I occasionally design projects requiring explosion proof and/or intrinsic safe control system design. Our customer verbally instructs us on the area and size of the safety zone. A typical zone being a 5-foot radius around an open container of liquor. My question is how do I protect myself and my company from being held liable if the zone we are given is proven to be insufficient and something blows up? Is it sufficient to get the requirement (Class, Div, Group and zone area) in writing from the customer?