:doctor:
It would not hurt for a wreck diver to take cavern training (if not cave) in addition to your wreck training, there are some differences understood, but the same principles are applicable. The lines ran in a wreck are not usually as long as that for a cave. BUT the overhead environment is just as dangerous. Lines arrows can be placed, ("always on the exit side") of a line especially at a junction or turn. Example if you are maping out a wreck (without having done any top side research) lines will help you do that. You may not lay permanent line but may run temporary line until you complete the mapping process. Line arrows provide reference to exits and a means of measuring distance and bearings, you only run line to EXIT the wreck not enter. NOW An EXAMPLE
If by chance lets say you are diving a very large wreck and you and your buddy work your way to the engine room. You tie off your line reel and you and your buddy leave the line to look at something near the boilers, Your buddy silts the room, your lights are now useless. In the silt you have turned around so many times you are now lost in referencing where your line is, (AWARENESS is important). When you ran your reel it was in the mid water column not on the wall. Using your safety reel you successfully find the main line again. In the silt you can't see more than 6 inches provided your lights are still working, somewhat (you don't have natural lighting through a port hole here folks). You make a choice and turn to what you believe to be the exit. Air supply is now getting real low because of the time you spent to calm down and deploy a second reel to find the main line and find your buddy. You think all is fine again and you swim to exit, that is until you realise that you just went deeper into the engine room. Air is now really getting low, you are breathing heavier you turn to correct yourself and your buddy (anxiety build up) and make the exit 50 feet to the engine room door you came through, Now you need to ascend the two levels of stairs you went down and still no natural lighting or a doorway to escape to open water and you are 50 feet down inside the wreck (100 ft penetration), the wreck is 90 feet to the deck (140 feet to the sand) where the first door is that you entered (190 ft penetration , includes virtual overhead, depth). Some of the corridors are tight and require that you move single file and you need to twist to get through a bulkhead doorway and past fallen stairs before you can ascend to get back to the first door you see that can take you to the main deck and open water. Had you smartly placed line arrows you may not of wasted that time trying to guess which way is out in the first place, the line arrows provide a reference to the exit in a complete blackout/siltout scenario. Dramatic Yes But realistic Yes. Divers have been recovered from just such an accident as this. If you do not have line arrows and deploy them correctly when needed then you are playing underwater poker with the Devil. Line arrows work in all overhead environments. (Ice divers have a teather to the surface)
Wreck Divers need to do Accident Studies as to why deaths occur and then maybe Line Arrows will become standard equipment in wreck penetration.