Two divers were airlifted to Poole after ascending too quickly on Saturday afternoon.
The first incident took place off the west coast of Portland around 2.09pm.
The skipper of the dive boat Scimitar called the coastguard who flew the casualty to the landing site at Poole, where he was met by a dive doctor and taken by ambulance to the nearby Hyperbaric Recompression Chamber for treatment.
At 3.38pm, the coastguard helicopter was called to Lulworth Cove after a mayday call to another male diver who had made a rapid ascent.
He was also taken by ambulance to the landing site at Poole and then transported to the chamber for treatment.