If you're looking for an example, a real-world application you might also consider is emergency ventilation in a data center. If the AC fails, the equipment will quickly overheat, and is frequently fitted with emergency ventilation fans so the data center can maintain operation.
I've never seen these fitting with VFD, it's either required because the AC failed, or it's not, there's very little in-between.
As in everything else, it must be tied into the fire protection system to not spread smoke and fan the flames. Also, FM200 requires the space be absolutely sealed.
