# Tarzan, Fluids, and Pressure

Ape Man in a movie is shown evading his captors by hiding underwater for many minutes while breathing through a long reed. Assuming the maximum pressure difference lungs can manage and still breathe is -80 mm-Hg , calculate the deepest he could have been.

I immediately thought of P = p*g*h, where p = density. h is the depth, but this is for gauge pressure. Do I use the formula for absolute pressure P = atmospheric pressure + pgh?

Am I correct in my reasoning?

Thanks.

Yes the absolute pressure under water is $\rho g h + 1atm$... however, the pressure inside the (uncompressed) lung is 1atm... so the DIFFERENT of the pressue is $\rho g h$