Why does avgas 100LL smell differently than automobile gasoline? And why don't avgas 100LL fumes from a fuel tester located in the cabin make pilots ill?
The sweet smell of 100LL AvGas is due in large part—if not entirely—to the additive Tetraethyllead (TEL). TEL is included in the formulation of 100LL as an anti-detonation additive, octane booster, and lubricant.
A fuel tester stored in the aircraft cabin should not induce crew illness because the tester should be drained of all but residual fuel, that residual fuel will evaporate very quickly—usually long before startup, and aircraft cabins are typically well ventilated.