The fire board is a lower-density version of the calcium silicate family, formulated with heat-resistant material. Standard thickness is 12 and 15 mm in 1220 × 2440 mm sheets, apparent density not more than 1.0 g/cm3, thermal shrinkage no more than 2 % at high temperature, thermal stability class G1, smoke toxicity AQ1, moisture expansion no more than 0.25 %, drying shrinkage no more than 0.05 %, bending strength at least 10 MPa and thermal conductivity not more than 0.18 W/(m·K).
The reference standard is T/CBMF 79-2020, the calcium silicate board specification for fire use. A specifier should read the test report against the assembly, not against the board alone: a fire rating belongs to a tested system of boards, studs, fixings and joints, and substituting one component usually voids the result.
Typical applications are fire compartment walls in new and refurbished buildings, fire-rated ceilings, smoke exhaust duct encasement and steel structure protection. In each case the board is doing a different job: in a compartment wall it is holding back flame and limiting temperature rise on the unexposed face; around a duct it is keeping the duct below its limiting temperature for the required period; on steel it is slowing the rate at which the section reaches its critical temperature.
The installation rules are the ones that matter more than the board data: joints must be tight and staggered, fixings must be at the tested spacing and length, and penetrations must be sealed with an approved detail. A fire wall with a cable tray passing through an unsealed hole is not a fire wall, whatever the board's certificate says.