“The purpose of layout and spacing is to design a workplace that will minimize personnel injuries, overall property damage, and related business interruption resulting from potential toxic releases, fires, and explosions. Areas to address during layout and spacing include both those that will minimize the incident size and those that will minimize the incident impact.”
Reference: Center for Chemical Process Safety. Guidelines for Fire Protection in chemical, petrochemical and hydrocarbon processing facilities. Chapter 7: Fire protection Fundamentals. Page 141
On a different scale but important as human factor is also spacing and layout to be considered for work space and area required for anticipated maintenance, such as replacing heat exchanger tube bundles, etc.