How strong do you have to be to play blindfold?

I've heard that all the stronger chess players (GMs and the like) are naturally able to play blindfold as a consequence of their chess visualization skills.  What's the minimum rating where this happens - can 2300s play blindfolded?  2000s?

And also, if I train to be able to play blindfolded will my rating increase?

I don't think there's a minimum rating that enables one to play blindfolded.  I've heard stories of 1800's being able to do it and 2200's not being able to do it, it's very person dependent.  But the odds of someone rated 1200 being able to play blindfolded is pretty slim.

I think training to play blindfold chess specifically won't help your rating or overall play very much.  Even if you are able to play blindfolded, if your chess understanding hasn't increased, you'll just play very poor moves without sight of a board.  For instance, say a 1200 is playing a 2400.  The 2400 is blindfolded and the 1200 is allowed to use the board, and move the pieces all over the board analyzing his moves.  The 1200 can theoretically see as far in advance as possible, but he'll still get crushed easily because his overall game understanding isn't up to par.

Instead of trying to work on playing blindfolded, I think your time would be much better spent working on your openings and middlegame transition/plans, studying the endgame, and analyzing GM games.  If you really force yourself to focus when studying and playing, your ability to calculate and "see" many moves ahead will get better.

It was my opinion that I doesn't help your chess at all. I've come back from that somewhat. It may help your visualization when calculating lines.

But there probably are more time effective ways to train this. I don't see the use in it

I think there are blind players at all levels. Plenty of blind people play.

The other thing I think it might help train is memory of games.  If you can play blind then you can remember the game and recognize patterns from it later on.

A good point, do you know where to find information about the ratings of visually disabled people?  I found http://www.americanblindchess.org/ratings.html however that is only for correspondence chess, which is not necessarily the same as playing "blindfold," i.e. a blind correspondence player might review the move history repeatedly, or set up the position on an analysis board.

I think a related, and more pressing, question is just how good do you have to be at blindfold chess to keep it from being hazardous or dangerous?

Being blindfolded like that for long periods of time obviously can be tricky.  It's easy to see how a player might accidentally set himself on fire, stumble over something and crack his head open, or even fall down a flight of stairs.

I could play a game blindfold when I was c. 1200, before my first USCF tournament, so I think it can be done by pretty weak players.

I'm not very highly rated, but I find it next to impossible to play without seeing the board for longer than a moves. I have a weird thing with my brain where I lterally cannot form images in my head. I have an obscene amount of memory and prcoessing for words, but not images. Blindfolded playing can increase your chess skill, but not all people are able to do it.

I think blinfold chess can help you. I remember GM Christiansen mentioning that after he did a simultanous blindfold play against amatures, he have a good result in the tournaments that follows.

I can play blindfold and I can bench press 200 lbs.

Playing through past games blindfold may be helpful too. I have done that with some classic games. Once I memorized the moves visually, I then did various exercises such as listing attacking or defending pieces in each position (similar to the Attack Training and Defence Training options in Fritz).

I had some college friends who could do it and they were not super strong - a bit above 1800 I think but certainly not 2000.

I am doubtful as to whether it helps your chess much.  There was a vogue for massive simuls a century or so back and some masters were competitive about playing the most opponents.  Quite a few of the simuls were played blindfold but after a while it became clear that the mental techniques developed to pull off these tricks damaged one on one playing strength.  Maybe the damaging techniques were solely associated with playing 100 plus people simultaneously but I would not be surprised to find that the blindfold aspect plays a part too.

Anyway massive simuls, blindfold or not, disappeared.

I could play blindfold when I had a rating of 1500.  I don't think it helped my chess playing at all, but did give me some severe headaches.  At the Amber tournament they play with a blank board in the "blindfold" games which helps a lot.  One tip if you want to try playing blindfold is to divide the board in quarters.  Each quarter board is identical consisting of 16 squares (4x4) with a light square on the left bottom and upper right corner.  When I visualize the board only a quarter is "in focus" and the rest of the three quarters are kind of fuzzy.   It is much easier to try to visualize the board a quarter of board at a time, and you can learn to follow a diagonal from one quarter to another (very easy with the two long diagonals).  Larry Christensen may find it useful for warming up for a tournament, I found it detrimental to my tournament play (hard to concentrate when you already have a headache at the beginning of a game).  In the old Soviet Union blindfold simuls were illegal as it was considered a health hazard.

It depends to what standard. I can manage blindfold but I would be playing 500-600 pts below my normal standard. Anyone who can play close to their normal level blindfolded is really impressive.

And the most impressive thing is simultaneous blindfold, believe it or not there are people who can do this.

If you practice, you can probably do it. I haven't seen real beginners do it, but more experienced players in the 1800 range, sure.

I can somewhat do it myself, but there are risks of serious mistakes later in the game. 

My blindfold play was very much inferior to my OTB.  I would occasionally play some college friends of mine who were very casual players (they would be below 1000 in strength) and it was a pretty even match.

"It is not that hard"

Maybe not, but I am sure some people find it easier (to improve) than others - we are not all blessed with the same aptitudes.