That rule is right from ANSI Z358.1. Eyewashes and showers cannot have a barrier such as a door between the user and the equipment unless that door opens out and is incapable of being locked from the inside.
Monona
In a message dated 10/21/2012 6:32:09 AM Eastern Daylight Time, Carole.Herriott**At_Symbol_Here**WEYERHAEUSER.COM writes:
In Washington safety showers can't be placed outside of doors unless crash bars are on the doors. In the event of chemical splashing you wouldn't want to have to find a door knob if your face were splashed.