At this point, most state and local governments have adopted the 2003 or later International Plumbing Code (IPC) which requires the use of "tepid" (moderately lukewarm) water in emergency showers and eyewash stations. Consult this chart from the International Code Council to see if your state or local government has adopted the IPC or contact your local government for plumbing code requirements.
American National Standards Institute (ANSI) Standard Z358.1-2014 at (Section 6.4.6; B6) states that water delivered by emergency equipment be "tepid" which is defined as between 60 °F (16 °C) and 100 °F (38 °C) except when this would accelerate an adverse chemical reaction. ANSI is an internationally respected body that fosters "best practices" standards in a variety of areas. Thus, even if your state/local government does not require tepid water, your insurance carrier or attorney may require or advise you to follow the ANSI recommendation.
Tepid water delivery is achieved with a tempering unit (also called a thermostatic mixing valve or blending valve) that automatically mixes hot and cold water supplies to deliver water in the recommended temperature range. On our individual eye/face wash, shower and drench hose pages, you will find the appropriate valve listed in the Options column; follow the link for the recommended model for full information.