The short version
- Class A and Class C are flame spread ratings from the ASTM E84 tunnel test. Lower numbers mean slower-spreading fire.
- Class A means a flame spread index of 0–25. Class C is 76–200. All classes must keep smoke at 450 or below.
- Building codes require better-rated finishes in exits and corridors than in rooms, and loosen the rules in fully sprinklered buildings.
- FRP is sold almost entirely as Class A or Class C. If your space calls for Class A or Class B, buy Class A FRP.
Why the rating matters
FRP panels are chosen for moisture resistance and cleanability, so it's easy to treat them as a commodity and order whatever is cheapest. But FRP is an interior wall finish, and interior finishes are regulated by the building code for one reason: in a fire, the surfaces lining a room or hallway can carry flames toward the exits faster than people can reach them.
That's why an inspector may ask for the fire rating of your wall panels, and why installing the wrong class can mean tearing out finished walls. Standard FRP is usually Class C. Class A FRP uses a fire-retardant resin formulation and typically costs more. Knowing which one your project needs before you order saves money in both directions.
ASTM E84 in plain terms
ASTM E84, also published as UL 723, is the standard test for how fast flame travels across a building material's surface. It's often called the Steiner tunnel test after the long, narrow furnace it uses.
Both results are expressed relative to two reference materials. Inorganic reinforced cement board is set at 0, and red oak flooring is set at 100. So a material with a flame spread index of 25 spreads fire at roughly a quarter the rate of red oak, and a material rated 150 spreads it about one and a half times as fast.
From test scores to letter grades
The building code turns those index numbers into three classes. The smoke limit is the same for all of them. The difference is entirely in flame spread.
Class C
FSI 76–200Smoke index 450 max. Standard FRP. Allowed in many rooms and sprinklered buildings.
Many Class A FRP panels earn that rating when tested over a specific substrate, often gypsum board or another noncombustible backing. Installed over plywood or foam, the same panel may not carry the rating. Check the manufacturer's data sheet for the tested assembly and install to match it.
Where the code requires Class A
Most U.S. jurisdictions adopt the International Building Code (IBC), and some use NFPA 101, the Life Safety Code. Both use the same Class A, B and C system. In the IBC, the required class comes from a table (Table 803.13 in the 2021 edition) that looks at three things:
- Occupancy group. What the building is used for: restaurant, school, hospital, warehouse and so on. Places where many people gather or can't evacuate on their own get stricter limits.
- Location in the building. Exit stairways and exit passageways are held to the tightest standard, then corridors, then rooms and enclosed spaces.
- Sprinklers. A fully sprinklered building is generally allowed a less restrictive class, often one step down.
| Occupancy | Fully sprinklered | Not sprinklered | ||||
|---|---|---|---|---|---|---|
| Exits | Corridors | Rooms | Exits | Corridors | Rooms | |
| A-2 AssemblyRestaurants, bars, banquet halls | B | B | C | A | A | B |
| B BusinessOffices, clinics, car washes | B | C | C | A | B | C |
| E EducationalSchools, daycare | B | C | C | A | B | C |
| M MercantileRetail, grocery stores | B | C | C | A | B | C |
| I-2 InstitutionalHospitals, nursing homes | B | B | B | A | A | B |
| R-2 ResidentialApartments, dormitories | C | C | C | B | B | C |
| F FactoryManufacturing, food processing | C | C | C | B | C | C |
| S StorageWarehouses, cold storage | C | C | C | B | B | C |
A few patterns stand out:
- Non-sprinklered exits and corridors are where Class A shows up most. Restaurants, hospitals and nursing homes need it in both.
- Sprinklers change the answer. A room in a fully sprinklered restaurant can use Class C. The same room in a non-sprinklered building needs Class B, which in practice means Class A FRP.
- Factories and warehouses are the most forgiving. In a sprinklered food plant or cold storage building, standard Class C FRP generally meets code throughout.
Which one should you buy?
Because FRP is almost always sold as either Class A or Class C, the decision comes down to one question: does any wall you're covering require Class A or Class B?
Common mistakes to avoid
- Confusing flame spread with fire resistance. Class A is a surface rating. It is not an hourly fire-resistance rating like a 1-hour or 2-hour wall. FRP doesn't make a wall assembly fire-rated.
- Assuming health code approval covers fire code. Health departments and USDA inspectors care that walls are smooth, durable, nonabsorbent and easy to clean. Fire rating is a separate requirement enforced by the building or fire official.
- Ignoring the tested substrate. A Class A panel glued to plywood may not be a Class A installation.
- Mixing stock on site. Class A and Class C panels can look identical. Keep them labeled and separated if you use both.
- Waiting until inspection to ask. Confirm the required class with the architect, contractor or building department before ordering.
How Emco can help
Emco Industrial Plastics stocks FRP wall panels and matching trim and cuts panels to size in our Cedar Grove, NJ shop. Tell us what kind of building it is, where the panels are going, and whether it's sprinklered. We'll help you match the rating to your application and supply manufacturer data sheets for your submittals.
This article is general information to help you ask the right questions. It is not a code interpretation. Fire rating requirements depend on the code edition and amendments your jurisdiction has adopted, the building's construction and occupancy, and the product's tested assembly. The authority having jurisdiction makes the final call.