Why are W/D Ratios Important in IFRM Listed Designs for Structural Steel Fire Protection?

Why are W/D ratios important in IFRM listed designs for structural steel fire protection?

W/D
W = Weight (per lineal foot)
D = Heated Perimeter (inches)

Building Product Directories from accredited third-party laboratories such as Intertek & Underwriters Laboratories publish FULL SCALE listed designs that meet IBC (International Building Code) fire resistance requirements for IFRM manufactures. W/D ratios are specific to individual structural steel members within these design listings to determine the required final DFT (dry film thickness) of IFRM that must be applied to achieve the hourly rating.

Listed designs found in these directories provide the minimum column or beam sizes that have been tested by the manufacturer. For example, the minimum wide flange column size in Contego International’s design CII/IF 120-02 has a W/D ratio of 0.29 for up to a 2-hour fire resistance rating. This makes Contego International the only IFRM manufacture on the market today able to safely protect the smallest wide flange columns for up to 2-hours while doing so with up to 20% less IFRM product keeping your project on time at a lower cost per square foot.

IFRM W/D Ratios 101:

+ IFRM applied to meet equal or greater W/D ratios of a steel member of the same configuration tested to full scale hourly ratings is acceptable.

– IFRM applied using a thickness or extrapolation of a larger steel member to cover a smaller steel member that has a lower W/D ratio than listed is not acceptable.

At Contego International LIFE SAFTEY is our highest priority. Before using an IFRM on your project, investigate the manufactures published design listings to ensure testing has been done to FULL SCALE and the W/D ratios of the steel members have been tested to the specific hourly rating requirements.