The purpose of the test is to provide a comparative measurement of surface flame spread and smoke development of materials with that of a select grade red oak and reinforced cement board under a specific fire exposure conditions.
Initially written by ASTM, the standard was adopted by NFPA and named American NFPA 255 / ASTM E 84 and UL 723 as American Nationals Standard (ANSI) and approved for the use by agencies of the department of Defence for listing in the DoD Index of Specifications and Standards.
American NFPA 255 / ASTM E 84 standard refers to the test as "American NFPA 255 / ASTM E 84/ASTM E-84". Please note that a certificate for ASTM E-84 covers American NFPA 255 / ASTM E 84.
American NFPA 255 / ASTM E 84 / ASTM E-84 is an extremely stringent test, probably the strictest in the United States as it also assesses smoke generation.
A 20 inch wide by 24 feet long sample is placed into a long brick tunnel.
When tested un-adhered, the fabric is supported by chicken wire netting. The specimen is subjected to the flames which come out of the U-shaped burner pictured in the front view for 10 minutes. During the ten minute test duration, flame spread over the specimen surface and density of the resulting smoke are measured and recorded.
Test tunnel side view
Test tunnel front view
The test measures how quickly and how far the flame spreads and is calculated relative to red oak, which has an arbitrary rating of 100, as well as reinforced cement board, which has a rating of 0.
From these numbers, a flame spread index is calculated (Class 1 being the best).
Class Flame Spread Index Smoke Development Index
1 or A 0-25 0 - 450 maximum
2 or B 26-75 0 - 450 maximum
3 or C 76-200 0 - 450 maximum
Anything above 200 is unrated
Code officials and regulatory agencies frequently use the Flame Spread Index and Smoke Developed Index values obtained by the American NFPA 255 / ASTM E 84/ASTM E-84 test in the acceptance of interior finish materials for various applications.