Reference the sad news of the crashed Cypriot 737:
See:
http://www.cyprus-mail.com/news/main...21375&cat_id=1
“There are many theories being discussed. For example, I have just got off the phone to some colleagues in Greece who suspect that toxic and non-detectable fumes, like carbon monoxide, from the air condition system, may have leaked into the cockpit and caused the pilots to lose consciousness. However, that would not explain any possible cabin pressure drop.”
It may be nothing to do with this thread but surely this should be a reminder that detection systems be fitted URGENTLY.