It can happen for a variety of reasons which include having an old hatch cover or companionway door slam shut after it s been disturbed, having old cargo fall, or getting lost inside the vessel. Getting trapped by falling cargo or an old hatch cover sounds far-fetched, but it has happened. Divers have died from such accidents. As for getting lost, the interior of most wrecks are pitch black and everything is covered with silt. Once a diver enters a room or compartment and moves around, the silt is stirred up.
Divers can avoid becoming lost by tying a rope outside the ship and letting it out as they enter.
This provides something to follow back. Of course, divers should carry a diving light to see inside the ship. The bottom line is you re never completely safe inside a shipwreck. A final danger often faced by wreck divers is that of depth. Most wrecks are fairly deep, especially the larger ones, and the deeper the diver goes the less time he has before decompression becomes a problem.