Agreed, more info is needed here. Many of those 'silencers' (they're not called mufflers for a reason) are wrapped inside with fire and heat retardent. That means it may not get as hot as you'd think, but that should be in the submittal documents. It also appears that it was here for some time prior to the EMT, so who's problem is that?
I'd be more concerned with the "air over" portion of the cooling. That's something that will get overlooked over the years.
