ASTM E84 25/50 is an important fire safety standard developed to protect the lives of building occupants. It appears frequently in mechanical insulation project specifications and is commonly adopted by authorities having jurisdiction (AHJ’s) for commercial and residential building codes.
For engineers, contractors, and owners, understanding ASTM E84 25/50 is essential to ensuring materials meet code requirements and are suitable for use in plenums, duct systems, and mechanical piping.
Another commonly referenced fire safety standard is the UL 723 (UL Solutions) rating, which is often considered a reciprocal standard that uses almost exactly the same test method by two separate standard and test method organizations. To learn more about how the two compare, you can read more in this article.
What Does ASTM E84 25/50 Mean?
ASTM E84 25/50 refers to the flame and smoke thresholds established by ASTM International under the ASTM E84 Standard Test Method for Surface Burning Characteristics of Building Materials, which evaluates how materials perform when exposed to fire. ASTM International, formerly known as the American Society for Testing and Materials, is a nonprofit international standards organization that developed, published, and periodically updates E84. All ASTM testing standards are given a designation number. ASTM E84’s current full designation number is ASTM E84-25 and can be broken down as follows:
- E: Miscellaneous subjects
- 0084 is the assigned sequential number
- 25 is the year in which the standard was last revised
- A indicates if there are any subsequent revisions in that same year
To comply with a 25/50 rating, a material must achieve:
- Flame Spread Index (FSI) of 25 or less
- Smoke Developed Index (SDI) of 50 or less
These values indicate that the material limits the speed at which flames spread across its surface and produces a controlled level of smoke during combustion.
Where 25/50 Fire Ratings Are Required
A 25/50 fire rating is typically required in areas where insulation is exposed to air movement or installed in code-regulated spaces. This can be highly dependent upon your project’s geographic location and local building and fire code requirements. However, some common applications include:
- Plenum spaces (return air and supply air)
- Duct insulation (liner and wrap)
- Mechanical piping systems
- High occupancy commercial and institutional buildings
Building codes such as the International Mechanical Code (IMC) and International Building Code (IBC) often reference ASTM E84 25/50 requirements for these applications.
ASTM E84 25/50 for Plenum Spaces
When mechanical insulation is installed within a building’s plenum, the space between a suspended ceiling and the roof, exposed pipe, and duct insulation (plus insulation adhesives) must pass E84’s 25/50 rating system and be listed and labeled, per the International Mechanical Code® (IMC®) 602.3.9 Pipe and duct insulation within plenums. The IMC code requirement suppresses the potential for insulation to spread flame and smoke within a plenum to other occupant spaces through the air distribution system. Insulation tested according to E84 “shall not flame, glow, smolder or smoke” at a minimum test temperature of 250°F (121°C).
What ASTM E84 Doesn’t Test
ASTM E84 is a surface burn test performed under very specific constraints, as described above. It is not designed to measure certain material properties, like those listed below, where other ASTM standards exist to provide evidence of these properties:
- Measurement of heat transmission through the tested surface, which is instead tested via ASTM C177/C518
- Classifying or defining a material as noncombustible by means of a flame spread index by itself. This is defined by the standard ASTM E136
- Hourly fire resistance rating. The primary standard for this is ASTM E119
- The rate and extent of burning of self-supporting plastics in a horizontal position, which is measured using ASTM D635
Common Mistakes When Specifying 25/50 Insulation
Even though ASTM E84 25/50 is widely referenced, it is frequently misunderstood in practice.
Common mistakes include:
- Assuming all ASTM E84 rated insulation meets 25/50 Requirements
Not all insulation products are tested or compliant. Always be sure to verify before specifying specific insulation materials. - Not properly specifying duct insulation to meet IMC
It’s important to note that duct insulation (wrap and liner) must be 25/50-rated throughout the building interior. Within plenum space, duct insulation must also be listed and labeled to meet IMC. - Confusing material components with system performance
Jackets, facings, or adhesives may impact overall fire performance. IMC requires that products be tested and pass as a composite assembly. For example, pipe insulation with a PVC jacket or coating must pass 25/50 together (not separately). - Overlooking installation conditions
The results of ASTM E84 testing provide relative results, not exact numbers. It’s important to remember that how insulation is installed can affect real-world performance. * - Substituting materials without confirming compliance
Not all alternative insulation materials meet the same fire performance criteria. Please be sure to review a product’s technical data sheet or reach out directly to material manufacturers for confirmation if you’re unsure if a material meets your specification’s fire protection requirements.
Avoiding these issues is critical to maintaining code compliance and system integrity.
*For more information about proper installation of AEROFLEX EPDM™ Insulation, please refer to our Installation Guide.
Source: 2024 International Mechanical Code
Mechanical Insulation Products That Meet ASTM E84 25/50
Many elastomeric and closed-cell insulation products are designed to meet ASTM E84 25/50 requirements when properly specified and installed. Aeroflex USA’s AEROFLEX EPDM closed-cell elastomeric pipe insulation, duct insulation, sheet and roll, and insulation fittings are all 25/50-rated through 2” [50 mm] thick. Additionally, Aeroflex USA’s Breath-EZ EPDM Duct Insulation complies with the International Mechanical Code’s “Listed & Labeled” requirement for duct insulation contained within plenums.https://aeroflexusa.com/aerocel-elastomeric-pipe-insulation
These products are commonly used in:
- Mechanical piping systems
- HVAC duct applications
- Plenum-rated installations
When selecting insulation, it’s important to verify:
- Tested performance to ASTM E84
- Compliance with project specifications
- Suitability for the intended application
Frequently Asked Questions About ASTM E84 25/50
What does 25/50 fire rating mean?
It refers to a Flame Spread Index of 25 or less and a Smoke Developed Index of 50 or less, as measured by ASTM E84.
Is ASTM E84 25/50 required for plenum insulation?
In many cases, yes. Building and mechanical codes often require 25/50-rated materials for use in plenums.
Does all insulation meet ASTM E84 25/50?
No. Only materials that have been tested and meet the required limits are compliant.
What is plenum-rated insulation?
Plenum-rated can mean either (1) the insulation passes ASTM E84/UL723 25/50 or (2) the insulation is listed and labeled.
Is ASTM E84 the same as UL 723 or NFPA 255?
These standards utilize similar test methods to evaluate surface-burning characteristics. To learn more about these standards, please read our article.
Sources:
ASTM E84 Standard Test Method for Surface Burning Characteristics of Building Materials
https://www.astm.org/Standards/E84.htm
2024 International Mechanical Code
https://codes.iccsafe.org/content/IMC2024V3.0/chapter-6-duct-systems#IMC2024V3.0_Ch06_Sec602.3
