Fire-resistance Ratings - ANSI/UL 1709, BYBU

Guide Information for Fire-resistance Ratings



This category covers fire-rating Classifications based upon the test method and acceptance criteria in ANSI/UL 1709, "Rapid Rise Fire Tests of Protection Materials for Structural Steel." These ratings are expressed in hours and are applied to steel columns.

The fire ratings in this category are similar to the ratings for columns covered under Fire Resistance Ratings (BXUV) except for the following two major differences: (1) the rate of temperature rise of the fire exposure, and (2) the inclusion of environmental exposure simulating potential environments in which the fire-resistive assemblies may be located.

The temperature of the fire exposure in which rapid temperature rise ratings are established reaches 2000°F within the first 5 minutes of the fire exposure test. The fire temperature is maintained at 2000°F throughout the rating period. This fire exposure was developed to provide a means to investigate fire-resistive assemblies intended for use in areas such as petrochemical production facilities, which may develop fire temperatures at a more rapid rate than assemblies tested under ANSI/UL 263, "Fire Tests of Building Construction and Materials."

The systems covered under this category are subjected to standardized environmental tests, which include accelerated aging, high humidity, salt spray exposure, cycling effects of water/freezing temperatures/dryness, and exposure to air containing carbon dioxide and sulfur dioxide. The systems may also be exposed to optional environmental tests, which simulate environments containing various solvents and/or acids. These environmental exposures are intended to measure the ability of the fire-resistive assemblies to retain some degree of fire resistance when subjected to conditions that may occur at production facilities exposed to weathering. A list of the environmental exposures is included in the Classification information for each material described in this category.

The assemblies covered under this category are identified by an alphanumeric system. The identification system is similar to the assemblies in BXUV except an R is included in the number. For example, a column coated with an SFRM (spray-applied fire-resistive material) is identified as Design No. XR7___ (X for column, R for rapid temperature rise fire, 7 for SFRM, and ___ reserved for the sequential numbering of each design).

Unless specifically prohibited in a design, materials identified as Spray-applied Fire-resistive Materials (CHPX) may be applied to primed or similarly painted wide-flange steel shapes, provided: (A) the column flange width does not exceed 16 in., (B) the column web depth does not exceed 16 in., and (C) bond tests conducted in accordance with ANSI/ASTM E736, "Standard Test Method for Cohesion/Adhesion of Sprayed Fire-Resistive Materials Applied to Structural Members," indicate a minimum average bond strength of 80% and a minimum individual bond strength of 50% when compared to the bond strength of the fire-resistive coating as applied to clean, uncoated 1/8 in.-thick steel plate. The average and minimum bond strength values are determined based upon a minimum of five bond tests conducted in accordance with ANSI/ASTM E736.

The bond tests need only be conducted when the fire-resistive coating is applied to a primed or similarly painted surface for which acceptable bond strength performance between the primer or other similar material and the fire-resistive coating has not been measured. A bonding agent may be applied to the primed or similarly painted surface to obtain the minimum required bond strength where the bond strengths are found to be below the minimum acceptable values.

As an alternative to the bond test conducted on control samples applied to an uncoated steel plate, the following method may be used for unknown coatings in existing structures. Sections of painted steel are coated with a bonding agent compatible with the sprayed material being used on the project. The treated and untreated substrates are coated with material, cured and subjected to five bond tests each, in accordance with ANSI/ASTM E736. If the failure mode of the sections treated with the bonding agent is 100% cohesive in nature, it is acceptable to use this bond test value as the control bond strength. The value obtained on the untreated painted section is compared to the control value using the minimum 80% average, 50% individual bond strength acceptance criteria established in ANSI/ASTM E736.

If condition (C) is not met, a mechanical bond may be obtained by wrapping the structural member with expanded metal lath (minimum 1.7 lbs per sq yd).

If any of the conditions specified in (A) or (B) are not met, a mechanical break is provided. A mechanical break may be provided by mechanically fastening one or more minimum 1.7 lbs per sq yd metal lath strips to the flange or web either by weld, screw, or powder-actuated fasteners, on maximum 12 in. centers, on each longitudinal edge of the strip, so that the clear spans do not exceed the limits established in conditions (A) or (B) as appropriate. No less than 25% of the width of the oversize flange or web element should be covered by the metal lath. No strip of metal lath should be less than 3-1/2 in. wide.

As an alternative to metal lath, the mechanical break may be provided by the use of minimum No. 12 gauge steel studs with minimum No. 28 gauge galvanized steel disks if such a system is described in a specific design (usually bottomless trench in an electrified floor design) for the fire-resistive coating being applied. The studs are welded to the oversize element in rows such that the maximum clear span conforms to conditions (A) or (B) as appropriate. The spacing of studs along each row should not exceed 24 in. and a minimum one stud 256 sq in. is provided. Where metal lath strips or steel studs and disks are used, acceptable bond strength as described in item (C) is also provided. A bonding agent may be applied to the painted surface to obtain the required minimum bond strength where bond strengths to a painted surface are found to be below minimum acceptable values.


For additional information, see Fire Resistance Ratings (BXRH).

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Last Updated on 1998-12-15
BYBU.GuideInfo BYBU ACTIVE 19981215 19981215

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