Professionals evaluating buildings for fire safety must consider many factors and metrics, including the building’s construction materials. Some materials are more fire-resistant than others, which is why they have unique fire-retardant standards and ratings. Keep reading to learn more about time ratings, class ratings, and which materials often fall into these categories.
Types of Fire Resistance Ratings
There are distinct types of fire-retardant ratings for fireproofing materials and products. For example, two of the most common metrics for measuring fire resistance are time and class ratings. Both rankings measure how easily and quickly flames spread across materials in a certain period.
Time Ratings
Time ratings measure how long a fire-resistant material can withstand exposure to fire and how fast flames spread. For example, fire inspectors classify exterior walls with a four-hour, three-hour, two-hour, one-hour, or non-rated rating. These ratings describe how long fire-resistant construction can withstand fire exposure before it loses structural integrity. Many plywood and wallboard construction materials have a non-rated ranking, which means they will last less than one hour. Therefore, many residential and commercial buildings utilize fire protection coatings to improve their ratings and structural integrity.
Class Ratings
Class ratings use letters or Roman numerals to designate flame-spread ratings. Class A (or Class I) is the best class rating for materials. Materials with a Class A Flame Spread Index boast less flame spread over a certain period. Materials must have a Flame Spread Index of 25 or less to achieve a Class A rating. Class B or II materials have a Flame Spread Index of 26 to 75, and Class C or III materials have a Flame Spread Index of 76 to 200. Typically, Class A features inorganic materials, while whole wood and reconstituted wood make up Classes B and C, respectively.
Utilize fire protection coatings and more to protect materials with lower time and class fire spread ratings and reach fire retardant standards. Learn more about intumescent paints and other fire-retardant coatings here at FireFree Inc.