On Fri, 13 Nov 2020 16:03:27 +0000, John Rumm
wrote:

snip

I had a chains saw blade jumps off the bar
last week Apart from damaging the blade it caused no problem

Yup, its not usually a problem when the whole chain loses tension like
that IME. (Also modern saws have chain catchers near the return side of
the sprocket to catch and snag a wayward chain).

I saw a bar drop off a saw in use and watched the chain shoot forward
(luckily) about 3m. ;-(

Cheers, T i m