Appendix H to Part 173 - Method of Testing for Sustained Combustibility
49:2.1.1.3.10.12.25.1.12 : Appendix H
Appendix H to Part 173 - Method of Testing for Sustained
Combustibility 1. Method
The method describes a procedure for determining if the material
when heated under the test conditions and exposed to an external
source of flame applied in a standard manner sustains
combustion.
2. Principle of the method
A metal block with a concave depression (test portion well) is
heated to a specified temperature. A specified volume of the
material under test is transferred to the well, and its ability to
sustain combustion is noted after application and subsequent
removal of a standard flame under specified conditions.
3. Apparatus
A combustibility tester consisting of a block of aluminum alloy
or other corrosion-resistant metal of high thermal conductivity is
used. The block has a concave well and a pocket drilled to take a
thermometer. A small gas jet assembly on a swivel is attached to
the block. The handle and gas inlet for the gas jet may be fitted
at any convenient angle to the gas jet. A suitable apparatus is
shown in Figure 32.5.2.1 of the UN Manual of Test and Criteria
(IBR, see (171.7 of this subchapter), and the essential dimensions
are given in Figures 32.5.2.1 and 32.5.2.2 of the UN Manual and
Tests and Criteria. The following equipment is needed:
(a) Gauge, for checking that the height of the center of
the gas jet above the top of the test portion well is 2.2 mm
(see Figure 32.5.2.1);
(b) Thermometer, mercury in glass, for horizontal
operation, with a sensitivity not less than 1 mm/ °C, or other
measuring device of equivalent sensitivity permitting reading at
0.5 °C intervals. When in position in the block, the thermometer
bulb must be surrounded with thermally conducting thermoplastic
compound;
(c) Hotplate, fitted with a temperature-control device.
(Other types of apparatus with suitable temperature-control
facilities may be employed to heat the metal block);
(d) Stopwatch, or other suitable timing device;
(e) Syringe, capable of delivering 2 mL to an accuracy of
±0.1 mL; and
(f) Fuel source, butane test fuel.
4. Sampling
The sample must be representative of the material to be tested
and must be supplied and kept in a tightly closed container prior
to test. Because of the possibility of loss of volatile
constituents, the sample must receive only the minimum treatment
necessary to ensure its homogeneity. After removing each test
portion, the sample container must be immediately closed tightly to
ensure that no volatile components escape from the container; if
this closure is incomplete, an entirely new sample must be
taken.
5. Procedure
Carry out the determination in triplicate.
WARNING - Do not carry out the test in a small confined area
(for example a glove box) because of the hazard of explosions.
(a) It is essential that the apparatus be set up in a completely
draft-free area (see warning) and in the absence of strong light to
facilitate observation of flash, flame, etc.
(b) Place the metal block on the hotplate or heat the metal
block by other suitable means so that its temperature, as indicated
by the thermometer placed in the metal block, is maintained at the
specified temperature within a tolerance of ±1 °C. For the
appropriate test temperature, see paragraph 5.(h) of this appendix.
Correct this temperature for the difference in barometric pressure
from the standard atmospheric pressure (101.3 kPa) by raising the
test temperature for a higher pressure or lowering the test
temperature for a lower pressure by 1.0 °C for each 4 kPa
difference. Ensure that the top of the metal block is exactly
horizontal. Use the gauge to check that the jet is 2.2 mm above the
top of the well when in the test position.
(c) Light the butane test fuel with the jet away from the test
position (i.e. in the “off” position, away from the well). Adjust
the size of the flame so that it is 8 mm to 9 mm high and
approximately 5 mm wide.
(d) Using the syringe, take from the sample container at least 2
mL of the sample and rapidly transfer a test portion of 2 mL ±0.1
mL to the well of the combustibility tester and immediately start
the timing device.
(e) After a heating time of 60 seconds (s), by which time the
test portion is deemed to have reached its equilibrium temperature,
and if the test fluid has not ignited, swing the test flame into
the test position over the edge of the pool of liquid. Maintain it
in this position for 15 s and then return it to the “off” position
while observing the behavior of the test portion. The test flame
must remain lighted throughout the test.
(f) For each test observe and record:
(i) whether there is ignition and sustained combustion or
flashing, or neither, of the test portion before the test flame is
moved into the test position;
(ii) whether the test portion ignites while the test flame is in
the test position, and, if so, how long combustion is sustained
after the test flame is returned to the “off” position.
(g) If sustained combustion interpreted in accordance with
paragraph 6. of this appendix is not found, repeat the complete
procedure with new test portions, but with a heating time of 30
s.
(h) If sustained combustion interpreted in accordance with
paragraph 6. of this appendix is not found at a test temperature of
60 °C (140 °F), repeat the complete procedure with new test
portions, but at a test temperature of 75 °C (167 °F). In the case
of a material which has a flash point above 60 °C (140 °F) and
below 93 °C (200 °F), if sustained combustion interpreted in
accordance with paragraph 6. of this appendix is not found at a
test temperature of 5 °C (9 °F) above its flash point, repeat the
complete procedure with new test portions, but at a test
temperature of 20 °C (36 °F) above its flash point.
6. Interpretation of observations
The material must be assessed either as not sustaining
combustion or as sustaining combustion. Sustained combustion must
be reported at either of the heating times if one of the following
occurs with either of the test portions:
(a) When the test flame is in the “off” position, the test
portion ignites and sustains combustion;
(b) The test portion ignites while the test flame is in the test
position for 15 s, and sustains combustion for more than 15 s after
the test flame has been returned to the “off” position.
Note to paragraph 6 of this appendix:
Intermittent flashing may not be interpreted as sustained
combustion. Normally, at the end of 15 s, the combustion has either
clearly ceased or continues. In cases of doubt, the material must
be deemed to sustain combustion.
[Amdt. 173-241, 59 FR 67517, Dec. 29, 1994, as amended by Amdt.
173-255, 61 FR 50627, Sept. 26, 1996; 66 FR 45381, Aug. 28, 2001;
68 FR 75747, Dec. 31, 2003; 69 FR 76179, Dec. 20, 2004; 71 FR
78634, Dec. 29, 2006]