49 CFR Appendix H_to_part_173 - Method of Testing for Sustained Combustibility
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.
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.
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 188.8.131.52 of the UN Manual of Test and Criteria (IBR, see (171.7 of this subchapter), and the essential dimensions are given in Figures 184.108.40.206 and 220.127.116.11 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 18.104.22.168);
(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.
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.
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.
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.
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.