Was This A Permit Required Confined Space? By Hector V. Pazos, P.E. This accident happened in a large compartment of an Offshore Supply Vessel (OSV), which, because of lack of appropriate ventilation and toxic atmosphere it should have been treated as a confined space. An OSV is a vessel that carries supplies to offshore platforms and rigs drilling for oil and gas in the oceans, such as the waters of the Gulf of Mexico. Most of the supplies are carried on the cargo deck, but drilling mud and other chemicals are carried below the cargo deck in a compartment designated as "Bulk Mud Room", which on some OSV's may be 60 to 100 feet long. In this compartment some 10 to 20 large pressurized cylindrical tanks measuring 15 to 18 ft. in diameter and 10 to 12 ft.