yeah I was referring to the specific case where the observer is roughly close to x_max for a 10^19 or above event and quite literally in the ionization column.

yeah I was referring to the specific case where the observer is roughly close to x_max for a 10^19 or above event and quite literally in the ionization column. You can get rid of almost all of the electronic and gamma components in with about 10 feet sand, 5 feet concrete or 1 foot of lead, but that of course doesn't stop the muonic component. (I worked on HiRes/Telescope Array for 4 years on muon detectors and bi-static radar techniques for UHECRs, but that was quite a while ago and some of my memory might be slightly off) Not sure how much energy would be deposited, but I'm sure it's not insignificant. It's rare enough that no one person could expect it to happen but probably frequent enough that it does happen at least once a decade in a densely populated area.