The Abyss is widely regarded as the toughest shoot in movie history. The actors spent up to 11 hours a day on set, which, incidentally, was located 80ft down, near an incomplete nuclear reactor! Apparently, the water was so heavily chlorinated that Ed Harris's hair began to turn white, Ed Harris hated working on 'The Abyss' and has consequently never spoken to anyone about his experiences.
The 'oxygenated fluorcarbon emulsion' featured in the film is the real deal. It was developed from experiments in the late 60's, though after some dubious results with a saline solution on a human subject, it was banned from being tested on people. However, the more modern fluorcarbon version has been successfully used on animals. The scene where the rat, Beany (although there were several rats used), is submerged in a small tub of the stuff is genuine, though in the equivalant scene with Ed Harris, he is just holding his breath. There is also a medical version being developed by a pharmaceutical company as a respiratory therapy.
The masks were specially designed to show the actors' faces, they had microphones fitted so that dialogue spoken at the time, by the actors, could be used in the film. The noises made by the regulators in the helmets were erased during sound post-production.
The scene with the water tentacle coming up through the moon pool was written so that it could be removed without interfering with the story, because no one knew how the effect would come out. The actors were interacting with a length of heater hose being held up by the movie crewmen. When the effects were completed, they surpassed everyone's wildest hopes.
The crew frequently spent enough time underwater to force them to undergo decompression before surfacing. Cameron would often watch dailies through a glass window, while decompressing and hanging upside down to relieve the stress on his shoulders from the weight of the helmet.
The tank was filled to a depth of 40 feet, but there was still too much light from the surface, so a giant tarpaulin and billions of tiny black plastic beads were floated on the surface to block the light. During a violent storm the tarpaulin was destroyed, thus, shifting production to night time.
Very few scenes involved stunt-people. When Bud drags Lindsey back to the rig, that's really Mary Elizabeth Mastrantonio holding her breath. When the rig is being flooded and characters are running from water, drowning behind closed doors and dodging exploding parts of the rig, those are all actors, not stunt-people.
Some of the cast and crew hated working on the "Abyss" so much that a few special T Shirts were made for the company, Like "Cast member on the "Abuse" " or "Hey, you can't scare me, I've worked for James Cameron" and "Nuclear Missiles, Aliens and James Cameron, talk about an adventure".
Cameron's director's cut is a good solid hour longer. The added footage primarily concerns a deleted subplot wherein the divers see on the television feeds that the aliens bring gigantic tidal waves to the brink of breaking on the shores of all the continents. It changes the feel of the movie and makes the alien experience less touchy-feely.
One of the listings submitted states that the Director's Cut is a "good solid hour longer". This is false.The director's cut, or, as Cameron prefers, the "Special Edition" or "Extended Edition", is merely 31 minutes longer...comprising of 28 minutes of footage and 3 minutes of additional credits.