Police divers brave dark, dirty world to bring justice to light

"Divers have to withstand pressure in deep water, so we need to pass a pressure test - the most difficult part of a police diver's physical test - in a simulated pressure situation equal to an underwater depth of 30 meters," Li said, adding that people usually experienced earache at a depth of 2 to 3 meters.

However, the psychological pressure police divers need to overcome is much bigger.