Marine Safety Information Bulletins

MSIB: Acceptance of IMO code for fire safety systems for tank vessel inert gas systems – double block and bleed non-return device

The Coast Guard Office of Design and Engineering Standards has released Marine Safety Alert 05-22, to inform the Coast Guard Officers in Charge, Marine Inspection (OCMI) and the maritime industry that double block and bleed systems design, installed and operated in accordance with 74 SOLAS (14) II-2/5.5 are authorized under 46 CFR § 32.53-10(b) without the need for approval from the Coast Guard Marine Safety Center (MSC).

A “non-return device” functions in the Inert Gas System (IGS) to prevent hazardous or flammable cargo vapors from flowing from cargo areas back towards machinery spaces and possible ignition sources. The double block and bleed valve arrangement isolates or blocks the return of gas from the cargo area to the engine room and permits the bleeding of any residual gas in the IGS.

Title 46 CFR Subchapter D, Subpart 32.53 contains the applicability and technical requirements for IGS on tankship vessels. Currently, 46 CFR § 32.53-10(b) requires each IGS be “designed, constructed, and installed in accordance with the provisions of SOLAS II-2, Regulation 62 . . . .” However, Regulation 62, has been superseded by SOLAS Chapter II-2, Regulation 5.5.1 This revised regulation requires compliance with the International Maritime Organization (IMO) Fire Safety Systems Code (FSS Code), Chapter 15, which includes the ability of applicable vessels to use a double block and bleed system in addition to a deck water seal. 2

As such, a non-return device arranged as a double block and bleed in accordance with the FSS Code may be accepted without MSC approval. However, MSC approval or certification by a Recognized Organization (RO) under 46 CFR Part 8 must still be obtained for dry seal types. Coast Guard Port State Control Officers who examine a vessel without an MSC or RO approval for a dry deck seal type should issue a deficiency to be rectified prior to next U.S. port after sailing foreign (Code 40).

This notice should be utilized until changes are incorporated into the Code of Federal Regulations (CFR). Questions concerning this notice or vessel inert gas systems may be forwarded to Coast Guard Office of Design and Engineering Standards, at:

1 Under SOLAS Chapter II-2, Regulation 5.5, the Administration has the ability, after giving consideration to the ship’s arrangement
and equipment, to accept other fixed installations.
2 Chapter 15 is amended by IMO Circular MSC.367(93). Paragraph of IMO MSC.367(93) states, “The first non-return
device shall be a deck seal of the wet, semi-wet, or dry type or a double block and bleed arrangement.”

This blog is not a replacement or substitute for the formal posting of regulations and updates or existing processes for receiving formal feedback of the same. Links provided on this blog will direct the reader to official publications, such as the Federal Register, Homeport and the Code of Federal Regulations. These publications remain the official source for regulatory information published by the Coast Guard.

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