Underwater pressure demonstration using water bottle - GIF

[hemmjo]

Yep. your lungs do the same thing if you are free diving.

Most PET bottles can hold a lot more than 1 atm 14-15 psi. But you lungs sure cannot!!!

I used to do an activity with my students making rockets. We used 2 liter PET pop bottles with compressed air for propulsion. We typically used 75-80 psi in class. As I developed the activity, I tested a lot of bottles to assure safety. Many bottles that held in excess of 100psi. The only one that burst below 70 psi is one that I found along the road that had been out in the sun for an unknown length of time.