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A contractor is installing suspended acoustical ceiling panels in a new office building. The specifications call for a Class A fire rating. Which characteristic primarily determines a material's Class A fire rating?

  1. ASmoke Developed Index
  2. BHeat Release Rate
  3. CIgnition Temperature
  4. DFlame Spread Index
Show answer & explanation

Correct answer: D. Flame Spread Index

A material's Class A fire rating, as defined by ASTM E84 or UL 723, is primarily determined by its Flame Spread Index (FSI) and Smoke Developed Index (SDI). For Class A, both FSI and SDI must be 0-25 and 0-450 respectively, with FSI being the more critical factor for surface burning characteristics.

Why the other options are wrong

  • A. Smoke Developed Index is also part of the Class A rating but is not the primary determinant for surface burning characteristics; it measures visibility obstruction.
  • B. Heat Release Rate is a factor in fire testing but not the primary determinant for a Class A rating in the context of surface burning characteristics.
  • C. Ignition Temperature is a material property related to fire but is not directly used for classifying surface burning characteristics into Class A, B, or C ratings.

Class A Fire Rating (ASTM E84)

The highest classification for surface burning characteristics of building materials, primarily based on a Flame Spread Index of 0-25 and a Smoke Developed Index of 0-450.

  • Highest fire safety classification
  • FSI 0-25
  • SDI 0-450

Memory trick: To get a Class A, the 'Flame' must 'Spread' slowly, and 'Smoke' must be 'Developed' minimally.

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