Fire Retardant Classifications


In 2007, fire departments in the United States responded to nearly 1.6 million fire calls. Each year, fires are responsible for thousands of deaths, tens of thousands of injuries and billions of dollars in damage. The use of strict building codes is one way to reduce these losses. Local building codes often require the use of fire retardant materials. These materials are classified by their impact on the spread of flames.

Reason for Classifications

  • During the 1940s and 1950s, combustible building materials were linked to numerous tragedies involving fires in commercial structures, leading to high numbers of fatalities. Over time, revisions were made to the fire protection standards at various levels of government. This led to strict building code requirements for building materials based upon a fire retardant classification system.

Flame Spread Ratings

  • Fire retardants serve to impede the spread of flames by forming a protective barrier between a fire and a combustible material, such as wood. The degree to which a given product accomplishes this task is defined as its flame spread rating. This rating provides the relative rate that a flame will spread across the surface of a treated material, as compared to a control material. Typically, the control materials are red oak, which has a flame spread rating of 100, and asbestos cement board, which has a rating of zero.

Material Testing

  • Fire retardant materials are tested by Underwriters' Laboratories Inc. They conduct flame spread testing in accordance with the requirements of their "Fire Hazard Classification of Building Materials" code, known as UL 723. This code uses the National Fire Protection Association's "Method of Test of Surface Burning Characteristics of Building Materials" code, also known as NFPA 255. However, UL 723 also measures smoke generated and fuel contributed.

Life Safety Code 101

  • In terms of fire safety, the majority of local building codes across the United States adhere to the recommendations laid down by the National Fire Protection Administration in their "Life Safety Code." Section 101 of this code presents a classification system for fire retardants. The classification system is based upon the flame spread rating of retardant materials. The system features five divisions, represented by the letters A through E.

NFPA Fire Retardant Classifications

  • Class A fire retardants have a flame spread rating of between zero and 25. These materials are effective against severe fire exposure. Class B fire retardants have a flame spread rating of between 26 and 75. These materials are effective against moderate fire exposure. Class C fire retardants have a flame spread rating of between 76 and 200. These materials are effective against light fire exposure. Class D materials have a flame spread rating of between 201 and 500. Class E materials have a flame spread rating of over 500. Class D and E materials are not considered effective against any fire exposure.

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