The nature of diesel, oil, etc., did not alter during the air war, suddenly causing the alarms to sound. These substances were present before the initiation of the air war, and did not set off the chemical alarms. (The automatic alarms have no sensitivity control.)
These chemical alarms are battlefield instruments. Battlefields are full of fumes, propellants, explosives, and so forth. It is difficult to believe that they would have been procurred if they were ineffective in this environment.