Federal OSHA regulates eyewash stations in its 1910.151(c) standard on medical services and first aid. Unfortunately, OSHA does not go into much more detail on eyewashes. However, where the regulations are silent on the details regarding eyewashes and showers, OSHA has referred to the ANSI standard Z358.1 Emergency Eyewash and Shower Equipment for specific requirements.
The ANSI standard requires that plumbed and self-contained eyewash units must provide flushing fluid to “both eyes simultaneously.” It may be a good idea to check with your safety supplier as to whether or not this “simultaneous” flushing can be accomplished with one flush head.