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Detailed Test Procedures of oxygen Index
2019/03/15
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oxygen Index tester applies to the Chemistry Team, Materials Test Branch, of the Materials and Processes Laboratory. The test method shall be used to measure and describe the properties of materials, products, or assemblies in response to heat and flame under controlled laboratory conditions and shall not be used to describe or appraise the fire hazard or fire risk of materials, products, or assemblies under actual fire conditions. Results of this test may be used, however, as elements of a fire-risk assessment that takes into account all of the factors pertinent to an assessment of the fire hazard of a particular end use.
If the actual oxygen index of a material is needed or in case of a dispute, use Procedure A, as described in section 4.6.1. Otherwise, use Procedure B.
Procedure A
1. Verify that the ambient temperature for the test apparatus is 23 (±2)
°C.
2. Verify that both the oxygen and nitrogen valves are in the OFF position.
3. Select an initial concentration of oxygen to be used.Whenever possible, base the initial concentration on experience of results for similar materials. Alternatively, try to ignite a test sample in the air, and note the burning behavior. If the test sample burns rapidly,select an initial concentration of about 18% oxygen; if the test sample burns gently or unsteadily, select an initial oxygen concentration of about 21%; if the test sample does not continue to burn in air,select an initial concentration of a least 25%, depending upon the difficulty of ignition or the period of burning before extinguishing in air.
4. Turn the nitrogen valve slowly to the ON position; turn the oxygen valve to the ON position. Note: Turning the valves slowly to the ON position avoids an undesirable initial flow surge, a result of the back pressure in the system. When turning on the valves, always turn the nitrogen valve on fully before turning the oxygen valve.
5. Use the oxygen gas needle valve to obtain the selected oxygen concentration at the flow rate used in steps 4.4.9 and 4.4.10. Note: For oxygen concentrations in excess of approximately 50%, the oxygen needle valve shall be fully open, and the nitrogen valve shall be used to obtain the calculated oxygen concentration. Always verify that one of the needle valves is fully open, using the other to adjust the concentration.
6. Let the gas flow purge the chimney for at least 30 sec before ignition of each test sample. Maintain the flow without change during ignition and combustion of each test sample.
7. With the character generator in the RECORD TITLE mode, record the test information sign on video for at least 10 seconds. After 10 seconds, switch the character generator to the STOP WATCH mode, and ensure that the stop watch is reset to 00:00:00.
8. Verify that the temperature at the lower end of the chimney is 23 (±2)°C, and record the oxygen concentration used as the volume percent in the appropriate Oxygen Index Data Sheet (Figure 7-1) cell.
8.1. Select one of the following two ignition methods, depending on the test sample form:
8.2. For test sample Types I, II, III, IV, and VI, select Method A, Top Surface Ignition. Proceed to step 4.6.1.9.
8.3. For test sample Type V, select Method B, Propagating Ignition.
Note: For tests on materials that exhibit steady burning and spread of combustion in oxygen concentrations at, or close to, their oxygen index value,or for self-supporting test samples ≤3 mm (0-12 in.) thick, Method B may give more consistent results than Method A. Method B may then be used for test samples of Types I, II, III, or IV.
9. Perform Top Surface Ignition (Method A).
9.1. Use the igniter to initiate burning only on the top surface of the upper end of the test sample. Apply the lowest visible part of the flame to the top of the test sample. Use a sweeping motion, if necessary, to cover the whole surface, but take care not to maintain the flame against the vertical faces or edges of the test sample.
9.2. Apply the flame for up to 30 sec; remove it briefly every 5 sec to observe whether the entire top surface of the test sample is burning.
Note: The test sample is considered to be ignited as soon as removal of the igniter (after a contact period increment of 5 sec) reveals burning supported by the whole of the top end of the sample.
9.3. Begin measurement of the period and distance of burning when the test sample is ignited by pushing the START/STOP button on the character generator.
10. Perform Propagation Ignition (Method B)
10.1. Use the igniter to produce burning across the top and partially down the vertical faces of the test sample.
10.2. Lower and move the igniter sufficiently to apply the visible flame to the end face of the test sample and to a depth of approximately 6 mm to its vertical faces. Apply the igniter for up to 30 sec, interrupting application to inspect the test sample every 5 sec, until:
its vertical faces are burning steadily or the visibly burning portion first reaches the level of the upper reference mark on the support frame or, if used for test samples of Type I, II, III, IV or VI , the reference mark on the sample.
Note: The test sample is considered to be ignited as soon as any part of the visibly burning portion reaches the level of the upper reference mark.
10.3. Begin measuring the period and extent of burning when the test sample is ignited by pushing the START/STOP button on the character generator.
11. Assess and record the burning behavior of the test sample as described in section 4.8 and in accordance with the Oxygen Index Data Sheet (section 7, Figure 7-1). If burning ceases but spontaneous reignition occurs within 1 sec, continue the observation and measurements.
12. Return both gas valves to the OFF position.
13. Remove the test sample, and as necessary, clean any surfaces within the chimney or on the igniter that have become contaminated with soot, etc.
14. Allow the chimney to regain a temperature of 23 (±2) °C, or replace it with another so conditioned.
15. Determine the oxygen index of the test material by performing the following steps:
15.1. Mount a new test sample, and choose a new oxygen concentration while adhering to the following: decrease the oxygen concentration if the burning behavior of the preceding test sample yielded an “X,” or increase the oxygen concentration if the burning behavior of the preceding test sample yielded an “O.” The determining criteria for the size of the decreasing or increasing oxygen concentration are found in step 15.2 or step 4.6.1.15.4.
15.2. Determining the Preliminary oxygen concentration involves burning a number of test samples while using a series of oxygen concentration changes of any convenient step size. These changes shall be made until two oxygen concentrations are found to differ by ≤1.0% and of which one gave an “O” response and the other an “X” response. The oxygen concentration yielding the “O” response is the Preliminary oxygen concentration.
Note: The pair of oxygen concentrations resulting in the Preliminary oxygen concentration need not be the result of two consecutive test samples.
15.3. Test another sample at the Preliminary oxygen concentration, and record its response. A response different than that of the original test is acceptable. This test is the first in the NL – NT series of tests.
15.4. Test a new sample with an oxygen concentration change step size of d = 0.2% (refer to section 7.1.1) and with the step direction in accordance with step 4.6.1.15.1. Record the oxygen concentration and the test sample response. Continue to repeat this step until a response different than that observed in first test of this step occurs. The group of same response tests conducted in this step before this opposite response constitutes the NL series.
15.5. Test four more test samples with an oxygen concentration change step size of d = 0.2% and with the step direction in accordance with step
15.1. Record the oxygen concentration and the test sample response for each test. The last five tests and the tests in the NL series constitute the NT series; therefore, NT – NL = 5. These results are recorded on the Oxygen Index Data Sheet (Figure 7-1).
15.6. Calculate the estimated standard deviation of the oxygen concentration (σ*) measurements from the last six responses in the NT series (including CF). (Refer to section 7.1.3.) If the condition 2σ*/3 < d < 3σ*/2 is satisfied, calculate the oxygen index (OI). (Refer to section 7.1.1.).
Note: If d<2σ*/3, repeat steps 4.6.1.15.3 through 4.6.1.15.5 using increased values for d until the condition is satisfied.
Note: If d>3σ*/2, repeat steps 4.6.1.22.3 through 4.6.1.22.5 using decreased values for d, until the condition is satisfied, with one exception: that d shall not be reduced below 0.2% unless so directed by the relevant material specification.
16. When testing is complete and the unit has been shutdown in accordance with section 4.7, clean the unit, chimney, debris screens, and test sample holders using non-abrasive cleaners.
2. Procedure B
(Procedure C in ISO 4589-2) Procedure B is a comparison with a specified minimum value for OI (short procedure). If the actual oxygen index of a material is needed or in case of a dispute, use Procedure A, described in section 4.6.1.
1. Follow the instructions for setting up the apparatus and the test sample as described in steps 4.6.1 through 4.6.1.8, with the following exception: use the specified minimum concentration of oxygen in place of the initial oxygen concentration establishment method described in step 4.6.1.3.
2. Ignite the test sample in accordance with steps 4.6.1.9 or 4.6.1.10.
3. Use up to 3 test samples to assess the burning behavior of each sample as described in section 4.8. If, for at least two of the three samples tested, the flame is extinguished before attaining the relevant criteria from Table 7-1, i.e., if an “O” response is recorded, record that the oxygen index of the materials is not less than the specified value. Otherwise, record that the oxygen index of the material is less than the specified value, or determine the oxygen index in accordance with section 4.6, as appropriate.
4. When testing is complete and the unit has been shutdown in accordance with section 4.7, clean the unit, chimney, debris screens and test sample holders using non-abrasive cleaners.
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