What is the flame spread index (FSI)?

The FSI is a dimensionless number from 0 to 450+ that compares how fast flames travel across a material's surface relative to red oak (FSI = 100) and cement board (FSI = 0). A lower number means slower flame spread.

What is the smoke developed index (SDI)?

The SDI measures the amount of smoke a material generates during the ASTM E84 test. Red oak is the benchmark at SDI = 100. Most codes require SDI ≤ 450 for all classes.

What is a Class A fire rating?

Class A (also called Class I) requires FSI ≤ 25 and SDI ≤ 450. It is the most restrictive class and is required in high-rise buildings, healthcare facilities, and assembly occupancies.

Are these values exact or typical ranges?

Values shown are typical ranges from published ASTM E84 test data. Actual results vary by product thickness, treatment, and manufacturer. Always verify with the specific product's test report before specifying.

Does ASTM E84 apply to all materials?

ASTM E84 is designed for interior finish materials — walls, ceilings, and floors. It does not apply to structural materials, exterior cladding, or some composite systems that require different test standards such as NFPA 285.

What class is required by the International Building Code (IBC)?

Requirements vary by occupancy and location. High-rise buildings and Group I occupancies typically require Class A throughout. Most other occupancies allow Class B or C in certain areas. Always confirm with the applicable adopted code edition.

Flame Spread Index Lookup

Name: Flame Spread Index Lookup
Availability: InStock
Author: Nham Vu

Look up ASTM E84 flame spread index and smoke developed index values for common building materials and understand Class A, B, and C fire ratings.

ASTM E84 Class Thresholds

Class A (Class I) Best

FSI: 0 – 25

SDI: ≤ 450

High-rise, healthcare, assembly, corridors

Class B (Class II) Moderate

FSI: 26 – 75

SDI: ≤ 450

Most commercial, educational, lodging

Class C (Class III) Standard

FSI: 76 – 200

SDI: ≤ 450

Low-occupancy, storage, some residential

Unclassified Fails

FSI > 200 or SDI > 450 — not permitted as interior finish in most occupancies

FSI Classifier

Enter an FSI value to see its ASTM E84 class.

Benchmark Materials

Inorganic reinforced cement board FSI = 0

Red oak flooring FSI = 100

Both are ASTM E84 calibration standards

Material FSI / SDI Reference

Material	FSI	SDI	Class

Values are typical ranges from published ASTM E84 test data. Verify with manufacturer test reports for specification use.

Summary

Look up ASTM E84 flame spread index and smoke developed index values for common building materials and understand Class A, B, and C fire ratings.

How it works

Select a material category or type a name to filter the list.
The table shows each material's typical FSI and SDI range.
Compare the values against the Class A/B/C thresholds shown in the rating guide.
Use the FSI calculator to enter a custom value and instantly see its class.
Reference the class requirements for your specific building occupancy or code.

Use cases

Verify that an interior finish material meets IBC or local code requirements.
Compare flame spread ratings when selecting wall or ceiling finishes.
Explain Class A, B, C differences to a client or project team.
Quickly check whether a specific product needs a fire-retardant treatment.
Review SDI limits for materials in corridors, stairwells, or egress paths.
Confirm compliance for healthcare, educational, or high-rise occupancies.

Frequently Asked Questions

Last updated: 2026-07-23 · Reviewed by Nham Vu