The U.S. Coast Guard Commandant’s Office of Design and Engineering Standards (ENG-3) released Maritime Safety Information Bulletin No. 05-22 (MSIB) for tank vessels on June 16, 2022. 1 In particular, in accordance with 46 CFR 32.53-10, the MSIB authorised and approved double block and bleed systems for the inert gas systems on tank ships that are created, installed, and used in accordance with 74 Safety of Life at Sea Convention (SOLAS) (14) II-2/5.5 (b) as reported by Mondaq.
SOLAS compliant systems
The significance of the MSIB is that shipowners and operators with SOLAS-compliant double block and bleed systems for Inert Gas Systems on tank vessels do not need approval for their system by the Coast Guard Marine Safety Center.
What is a Non-Return Device for an Inert Gas System?
Hazardous or flammable cargo is frequently transported by large tank boats. There is an inherent risk that the various types and grades of oil cargo in the cargo hold will cause combustible gas and vapour to be produced while loading. Furthermore, an empty cargo compartment that still contains volatile gases poses a threat of explosion. An isolating valve, scrubbing tower, demister to absorb moisture, gas blower, inert gas pressure reducing valve, deck seal, deck isolating valve, pressure vacuum breaker, cargo tank isolating valve, mast riser, and safety and alarm system are typically included in inert gas systems designed to reduce explosions.
The “non-return device” of the Inert Gas System acts as a wall to stop flammable and hazardous cargo vapours from entering machinery compartments and other potentially explosive parts of the ship. The double block and bleed valve setup “isolates or limits the return of gas from the cargo area to the engine room and facilitates the bleeding of any leftover gas in the Inert Gas System,” according to the Coast Guard MSIB.
The Amendment of SOLAS
The current edition of 46 C.F.R. Subpart D, Subpart 32.53 contains the technical specifications for Inert Gas Systems onboard tank vessels. However, these regulations are no longer in effect because they still refer to SOLAS II-2, Regulation 62, which has since been replaced by SOLAS II-2, Regulation 5.5. Shipowners must adhere to the International Maritime Organization’s Fire Safety Systems (FSS) per the new SOLAS regulation, Regulation 5.5. (IMO). This new rule stipulates that vessels may utilise both a deck water seal and a double block and bleed the system.
The MSIB makes it clear that ships having non-return devices that conform with the FSS Code and have a double block and bleed are acceptable to the Coast Guard without further Coast Guard Marine Safety Center certification.
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