Where did you see it and what were they doing? Were they locking carabiners?

I've heard it said that this should be avoided, but common sense will tell you that if the carabiners are oriented right (i.e. loading along the major axis) then they will be as strong as if they are being pulled on rope.

There are some applications where it can be advantagous to stack carabiners....descending for example.

Fill us in and we may be of more help.

love
nick

Chaining biners isn't a good practice. Use a runner/quick draw inbetween. Too likely to have the gates cross each other and load. That could lead to failure.

If you can't avoid chaining, make sure that you use autolocking gates. NEVER use snap gates without a runner.

Tom

Chain biners are a bad idea, in fact, it is best not to use biners at all, it is safer and more reliable(generally), than using biners, since there is less to fail.

Nick