APPLICATION FIELD
IACS UR M84, “Capacity and availability of compressed air for essential services”
is a genuinely new requirement, published by IACS in February 2024.
It is entering into force from mid-2025/2026 depending on the individual Classification Society’s implementation timeline.
It applies to compressed air systems supplying essential services aboard ship.
It means any function where a loss of compressed air supply would compromise propulsion, safety, or another essential operation, which in modern ships extends well beyond engine starting to include pneumatically operated quick-closing valves, control and instrumentation air, and various automation and safety functions.
The rule requires that the arrangement guarantee sufficient capacity and availability of compressed air across three distinct operating conditions: normal operation, maintenance of part of the system, and failure of part of the compressed air system.
PIPE CLASS / SYSTEM TYPE
M84 isn’t a P2.2 piping classification rule, the compressed air piping itself remains classified and constructed under P1/P2 in the ordinary way, typically as Class II or III piping depending on service.
What M84 adds is a system-level availability and redundancy requirement, in the same spirit as M61’s long-standing treatment of engine starting air capacity, but generalized to cover all the essential services that depend on compressed air.
RELATED RULES
- Direct sibling: UR M61, “Starting Arrangements of Internal Combustion Engines,” is explicitly cross-referenced, where compressed air for essential services is drawn from the same source as the engine starting air system, M84 requires that this additional source must not reduce the capacity and availability M61 mandates for engine starting itself.
- Direct sibling: UR M11, “Protective devices for starting air mains,” shares the same physical starting/compressed air system but addresses a different concern, M11 is about explosion protection, M84 is about capacity and availability.
- Cross-reference: UR E21 Rev.2 (Requirements for Uninterruptible Power System units) was updated by IACS specifically to cross-reference the newly developed M84, so that the availability requirements for essential pneumatic services and essential electrical services are considered together rather than in isolation.
- Direct sibling: UR P1/P2 continue to govern the strength, classification and construction of the compressed air piping itself; M84 sits above that as a system-design and redundancy requirement.
RESTRICTION
The capacity M61 requires for engine starting has to remain intact regardless of what essential services are also pulling from that source. Beyond that, the rule’s core structural requirement is that the system must always have adequate capacity, regardless of whether it is under maintenance or not.
DESCRIPTION
M84 treats compressed air availability as a system-level requirement that has to be engineered with redundancy in mind, recalling the same logic that already applies to essential electrical services expected to survive a single failure through duplicated generation or UPS backup. The same compressors and receivers that start the main engine are also used to produce compressed air for these other essential pneumatic demands. Without a rule addressing that overlap directly, a designer could inadvertently undersize a shared system, so that drawing air for one essential function during an emergency reduce the availability for the another.
IMPORTANT NOTE
- M84 is a new UR, with an implementation timeline still rolling out across individual Classification Societies as of 2025/2026
- Where essential-services compressed air and engine starting air share a common source, the design has to demonstrate compliance with M84’s availability requirement and M61’s starting-capacity requirement simultaneously.
Frequently Asked Questions
Q: What is IACS UR M84?
A: A new Unified Requirement, published February 2024, setting capacity and availability rules for compressed air supplying essential services on ships.
Q: When does UR M84 enter into force?
A: From 1 July 2025 under IACS, though each Classification Society rolls out the requirement on its own implementation timeline.
Q: Does M84 replace UR M61 for engine starting air?
A: No. M61’s starting-air capacity requirement still applies in full; M84 adds an additional layer for other essential pneumatic services drawing from the same source.
Q: What counts as an “essential service” under M84?
A: Any function where losing compressed air would compromise propulsion, safety, or another essential operation – including quick-closing valves, control and instrumentation air, and automation and safety functions.
Q: What operating conditions does the compressed air system need to cover?
A: Three: normal operation, maintenance of part of the system, and failure of part of the system.
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