Lots of homebrewers, especially British ones, use plastic PET bottles. So, I guess under normal pressures, it won't explode. I have used them a couple of times but only when counterpressure filling, so I knew the pressure was right. I imagine you'll be fine. If it freaks you out, you could always loosen the caps just for a second and let some gas hiss out.
Chase them crazy bald heads out of town....
