Making Sense of the Most Common Fire-Ratings Terminology

Published July 17, 2024

If you get confused by the terminology around fire safety ratings in construction materials, you aren’t alone. The language has evolved over decades, with contributions from regulatory bodies, trade associations and organizations that conduct testing on materials and systems.

Starting at the highest level, here’s a rundown of the most relevant terms that apply to fire safety in building design and construction.

Fire Resistance Level (FRL)

Fire Resistance Level is the regulatory requirement in building codes for various construction elements to withstand fire. It can apply to:

• Structural elements, such as load-bearing walls, columns and roof assemblies;
• Non-structural elements such as stair and elevator shaft enclosures;
• Fire-resistant construction systems, such as fire-rated floor/ceiling assemblies, and fire-rated wall assemblies;
• Fire-resistant coatings and construction materials.

So FRL is the code that architects and engineers must comply with in their design process, and it can vary from one project to another depending on the building’s location, purpose and the type of construction being used.

Three factors are considered in FRL:

1. Structural Adequacy: The ability of the building element to maintain its load-bearing capacity during a fire. 
2. Integrity: The ability of the building element to prevent the passage of flames and hot gases to adjacent areas. 
3. Insulation: The ability of the building element to prevent the transfer of excessive heat to the unexposed side, which reduces the risk a fire will spread and improves safety for evacuation and firefighting.

FRL is measured in minutes and expressed in a three-number format. A Fire Resistance Level of 90/60/30 means a building element must retain its structural adequacy for 90 minutes, its integrity for 60 minutes and its insulation for 30 minutes. FRL of -/60/60 means that there is no rating requirement for structural adequacy, while integrity and insulation of the component must each achieve 60 minutes.

FRL is often shortened in conversation to Fire Rating, which risks confusion with the related-but-different Fire Resistance Rating (see below). 

Fire Resistance Rating (FRR)

While FRL is the regulatory requirement that a building element must meet, Fire Resistance Ratings are the lab-tested results for how materials and assemblies perform. The testing considers all three factors used in FRL: structural adequacy, integrity and insulation.

A standard sheet of ½-inch drywall has 30-minute FRR. Type X drywall, or fire-code drywall, is generally 5/8-inch thick—with that extra 1/8th inch doubling the level of fire resistance to 60 minutes. That’s why it’s often referred to as one-hour drywall.

Typical values you’ll find on various materials are 1-, 2- and 4-hour FRR. The higher the number, the longer it takes for the material or component to lose its load-bearing capacity, integrity and insulating properties.

From there it starts to get more complicated. 

Fire Protection Rating (FPR)

FPR is the equivalent of FRR as it applies to so-called opening protectives: doors, windows, access panels, etc. Different terminology is used for opening protectives because the testing methods differ. But a door or window that has an assigned FPR will typically be joined with wall panels that have an FRR, to create a building assembly required to meet FRL of a specific building code.

In such instances, “If the opening protective is being tested as a wall, it will be subject to the same fire test as the wall itself,” according to the National Fire Protection Association. So a door might carry an FPR, but the wall assembly that it’s part of will have an overall FRR. 

Agency Overlap

There are a number of agencies involved in establishing the various ratings. In some areas, their work overlaps, while in other areas they complement each other. 

In the United States, the most commonly referenced agencies are:

• National Fire Protection Association (NFPA): Conducts research, establishes safety codes and standards and provides training and public education about fire and electrical safety.
• ASTM International (American Society for Testing and Materials): Develops and publishes international standards for materials, products, systems and services including those used in construction, manufacturing and transportation. 
• Underwriters Laboratories (UL): Testing and certification agency. With respect to fire safety in the construction industry, it’s most commonly seen in reference to electrical and mechanical devices. 

Together, along with other organizations that have less influence in the United States, these entities devise and conduct tests that quantify the properties defined in Fire Resistance Level. Technical specifications for many materials may reference the standards of one or more of these agencies. But those standards generally are more important to engineers and architects than to builders. For builders, it’s usually enough to know the FRR or FPR of a material, component or assembly—precisely because those ratings represent composites of the test results and standards from the various agencies.

Here are some of the most frequently cited fire safety tests:

• ASTM E119: Measures the period of time an element will serve as a barrier to the spread of fire and how long the assembly maintains its structural adequacy, according to USG, a leading supplier of wallboard. Comparable to UL 263 standard, as well as the now-retired NFPA 251 standard. 
• NFPA 285: Quantifies the potential for vertical and lateral flame spread on exterior wall assemblies that contain combustible materials.
• NFPA 268: Simulates the effects of a fire in a nearby building by quantifying the fire resistance of exterior wall assemblies when exposed to an outside radiant heat source.
• NFPA 286: Considers factors like flame spread, smoke development and heat release rates in interior spaces to assess interior wall and ceiling finishes for their ability to resist the spread of fire within a room.
• ASTM E84/UL 723/NFPA 255: Also known as the Steiner Tunnel Test, it measures how fast fire spreads across the surface of a material (Flame Spread Index) and how much smoke it produces (Smoke Developed Index) and is most often used for testing interior finishes. Materials are sorted into classes A-E, with Class A materials offering the best properties. If you see numbers associated with a class of materials, it’s important to note that these numbers are relative to each other, and they do NOT correspond to a time frame like FRR levels.

If you’re interested in digger deeper, here are some helpful resources:

• NFPA: The difference between FPR and FRR
• Industrial Paint and Protection Magazine: Fire rating classifications explained
• Buildings Magazine: Making Sense of Material Fire Ratings
• NFPA: Types of Construction and Material Combustibility
• Glass Magazine: How to Determine Fire Rating

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