The tests are carried out in a room of greater than 30 m 3 (see Fig. 10) [12]. TABLE 8 DOE/PSA FR6 sample data Ignition source Temperature of smoke °C at min M a x . t e m p e r a t u r e - - °C at - - m i n Volume of smoke/m 3 at -- min Total volume of smoke -- m 3 O p t i c a l d e n s i t y - - O D m - 1 at - - m i n R a d i a n t h e a t at - - m i n shall n o t e x c e e d - - W - -
- -
• Q J
- -
Ternperature D
Smoke density Carbon monoxide
~
Fig. 10. F u l l scale c h a i r
E..~e'l I ,
test,
,
/ /
DOE PSA FR6.
6, C O N C L U S I O N S
Full scale fire tests permit the burning characteristics of products and prototypes to be determined under likely or specified fire conditions. The results of such tests enable the complex interactions of material combinations, design features and environmental factors to be determined. The results of such tests can frequently be affected by the experimental conditions, and great care must be exercised when making comparisons. Smoke, the subject of this paper, is a direct consequence of less than complete combustion and is affected by many factors including the materials burned, the rate of burning, ventilation, etc. These facts are obvious from full scale smoke/fire tests b u t tend to be overlooked when standard test data are considered. For this reason it is necessary to consider smoke density and its rate of formation as a function of time and to be aware
that these are directly related to ignition (without which there can be no fire) and to the rate of combustion. Recently the BSI has published DD64, Guidelines for the Development and Presentation of Fire Tests and for their use in Hazard Assessment [13]. This is essentially a philosophy intended to assist specification writers, regulatory bodies, designers and architects, manufacturers and fabrication, wholesalers and retailers, consumer advice services, and educational bodies. The following summarises the considerations of DD64 which should be given to assessing and controlling fire hazards when specifications or codes of practice are being prepared. (a) In consultation with fire experts, assess the actual or potential fire hazards in the use of the material, product, structure or system. (b) Appraise the levels of fire hazard acceptability in the end use of material, product, structure or system, and the scope for controlling fire hazards. (c) Identify the critical factors which need to be controlled, in terms of ignition hazard and fire growth hazard. (d) Develop fire tests capable of providing information which will assist in the assessment of fire hazard in terms of the hazardous properties of one or more aspects of fire. (e) Clearly state, in specifications, codes of practice, fire test methods, and fire test reports, any limitations in the use of fire tests to assess or control potential fire hazard. (f) Recognise that the results of fire tests can never guarantee fire safety. The assessment of actual or potential fire hazards and the appraisal of the levels of fire hazard acceptability are obviously extremely complex processes and must involve environmental and human factors as well as the actual ignition and burning characteristics of products. It is not proposed to deal with the environmental and human factors in detail but merely to point out that even for a single item or product, the hazard may vary as it m a y be placed in the open, in the upper stories of a high rise building, in a hospital, in a prison, underground, in an aircraft, etc. Similarly, it will vary with the mobility, background training and discipline of personnel, and with the availability of fire preventive measures such as sprinklers, proximity of fire
102
fighting services, etc. The effects of possible fires should be considered with relation to life and property. All these and many more factors will need to be considered in the assessment of fire hazard and risk.
LIST OF SYMBOLS
T To L I--T D
Light flux transmission Initial light flux Alternation coefficient Length of optical path Obscuration Optical density per unit path length NB: These are given in the text.
REFERENCES 1 D. J. Rasbash, Smoke and toxic products produced at fires, Plast. Inst. Trans. J., Jan., (1967) Conference supplement No. 2, pp. 55 - 61. 2 T. Jin, Visibility through fires, J. Fire Flammability, 9 (1978) 135. 3 T. Jin, Studies of emotional instability in smoke in fires, J. Fire Flammability, 12 (1981) 130 142. 4 P. G. Edgerley and K. Pettett, Effect of pyrolysis and combustion temperatures on smoke density, European Conf. on Flammability and Fire, Brussels, 1977.
5 S. A. Ames, An automated system for the examination of experimental Compartment fires, CP7/79, Building Research Establishment, Borehamwood. 6 Report o f the Technical Sub-Committee on the Fire Risks o f New Materials, Home Office, Fire Department, London, 1978. 7 S. A. Ames and P. J. Fondell, A study of the flammability of bulk solids and their smoke production in fires in a small compartment, BRE, CP3/80, Building Research Establishment, Borehamwood. 8 S. A. Ames, Personal communication, BRE, Fire Research Station. 9 W. D. Wooley, S. A. Ames, A. I. Pitt and K: Buckland, The ignition and burning characteristics of fabric covered foam, BRE CP 30/78, Building Research Establishment, Borehamwood. 10 A. Ballistrevi, G. Montando, C. Puglisi, E. Scamporrino and D. Vitalini, Smoke dilution methods for evaluation of the smoke emission from burning polymers: a comparative approach, Fire Mater., 5 (2) (1981) 61 - 65. 11 K . T . Paul, Demonstration of the effect of softening and fire resistance of materials on burning characteristics, Fire Mater., 4 (2) (1980) 83 - 86. 12 Department o f Environment/Property Services Agency, Fire Retardant Specifications No. 5. 6. 7, I0 and 14. 13 BS DD64, Guidelines for the Development and Presentation of Fire Tests and their use in Hazard Assessment, British Standards Institution, London. 14 H. L. Wright, Atmospheric opacity, QJ R. Met. Soc., 65 (281) (1939) 411 - 442. 15 P. C. Bowes, P. Field and G. Ramachaudran, Assessment of smoke production by building materials in fires, BRE Fire Research Note No 775, October, 1969.
89
Measurement of Smoke in Large Scale Fire Tests* K. T. PAUL
Rubber and Plastics Research Association of GB, Shawbury, Shrewsbury, Shropshire SY4 4NR (Gt. Britain) (Received July 28, 1982)
SUMMARY
Large scale fire tests involving actual products and prototypes are o f major importance in that they enable the interactions o f various materials, prototypes and design features to be evaluated. The fire regime can be selected to reproduce the anticipated end-use hazard. This paper discusses the various approaches used to measure s m o k e in large scale fire tests, and their requirement and their limitations, as well as correlations between full scale test rigs.
1. INTRODUCTION
Large scale fire tests and fire tests involving actual products and prototypes are of major importance in that they enable the interactions of various materials, components, and design features to be evaluated. The fire regime can be selected to reproduce a likely or anticipated real life situation. For example, prototypes may be ignited with a cigarette, match or by a larger source, often a timber crib, designed to represent a major item such as a chip-pan fire, a fuel heater, an item of furniture, etc. Many items of the contents of buildings are sufficiently small to permit full scale testing and this, coupled with the difficulty of modelling such highly complex designs as upholstered furniture, has led to the suggestion that small scale tests are not needed for such items. However, the cost, in terms of time, manpower and complex facilities acts against this and, in practice, full scale
tests tend to be limited to product developm e n t or type approval tests. By contrast, the more simple constructions such as large surfaces and rooms cannot be tested full scale except in very isolated cases, and fire data are then frequently obtained by a combination of measuring fire properties, e.g., spread of flame, heat release, etc., by standard tests and combining these with mathematical modelling. An important observation arising from full scale or product based smoke tests is that the smoke density is directly related to a number of factors including the materials involved, the rate of burning, and the fire environment. Smoke (and incidentally heat and toxic gases) is directly related to the rate of burning, a fact which is often not apparent from, and frequently overlooked with, small scale standard tests. The measurement of smoke is important because in real life fires, smoke restricts visibility causing people to become trapped when they may then be overcome by heat and toxic gases.
2. MEASUREMENT OF SMOKE
2.1. Theoretical aspects The a m o u n t of smoke produced in a fire is frequently determined by measuring the a m o u n t of light passing through the smoke or as the obscuration of the smoke. These tests may be directly related to the optical density of the smoke using Bouguer's or Beer's Law where T = T O exp(--oL)
*Paper presented at Conference organised by QMC Industrial Research Ltd., and the Fire Research Station, at The Royal Garden Hotel, London, January, 1982. 0379-7112/83/$3.00
where T = light flux transmission, T o = initial light flux, o = attenuation coefficient, L = length of optical path, I -- T = obscuration. © Elsevier Sequoia/Printed in The Netherlands
90 The optical density per unit path length (D) can be obtained by rearranging the above equation to give D =~
1
To log -~-.
The importance of this value (D) is that it can be factored for the purposes of calculation, and it can be related to visibility [1 - 3]. It has been used to define escape paths, etc. In practice, smoke does n o t conform exactly to this relationship but it can be considered to do so for most purposes. Smoke density is not the sole factor affecting visibility, as lacrimatory and irritant effects have a direct influence on limiting visibility and walking speed [ 2, 3 ] while "panic" also plays an important role [3]. Other ways of measuring smoke include light reflection and gravimetric measurements to determine the mass of smoke particles produced. The relationship between obscuration and optical density is given in Fig. 1 which shows that the resolution and accuracy of smoke measurement decreases markedly above a b o u t 8 5 - 90% obscuration. Even with sensitive measuring instruments, the relationship becomes critical at 99% obscuration where even a small error in measurement gives a large error in smoke density (Table 1). 100,
~
9o
of poor re~olution
8O 7O ~o
= 50 4o 3o
2O I0
0'1
0'2 013 014 015 0'6 017 08 Optical density
019 /0
/1
112
Fig. 1. Relationship between percentage obscuration and optical density.
2.2. Data required The density of the smoke produced by a fire depends on a number of factors including the materials involved (design and materials interaction), the rate of burning, and the dilu-
TABLE 1 Relationship between optical density and light transmittance and obscuration Optical density
Transmittance (%)
Obscuration (%)
1 2 3 4 5
10.0 1.0 0.10 0.01 0.001
90.0 99.0 99.9 99.99 99.999
tion of the smoke. Both the rate of burning and the dilution of the smoke can depend on the air supply and, depending on the size of the fire, on the geometry of the test rig. The need to ensure an adequate supply of air is discussed later, but the dilution of the smoke has an important effect on the smoke density measured. A more absolute measure of the smoke produced is to determine the total volume of smoke produced at a specified optical density. This is essentially the parameter measured in the majority of standard smoke tests. It is usual to determine three smoke parameters during full scale tests: (a) smoke density -- which is related to visibility (see refs. 2 and 3); (b) rate of smoke p r o d u c t i o n - which is related to the rate of smoke spread in a building and the escape time; (c) total volume of smoke produced. Both smoke density and the rate of s m o k e production are determined as a function of time and will vary considerably during the fire and with the fire temperature and radiant heat levels [4]. The effect of humidity on smoke production has been calculated [14] for combustion nuclei. An increase in relative humidity from 30% to 90% will increase the particle radius by a factor of 2 for small particles (10 -6 cm), b u t the factor decreases with increasing size. Smoke measurements during fire propagation box tests (BS 476 Pt. 6/BS DD36) led to conclusions that the measured optical density could be increased by from zero to 34% by increasing the relative humidity from 30% to 90% depending on the material tested [15]. In this test, the s m o k e was collected in a large room and was at a relatively low temperature. Measurements of smoke density during large
91
scale tests are usually made at higher temperatures where condensation of water vapour, HC1, etc., are less likely to affect results.
/
/t / /
2.3. Practical considerations In order to determine the smoke produced from an article, it is necessary to burn the article c o m p l e t e l y Thus, to obtain meaningful smoke measurements, the test needs to be carried out with an adequate supply of air (oxygen). It is a relatively simple matter to calculate the oxygen demand of a material based on complete or partial combustion. In practical terms, the actual oxygen demand lies between these two results, but since burning ceases once the oxygen becomes seriously depleted, it is desirable to maintain the oxygen level above 15 - 16%. The theoretical relationship between the size of test chamber and the mass of material needed to deplete the oxygen level to 15% is shown in Fig. 2. When these figures are related to actual products, it will be seen that exceptionally larger rooms are necessary to burn items such as armchairs, storage units, etc. In these cases the smoke density is simply measured, using a vertical light path, as the smoke stratified at ceiling level, Fig. 3(a).
I I
Complete combustion / " J l ( c o ~ H~O) /
I
-C'] CO H20
J
/
/ ' 1 Cellulose
/ / 2
~
/
J
/
~
~
I I
Polyester I Polymethyl methacrylat, EuPVC
'
IPolyure,ho..
, 10
20 30 Volume oF test chamber m3
, 40
Fig. 2. Mass of material needed to deplete o x y g e n to 15% in 35 m 3 r o o m .
(a)
(b) 2.4. Ventilated room corridor facility The alternative is to carry out the fire test in a ventilated room. Many variations exist because these test facilities were often built to individual research requirements, but a typical unit will comprise a room of 20 - 35 cubic metres combined with a corridor about 2 m wide and 15 - 20 m long (Fig. 3(b)). Air flows along the corridor and enters the test room where it is consumed in the fire. The b u o y a n t smoke then passes from the room, along the corridor, and finally to the atmosphere. Alternatively, the test room and corridor may be built inside a hanger or warehouse type of building to minimize the effects of weather (on both test and operators) and of smoke pollution. UK examples of the former rig are the QMC test facility, and of the latter, the FRS rigs at Borehamwood and Cardington [5]. The measurement of smoke with this type of facility involves determining the air flowing into the test room by measuring its velocity and the cross-sectional area of flow. The latter depends on the corridor geometry and on the depth of the escaping smoke layer,
(e) Fig. 3. Measurement of smoke in large scale fire tests. (a) Large r o o m test, s m o k e m e a s u r e m e n t by vertical light path or a series of horizontal systems. Fan dispersed s m o k e is not acceptable because of effect on fire. (b) Ventilated r o o m , air entry and s m o k e exit via corridor. S m o k e m e a s u r e m e n t by angled light/path, and air flow measurements. (e) Modified ventilated r o o m ( R A P R A ) air e n t r y via duet, smoke exit via corridor/after burner (Schematic).
this being determined visually. The density of the escaping smoke and its temperature are determined and the results integrated with respect to time. See Fig. 3(b).
3. SMOKE M E A S U R E M E N T IN R A P R A F U L L SCALE FACILITY
The RAPRA test facility is essentially the same as that described above but because of
92 local building restrictions and its location in a smokeless zone, it was necessary to destroy any smoke produced using an after burner and water curtain system, Fig. 3(c). This prevents the use of the corridor for air supply. The original facility was designed such that the fire room was ventilated directly, but the building of a second chamber and the desirability of burning single products in a typical domestic type situation has led to the supply of air via the second test chamber (Fig. 4). Air now enters the building and passes into the fire room via a duct. This duct, which is of similar width to a domestic doorway, physically separates the incoming air from the outgoing smoke and essentially corresponds to the neutral plane of the open-ended type of rig. The duct contains an anemometer and provides a reasonable measure of air flow into the fire room. The smoke passes above the duct into the corridor and thence to the after burner. The smoke density and temperature are measured in the corridor. In practice vane anemometers tend to be unreliable at very low air speeds, and during the very early stages of a test the smoke is contained in an enclosed environment (100 m 3) and its density is measured using a vertical photocell/lamp system. This is facilitated by layering of the smoke along the upper part of the corridor. As the fire grows
F XDC
D E I
>~
%0
.o
Tesl pfodu(~
i
.
room
Fig. 4. L a y o u t of fire chamber showing furniture and position of temperature, smoke, and gas determining points. A, Thermocouple on ceiling; B, thermocouple on lintel; C, thermocouples positioned on test product; D, smoke measuring apparatus (knee level) horizontal beam; F, smoke measuring apparatus vertical beam; G, toxic gas probe (for CO, CO2, O2, NOx, HCs etc.); H, air flow anemometer; J, crib ignition source; K, afterburner and extractor fan; O, observation room.
the anemometer air flow readings become more reliable and a dynamic smoke measurem e n t is made by a horizontal photocell/lamp system positioned in the smoke path. Airpurged tubes are used to reduce the path length of the smoke measuring system and to increase its sensitivity. In practice, the existence of the two alternative systems as a semipermanent installation offers considerable flexibility for burning tests under dynamic or static conditions and in various sized rigs. 3.1. Measurements o f s m o k e - - a c t u a l measuremen ts In fire tests involving a ventilated fire room, all smoke parameters are calculated from measurements of the following: air inlet velocity; air inlet width and breadth; air inlet temperature; smoke path length; smoke obscuration based on zero deflection, full scale deflection, actual reading of photocell/lamp system. 3.2. S m o k e temperature The air inlet width and breadth and the smoke path length are constant. For the majority of tests, the temperature of the inlet air and the zero- and full scale deflections of the smoke recording equipment are essentially constant. The actual air inlet velocity, the smoke density, and temperature vary during each fire test and are recorded as a function of time using potentiometric recorders. The effect of errors in each measurement can be calculated theoretically by deliberately introducing errors into a single set of experimental data. Typical results are given in Table 2 for the total volume of smoke produced in a small/medium fire test. It can be seen that potentially large errors arise from measurements of the volume of the air entering the fire room, where errors in any one of three measurements have a directly proportional effect on the calculated smoke volume. The importance of accurately determining this figure is obvious if the results are to relate to tests carried out in other facilities or by other methods. Ensuring the smoke path length is constant is also very important, but this is primarily a matter of good equipment design and maintenance. Errors in the actual smoke readings
93 TABLE 2 Significance of potential errors in full scale fire smoke determinations Parameters
Typical value
Induced error
Effect on smoke volume
(%) Air entry Airflow rate
0.14
+50%
+50
0.8
+20%
+20
15
--5
+2
+20% + 40% + 4%
--20 + 0.5 --48
+50 + 100
+14 + 27
(m/s) Air inlet area (m2) Ambient temp.
(°c) Smoke measurement Path l e n g t h ( m ) 2/3 Zero reading 5 Full scale 85 reading Smoke 20 - 300 temperature
(°C)
only become important as the full scale value is approached. To minimize gross errors that can arise in transposing data from recorders to the computer, a limit has been placed in the calculation such that all readings greater than 99.3% are held at that value and the data identified as such. This is because of the relationship between optical density and per cent. obscuration where major errors in optical density result from minor errors in per cent. obscuration (see Fig. 1, Table 1).
3.3. Position of instruments Air enters the fire chamber via a duct approximately 0.9 m square and 2 m long. The air flow profile has been established for a series of steady state flows created with after burner and extraction fans. The velocity profile of air entering the duct is essentially planar but becomes curved as the air passes along the duct, with greater distortion in the upper part of the duct. The position of the anemometer in the duct is important, and it is necessary to use a duct ratio of at least 1 2 lengths:height to obtain a satisfactory measure of air flow. It is usual to record the linear air flow through a duct and calculate the volumetric air flow using an experimental factor reflecting the flow profile in the duct. The
actual factor varies with the air velocity, and with whether the air flow is assumed to be essentially square or circular in section. Calculated factors relating the linear velocity to the volumetric flow rate are 0.54 - 0.76 for square section flow and 0 . 4 6 - 0 . 6 for circular flow. For single product tests a figure of approximately 0.6 may be used. The velocity profile of smoke in the corridor varies with the type of fire and also with the position at which measurements are made. The maximum velocity is, as expected, near the ceiling, and for many fires the velocity is effectively zero below the mid-height position. The velocity profile also varies across the corridor, with smoke from the burn room moving across to the far corridor wall before moving to a more central flow. The optimum position of the smoke measurement position will vary with different fires and the position normally chosen represents a compromise for the medium scale, single product type of test. The position is approximately 5 m from the smoke exit and has a light path length of 2/3 m. The instruments are m o u n t e d outside the corridor and the path length reduced by using air-purged tubes. Typical smoke velocity profiles for medium scale crib tests are shown in Fig. 5. Ceillng~
2/2
1 / 2 ~ 1/3 - - [ Test
Floor
1
0
Test
10 m/s
3
m/s
Ceiling
est
Floor
l
1
3 i
i
10 m/s
10 m/s
i O
i 10
Fig. 5. Typical velocity profiles in corridor. A, Fire chamber end; B, afterburner end; 1, nearside of corridor; 2, centre of corridor; 3, far side of corridor; X, smoke monitoring position horizontal light beam.
94 Smoke densities are measured using a selenium barrier photocell/light path system which produces signals of 200 - 300 mV for zero obscuration and microvolts for optical densities of 5 - 6. The signals are recorded using potentiometric recorders and an upper limit is introduced to avoid gross inaccuracies due to measurement of very small voltages. The upper limit coupled with the short path length limits the m a x i m u m optical density of 4.5 o.d./m. Although certain fires exceed this value, it is n o t a major restriction on the rig. Temperature measurements are made using chromel/alumel thermocouples connected to potentiometric recorders.
3.4. Calculation o f results Recorded data are transcribed to the RAPRA computer and the following data c o m p u t e d and printed. Optical density: OD/m Rate of smoke production: m 3 of OD/m = 1 per min at selected time periods, typical 1/2 min intervals Volume of smoke: m 3 of OD/m = 1 {running total). The c o m p u t e r programme is arranged such that the input data can be varied to suit different sized test rigs and different instrument arrangements, e.g., horizontal or vertical light paths.
3.5. Reproducibility of results The reproducibility of results is given in Table 3 for small to medium scale fires using single materials. The rate of burning of these fires is quite good with coefficients of variance of 8 - 15% of the mean. The coefficients of variance for the smoke data range from 20 - 30% with that of certain tests being as low as 6.5%. When the complications of the smoke measuring process and the size of the test room (34 m 3) and corridor (66 m 3) are considered, the results do not compare unfavourably with those of the standard smoke tests. The effect of different smoke measuring positions has been studied. Within the limits of experimental error and scatter of results, it is surprising that major positional changes have relatively small effects on the results.
4. C O M P A R I S O N O F S M O K E T E S T D A T A
4.1. Large scale test results It has previously been pointed out that full scale fire test facilities differ considerably in their geometry, size, and methods of construction. However, as the recent Home Office technical paper [6] pointed out, it is necessary to be able to correlate the results of large scale tests, and two series of tests have
TABLE 3 R e p r o d u c i b i l i t y o f s m o k e d a t a , large scale t e s t s Parameter
R u b b e r latex f o a m block Mean value Range of values No. of values C o e f f . o f v a r i a n c e (%)
Time to max. OD(min)
Max. optical density (OD/m)
Vol. u p t o max. OD (m 3 )
Vol. ( O D / m = 1) up to OD/m = 2 m 3
T o t a l vol, ( O D / m = 1) ( m 3)
-----
2.10D/m 1.97 - 2.28 5 6.1
16.3 m 3 15,1 - 17.8 4 6.5
45 m 3 30 - 57 4 24
104 m 3 70 - 113 4 26
S i m u l a t e d chair s t a c k - - p o l y p r o p y l e n e Mean value 7.2 Range of values 7 -8 No. of values 5 C o e f f . o f v a r i a n c e (%) 6.2
0.94 OD/m 0.7 - 1.3 m 5 23.5
S i m u l a t e d chair s t a c k - - cellulosic boards Mean value 6.7 Range of values 6 - 7.5 No. of values 6.8 C o e f f . o f v a r i a n c e (%) 10.8
0.23 OD/m 0.2 - 0 . 2 5 3 15.7
93 m 3
54 - 118 5 29.8
m
-
-
4
22 m 3 19 - 25 3 19.3
95 b e e n carried o u t to c o m p a r e results f r o m R A P R A a n d F R S t e s t rigs. T h e c u r r e n t c o n cern over u p h o l s t e r e d f u r n i t u r e is directly r e f l e c t e d in t h e R A P R A p r o g r a m m e a n d in r u n n i n g o f t h e following tests. T h e first c o m p a r i s o n involved h a l f scale tests [7] w i t h the BS D D 58 f u r n i t u r e rig [8]. T h e m a j o r d i f f e r e n c e s which existed b e t w e e n t h e t e s t rigs f o r these tests a n d f o r a later series o f full scale m o c k - u p u p h o l s t e r e d chairs is s h o w n in T a b l e 4. D a t a f o r the full scale F R S b u r n s are r e p o r t e d in B R E CP 3 0 / 7 8 [9] a n d in all tests, the s p e c i m e n was ignited b y a No. 7 crib t o BS D D 58. A c o m p a r i s o n o f d a t a o b t a i n e d f o r t h e halfscale tests s h o w s t h a t m a x i m u m s m o k e densities r e c o r d e d at R A P R A are l o w e r t h a n t h o s e o f F R S , w h e r e a s the t o t a l v o l u m e o f s m o k e is greater. T h e v e r y great d i f f e r e n c e s b e t w e e n t h e t e s t rigs, especially in t h e m a t e r i a l s o f c o n s t r u c t i o n (which significantly a f f e c t s fire
TABLE 4 Comparison of full and half-scale fire test
facilities
Parameter
Half scale
Units
t e m p e r a t u r e s ) , o f v e n t i l a t i o n (which a f f e c t s b u r n r a t e , s m o k e d i l u t i o n ) and, p e r h a p s , most important, the destruction of smoke by burning, m a d e direct c o m p a r i s o n o f t h e results u n l i k e l y , b u t t h e c o r r e l a t i o n s s h o w n in Fig. 6(a), (b), (c) are n o t as p o o r as t h e y c o u l d be, P e r h a p s b e c a u s e o f t h e greater similarity in materials o f c o n s t r u c t i o n and g e o m e t r y , b e t t e r c o r r e l a t i o n is o b t a i n e d w i t h the full scale tests (Fig. 7). In this case, p e a k t e m p e r a tures a n d t i m e to p e a k t e m p e r a t u r e s are similar, indicating m o r e c o n s t a n t fire c o n ditions. T h e d i f f e r e n t s m o k e m e a s u r i n g positions and techniques and ventilation a i r / s m o k e m i x i n g w o u l d indicate t h e likely cause o f t h e a b s o l u t e d i f f e r e n c e s in s m o k e d e n s i t y a n d v o l u m e . T h e a p p r o x i m a t e straight line r e l a t i o n s h i p b e t w e e n the results f r o m t h e t w o t e s t rigs at least f o r m s t h e basis f o r c o m parisons a n d f o r f u t u r e investigations.
Full scale
RAPRA
FRS
RAPRA
FRS
Fire room width depth height
m m m
0.9 0.9 0.9/1.2
0.94 0.92 0.92
4.5 3.0 2.4
3.0 3.0 2.4
Corridor width length height
m m m
0.9 0.9 0.9
0.45 5.96 0.92
1.8 15.0 2.4
1.3 12.6 2.4
Smoke exit width height
m m
0.9 0.2
0.92 0.23
0.9 2.4
0.6 2.4
corridor
corridor
corridor
Air entry Air entry width height
m m
chamber top Duct 0.9 0.9
corridor 0.23 0.92
duct afterburner 0.9 0.9
corridor 1.3 2.4
Materials of construction
--
sheet
denoted
metal
concrete
brickwalls reinforced concrete ceiling
reinforced concrete
smoke
corridor
corridor
corridor
corridor
corridor
corridor
corridor
duct
corridor
Smoke exit
Position of measurement Smoke temp.
--
exit
Smoke
density
--
smoke exit
Air entry Flow rate
--
duct
96
OD/m
(a)
I 2
I
i 3
i 4
i 5
L 6
(b)
i OD/m
.........
I d ......
600
/ 50O
/ / /
E
// O
//
% v % 3oo
/ ,/
E
• 200
100
/f /
/ 20
/
•
40'
60 '
80 '
1O0 '
FRS
'
-
'
Toto~ smokq volume m
of O 0 / m
R 1
(e)
.J
20
~15 2
o ~i0 E I
i
L
L
5
10
15
.
20
Temperature
i
,
25
30
i
35
,
40
~ndex FRS
Fig. 6. (a) M a x i m u m s m o k e d e n s i t y ; ( b ) t o t a l s m o k e v o l u m e m 3 o f O D / m = 1 ; (c) t e m p e r a t u r e i n d e x [7 ].
4.2. Dynamic and static s m o k e measurements, large scale tests In small, standard smoke tests, the smoke density is frequently measured after the smoke has been stored and distributed around the test chamber, i.e., a static system. Whereas,
large scale tests usually determine the smoke as it is produced using a dynamic system. A recent paper [9] discusses the use of static and dynamic small scale smoke tests and shows that for PVC compounds and for polyacrylonitrile, a significant difference occurs between unaged and aged smoke at high temperatures. This is because the latter permits deposition and condensation of smoke particles, aerosols, and vapours as the smoke cools. To assess this effect, which is obviously important when comparing the results of full scale tests with those of half-scale standard tests a series of tests were carried out using a half-scale rig, similar to that used in full scale tests, but with a similar sized entry. Smoke from the fire passed from the rig exit and was quantified using the procedures described above. The smoke was then collected in an enclosed chamber of 100 m ~ volume and determined using a vertical light path. Two series of upholstered cushions were burned. The first series was ignited with a small gas flame and the second series with a 126 g wooden crib. The fire load was typically 6800 Kcal. Results for a series of half-scale upholstered chair tests {using a BS DD 58 rig) are shown in Fig. 8. Assuming an air flow entry correction factor of 0.6 (see above), the ratio between the volume of smoke determined by the static accumulation and the dynamic flow methods is about 1:2.8. This figure is similar to that reported for static and dynamic flow measurements in bench scale tests for PVC (9 compounds) and polyacrylonitrite. The range of figures quoted for tests at 750 °C is 1:2.5 1:6, but most values typically lie between 1:3.5 and 1:4.5. Figures quoted for low temperature (470 °C) smoke tests are 1:0.75 1:1.1 [10]. Another important factor is that the dynamic results are expressed as the volume of smoke leaving the test chamber and wilt depend directly on the smoke and fire temperature which will vary continuously throughout the fire test. An alternative m e t h o d which is not generally used would be to normalize the smoke volume to a specific temperature, e.g. STP. The smoke volume ratios referred to above for the bench tests reduce to 1:1.75 - 1:4.5 for the overall range
97
M a x OD 3
./ / / / 500
/ / /
400
/
Max smoke density OO/m
•
II
/
a 0
/
300
"'6
/
E
2OO
/ / /
tO0
/
I 1O0
/
I 200
Totol volume of smoke m3 of O D / m = 1
/ Max
(a)
I 1 optical density FRS
(b) OD/m
Comparison of full scale fire test data
300
/
/
2
/ / / / E
/ / ~0
/ /
100
./. / / I 10
I 20
I 100
Time mins FRS
(c)
I 200 FRS Temp °C
i 300
(d)
Fig. 7. (a) Maximum smoke density; (b) total volume of smoke; (c) time to maximum temperature; (d) maximum fire temperature.
and 1 : 2 . 5 - 1:3.25 for the central portion when the temperature correction is applied to reduce all values to 470 °C. These figures suggest that there was a major reduction of smoke due to ageing, the static measurement being carried out at the end of the test {i.e., 15 - 20 min after the fire was controlled). There were also small leaks of smoke through the sampling holes but these were unlikely
to have affected the final smoke volume significantly.
4.3. Comparison of products A comparison of the smoke produced and the effect of the composition of upholstered composites is shown in Table 5. When considering the results of actual product tests, it is important to realize that
98 t h e y can be directly a f f e c t e d b y the experim e n t a l c o n d i t i o n s . T h e e f f e c t o f air flow has already been discussed. T h e ignition s o u r c e used can directly a f f e c t t h e m a n n e r in w h i c h a p r o d u c t b u r n s and, c o n s e q u e n t l y , the rate at w h i c h s m o k e is prod u c e d . Where a m a j o r d i f f e r e n c e exists, e.g., flaming or s m o u l d e r i n g f o l l o w e d b y flaming,
1O0 E%.-~E
g~E Eo~ EO "~- ~ O x
x
o
o
517 tch i g m h o n ~ource ,~
10
~
I O0
Dynamic measurement
0
I 200
Crlb i g n i t i o n source
i 300
V o l u m e of smoke of O D / m
I 400 =
500 1, m3
Fig. 8. Correlation of static and d y n a m i c determinations of volume of smoke produced by burning u p h o l s t e r e d p o l y e t h e r foam cushions.
the t o t a l a m o u n t o f s m o k e p r o d u c e d can be very different, see Fig. 9. With h i g h l y - c o m p l e x p r o d u c t s such as u p h o l s t e r e d f u r n i t u r e , the rate of s m o k e prod u c t i o n can be significantly altered by changing t h e p o i n t o f ignition, even t h o u g h a c o n s t a n t ignition s o u r c e m a y be used. The total v o l u m e o f s m o k e m a y n o t be altered. S t a n d a r d s m o k e test data (NBS test) o f t w o wall signs i n d i c a t e d t h a t a s t a n d a r d grade o f polyester/glass l a m i n a t e w o u l d be e x p e c t e d to p r o d u c e less, or at least as m u c h , s m o k e as the fire r e t a r d e d equivalent. The a n t i c i p a t e d fire scenario c o m p r i s e d a large rubbish fire. Full scale tests were carried o u t using a 14 kg t i m b e r crib to simulate a large b u r n i n g rubbish fire. The signs were fixed t o brick walls as i n t e n d e d in the p r o t o t y p e installation a n d the " r u b b i s h " p l a c e d b e n e a t h the sign. In the resulting fires the s m o k e levels p r o d u c e d b y the fire-retarded sign were very m u c h less t h a n t h o s e f r o m the s t a n d a r d sign. This difference was entirely due to the relatively small a m o u n t t h a t the fire r e t a r d e d sign b u r n e d (9% as against 44% f o r the s t a n d a r d sign) (Table 6) [ 1 0 ] .
TABLE 5 Comparison of upholstered composites BS DD 58 rig No. 5 crib ignition Material
Ignitability*
Max. temp.
(°C)
1 2 3 4 5 6
Acrylic/cotton/SPE Polypropylene/SPE Viscose/SPE Wool/SPE Wool/cotton wad/SPE PVC/cotton/SPE
1P 1P 1P 2P 3/4P 6P
Viscose fabric, with alternative fillings 7 SPE foam 1F 8 FR PE foam 1F 9 H R P E foam*** 1P 10 Polyester fibre 1P 11 Latex foam*** 1F 12 Cotton wad/SPE 1F 13 FR cotton int/SPE 1F
Time to max. temp. (min)
Max. smoke (OD/m)
Time to max. smoke (rain)
Vol. smoke m 3 of OD/m = 1
Initial** mass of sample (kg)
180 283 190 125 38 280
4 3 8 4 3.5 9
0.7 0.9 0.3 0.4 0.1 1.9
4 2.5 8.5 6.5 3.5 15
307 114 71 132 4 500
1.2 1.1 1.1 1.1 1.5 1.4
190 172 170 250 170 324 280
8 8 7 4.5 12 11.5 6.5
0.3 0.5 0.3 1.2 > 1.3 1.1 0.3
8.5 11 9 3.5 10 10.5 6.5
71 141 56 177 > 300 314 75
1.1 1.5 1.5 2.0 3.1 1.5 1.2
* T o BS D D 5 8 . * * A m o u n t burned in test was approx. 8 0 - 90% o f initial mass. ***Estimated. P, Pass cigarette test. F, Fail cigarette test.
99 The importance of this comparison is that the way a product burns can directly affect the smoke measurements made and the smoke hazard generated. The limitation of these
results is that they refer to the test conditions, i.e., a simulated rubbish fire, and do not show what could occur in another fire scenario, e.g., a major fire could destroy each type of sign.
IJ
o 0
E
0 O. 0
E
2
4
6
8
10
12
14
1~
18
Time
mins Specimen Acrylic velour Polyether foam Acrylic velour Polyether foam
Ignition source Small flame
Mode of combustion Flame
Total vol. m 3 184
No. 7 c r i b
Flame
177
Smoulder flame
188
Flame
70
Cotton velour. Small wadding polyether flame foam Cotton velour. No. 7crib wadding polyether foam
Fig. 9. E f f e c t o f using d i f f e r e n t i g n i t i o n sources o n
smoke p r o d u c t i o n of u p h o l s t e r e d c o m p o s i t e s .
4.4. Correlation of full scale and standard smoke test data The correlation of smoke procedures from full scales fires with the results of standard tests is important, as smoke tests are used to quantify the smoke producing properties of materials, and thence to control the use of materials. Fire research work at RAPRA has involved a number of "full scale" tests and the results of these tests are being correlated with the results of standard smoke tests in order to provide an improved basis for test selection and application. The correlation of the smoke produced from simulated chair stack tests (see R A P R A work on the role of softening in fire growth [10]) shows that the results of the XP2 test may be used to indicate high and low smoke producing materials but that the correlation is uncertain for intermediate measurements. The rate of smoke generation during the stack tests was directly related to the rate of fire growth (and thence to the softening point of the material) and could not be predicted from the XP2 test results (Table 7).
TABLE 6 C o m p a r i s o n of s m o k e p r o d u c e d f r o m G R P signs
Parameter
S t a n d a r d grade
Fire retarded grade
690 625
L a b o r a t o r y tests Smoke density Flaming ASTM E 6 6 2 Non-Flaming
(Din) (Dm)
630 435
Max. c a r b o n m o n o x i d e c o n c n .
(ppm)*
3000 - 4000
3000 - 4000
Max. c a r b o n d i o x i d e c o n c n .
(ppm)*
5000 - 9000
6000 - 8000
Max. h y d r o g e n c h l o r i d e c o n c n .
(ppm)*
0
94
Full scale t e s t Max. ceiling t e m p Max. s m o k e d e n s i t y Typical s m o k e d e n s i t y 1 - 10 rain Max. c a r b o n m o n o x i d e Max. c a r b o n d i o x i d e Max. h y d r o g e n c h l o r i d e
(°C) (OD/m) (OD/m) (ppm) (ppm) (ppm)
800 >3.0 > 3.0 500 15 0 0 0 0
460 0.75 0.3 - 0.6 250 13 0 0 0 6
44%
9%
14 k g w o o d crib source
Weight loss * C a l c u l a t e d f r o m b e n c h test d a t a for 35 m 3 r o o m .
100 TABLE 7 Correlation of XP2 smoke test results with results of full scale simulated chair stack tests Material
XP2 Test**
Full scale simulated
Chair stack
Max. OD (OD/m)
Total vol. (m 3) 0D/m = I
0.9 0.47 1.0 0.03 0.01 0.1 0.3 0.1 0.1 0.03 0.1
0.077 0.04 0.085 0.003 0.001 0.009 0.03 0.009 0.009 0.003 0.009
0.95 0.82 0.75 0.7 0.6 0.3 0.47 0.35 0.2 0.45 0.5
87 68 63 91 110 43 29 26 22 57 96
2.9 2.9 1.6 1.8 1.5 2.9
0.25 0.25 0.14 0.15 0.13 0.25
2.2 4.5 3.3 1.9 4.5 4.5
]07 590 265 1100 > 500
4.2 9.8"* 8.9** 9.8** 6.2 4.5 9.8** 8.2**
0.36 0.83 0.76 0.83 0.53 0.38 0.83 0.70
>4.5 >4.5 >4.5 >4.5 >4.5 >4.5 >4.5 >4.5
1100 > 400 >475 > 400 >450 > 400 > 400 :>210
Max. OD/m
Total smoke vol. (m '~) OD/m = !
L o w s m o k e levels* O D / m < 1.0
Polypropylene Polypropylene/glass spheres Polypropylene/glass laminate Polypropylene/CaCO3 Polypropylene/MgCO3 Polypropylene/hydrated alumina Polyethylene Acrylic (PMMA) Hardboard Plywood (6 mm) Plywood (12 mm)
M e d i u m s m o k e levels* O D / m > 1.0 < 3.5
Cellulose acetate Polypropylene FR Polypropylene FR Polypropylene FR Polypropylene FR PPO modified
V2 (1) V2 (2) filled (1) filled (2)
High s m o k e levels* O D / m > 3.5
Polycarbonate uPVC Polystyrene (HI) ABS Polypropylene FR VO Polypropylene FR asbestos GRP (Std) GRP FR (Class BS 476 Pt. 7)
*XP2 Test, method based on ASTM D2843. **Specimen size 25 x 25 × 3 mm.
Correlations b e t w e e n the XP2 tests a n d smoke measurements of upholstered composites s h o w p r o m i s e and w o r k is c o n t i n u i n g o n this topic. F u t u r e w o r k will include correlations b e t w e e n the NBS s m o k e test, M e t h o d A S T M E 6 6 2 a n d N E S 7 1 1 a n d full scale fire test data. It is i n t e n d e d to include results f r o m the ISO (Munich) a n d A r a p a h o e tests at a f u t u r e date.
5. FULL SCALE STANDARDIZED SMOKE TESTS It has already been p o i n t e d o u t t h a t standard full scale fire tests are relatively rare a n d are usually o n l y carried o u t f o r p r o d u c t d e v e l o p m e n t , c o m p a r i s o n , or t y p e approval
purposes. Perhaps the best k n o w n full scale s t a n d a r d tests are t h o s e issued by D O E / P S A . These were originally issued in 1 9 7 5 a n d have been progressively d e v e l o p e d a n d e x t e n d e d to provide a c o m p r e h e n s i v e range o f test and c o n t r o l p r o c e d u r e s . The full scale tests include: D O E / P S A F R 5 f o r mattresses and b e d d i n g D O E / P S A F R 6 f o r seating DOE/PSA FR7 for curtaining D O E / P S A F R 1 4 f o r archival a n d o t h e r containers a n d f o r carcase f u r n i t u r e in general. T h e tests are primarily ignition tests a n d require resistance t o specified sources (listed in D O E / P S A F R 1 0 ) . Ignition tests are f o l l o w e d b y b u r n i n g tests in w h i c h t e m p e r a t u r e / t i m e , smoke density/time and carbon monoxide/
1 0 1
time curves are determined (DOE PSA FR6). The following information (Table 8) is also tabulated. The tests are carried out in a room of greater than 30 m 3 (see Fig. 10) [12]. TABLE 8 DOE/PSA FR6 sample data Ignition source Temperature of smoke °C at min M a x . t e m p e r a t u r e - - °C at - - m i n Volume of smoke/m 3 at -- min Total volume of smoke -- m 3 O p t i c a l d e n s i t y - - O D m - 1 at - - m i n R a d i a n t h e a t at - - m i n shall n o t e x c e e d - - W - -
- -
• Q J
- -
Ternperature D
Smoke density Carbon monoxide
~
Fig. 10. F u l l scale c h a i r
E..~e'l I ,
test,
,
/ /
DOE PSA FR6.
6, C O N C L U S I O N S
Full scale fire tests permit the burning characteristics of products and prototypes to be determined under likely or specified fire conditions. The results of such tests enable the complex interactions of material combinations, design features and environmental factors to be determined. The results of such tests can frequently be affected by the experimental conditions, and great care must be exercised when making comparisons. Smoke, the subject of this paper, is a direct consequence of less than complete combustion and is affected by many factors including the materials burned, the rate of burning, ventilation, etc. These facts are obvious from full scale smoke/fire tests b u t tend to be overlooked when standard test data are considered. For this reason it is necessary to consider smoke density and its rate of formation as a function of time and to be aware
that these are directly related to ignition (without which there can be no fire) and to the rate of combustion. Recently the BSI has published DD64, Guidelines for the Development and Presentation of Fire Tests and for their use in Hazard Assessment [13]. This is essentially a philosophy intended to assist specification writers, regulatory bodies, designers and architects, manufacturers and fabrication, wholesalers and retailers, consumer advice services, and educational bodies. The following summarises the considerations of DD64 which should be given to assessing and controlling fire hazards when specifications or codes of practice are being prepared. (a) In consultation with fire experts, assess the actual or potential fire hazards in the use of the material, product, structure or system. (b) Appraise the levels of fire hazard acceptability in the end use of material, product, structure or system, and the scope for controlling fire hazards. (c) Identify the critical factors which need to be controlled, in terms of ignition hazard and fire growth hazard. (d) Develop fire tests capable of providing information which will assist in the assessment of fire hazard in terms of the hazardous properties of one or more aspects of fire. (e) Clearly state, in specifications, codes of practice, fire test methods, and fire test reports, any limitations in the use of fire tests to assess or control potential fire hazard. (f) Recognise that the results of fire tests can never guarantee fire safety. The assessment of actual or potential fire hazards and the appraisal of the levels of fire hazard acceptability are obviously extremely complex processes and must involve environmental and human factors as well as the actual ignition and burning characteristics of products. It is not proposed to deal with the environmental and human factors in detail but merely to point out that even for a single item or product, the hazard may vary as it m a y be placed in the open, in the upper stories of a high rise building, in a hospital, in a prison, underground, in an aircraft, etc. Similarly, it will vary with the mobility, background training and discipline of personnel, and with the availability of fire preventive measures such as sprinklers, proximity of fire
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fighting services, etc. The effects of possible fires should be considered with relation to life and property. All these and many more factors will need to be considered in the assessment of fire hazard and risk.
LIST OF SYMBOLS
T To L I--T D
Light flux transmission Initial light flux Alternation coefficient Length of optical path Obscuration Optical density per unit path length NB: These are given in the text.
REFERENCES 1 D. J. Rasbash, Smoke and toxic products produced at fires, Plast. Inst. Trans. J., Jan., (1967) Conference supplement No. 2, pp. 55 - 61. 2 T. Jin, Visibility through fires, J. Fire Flammability, 9 (1978) 135. 3 T. Jin, Studies of emotional instability in smoke in fires, J. Fire Flammability, 12 (1981) 130 142. 4 P. G. Edgerley and K. Pettett, Effect of pyrolysis and combustion temperatures on smoke density, European Conf. on Flammability and Fire, Brussels, 1977.
5 S. A. Ames, An automated system for the examination of experimental Compartment fires, CP7/79, Building Research Establishment, Borehamwood. 6 Report o f the Technical Sub-Committee on the Fire Risks o f New Materials, Home Office, Fire Department, London, 1978. 7 S. A. Ames and P. J. Fondell, A study of the flammability of bulk solids and their smoke production in fires in a small compartment, BRE, CP3/80, Building Research Establishment, Borehamwood. 8 S. A. Ames, Personal communication, BRE, Fire Research Station. 9 W. D. Wooley, S. A. Ames, A. I. Pitt and K: Buckland, The ignition and burning characteristics of fabric covered foam, BRE CP 30/78, Building Research Establishment, Borehamwood. 10 A. Ballistrevi, G. Montando, C. Puglisi, E. Scamporrino and D. Vitalini, Smoke dilution methods for evaluation of the smoke emission from burning polymers: a comparative approach, Fire Mater., 5 (2) (1981) 61 - 65. 11 K . T . Paul, Demonstration of the effect of softening and fire resistance of materials on burning characteristics, Fire Mater., 4 (2) (1980) 83 - 86. 12 Department o f Environment/Property Services Agency, Fire Retardant Specifications No. 5. 6. 7, I0 and 14. 13 BS DD64, Guidelines for the Development and Presentation of Fire Tests and their use in Hazard Assessment, British Standards Institution, London. 14 H. L. Wright, Atmospheric opacity, QJ R. Met. Soc., 65 (281) (1939) 411 - 442. 15 P. C. Bowes, P. Field and G. Ramachaudran, Assessment of smoke production by building materials in fires, BRE Fire Research Note No 775, October, 1969.