Remarkable increases of the ECT were not detected in the accelerated aging test of alkyl benzene. Remarkable increases of the ECT were also not detected in the room-temperature addition test of alkylbenzene with various organic acid compounds that are produced by aging deterioration of hydrocarbon compounds. The deterioration of hydrocarbon compounds alone has only a small influence on increasing the ECT. On the other hand, the ECT changed in various tests of alkyl benzene with sulfur or nitrogen compounds that are regard as bei