I based this on what the government tells us - that film is safe to iso 800. Is it unreasonable then to assume then that 1600 is possibly unsafe? In that case, a 2nd exposure could cause fog on iso 800 film. 2 more exposures could affect iso 400, another 4 could affect iso 200, and so on. I hate to do this, but have to ask for a citation for the comparative levels of exposure in flight vs xray.