I have a vendor citing NFPA 496 requires 6 air changes per hour is the reasoning for their HVAC sizing. I read through, but couldn't find any mention of it.
I read through it and found no referencing to the air changes. It appears that this NFPA standard is a performance standard for an engineered system for a particular applications. You may want to refer to the engineering documentation of the pressurization system to see if the air change were appropriate.
Hopefully your vendor is using an engineer to design the system.
This 2014 article says five, but no standard reference
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