In building fires, the speed at which fire spreads along walls and ceilings affects whether people can escape safely. If interior materials lack sufficient fire retardancy, flames can spread throughout the room within minutes, and dense smoke obscures visibility, increasing the risk of injury or death.

US building codes have specific requirements for the fire resistance of wall and ceiling interior materials. Among these, the ASTM E84 Steiner Tunnel Test is the most commonly used test method and is a reference standard in the International Building Code (IBC) and NFPA 101 Life Safety Regulations. This article introduces the core content of this test.

What is the ASTM E84 Steiner Tunnel Test?

The Steiner Tunnel Test is a test method used to evaluate the surface combustion characteristics of building materials. During the test, the sample is installed on the ceiling and exposed to a controlled flame for 10 minutes, and the flame spread rate and smoke production are recorded.

ASTM E84 Steiner Tunnel Test Principle

The test was conducted in a 7.3-meter (24-foot) long tunnel furnace. The sample was mounted in a ceiling position with the test surface facing down, exposed to the ignition source. The flame was ignited from one end and spread along the sample surface for 10 minutes.

The testing equipment records two key data points: the Flame Spread Index (FSI) and the Smoke Development Index (SDI). To provide a reference point, the standard uses two benchmark materials—fiber cement board defined as 0 and red oak as 100. The values ​​for the tested material are derived by comparing them.

Scope of ASTM E84

ASTM E84 applies to interior building finishes and ceiling materials.

Common testable samples include:

Wall/ceiling materials: drywall, wood panels, plywood, composite panels, wallpaper, wall coverings, paint, coatings.

Insulation materials: foam plastics (EPS/XPS/PU), rock wool, glass wool, sprayed polyurethane, etc.

Flooring materials (requiring flooring installation): carpet, vinyl flooring, rubber flooring, etc.

Others: wood structural panels, plastic panels, composite materials, fire-retardant treated materials, cooling tower packing, cable sheaths (related standards such as UL910/NFPA262 for conduit cables), etc.

Sample Preparation Requirements:

Samples are typically 24 inches wide × 24 feet long (610 mm × 7.32 m) and can be continuous or segmented.

Samples must be conditioned to equilibrium moisture content (typically ~7%) under standard temperature and humidity conditions.

Samples can be mounted with a substrate (e.g., adhesive, mechanical fastening) or self-supported without a substrate.

Samples must represent the final product condition (thickness, density, coating, etc.) for actual use.

Not suitable or restricted for: certain extremely thick/heavy materials, overall fire resistance testing of structural components (these may be tested using other standards such as NFPA 285).

Two key indicators of ASTM E84

(1) Frame Spread Index (FSI): Reflects the speed at which a flame spreads across a material surface. A lower value indicates that the flame is less likely to spread.

Calculation Steps: Plot the flame spread distance versus time over a 10-minute test period and calculate the area under the curve (AT).

 If AT ≤ 97.5 ft·min, FSI = 0.515 × AT; if AT > 97.5 ft·min, FSI = 4900 ÷ (195 - AT). Finally, round to the nearest multiple of 5.

(2) Smoke Developed Value (SDI): Reflects the amount of smoke produced during material combustion. A lower value indicates less smoke.

Calculation Steps: Record the light absorption rate every 15 seconds during the test, plot the smoke density curve, and calculate the area under the curve.

Compared to red oak (defined as 100): SDI = 100 × A (sample) ÷ A (red oak). Round the result to the nearest multiple of 5; if it exceeds 200, round to the nearest multiple of 50.

Grading Standards

Based on the FSI and SDI values, materials are classified into three grades: A, B, and C.

Summary

The Steiner Tunnel Test (primarily based on ASTM E84 / UL 723) is a core standard method for evaluating the surface flammability of building materials, primarily measuring the Flame Spread Index (FSI) and Smoke Density Index (SDI). This test is widely used for fire resistance certification of building materials and is an important basis for export projects and market access in the United States/Canada. Gold provides Steiner Tunnel Test equipment. If your product needs upgrading, or if you would like to learn more about the equipment, such as furnace structure and furnace temperature, please contact us.