tsa.gov actually covers this in some detail. The web site says to request hand inspection for:
Film with an ASA/ISO 800 or higher
Highly sensitive X-ray, medical or scientific films
Film of any speed which is subjected to X-ray surveillance more than 5 times (the effect of X-ray screening is cumulative)
Film that is or will be underexposed
Film that you intend to 'push process'
Sheet, large format and motion picture film
(emphasis mine)

The problem is (as Iworkhere notes, "we were told ...over 1000") the training & practice doesn't always match published policy. Plus the site says you should "ask for" - not that it will be granted. Though I never had any trouble when I asked and explained that I would be or had been passing though multiple checkpoints.

Don't know that it will help when a TSO doesn't want to grant a hand inspection, but I think you could make a pretty good arguement that any blank film "is or will be underexposed".