expanded minerals such as perlite or vermiculite, the insulating properties are enhanced and the resulting lightweight plaster can be used to provide fire protection for steel columns. The column section is wrapped with metal lath or paperbacked wire fabric to create a substrate for the plaster. Columns protected with lath and plaster enclosures are reported in the UL Directory and have designations X401 through X413. Fire protection ratings up to 4 hours have been confirmed. Plaster fire protection systems can often be applied directly to lath around the column. However, some systems require a 14 in. (31.8 mm) stand-off from the column using lath spacers. The required plaster thickness varies with the rating and needs to be confirmed by referencing the UL listing. Representative plaster thicknesses are 1 in. (25.4 mm) for 2 hours, 1a in. (34.9 mm) for 3 hours and 1w in. (44.5 mm) for 4 hours.
Table VI.2 – Mineral Board Column Designs Designation
Rating Hours
Section Types
1, 12, 2, 3, and 4
W, Tubular, Angles, Pipe
Equation and explicit
W
Equation
W
Equation
X307
X309 X310 X311 X312 X313 X314
1, 12, 2, and 3 1, 12, 2, and 3 1, 12, 2, and 3 3 1, 12, and 2 1, 2, 3, and 4
Equation or Explicit
Pipe or Tubular W W W
Explicit Explicit Explicit
VI.8.6 Gypsum Board Systems (500-599). Gypsum board assemblies are noncombustible systems that protect columns by releasing chemically combined water in the form of steam when subjected to intense heat. The steam creates a thermal barrier known as the plane of calcination. The gypsum material immediately behind the barrier rises to temperatures only slightly greater than 212 ˚F (100 ˚C), the boiling point of water. This temperature is well below the point at which steel begins losing strength. ASTM C36 mandates strength and endurance requirements for both regular and the more heat resistive “Type X” gypsum boards. Many manufacturers also produce an “Improved Type X,” also called “Type C”
Explicit
VI.8.4.1 EXAMPLE VI -1 A 3-hour fire resistance rating is required for a W14x109 using mineral wool board protection in accordance with UL Design No. X307, Required thickness is determined by equation:
1 . 08 R ( VI − 1 ) W 1 . 13 + 0 . 47 D where h = Board Thickness (in.) R = Fire Resistance Rating (hours) W = Column weight (lbs per ft) D = Inside perimeter of the mineral board (in.) h =
D
= 2 x 14.3 + 2 x 14.6 = 57.8
W/D = 109/57.8 = 1.88 Alternatively, use W/D = 1.89 listed in Appendix A.
h=
1.08 ( 3 ) = 1.25 1.13 ( 1.88 ) + 0.47
use 14 in. (31.8mm) Fig. VI.2 Sketch of Mineral Board Placement5
VI.8.5 Lath and Plaster Enclosures (400-499). Plaster is normally a composition of sand, water, and lime that hardens on drying. If the sand is replaced with 23
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