Hear Peter von Zeipel explain the dangers of diving deep into the clip above.
During normal scuba diving, the diver goes down to a maximum of 30 to 40 meters and can make a direct ascent if something should go wrong.
At deeper dives, a "gas roof" enters.
- Then you have gases in the body's tissues that make it impossible to get up immediately, says Peter von Zeipel, who sits on the Swedish Scuba Diving Association's technical committee.
It is still unclear what caused Sunday's accident in Gullmarsfjorden.
According to the police, it was three experienced divers who carried out a planned dive to 90 meters.
One of them came up to the surface and was able to sound the alarm, while one died and a third is missing.