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 is the regulatory requirement in building codes for various construction elements to withstand fire. It can apply to:
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:
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).
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.
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.
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:
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:
If you’re interested in digger deeper, here are some helpful resources:
Best Supply’s expert team can help identify the right materials to meet the fire ratings specifications of your next project. Request a quote here.