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The National Fire Protection Association (NFPA) categorizes buildings based on their innate fire resistance level.

Making Sense of Material Fire Ratings

Jan. 3, 2023
All building materials have fire ratings, and they can be improved with certain coatings. Here’s what you need to know about using fire-resistant materials.

If you’re a facility manager or owner, you need to know about material fire ratings. Fire resistance ratings are the times that materials have withstood fire exposure according to stringent tests. Whether you’re building with lumber or steel, each material you use has a fire rating.

Below, we will discuss the types of building construction, as well as recommended fire-resistant materials and coatings.

Types of Building Construction

Buildings can be categorized into five types based on their innate fire resistance level, according to NFPA.

Type 1: Buildings over 75 feet tall (e.g., high-rise and commercial spaces) fit this categorization. They are designed to resist high temperatures. Firefighters find these buildings difficult to access and emphasize evacuating people through stairwells.

Type 2: Schools, shopping malls and newer commercial structures often fall into the Type 2 category. These buildings are made of non-combustible materials. For example, the walls, floors, columns, roofs and partitions are non-combustible.

Type 3: These buildings are made of masonry walls or tilt-slap (e.g., houses). They are fittingly known as brick-and-joist structures. Type 3 buildings contain combustible materials such as wood. Fire extension is higher for Type 3 buildings than for Types 1 and 2. However, ventilation is possible with this construction type.

Type 4: Lumber is the primary material in Type 4 buildings. The lumber is connected with metal plates and bolts. Type 4 structures typically include barns, churches and factories. Because of the structural mass of these buildings, they are resistant to collapse.

Type 5: This category is comprised of a wooden frame. These structures are cheap to develop, but they are also among the most combustible. There is no fire resistance for exposed wood, which leads to quick collapse and fire spread.

How to Determine a Building’s Required Fire Rating

It’s important to know how to test your building’s required fire rating to ensure you’re up to code.

You will need to meet the current standards for fire ratings (e.g., NFPA 252, NFPA 257, ANSI UL10B, ANSI/UL 10C, or ANSI/UL 9). There are three steps to determine your building’s fire rating.

Step 1: Identify the component that you need to test and determine its required fire resistance. You may want to consult codes for the current fire rating standards. For example, see NFPA 101, Life Safety Code and NFPA 5000 Building Construction and Safety.

Step 2: Using the codes outlined in NFPA 101, Life Safety Code and NFPA 5000 Building Construction and Safety, search for the “Minimum Fire Ratings For Opening Protectives in Fire Resistance-Rated Assemblies and Fire-Rated Glazing Markings.” These tables can be found in Chapter 8 of both codes. These will give you guidelines for the minimum level of fire protection.

Step 3: Consult footnotes and other code texts to determine if the fire ratings for your building need modification. You may also consider if your building requires changes in fire ratings based on its occupancy. For example, some materials in your building may be exempt from some codes.

Improving Fire Ratings with Materials

To meet the fire rating standards of the International Building Code, you should use fire-resistant materials. The goal of these materials is to slow the development and spread of a fire.

We will summarize six of the most fire-resistant materials below.

Flame-Treated Natural Products

On their own, natural materials have low fire resistance. For example, lumber is highly combustible. Yet, flame-treated lumber helps increase its fire resistance with the fire-treated barrier. Chemical treatments, such as borate, also help increase fire resistance.

Fire-resistant Glass for Windows

In a fire, windows may get too hot and break, allowing the fire to spread. There are modifications that you can make to increase fire resistance in windows. You could use dual-pane windows to reduce their chances of breaking in a fire. To strengthen the window structure, consider glass blocks, wired glass or steel framing.

Concrete

Because of its low thermal conductivity, fire develops slowly in concrete. Concrete is also non-combustible, which makes it an excellent fire-resistant material.

Stucco

Most stucco is made of cement and reinforced with metal mesh. It is a plaster that has been used for hundreds of years. An inch of stucco receives good fire ratings.

Brick

Because brick is made using a fire kiln, it has high fire resistance. Thick structures made of brick normally achieve a one-hour fire rating. The mortar that holds brick together is not as fire-resistant as brick. But brick is still one of the best materials for fire resistance.

Gypsum (or Drywall)

Gypsum is one of the most commonly used fire-resistant materials. The core of gypsum is non-combustible. Its core is made with chemically combined water in the form of calcium sulfate. Water is released when fire contacts gypsum and thereby blocks heat transfer.

Improving Fire Ratings with Coatings

You can improve a material’s fire rating by using a fire-resistant coating.

Specifically, there are two tests relevant to intumescent paint coatings. They include the ASTM E-119 and the ASTM E-84.

The ASTM E-119 is a time-based fire test. This fire test assesses resistance and structural integrity. Fire ratings for the ASTM E-119 typically fall between one to four hours. Longer times indicate better fire resistance.

The ASTM E-84 is based on two metrics of burning behavior. These metrics are flame spread and smoke development. The flame spread index is a measure of how quickly the flame travels after the fire is initiated. The smoke development rating tells you the smoke production over a period of times.

The fire ratings for the ASTM E-84 fall into three categories (Class A, B, or C). These ratings are in order from highest to lowest. Class A is the highest, and Class C is the lowest rating. In some cases, the ratings may be grouped numerically instead of alphabetically (e.g., Class 1, Class 2, or Class 3).

In summary, facility managers and owners can improve fire ratings in a variety of ways, from materials to coatings.

About the Author

Tommy O’Shaughnessy

Tommy O’Shaughnessy is the owner of Industrial Paint and Protection Magazine, an outlet dedicated to helping facility managers, engineers, and contractors understand the world of industrial coatings.

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