OSHA 1910 for General Industry does not have a standard about tornadoes or requiring a “severe weather shelter.” However, OSHA 1910.38 does require employers to have an Emergency Action Plan (EAP) — in certain circumstances — like in Process Safety Management.
There are many inclement weather situations which require workers to take shelter or shelter-in-place. In these situations, OSHA does not have a standard requiring employers to have a “severe weather shelter.” Instead, OSHA provides preparedness guidance — that includes use of a shelter as best practice.