FED-STD-791D
a. Fill one of the quart bottles about half full of water, and insert its 2-hole stopper (and
tubing) as indicated for bottle A of Figure 1.
b. Connect the water-filled bottle to the rubber tubing on the volumetric flask.
c. Connect the copper outlet tube to the drying tube, and the drying tube to the
combustible-gas indicator. Adjust the indicator needle to zero.
d. Reposition the copper outlet tube so that its side opening is exposed to the air-gas
mixture, and apply low-pressure air to the water-filled bottle.
e. Adjust the screw clamp to produce a uniform flow of water of approximately 500 mL in
20 s, and record reading at which the indicator becomes stable.
6.4 Prepare the sample as follows:
a. Fill one of the quart bottles (bottle B) half full of test sample.
b. Insert the 3-hole stopper with its inlet tube, outlet tube, and thermometer. Position the
outlet tube so that its side opening is covered by the stopper. Seal the inlet tube with a
short length of rubber tubing and a screw clamp. Position the thermometer so that its
bulb is approximately centered in the test sample.
c. Immerse the bottle (containing the sample) in the heating bath so that the level of the
sample is below the level of the bath, and allow the sample to reach approximately 52C
(125F). During the immersion (approximately 5 min) shake occasionally to insure
even heating.
6.5 Test the explosiveness of the gas and vapor mixture of the sample as follows:
a. When the temperature of the sample reaches 52C (125F), remove the bottle and shake
vigorously for a total of 5 min, with periodic immersions of the bottle in the water bath
to maintain the fuel oil temperature at 52C (125F).
b. Fill bottle A approximately one-half full of water at about 52C (125F) and as soon as
bottle B has been shaken for 5 min, connect the two bottles as shown in Figure 1.
c. Connect the outlet tube to the combustible-gas indicator, zero the indicator needle, and
push the copper outlet tube down to expose its opening to the vapors in the bottle.
d. Apply low-pressure air to bottle A. Then while observing the indicator needle, slowly
open and adjust the screw clamp to permit the water to flow into the sample-filled bottle
at a uniform rate over a period of approximately 20 s. When the reading becomes
constant, stop the flow, and record the reading.
CAUTION: Do not allow fuel oil to flow into the combustible-gas indicator.
7. CALCULATIONS
7.1 This section is not applicable to the test procedure.
8. REPORTING
8.1 Report the sample as having passed if its combustible-gas indicator reading does not
exceed the reading for the hydrocarbon gas.
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