OSHA does not address this in the standard (1910.151(c)), but where the regulation is silent, the agency refer employers to the applicable ANSI standard which OSHA uses in enforcement. ANSI Z358.1 says that self-contained eyewashes should be no more than 53 inches from the level on which the user stands, and have 6 inches minimum clearance from the wall or nearest obstruction. The eyewash manufacturer should also provide installation instructions.