Could you go to a steel mesh/expanded metal grid stair?
Will the stair be exposed to freezing temps? If so, make sure water won't accumulate. You won't want to ahve to salt it, even if it's stainless.
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"...students of traffic are beginning to realize the false economy of mechanically controlled traffic, and hand work by trained officers will again prevail."
Wm. Phelps Eno, ca. 1928