Thanks for the replies! All comments are thought provoking. The R22 does not have a engine fire light. Therefore it is possible that you will most probably know you have an engine fire by the time you really have one! However, the R44 has the light, and I take the point that you might get a false light on and therefore have to really look, listen,feel and smell for other indication before you pull the mixture and shut off fuel valve.
Thanks!
FS