Grasso OMC oil filter block

Working on one the other day, had to change oil filter, machine had been off overnight.

Isolated etc & went to empty, found it had a lot of liquid ammonia in it.
OK ran machine, warmed up oil, change filter.

It occurred to me that if you left all valves closed, it would be possible to over-pressurize block,pump & housing.
In Australian/New Zealand codes a pressure vessel that can be isolated from system has to have a relief valve on it to prevent over-pressure.
What is European standards or USA on this, or any thoughts?

Here is model from Europe. :)

Attachment 14338

Thanks,
So it has a relief valve to protect it if isolated?
Where is it piped too, is it back pressure affected?