Systems that may sit unused for decades yet be able to perform on extremely short notice without time for rehabilitation...

What's safer?

A system with moving parts subject to corrosion, (return mechanism) breakage, or (fire or earthquake induced) deformation.

or

An all steel stair set with no moving parts that can work despite considerable corrosion and deformation.

Depending on the weight of the user(s) is another idiocy.

Reminds me of a critique of (unnamed country) designs I heard...

Never use one part when ten will do.