F20 – Inert gas system

APPLICATION FIELD

IACS UR F20, “Inert Gas Systems,” applies to inert gas plants

It a requirement that apply on tankers required by SOLAS regulation II-2/4.5.5.1 to carry crude oil, petroleum product tankers, including chemical tankers or other product with similar fire hazard. The rule covers both major plant technologies in current use: traditional systems generating inert gas from boiler flue gas or a dedicated oil-fired generator, and the newer alternative of nitrogen generator systems that separate nitrogen directly from compressed air using membrane or adsorber technology.

PIPE CLASS / SYSTEM TYPE

F20 sits outside the P2.2 Class I/II/III system, it’s a fire and explosion prevention requirement for the cargo tank atmosphere, not a piping classification rule. The inert gas distribution piping itself is still classified and constructed under P1/P2 in the ordinary way; what F20 adds is a layer of safety-critical devices and material requirements. 

RELATED RULES

• Statutory backdrop: SOLAS II-2/4.5.5.1 (and the associated 4.5.5.2, 4.5.3.4.2, 4.5.6.3, 11.6.3.4) is the primary trigger requiring inert gas system fitment on qualifying new tankers.
• Statutory backdrop: FSS Code Chapter 15, as amended by MSC.367(93), supplies the core technical content F20 is built on top of, F20 explicitly reads any reference to “Administration” in that chapter as meaning the relevant Classification Society.
• Statutory backdrop: IMO Resolution A.567(14) provides the parallel technical basis for chemical tanker inert gas systems, alongside FSS Code Ch.15 for oil tankers; F20.3.4 layers additional requirements from F20.2.3 on top of it.
• Statutory backdrop: SOLAS II-2/16.3.3, as amended by MSC.365(93), governs how the inert gas system is to be operated once installed.
• Cross-reference (unusual cross-domain reuse): UR M74, the Ballast Water Management System UR, explicitly borrows F20.4.4, F20.4.5 and F20.4.6 for certain in-line and ozone-injection BWMS technologies that use nitrogen or oxygen generation, substituting “ballast tanks/piping” for “cargo tanks/piping” throughout.
• Direct sibling: IACS Unified Interpretations addressing FSS Code paragraph 15.2.2.3.2.3.3 (separation between inert gas piping and cargo tanks) and paragraph 15.2.4.1.4 (access and ventilation for nitrogen generator receiver spaces) refine the underlying FSS Code text F20 incorporates.

RESTRICTION

Nitrogen generator output can’t exceed 5% oxygen by volume, with automatic discharge of “not in compliance” gas during start-up or abnormal operation as a mandatory, automatic response rather than a manual fallback.

At least two non-return valves are required in the inert gas supply main, one specifically arranged as double block-and-bleed, the second fitted with positive means of closure.

Compartments housing an oil-fired inert gas generator are treated as Category A machinery spaces for fire protection purposes without exception, regardless of the unit’s size.

And discharge locations for nitrogen system vent gases carry fixed distance criteria — oxygen-enriched air must vent outside the hazardous area, not within 3 metres of areas personnel transit, and not within 6 metres of machinery air intakes or ventilation inlets.

DESCRIPTION

F20’s structure deal with the two  different ways ships generate that inert gas. The traditional generation is characterized by scrubs and cools boiler flue gas or the exhaust of a dedicated oil-fired generator; newer plant exploit compressor and adsorbers to produce nitrogen. F20 is specific about corrosion-resistant construction through the scrubber, blower and drain piping. The newer nitrogen generators strips oxygen out of compressed air introducing its own hazardous around feed air quality, continuous purity monitoring, and safe venting of the oxygen-enriched byproduct that separation inevitably produces.

IMPORTANT NOTE

• The two-non-return-valve requirement in the inert gas supply main, including the double block-and-bleed arrangement, exists specifically to prevent cargo vapor migrating into the machinery space 

• Nitrogen generator compartments carry their own siting and ventilation requirements, positioned outside the cargo area, independent mechanical extraction at 6 air changes per hour, a low oxygen alarm, and no direct access to accommodation.