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TEK 07-06A



Because of its inherent fire resistant properties, concrete masonry is often used as a non-structural fire protection covering for structural steel columns. Fire endurance of steel column protection is determined as the period of time for the average temperature of the steel to exceed 1,000 °F (538 °C), or for the temperature at any measured point to exceed 1,200 °F (649 °C) (ref. 1). These criteria depend on the thermal properties of the column cover and of the steel column (ref. 2). Using this technique, an empirical formula was developed to predict the fire endurance of concrete masonry protected steel columns (refs. 3, 4). This formula is presented in Figure 1, and is also included in the International Building Code (ref. 5)

Figure 1—Details of Concrete Masonry Protection for Commonly Used Steel Columns (ref. 5)
Table 1—Fire Resistance of Concrete Masonry Protected Steel Columns

Equivalent Thickness

Equivalent thickness is essentially the solid thickness that would be obtained if the volume of concrete contained in a hollow unit were recast without core holes (see Figure 2). The equivalent thickness is determined in accordance with Standard Methods of Sampling and Testing Concrete Masonry Units, ASTM C140 (ref. 7), and is reported on the C140 test report. Note that when all cells of hollow unit masonry are filled with an approved material, such as grout and certain loose fill materials, the equivalent thickness of the assembly is the actual thickness. For more detailed information, as well as typical equivalent thicknesses for concrete masonry units, see Fire Resistance Ratings of Concrete Masonry Assemblies, TEK 7-1C (ref. 8).

Figure 2—Equivalent Thickness
Table 2—Thermal Conductivity of Concrete Masonry Units (refs. 4, 5)


  1. Standard Test Methods for Fire Tests of Building Construction and Materials, ASTM E119-00. ASTM International, 2000.
  2. Lie, T. T. and Harmathy, T. Z. A Numerical Procedure to Calculate the Temperature of Protected Steel Columns Exposed to Fire, Fire Study No. 28, National Research Council of Canada, March 1972.
  3. Harmathy, T. Z. and Blanchard, J. A. C. Fire Test of a Steel Column of 8-in. H Section, Protected with 4-in. Solid Haydite Blocks, National Research Council of Canada, February 1962.
  4. Lie, T. T. and Harmathy, T. Z. Fire Endurance of Protected Steel Columns, ACI Journal, January 1974.
  5. 2006 International Building Code. International Code Council, 2006.
  6. Standard Method for Determining Fire Resistance of Concrete and Masonry Construction Assemblies, ACI 216.1-07/TMS 0216.1-07. American Concrete Institute and The Masonry Society, 2007.
  7. Standard Test Methods for Sampling and Testing Concrete Masonry Units and Related Units, ASTM C140-02a. ASTM International, 2002.
  8. Fire Resistance Ratings of Concrete Masonry Assemblies, TEK 7-1C. National Concrete Masonry Association, 2009.

NCMA TEK 7-6A, Revised 2009.

NCMA and the companies disseminating this technical information disclaim any and all responsibility and liability for the accuracy and the application of the information contained in this publication.