Another Grammar Q...

[jopakent at comcast.net]

I'm trying to come up with the correct hyphenation of the term "single failure proof"  (SFP)

The term refers to a design capability for a heavy duty crane.

My translation of this regulatory term is: "If one important component fails, (for instance the power fails or a gear breaks, or a lifting rope snaps), the crane won't drop its load."

Unfortunately, the standards themselves and a Google search yield no consistency whatsoever, within the same standard, I see multiple variations. (S-F-P, S-FP, SFP, & SF-P)

What I'm stuck on is coming up with a grammatical case for one scheme over the other. Here's the extent of my wit to date: 

"failure-proof " is a hyphenated adjective modifying crane. But the crane is not failure-proof, it's only single-failure-proof.  That is, if the power goes off and the brakes fail at precisely the same time then the crane could drop the load.

I guess my grammar chops weakness is finally exposed with this question: 
What is "single" in this case? Its modifying an adjective, right? I'm guessing that Words into Type or Chicago Manual of Style might be helpful, but I haven't brought my reference library into the office yet. Gad I hate posting my ignorance like this, but I'm truly stumped.

Humbly,
--
J. Paul Kent
206-383-0539