3. In Troupe, cited at the end of the principal case, Judge Frank, in a concurring opinion, said, at 234 F.2d at 260 61:

On the negligence issue, the judge, at defendant’s request, charged, “It is enough if the steps and paint are commonly used and accepted in the industry at the time.” This was as obvious an error, on a material matter, as one can imagine. For the Supreme Court, this court and others have often held that usual practices, by others in the same industry or trade, similar to a defendant’s practices, do not constitute a defense in a negligence action. * * *