Eyewash stations (emergency) must be connected to hard plumbed and provide continuous water for 15 minutes. Supplemental eyewash equipment can be portable or hard plumbed but doesn’t meet the time or pressure criteria of an emergency eyewash station. Portable eyewashes can be gravity-fed, air-pressurized, and bottles. These types of eyewashes are considered to assist in flexibility in the work setting but cannot replace an actual emergency eyewash. Supplementary devices can be used until a person gets to the emergency eyewash, or when chemicals are being used on a temporary basis.
Additional Info:
There are several Inspection, Testing, and Maintenance (ITM) requirements for emergency eye wash and shower stations in the American National Standards Institute (ANSI) Z358.1. Check out this blog from ANSI to learn more