Difference Between A, B & C-Class Divisions?

IMO Symbol A Class Division 

IMO Symbol B Class Division 

SOLAS has tables for structural fire protection requirement of bulkheads and decks. The requirements depend on the spaces in question and are different for passenger ships and cargo ships.
The Administration has required a test of a prototype bulkhead or deck in accordance with the Fire Test Procedures Code to ensure that it meets the above requirements for integrity and temperature rise.

Types of Divisions:

1. "A" Class
2. "B" Class
3. "C" Class

"A" Class:
"A" class divisions are those divisions formed by bulkheads and decks which comply with the following criteria:

• They are constructed of steel or equivalent material
• They are suitably stiffened
• They are constructed as to be capable of preventing the passage of smoke and flame to the end of the one-hour standard fire test.
• they are insulated with approved non-combustible materials such that the average temperature of the unexposed side will not rise more than 140'C above the original temperature nor will the temperature at any point including any joint rise more than 180'C above the original temperature with the time listed:
• class "A-60"   60 min
• class "A-30"   30 min
• class "A-15"   15 min
• class "A-0"      0 min

"B" Class:

"B" class divisions are those divisions formed by bulkheads, decks, ceilings or linings which comply with the following criteria:

• They are constructed of approved non-combustible materials and all materials used in the construction and erection of "B" class divisions are non-combustible, with the exception that combustible veneers may be permitted provided they meet other appropriate requirements.
• they are constructed as to be capable of preventing the passage of flame to the end of the first half hour of the standard fire test
• they have an insulation value such that the average temperature of the unexposed side will not rise more than 140ºC above the original temperature, nor will the temperature at any one point, including any joint, rise more than 225ºC above the original temperature, within the time listed:
• class "B-15"   15 min
• class "B-0"      0 min

"C" Class:
"C" class divisions are divisions constructed of approved non-combustible materials. They need meet neither requirements relative to the passage of smoke and flame nor limitations relative to the temperature rise. Combustible veneers are permitted provided they meet the requirements.