Dears
Air vent filter in production used from 2015 till now with proceed integrity test every 6 Months and passed ,its applicable to use it till now?
If this is a return vent, there is no law against you doing this. From a microbial stance you should change it. The air in clean rooms is circulated through that filter, into a plinum, into a hepa and back into the room. Keeping this filter may put strain on the hepa. Although this will provide great room pressures it’s a no no from a cleaniness stance. I would make sure the hepa gets changed yearly and get checked bi annually for physical contamination before you have a filter failure.