the allowed filter leakage of dust per kg of dust collected by the vacuum cleaner is
class L 10g/kg of dust
class m 1g/kg of dust
class h 0.05g/kg of dust
which is why i was suggesting that for major cleaning the the clean room and in the wood room we would want to consider using a h-grade filter, despite probably only needed an m class vac in the wood room.
BTW I am not suggesting we get a h class vac as I believe we have a hard time getting it repaired. I am suggesting a m class vac fitted with h class filters