| QUICK ANSWER
A Class A fire rating comes from ASTM E84 (also referenced as UL 723), the Steiner Tunnel Test, which measures a Flame Spread Index (FSI) and a Smoke Developed Index (SDI) for a material’s surface. IBC Section 803.1.2 assigns Class A to materials scoring an FSI of 0-25 with an SDI no higher than 450; Class B covers FSI 26-75, and Class C covers FSI 76-200, both with the same 450 SDI cap. A material must meet both the flame spread and smoke thresholds together to earn a given class; the two numbers aren’t averaged or traded off against each other. Class A is historically an interior finish classification (IBC Chapter 8), so when it’s cited for an exterior cladding product, it’s worth confirming exactly which test method produced the number, since a comparable but different method, such as Canada’s CAN/ULC-S102.2, can also be benchmarked against the same 25/450 thresholds without being an actual ASTM E84/UL 723 result. |
What “Class A” Actually Measures
Class A, B, and C are not themselves a test, they’re a classification system the IBC applies to the results of a specific test, ASTM E84, based on two separate numbers: the Flame Spread Index (FSI), which measures how quickly flame travels across a material’s surface relative to two reference materials, and the Smoke Developed Index (SDI), which measures how much smoke the material produces while burning. Both numbers come from the same physical test, run at the same time on the same specimen, but they measure genuinely different hazards, one about how fast a fire might spread across a surface, the other about how much smoke occupants would have to evacuate through.
How the Steiner Tunnel Test Works
ASTM E84 is commonly called the Steiner Tunnel Test after the horizontal test chamber it’s performed in: a roughly 25-foot enclosed tunnel with the test material mounted along the ceiling, exposed to a gas burner flame at one end while air is drawn through the tunnel at a controlled rate. Flame spread distance is tracked over a fixed time period and compared against the performance of red oak flooring (assigned a reference FSI of 100) and inorganic reinforced cement board (assigned a reference FSI of 0), which is how the index numbers get their scale. Smoke density is measured simultaneously using a photometric system that tracks how much light a smoke detector-style sensor loses as smoke passes through the tunnel’s exhaust.
Class A vs. Class B vs. Class C
IBC Section 803.1.2 sets three classes from the same test result. Class A, the strictest, requires an FSI between 0 and 25. Class B allows an FSI between 26 and 75. Class C allows an FSI between 76 and 200. All three classes share the same smoke ceiling: an SDI no higher than 450. A material has to satisfy both its class’s flame spread range and the shared smoke limit at the same time; a very low flame spread number doesn’t offset a smoke developed number above 450, and a material that produces too much smoke doesn’t earn Class A regardless of how slowly its flame spreads.
| Class | Flame Spread Index (FSI) | Smoke Developed Index (SDI) | Typical Interpretation |
| Class A | 0-25 | 0-450 | Best-performing surface burning classification under ASTM E84 |
| Class B | 26-75 | 0-450 | Mid-range surface burning classification |
| Class C | 76-200 | 0-450 | Lowest surface burning classification the IBC still recognizes for most interior finish uses |
Where Class A Actually Applies in the Code
Class A, B, and C classifications live in IBC Chapter 8, which governs interior finish materials, wall and ceiling finishes, floor finishes, and similar interior surface applications, not exterior wall assemblies specifically. For exterior cladding, the code’s more directly applicable fire requirements are typically the plastic veneer provisions (IBC Section 2606) for polymer-based products and, for combustible-component wall assemblies on qualifying buildings, NFPA 285 assembly testing. In practice, many exterior cladding manufacturers still test and report their material’s ASTM E84 performance against the Class A/B/C scale anyway, since it’s a widely recognized, easy-to-communicate benchmark that specifiers and AHJs are already familiar with, even when it isn’t the code section actually governing the exterior application.
A Common Point of Confusion: Class A Doesn’t Mean “Fireproof”
A Class A rating describes surface burning behavior under a specific, standardized test condition, not an absolute guarantee against fire damage or spread under all real-world conditions. It also doesn’t substitute for assembly-level fire testing (NFPA 285) where that’s the code-required test for a given building’s construction type and height, and it doesn’t by itself confirm anything about a plastic material’s burn rate, ignition temperature, or post-ignition combustion behavior, which are separate tests (ASTM D635, D1929, D2843) commonly required alongside Class A data for PVC and other plastic cladding products under the IBC’s plastic provisions.
Not Every “Class A” Claim Comes From the Same Test Method
ASTM E84 and UL 723 are the test methods IBC Section 803.1.2 references directly, but they aren’t the only surface-burning test method in use across North America. Canada’s CAN/ULC-S102.2, for example, uses a comparable methodology and reports results on a comparable flame-spread and smoke-developed scale, which is why it’s common to see a product’s CAN/ULC-S102.2 result described as “numerically within the Class A benchmark.” That phrasing is deliberately precise: CAN/ULC-S102.2 is a different test method than ASTM E84/UL 723, so a result within the same numeric range is a benchmark comparison for reference, not an actual ASTM E84/UL 723 Class A listing. Confirming exactly which test method underlies a stated “Class A” claim, not just the numbers themselves, is worth doing before relying on it in a specification.
| ASK WHICH TEST METHOD PRODUCED THE “CLASS A” NUMBER
When a manufacturer cites Class A performance for an exterior cladding or soffit product, confirm whether the result comes from ASTM E84/UL 723 directly or from a comparable but distinct method, such as CAN/ULC-S102.2, benchmarked against the same numeric thresholds. Both can be valid, useful data points, but they aren’t the same listing, and code officials may treat them differently depending on the jurisdiction. |
Where Sagiper’s Product Lines Fit
SAGIREV, Sagiper’s FR-HPPS PVC soffit and ceiling panel system, was tested by UL to CAN/ULC-S102.2 and recorded a flame spread value of 25 and a smoke developed value of 315, both numerically within the IBC Class A benchmark of 0-25 FSI and 0-450 SDI, though, consistent with the distinction above, this is a CAN/ULC-S102.2 result reported against the Class A benchmark rather than an ASTM E84/UL 723 Class A listing. SAGIREV’s fire-test package also includes ASTM D635 burn rate testing (0 mm/min linear burn rate, no visible combustion after ignition source removal), ASTM D1929 ignition temperature testing (840°F self-ignition, exceeding the IBC §2606.4 plastic criterion of 650°F), and ASTM D2843 smoke density testing (61.88%, below the IBC §2606.4 maximum of 75). Full third-party test reports are available to specifiers on request.
Frequently Asked Questions
What flame spread index is required for a Class A rating?
A Flame Spread Index (FSI) of 0-25 under ASTM E84, combined with a Smoke Developed Index (SDI) no higher than 450. Both thresholds must be met together.
Is Class A fire rating required for exterior siding?
Class A, B, and C classifications live in IBC Chapter 8, which primarily governs interior finish. Exterior cladding fire requirements more directly come from the IBC’s plastic veneer provisions (Section 2606) and, for qualifying buildings, NFPA 285 assembly testing, though manufacturers often test and report ASTM E84 results anyway as an additional, widely recognized benchmark.
Does a Class A rating mean a material won’t burn?
No. Class A describes surface burning behavior (flame spread and smoke) under a specific standardized test, not an absolute fireproof guarantee, and it doesn’t substitute for other required fire tests like NFPA 285 assembly testing or plastic-specific tests such as ASTM D635.
Is CAN/ULC-S102.2 the same as ASTM E84?
No. They’re comparable, related test methods that report results on a similar flame-spread and smoke-developed scale, but they are distinct standards. A CAN/ULC-S102.2 result reported as “numerically within the Class A benchmark” is a benchmark comparison, not an ASTM E84/UL 723 Class A listing.
Does SAGIREV have a Class A fire rating?
SAGIREV was tested by UL to CAN/ULC-S102.2 and recorded values numerically within the IBC Class A benchmark (25 flame spread, 315 smoke developed), though this is a CAN/ULC-S102.2 result rather than an ASTM E84/UL 723 Class A listing. Confirm current documentation directly with Sagiper for project-specific code submittals.
Sources & References
- ASTM International, ASTM E84, astm.org
- International Code Council (ICC), International Building Code, Section 803.1.2, iccsafe.org
- SAGIREV Interior Fire Performance Summary (Sagiper North America), citing UL — CAN/ULC-S102.2 (July 7, 2014), Intertek — ASTM D635 (July 26, 2016), and QAI — ASTM D1929 & ASTM D2843 (July 30, 2023)
- com — SAGIREV technical documentation
