Masonry Magazine January 1966 Page.25
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An information series from National NCMA TEK 6 1966 National Concrete Masonry Association Concrete Masonry Association
Estimating The Fire Resistance Of Concrete Masonry
concrete masonry wall during fire test
The fire resistant qualities of concrete masonry wall construction are well known and well respected among the building professionals who work with this versatile product. Since concrete masonry walls can vary in design and the concrete masonry units themselves vary in composition, this booklet was designed to create guideposts in the fire resistance of block units.
Building codes are quite specific in the degree of fire protection required in various areas of buildings. Local building regulations will govern the concrete masonry wall section best suited for specific applications.
Fire-resistance ratings of concrete masonry walls are based on fire tests made at Underwriters Laboratories, Inc., National Bureau of Standards, Portland Cement Association, and other recognized laboratories. Methods of test are described in ASTM E 119 "Standard Method of Fire Tests of Building Construction & Materials." The test consists of exposing one side of a wall to a fire of controlled intensity for a time equal to or greater than its rated fire-resistance time. Immediately, the hot face of the wall is subject to a fire hose stream. Bearing walls also carry a load equal to 80 psi based on gross wall area. The wall must withstand the fire test without passage of flame or gases. Heat transmission must be limited to less than 250° F gain in temperature.
Since testing every conceivable design possibility of concrete walls is unfeasible, rational methods of estimating fire-resistance ratings have been developed. These are discussed here.
Actually, ASTM E 119 requires only that a duplicate specimen be subjected to fire exposure for a period equal to one half of that indicated as the resistance period in the fire endurance test (but not for more than one hour) prior to the fire-hose test. Due to the excellent stability of concrete masonry walls, the fire-hose stream rest ordinarily is made on same specimen immediately after it has been subjected to the full fire endurance test, thus eliminating need for duplicate wall.