Marine Fire-resistant Partition Guide: SOLAS Classes, Testing, and Compliance

A marine fire-resistant partition is a bulkhead or deck division built to the SOLAS Chapter II-2 "A," "B," or "C" class standard, constructed from non-combustible steel or equivalent material with mineral wool insulation, engineered to block the passage of fire and smoke between shipboard compartments for a defined test period. The three classes are not interchangeable labels — they represent specific, independently verified performance levels: A-class divisions must resist fire for 60 minutes, B-class for 30 minutes, and C-class simply must be built from non-combustible material with no minimum time requirement. Which class applies to a given bulkhead or deck depends on what spaces sit on either side of it, as set out in the SOLAS fire boundary tables.

This article explains how each class is defined and tested, what materials and construction methods are used to achieve the ratings, and the practical details — such as penetration sealing and insulation subclasses — that determine whether a partition actually performs as intended once cables, pipes, and doors are installed through it.

The Three SOLAS Fire Classes Explained

SOLAS Chapter II-2 divides shipboard fire boundaries into three classes based on how long they must contain fire and smoke, and how much they must limit the rise in surface temperature on the unexposed side. Regulators use these classes — along with sub-ratings for insulation performance — to specify exactly which type of division is required between any two adjacent spaces on a vessel, such as between a galley and a corridor, or between an engine room and accommodation.

What the Sub-Ratings Mean

The number after the letter indicates how long the insulation must keep the unexposed side below the specified temperature rise, not how long the structure itself survives. An A-60 division is insulated to hold back heat transfer for the full 60-minute test, while an A-0 division is made of the same steel structure but carries no insulation requirement — it will still contain flame and smoke for 60 minutes, but the reverse side can heat up much faster. This distinction matters directly for space planning: a corridor wall next to a galley may only need A-0, while a stairway enclosure serving as an escape route typically needs full A-60 protection.

How a Fire Partition Is Tested and Certified

Every marine fire-resistant partition design must pass standardized furnace testing under the IMO 2010 FTP Code (Resolution MSC.307(88)) before it can be installed on a SOLAS-regulated vessel. The testing is split into distinct parts covering different properties, and a partition system must clear all of the relevant parts to receive type approval and the associated Wheel Mark certification.

Non-Combustibility Testing (FTP Code Part 1)

Core materials such as mineral wool or rock wool are first tested individually for non-combustibility. Cylindrical samples are placed in a furnace heated to approximately 750°C for 30 minutes. To pass, the average furnace temperature rise must not exceed 30°C, the specimen's own surface temperature rise must also stay under 30°C, sustained flaming must last less than 10 seconds, and mass loss must remain below 50%.

Fire Resistance Testing (FTP Code Part 3)

The assembled bulkhead or deck panel is then tested as a complete system in a furnace following the ISO 834-1 standard time-temperature curve, which replicates how a real compartment fire develops. For A-class insulation ratings, the criterion is that the average temperature rise on the unexposed face must not exceed 139°C above the starting temperature, with no single point exceeding 180°C, for the full duration of the class (60, 30, or 15 minutes). Integrity is checked with a cotton-wool pad test: if a pad held against any gap or crack on the unexposed side ignites or glows, the panel fails, regardless of the temperature readings.

Materials and Construction of Marine Fire Partitions

Most marine fire-resistant partitions are built as sandwich or lined panel systems: a steel or aluminum face sheet on each side with a non-combustible mineral wool core between them. The core material carries almost the entire fire-resistance burden, since it is what slows heat transfer from the exposed to the unexposed face during the test period.

• Core material: Marine-grade mineral wool or rock wool boards, commonly specified at densities in the 60–180 kg/m³ range depending on the class rating and panel thickness required.
• Facing sheets: Galvanized or stainless steel, or aluminum for weight-sensitive applications, typically finished with a protective foil or glass-cloth facing on one or both sides.
• Structural frame: Panels are commonly mounted on a stainless steel or steel channel framework fixed to the ship's structural stiffeners, sometimes with an air gap between the insulation and the hull for additional thermal performance.
• Joint treatment: Seams between adjacent panels are covered with insulated cover strips, since an untreated joint is one of the most common points of fire-test failure in field installations.

For A-60 rated structural insulation, panel thickness is generally determined during type approval testing and stated on the manufacturer's certificate — the FTP Code does not allow that thickness to simply be scaled down for lower ratings like A-30 or A-15 without additional dedicated fire testing at that thickness.

Penetrations: The Most Common Point of Failure

A perfectly rated bulkhead can still fail to perform its function if the cables, pipes, and ducts passing through it are not sealed with a matching fire-rated transit system. Every hole cut into an A-class or B-class partition for services must be closed with a penetration seal tested and certified to the same class as the surrounding structure, or the entire division's rating is compromised at that point.

Cable and Pipe Transit Requirements

Certified marine penetration seals typically combine a non-combustible filler material — such as calcium silicate blanket or mineral wool packing — with a fire-resistant, water- and gas-tight sealant around the outer surface. These systems are rated across the same range as the partitions themselves, from A-0 up to A-60, and multi-cable transit systems are commonly tested and approved for large bundles of mixed cable types and metallic or GRP pipes passing through a single opening.

Why Matching the Rating Matters

An unsealed or mismatched penetration creates a direct path for flame, smoke, and hot gases to bypass the insulation entirely, which is exactly the failure mode the cotton-wool pad test is designed to catch. Facilities specifying new construction or retrofits should confirm that penetration seal products carry documentation referencing the specific FTP Code Part 3 test and class rating that matches the host bulkhead or deck, not just a general "marine approved" label.

Choosing the Right Class for a Given Space

Selecting the correct partition class is not a design preference — it is dictated by the SOLAS tables that cross-reference every pair of adjacent shipboard space types (control stations, accommodation, machinery spaces, cargo areas, and so on). That said, several practical considerations should guide procurement and retrofit planning beyond simply meeting the minimum required class.

1. Identify the adjacent space types on both sides of the proposed bulkhead or deck, since the required class is determined by this pairing, not by the space alone.
2. Confirm whether insulation is required — a 0-rated division (A-0, B-0) meets the flame/smoke barrier requirement but offers minimal protection against heat transfer, which matters for spaces where people may need to remain for extended periods during an escape.
3. Verify all penetrations are specified with matching fire-rated seals at the design stage, rather than treating cable and pipe routing as an afterthought once the partition itself is approved.
4. Request FTP Code Part 3 type-approval documentation for the specific panel thickness and configuration being purchased, since thickness cannot be assumed to scale linearly between class ratings.