Intumescent coating thickness explored in latest e-book

Image courtesy Sherwin-Williams
Image courtesy Sherwin-Williams

The magazine’s series of sponsored e-books continues with a discussion on the appropriate thickness of passive fire-protection coatings, or intumescent coatings on structural steel.

Intumescent coatings, have been designed to buy time for building occupants—and the steel-framed structures themselves—during a fire. Applied to structural steel, the coatings swell to approximately 50 times their dry film thickness (DFT), to a maximum of 50 mm (2 in.), thereby providing a thick layer of insulation ‘char’ that reduces the rate of heat transfer to the structural steel.

Slowing the rate of heat transfer is important, as structural steel under load can quickly lose strength in a fire. Exposure to high heat for a specific period can cause the steel to eventually reach its critical failure temperature. At this state, the steel could start to collapse, possibly bringing down large building sections or even the entire structure.

Intumescent coatings help building owners avoid such catastrophic losses by providing fire resistance while first responders work to contain a fire.

To assist engineers, architects, and other building professionals achieve a specified fire-resistance rating, the American National Standards Institute/Underwriters Laboratories (ANSI/UL) 263, Standard for Fire Tests of Building Construction and Materials, and ASTM E119, Standard Test Methods for Fire Tests of Building Construction and Materials, list the required coating thicknesses for structural steel members. However, the specifications do not include every possible size, leaving data gaps, especially for very small and large steel sections. This presents challenges for specifying proper coating DFTs.

An article in our newest sponsored e-book cautions against using extrapolated data to determine DFT when encountering structural steel section sizes outside of UL’s listing. It appears along with a trio of other articles from the pages of The Construction Specifier in “Fire Protection: Keeping Buildings Safe” a free, downloadable resource. To get your copy in either pdf or digital edition, visit

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