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Fig. 1: A corridor is one of the places the code is strictest. Choosing the panel on colour and NRC first, then checking the fire class, is how projects lose a month.

01 /The test that decides whether you can use it at all

ASTM E84, run in what the industry still calls the Steiner tunnel, is the test behind almost every interior finish specification in the United States. UL 723 is the equivalent and the two are used interchangeably in the code.

It produces two numbers, and people routinely quote only the first:

• Flame spread index, FSI. How quickly flame travels across the surface of the material compared with reference materials.
• Smoke developed index, SDI. How much smoke the material produces while it burns.

A material is not "Class A" because of its flame spread alone. Both indices have to fall inside the band. A panel with an FSI of 15 and an SDI of 600 is not Class A, and it is not Class B or C either.

02 /Class A, B and C, exactly

The three classes under the 2024 IBC, for materials tested to ASTM E84 or UL 723:

Two things to notice. The smoke limit is the same for all three, so smoke is a pass or fail rather than a grading. And there is no class above 200 flame spread. A material that scores higher is simply not a permitted interior finish under this route.

03 /Where the code actually demands Class A

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Fig. 2: Exits and corridors carry the tightest requirements, because they are the route people use to get out. Rooms are usually treated more leniently.

IBC Table 803.13 sets the required class by occupancy group and by where the finish sits in the building. Three locations are treated separately:

1. Interior exit stairways and exit passageways. The strictest of the three.
2. Corridors and enclosures for exit access stairways. Usually one step less strict.
3. Rooms and enclosed spaces. Usually the most permissive.

Typical requirements for a building without sprinklers look like this:

Treat that as orientation, not as your answer. The full table covers every occupancy group and the sprinklered columns differ. A sprinklered building is generally allowed a reduction in some locations, and the mistake to avoid is assuming a blanket one class reduction everywhere. Read the row for your own occupancy, or ask the architect of record to confirm it in writing.

There is also a second route. A wall or ceiling finish tested to NFPA 286, the room corner burn test, and meeting all the criteria in section 803.1.1.1 is accepted as complying with Class A. This matters because some materials that struggle in the tunnel perform well in a full scale room test, and it is the path many textile and expanded vinyl wall coverings take.

04 /Smoke is what catches people out

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Fig. 3: The core, the facing and the adhesive all contribute. The label on the back refers to one tested build up, not to every version of the product.

In practice, flame spread is the easier index to satisfy and smoke is where products fail. Some materials that char slowly still produce a great deal of smoke, and the certificate then shows a respectable first number and a disqualifying second one.

When you read a report, check these five things:

1. Both indices, not one. If a datasheet quotes only flame spread, ask for the smoke number before anything else.
2. Which laboratory, and what date. A report with no lab name and no date is marketing, not evidence.
3. What was actually tested. The report names the specimen: the core, the facing, the thickness and the mounting. It applies to that build up.
4. The thickness tested. A result for a 25 mm panel does not automatically carry to a 50 mm version of the same product.
5. Whether the finish was included. Paint, fabric, stain and fire retardant coatings all change surface burning behaviour.

05 /The rating belongs to the assembly

This is the single most common misunderstanding I see on American projects. A fire classification is a property of a tested assembly, not a property of a brand.

• Change the fabric and you may have changed the result. A Class A core wrapped in an untested fabric is not automatically a Class A panel.
• Change the adhesive and you may have changed the result. The mounting method forms part of the specimen description in the report.
• Field applied coatings are a separate question. A fire retardant coating has its own test evidence, its own coverage rate and its own reapplication interval. Specifying it is easy, achieving the tested coverage on site is not.
• Acoustic performance and fire performance are independent. NRC 0.90 under ASTM C423 tells you nothing about flame spread, and Class A tells you nothing about absorption. You need both reports, and they are different documents.

06 /Choosing acoustic panels in the USA, in order

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Fig. 4: Assembly occupancies such as restaurants carry some of the strictest interior finish requirements in the code. Establish the class before anybody picks a colour.

1. Establish the occupancy group and whether the building is sprinklered. Everything follows from those two facts.
2. Look up the required class for each location. Exits, corridors and rooms may need three different answers in the same project.
3. Set the acoustic target separately. Reverberation time or absorption area, decided on the room, not on the catalogue.
4. Only then shortlist products that satisfy both, and ask for both reports on the exact assembly.
5. Record it. Keep the E84 and the C423 reports in the submittal file. The person who asks for them is usually asking eighteen months later, after something has happened.

If you are sourcing from overseas, the same documentation discipline applies, and our guide to what to ask an OEM acoustic supplier covers what a serious manufacturer should be able to send you. For a residential project, where the code is more forgiving, our home studio buyer's guide for the USA is the better starting point.

07 /Frequently asked questions