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....
Oh don't give me none more of that Old Janx Spirit
No, don't you give me none more of that Old Janx Spirit
For my head will fly, my tongue will lie, my eyes will fry and I may die
Won't you pour me one more of that sinful Old Janx Spirit