Fibre Reinforced Facade Encyclopedia: Testing and standards
The smoke developed index is a measure of how much smoke a material produces while burning, obtained by recording the obscuration of a light beam in the exhaust of a fire test and expressing the result on a scale calibrated against reference materials. Two different indices share the name: the ASTM E84 index used in North America, which is open ended and limited at 450, and the AS 1530.3 index used in Australia, which runs from 0 to 10.
Smoke kills more occupants than flame, and it does so by preventing escape long before temperatures become lethal. A material that spreads flame slowly but fills a corridor with dense smoke in ninety seconds has not performed well, which is why every interior finish classification pairs a flame measure with a smoke measure.
At a glance
| Property | Typical value | Note |
|---|---|---|
| ASTM E84 index | Open ended scale; 0 = cement board, 100 = select grade red oak | Area under the light obscuration against time curve |
| ASTM E84 limit | 450 or less for Class A, B and C interior finish | IBC Chapter 8; applies to all three classes |
| AS 1530.3 index | 0 to 10, lower is better | One of four indices from the early fire hazard test |
| NCC threshold | Smoke developed index not more than 8 where the spread of flame index is more than 5 | NCC 2022 Specification 7; check the edition adopted in your jurisdiction |
| European measure | s1, s2 or s3 under EN 13501-1 | From smoke production rate in the EN 13823 single burning item test |
| Group number measure | Smoke growth rate index, SMOGRA-RC | From the AS ISO 9705 room corner test |
| Measurement principle | Photometric light obscuration in the exhaust duct | Optical density, not chemical analysis |
| What it is not | A measure of toxicity | No index in common use measures the toxicity of the smoke |
How the ASTM E84 index is derived
A photocell and lamp across the exhaust duct of the Steiner tunnel record the fraction of light transmitted through the smoke stream for the ten minutes of the test. The area under the resulting obscuration against time curve is integrated and scaled so that the red oak calibration returns 100 and the cement board calibration returns zero. The scale has no upper bound; values in the thousands are recorded for some polymers and foams.
The index is reported alongside the flame spread index from the same test, and the IBC applies both. Class A, Class B and Class C interior finishes all carry the same smoke limit of 450 or less, so the smoke figure does not grade a material, it gates it. A panel with a flame spread index of 15 and a smoke developed index of 520 is not Class A and is not usable as a regulated interior finish.
The Australian index is a different animal
AS 1530.3, the early fire hazard test, produces four indices from one apparatus: an ignitability index from 0 to 20, and spread of flame, heat evolved and smoke developed indices each from 0 to 10. The smoke developed index here is a small integer scale and has no relationship to the ASTM number. A smoke developed index of 3 is an AS 1530.3 result; a smoke developed index of 300 is an ASTM E84 result; quoting one against the other’s threshold is a category error.
The NCC uses the AS 1530.3 pair in Specification 7 for materials not otherwise regulated, requiring a spread of flame index of not more than 9 and, where the spread of flame index exceeds 5, a smoke developed index of not more than 8. For wall and ceiling linings in most Class 2 to 9 buildings the Code moved to the group number system instead, which carries its own smoke criterion.
Smoke in the group number and European systems
The NCC group number system for wall and ceiling linings, set by AS 5637.1, adds a smoke criterion drawn from the AS ISO 9705 room corner test: the smoke growth rate index, written SMOGRA-RC. In certain building classes a lining must satisfy a limit on that index in addition to achieving the required group number, so a Group 1 classification alone does not always complete the assessment.
EN 13501-1 handles smoke with an additional classification of s1, s2 or s3, derived from the smoke production rate measured in the EN 13823 single burning item test, with s1 the most restrictive. It is written as a suffix on the main class. ShapeShell-RT is classified B-s2,d0 under EN 13501-1 by Intertek Testing Services, in which the s2 is the smoke classification and the d0 the flaming droplets classification.
What the number does not tell you
- It does not measure toxicity. Obscuration is an optical measurement of particulate density. Two smokes with identical optical density can have very different carbon monoxide and hydrogen cyanide content, and no index in routine building use addresses this.
- It does not scale up. The quantity of smoke from a 7.3 metre tunnel specimen does not predict the volume that fills a stairwell, which depends on the surface area involved, the ventilation and the fire size.
- It is sensitive to the tested build-up. Coatings, adhesives, cores and backing all alter smoke production, sometimes far more than they alter flame spread.
- It does not travel between jurisdictions. There is no conversion between the ASTM index, the AS 1530.3 index and the EN s classification, because the apparatus, the fire exposure and the reporting are all different.
Using it in a specification
For an Australian project, specify the property the Code actually regulates: a group number for wall and ceiling linings, non-combustibility for Type A and Type B external walls, and the AS 1530.3 indices only where Specification 7 calls for them. Ask for the indices as reported by an accredited testing body, with the report number and the specimen description, rather than a summary figure. Where the same product is being offered on a North American or European project, expect a separate set of numbers from a separate test, and read each against its own code.
Standards and references
- ASTM E84 Standard Test Method for Surface Burning Characteristics of Building Materials; UL 723
- IBC Chapter 8 Interior Finishes, smoke developed index limit of 450
- AS 1530.3 Simultaneous determination of ignitability, flame propagation, heat release and smoke release
- NCC 2022 Volume One Specification 7 Fire hazard properties (check the edition adopted in your jurisdiction)
- AS 5637.1 Determination of fire hazard properties: wall and ceiling linings; AS ISO 9705
- EN 13501-1 smoke classifications s1, s2 and s3; EN 13823 single burning item test
Related terms
Questions specifiers ask
What is the maximum smoke developed index allowed?
Under the IBC, 450 or less for Class A, B and C interior finishes. Under the NCC, an AS 1530.3 smoke developed index of not more than 8 where the spread of flame index exceeds 5. The two numbers are from different scales.
Is a smoke developed index of 5 good?
On the AS 1530.3 scale of 0 to 10, yes, it is mid range and within the NCC limit. On the ASTM E84 scale it would be an extremely low result. The scale must be named for the number to mean anything.
Does the smoke developed index measure toxicity?
No. It is an optical measurement of light obscuration. Smoke toxicity is a separate field and is not covered by any of the indices in routine building code use.
What is the European equivalent?
The s1, s2 and s3 classifications under EN 13501-1, derived from smoke production rate in the EN 13823 single burning item test. ShapeShell-RT is classified B-s2,d0 by Intertek Testing Services.
Do wall linings in Australia need a smoke developed index?
Usually not directly. Wall and ceiling linings in most Class 2 to 9 buildings are regulated on group number under Specification 7, which carries its own smoke growth rate index criterion from the AS ISO 9705 room test.
ShapeShift publishes the full classification string, including smoke and droplet ratings, with the testing body for each ShapeShell system. See ShapeShell fire test data
Reviewed by Richard Halvorsen, General Manager, ShapeShift Technologies. Last updated September 2026.