The lightning protection wire is run inside pvc through the building I am working on. However, a 50' stretch is run outside the pvc and simply strapped-up to the steel decking through the ceiling of one room. Surely this cannot be allowed? In the event of a lightning strike, couldn't the arcing and sparking created between the wire and the deck result in a fire?

I can't think of an NEC violation, but it might run against the... NFPA 780? Whatever the lightning one is.

Lightning protection here (NJ) are installed by "Certified Installers" to the best of my knowledge. As an EC, the sites that I worked on (Country Clubs) had a lightning contractor.

What you described does not sound 'right', but that's just a off the cuff comment. All the conductors that I have noticed were routed on the exteriors of the structures.

Just some items to be aware of besides the certified installer.

There is no typical requirement stating that the "down conductors" not allowed being run through the interior of a building. That being said, it does create alot more bonding issues that must be taken care of (flashovers).

There is no normal installation "shall" requirement that the conductors be in conduit.

But simply strapping a down conductor to steel decking does not meet bonding requirements assuming strapping means something to just hold the condutors in place (every 36" maximum). These are typically bonded via bonding plates or cadwelded. Whatever is used it is listed for lightning protection and has very specific requirements.

There are however requirements for regular yearly inspection of the system.

I am sorry that I can't put more information into this reply, but that would involve teaching a course on lightning protection.