I have been surprised at our profession’s lack of basic understanding regarding pressure and vacuum. I think most people of the general public have no idea that we live under 14.7 pounds of pressure per square inch on our bodies. We say this is what it is at SEA LEVEL, which means a lot. As with the recent catastrophic implosion of the submersible, it was well BELOW “sea level,” meaning there was considerably MORE pressure per square inch on its surface/shell. When we look at a pressure gauge that reads 0 psi, that is what we call PSIG (G stands for gage). If the gauge measured absolute pressure (and we were standing on a beach at sea level), it would read 14.7. So a gauge on a vessel reading 0 psig tells us there is actually 14.7 psi (at sea level) inside the vessel. When we see a vessel that is “caved in,” we will hear people state, “It was sucked in,” which is technically incorrect. What happened was we removed the pressure from within (created a vacuum), and the external pressure pushed the walls inward.
I had to explain that so the rest of this makes sense…