Structure and escape
"A", "B" and "C" class divisions
The divisions cut the ship into zones and hold back fire and smoke for a defined time. The letter and the number state the division’s fire resistance.
Key facts
- Class "A": fire-resisting divisions of steel (or equivalent material), tight to flame and smoke through the one-hour fire test.
- The number after the letter is the insulation time: A-60, A-30, A-15 and A-0 mean the side away from the fire will not heat up by more than an average 140°C for 60, 30, 15 or 0 minutes respectively.
- Class "B": fire-retarding divisions of non-combustible materials (bulkheads, ceilings, linings), with lower requirements than "A".
- Class "C": divisions of approved non-combustible materials, with no requirements on the passage of smoke and flame or the temperature rise.
- In the ventilation ducts the divisions are completed by fire dampers: normally open, closed during a fire so it cannot travel down the duct.
- A fire damper maintains the fire resistance of the division; a smoke damper only holds back smoke and hot gases.
Watch out
The definition of a non-combustible material rests on a test result: heated to about 750°C it neither burns nor gives off vapours able to self-ignite (tested per the FTP Code).
Legal basis
SOLAS II-2/3 (definitions of "A", "B" and "C" class divisions) and II-2/9; the FTP Code.
This is not a legal text: when in doubt, the current wording of the Convention and the FSS Code decides.