(a) one of them is hurt in a fashion that accepting help from strangers is required; bonus if the situation leaves him somewhat disoriented, or in too much pain to be clear-headed; and
(b) communication is cut off from the world at large.
My first thought for (a) is some sort of chemical in the eyes - the help from strangers could take the form of accepting water (his friend would take care of actual eye-washing). Some sort of all-over exposure to something that requires washing off could also work. My first thought for (b) is an EMP or a solar event. If I go with these I have plenty of sources; I just can't figure out how to tie these to (a).
I can see how widespread disruption could lead to being e.g. pepper sprayed or tear gassed, but I want them to be somewhat isolated (I'm thinking California desert, but I can move them pretty much anywhere on the planet). I could have my hero looking up right when a high-altitude nuclear explosion occurs, which might cause the right amount of damage, but I can't figure out how to work in the accepting-help scenario.
An EMP-caused crash of a plane carrying something caustic would work, but the internet tells me that losing control doesn't cause planes to just DROP; and, anyway, why'd they be flying, idk, lye in the first place?
I just feel I'm overlooking something obvious...