what is the safest way for black to avoid Catalan?

Are you avoiding the Catalan, or avoiding White from fianchettoing his Bishop?

As an advocate of the Catalan myself, it only works in 2 cases:

1) 1.d4 (I play it via 1.Nf3 d5 2.d4 Nf6 3.c4 e6 4.g3 or 1.Nf3 Nf6 2.c4 e6 3.g3 d5 4.d4) d5 2.c4 e6 (This move is important - The Bishop is BEHIND the pawn chain!) 3.Nf3 Nf6 4.g3

2) 1.d4 Nf6 2.c4 e6 3.g3 d5 4.Bg2

Against anything else, there is no Catalan:

A) Against the King's Indian or Grunfeld, you have the Fianchetto King's Indian or the Fianchetto Grunfeld

B) Against 1...f5, the move 2.g3 is BEST for White.  The f-pawn Blocks the Light-Squared Bishop, so Black would love to Fianchetto it to b7, but White beats him to the punch.  If you play say, the Stonewall or Classical, and play starts passive with say 1.d4 f5 2.c4 Nf6 3.Nc3 e6, then 4.Nf3 should be answered by 4...Bb4 and 4.e3 should be answered by 4...b6! now that you have solidified your control of e4.

C) Against the Slav, a few GMs may occasionally fiancetto their Bishop, but it's not any good for White.  Especially if Black develops his Bishop to f5, outside the pawn chain, before moving ...e6.

D) Even if you want to play the Nimzo-Indian (can't help you with the QGD), you can avoid the Catalan.  1.d4 Nf6 2.c4 e6 3.g3 c5 (instead of 3...d5).  You have to deal with the Fianchetto Variation of the Modern Benoni, but it's not a Catalan!

So if the Catalan is that scary to you, the KID (I play the Fianchetto Variation), Grunfeld (I also play the Fianchetto Variation), Dutch (I fianchetto the King's Bishop), Slav (I play the 4.Qc2 variation via 1.Nf3 d5 2.d4 Nf6 3.c4 c6 4.Qc2), and Benoni (which I avoid via the 1.Nf3 move order, after 1...Nf6 2.c4 c5 or after 1...c5 2.c4, you are in an English).

Hope this helps.

I should add, in addition to what is above, there is also the Modern Defense (1.d4 g6), which is what I actually play more often than anything else as Black, though I will play the KID, Dutch, Nimzo-Indian, and even the QGD or Slav occasionally as Black.  About the only openings I won't play against 1.d4 are the Benoni, Benko, and Grunfeld, but the Modern is my most common response.

There also is no Catalan against the Modern, and the Fianchetto lines as a whole against the modern are a lot more passive than many of the aggressive lines available to White, like the Austrian Attack.

I play d4, c4, and g3 in most white setups when it works, the main exception being the Slav. Like it's been said, only some of those systems are the Catalan, even if White has a similar setup in all of them.

It's another question why you would be scared of a catalan. In some lines white needs knowledge of a very subtle positional ideas to make progess, and in others there is sharp gambit play for the pawn. Very doubtful if players below FIDE 2100 or something will have the skill level to cause problems. 

Here's an approach I've used against titled players (with good results):

I like this setup because it takes the game away from the usual Open or Closed Catalan lines, while still giving black a comfortable setup to work with. As a nice bonus, it leaves white's "Catalan Bishop" diagonal blocked by his own d-pawn—which is usually the opposite of what Catalan players want.

Plans for black: Bishop often goes to f6 to hit the long diagonal. a7-pawn advances. Rook(s) often battery down down the semi-open b-file. White can end up pinned down by the queenside pressure if his moves aren't accurate.

Looks a lot like the Benko, yes, but with black's pawn on e6.

If safety/simplest is the priorty hard to beat 1.d4 Nf6 2c4 e6 3g3 bb4ch then if 4bd2 bxbch 5NxB move the pawns onto black squares with d6 and e5. 

If 5QxB then d5 yes this is technically a catalan but it is a very solid form. It turns out white queen is misplaced, and moving it to somewhere effective and getting an advantage is quite problembatic. In the trueth the methods to avoid catalan are getting into considerably more complicated positions for black, than allowing it.

That's a nice arrangement.   IQP to attack.   Catalan players are not thinking of being saddled with an IQP.