Hi Rick!
 >    I had not considered the point you brought up, which is that my blind
 >  friend Scott could cause inadvertant damage to the underwater ecology.
 > I'm  not sure how much of an issue this may be, though.  As I mention in
 > my other  replies, he will of course require a cadre of concerned and
 > talented co-divers  to keep him oriented.  I expect that if they can
 > keep him safe they can keep  the reefs safe also.
You've presented an interesting question, and I kicked it around
with some of my instructor-friends as well as contacting the HSA
(Handicapped Scuba Association).  Theoretically there's nothing
from preventing your friend from learning to dive -- although it
would require tremendous logistical considerations.
As several others have mentioned, your friend would require
specialized instruments (voice response) to monitor his depth,
tank pressure, etc.  In addition, he would probably need to be
"tethered" to his instructor to avoid damage to the environment
and himself.  Finally, it's going to take a very highly-trained
and patient instructor to help your friend get past the task-loading
associated with learning to dive.
Bottom line, it can be done, but it will take lots of work.
--- Nibbles on bits!
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