Intumescent Coating Calculator

Section factor is the ratio of a steel member's heated perimeter to its cross-sectional area. A high Hp/A means the steel has a lot of exposed surface relative to its own mass, so it absorbs heat quickly and has less thermal bulk to slow the temperature rise. The calculator raises Hp/A to the 0.6 power in the DFT formula, so thinner, higher-section-factor members always come out needing more dry film thickness for the same fire rating.

The calculator's k factor scales with critical temperature: k = 3.5 × (550/criticalTemp)^1.8. Columns are typically rated to a higher critical temperature (around 620°C) than beams (around 550°C) because of how they're loaded, and a higher critical temperature produces a smaller k, which lowers the resulting DFT. Physically, a column can tolerate getting hotter before failing, so it needs less insulation to survive the same fire duration.

That range reflects what thin-film intumescent coatings actually achieve in practice — thinner than 250 µm rarely provides meaningful fire protection, and thicker than 6000 µm starts pushing into thick-film or cementitious fireproofing territory instead. If the regression formula produces a value outside that band, the calculator clamps it to the nearest boundary so the reported number stays within a realistic product range, even though that means the clamped result no longer exactly matches the underlying formula.

It divides the required wet film thickness by 650 µm, the typical maximum wet film a single pass of thin-film intumescent can hold before sagging or slumping, and rounds up to the next whole coat. This is a generic ceiling, not a product-specific limit, so always check the actual maximum WFT per coat on your chosen product's data sheet before planning the application schedule.