Not sure about continuing to participate as this discussion will doubtless degenerate into another rather tiresome display of polarised intransigence.
But... For the sake of balance, there are two (at least) crashes still unexplained except as a 'cabin fire of unknown origin'. United Viscount 9/64 Tennessee and Varig 707 11/73 Orly. Smoking has been suggested as the cause of one or both, but never demonstrated satisfactorily. Unless someone knows better.
Agree about cabin air BTW. You can't see stale air, you could see cigarette smoke making its removal a necessity.
Edited to add the word 'cabin'
[ 22 October 2001: Message edited by: PaperTiger ]