Critical Radiant Flux is used to classify

Critical Radiant Flux (CRF) is the measure of a material's tendency to support flame spread and is the primary output of the test method defined in NFPA 253, Standard Method of Test for Critical Radiant Flux of Floor Covering Systems Using a Radiant Heat Energy Source. This test is specifically designed to evaluate the fire performance of interior floor finishes, such as carpets and resilient flooring, when exposed to a graded radiant heat flux in a corridor-like environment. Building and life safety codes, such as NFPA 101, use the CRF value (measured in W/cm²) to classify floor finishes into Class I or Class II, determining their suitability for use in different locations within a building, particularly in exit access corridors and other parts of the means of egress.

A. roofing materials. Roofing materials are classified based on their resistance to external fire exposure, typically evaluated using tests like ASTM E108 / UL 790, not the CRF test.

B. interior wall finishes. Interior wall and ceiling finishes are classified by their Flame Spread Index and Smoke Developed Index, which are determined by the Steiner Tunnel Test (NFPA 255 / ASTM E84).

D. exterior materials. Exterior wall assemblies are evaluated for fire propagation characteristics using large-scale tests such as NFPA 285, which assesses vertical and lateral flame spread, not CRF.

1. NFPA 101®, Life Safety Code®, 2021 Edition.

Section 10.2.7.2, Classification of Interior Floor Finish: "Interior floor finish shall be classified in accordance with ASTM E648, Standard Test Method for Critical Radiant Flux of Floor-Covering Systems Using a Radiant Heat Energy Source, as follows: (1) Class I interior floor finish — critical radiant flux not less than 0.45 W/cm²... (2) Class II interior floor finish — critical radiant flux not less than 0.22 W/cm²..."

2. SFPE Handbook of Fire Protection Engineering, 5th Edition.

Chapter 31, Fire Tests for Materials, Section 31.5.3, Flooring Radiant Panel Test (ASTM E648, NFPA 253, ISO 9239-1): "This test is intended to provide a basis for estimating one aspect of the fire exposure behavior of floor-covering systems... The test measures the critical radiant flux (CRF) at flameout." (p. 960).

3. NFPA, Fire Protection Handbook, 21st Edition.

Volume 1, Chapter 16, Interior Finish, Section 16.3, Floor Finishes: "The test method used to regulate the flammability of floor finishes is NFPA 253, Standard Method of Test for Critical Radiant Flux of Floor Covering Systems Using a Radiant Heat Energy Source... The result of the test is a critical radiant flux (CRF), which is the minimum heat flux necessary to sustain flame spread on the flooring." (p. 16-11).