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EuroWire – March 2008
213
english
The NBS smoke chamber measures smoke
density accumulated when a specimen of
specified form and thickness is exposed to
a radiant heat source of 25 kW/m
2
.
Depending on the application, either the
maximum smoke density or the smoke
density at a set time (usually 4 minutes)
can be specified.
The test can be run with or without the
application of a pilot flame (flaming and
smouldering mode, respectively). In this
work, all tests were run in the flaming
mode.
3.2 ASTM E1354 Cone Calorimeter
The cone calorimeter is a laboratory
instrument that measures combustibility
and smoke generation of materials under
a wide range of conditions.
For building materials that must pass
the expensive E-84 Steiner Tunnel test,
the cone calorimeter is often used as
a screening test. While no single fixed
irradiance test can predict performance
in the large-scale tunnel test, the cone
calorimeter test is widely recognised as a
useful development tool.
In the cone calorimeter test, described
by ASTM E1354, a square sample of
100mm x 100mm (4 x 4 in) is exposed
to the radiant flux of an electric heater.
The heater has the shape of a truncated
cone (hence the name of the instrument)
and is capable of providing heat fluxes
in the range of 10-110 kW/m
2
, but most
typically from 50-75 kW/m
2
. This is two
to three times the heat flux used in the
NBS smoke chamber.
The cone calorimeter can measure key
material fire performance characteristics
that have been used in fire modelling.
Smoke generation, is continuously mea-
sured using a laser beam in the exhaust
duct. The log of the intensity is used to
calculate an extinction coefficient, which is
a measure of the smoke in the air stream.
Integration of the extinction coefficient
versus time is combined with the total
volume of combustion products to give
the total smoke parameter. Normalised for
the surface area of the sample, the units on
total smoke are m²/m².
In this work, cone calorimeter testing was
performed at both Polymer Diagnostics, in
Avon Lake, Ohio, US, and at the College of
William and Mary, under the direction of
Professor William Starnes.
4. Results
4.1 NBS Smoke
Two model flexible PVC formulae were
selected for a comparison of the prototype
Kemgard STA with commercial AOM. In one
formula, aluminum trihydrate was added
at a 30 phr level. In the other formula, the
ATH level was 60 phr. The base formulae
are shown in
Table 4
.
Product comparisons were done at 5, 10
and 15 phr total AOM. Talc levels were
adjusted to maintain a fixed total filler
level.
Figures 3-5
present the smoke density
as a function of use level for various
compounds. D90 corresponds to the
smoke level at 90 seconds. D4 corresponds
to the smoke density at 4 minutes and
Dmax represents the maximum smoke
density achieved during the test.
The data clearly demonstrate that at all use
levels and all times, the KG-STA far exceeds
the performance of Climax WA 011GA. The
performance of KG-STA is also superior to
that of the best commercial sample, Climax
A2017I, again at all levels and all times.
In terms of maximum smoke density,
KG-STA shows the greatest performance
advantage at the lower use levels. In fact,
the performance of KG-STA at 5 phr is
comparable to the performance of the
best commercial AOM at 10 phr.
This is a remarkable result and suggests
a far more efficient use of the AOM
chemistry.
Figures 6-8
present the NBS
smoke results obtained in the higher
(60 phr) ATH containing formula.
Again, the smoke density is shown as
a function of use level for the various
compounds. As in the previous system,
comparisons were done at 5, 10 and
15 phr total AOM, with talc levels adjusted
to maintain fixed total filler content.
Figure 6
shows the 90 second smoke,
Figure 7
shows the smoke development
at 4 minutes and
Figure 8
shows the
maximum smoke development for the
various compounds.
Similar to the low ATH system, the data
again demonstrate that at all use levels
and all times, the KG-STA far exceeds the
performance of Climax WA 011GA.
Comparing just these two systems, the
performance KG-STA at 5 phr is superior to
that of the WA 011GA at 10 phr. This is true
at all times of the test.
KG-STA also demonstrated performance
superior to the smaller particle size
commercial sample, A2017I at both the
5 phr and 15 phr levels. At 10 phr, the
performance was comparable.
Figure 3
:
Ninety second NBS smoke density for
KG-STA and commercial AOM
▲
Figure 4
:
Four minute NBS smoke density for KG-
STA and commercial AOM
▲
Figure 5
:
Maximum smoke density for KG-STA and
commercial AOM
▲
Figure 6
:
Ninety second NBS smoke density for
KG-STA and commercial AOM
▲
Figure 7
:
Four minute NBS smoke density for KG-STA
and commercial AOM
▲
Figure 8
:
Maximum smoke density for KG-STA
and commercial AOM
▲