This publication describes those procedures that are considered good practice for gas freeing of. entry into. cleaning of. working in. and exit from open-top and covered floating-roof. nonportable. petroleum storage tanks. This publication supplements API Publication 2015. Cleaning Petroleum Storage Tanks. which does not include information specifically applicable to floating-roof tanks. Purpose and Application This publication sets forth those practices that. by general consensus. are considered advisable for the safety and health of personnel and the prevention of property damage. Specific circumstances will determine the application of the procedures described. The practices described are intended as a guide for personnel engaged learningopen-top and covered floating-roof tanks.