I recently sat the C.I.T.B Safe Handling of Ammonia course.

With our knowledgeable and helpful friends up in Doncaster.
(Other good trainers also run this course and are also on the Forum.)

One fact quoted was that a Plant room fan must be capable of 15 air changes per hour.
As stated in En 378.

One question I did not clarify is when the fan is expected to run. I have always assumed the fan is normally in "stand-bye?"
However I am attending more and more sites where these fans are left running in Manual (Always On Mode)
What's everyone's take on this?
Grizzly