Thermal barriers and the protection of foamed plastic

September 14, 2015

Photo courtesy W.R. Grace & Co.

By John A. Dalton
In Canada, products approved for use as a thermal barrier for foamed plastic must pass either CAN4-S124-M, Standard Method of Test for the Evaluation of Protective Coverings for Foamed Plastics, or CAN/ULC-S101, Standard Methods of Fire Endurance Tests of Building Construction and Materials, to comply with the National Building Code of Canada (NBC).

In the Canadian market, many products—typically fibre-based or cementitious materials—can meet these requirements. Unfortunately, there has been a growing trend amongst some suppliers of ‘paintable’ ignition barriers claiming their products meet the performance of a thermal barrier without actually passing either CAN4-S124-M or CAN/ULC-S101. This article provides the background on the qualities of acceptable solutions as a thermal barrier in accordance to the NBC, and discusses the current activities in the marketplace and the potential liability to the design/construction team and authority having jurisdiction (AHJ).

NBC test criteria for protecting foamed plastics
Sprayed polyurethane foam (SPF) insulation is combustible and may ignite when exposed to heat or fire. During the event of a fire, smoke and combustible gases can accumulate in interior, confined spaces and lead to a deadly flashover.1 These characteristics of foamed plastics are recognized within the NBC, which details the steps to be taken to protect building inhabitants from the effects of the materials’ burning.

The code specifically defines certain materials to be used as “thermal barriers” for foamed plastic insulation. These include gypsum board thicker than 12.7 mm (1/2 in.), concrete, and masonry. For other materials (that are not specifically identified), NBC stipulates testing/performance requirements to determine whether the material may be used as a thermal barrier. It splits this approval process into three categories based upon the flame spread rating of the foamed plastic insulation and details of the proposed building. Each category has its own testing requirements and pass/fail criteria.

As mentioned, the NBC includes testing thermal barriers according to CAN4-S124-M and/or CAN/ULC-S101—both standards use the same time-versus-temperature fire curve, but differ in the required sample size, orientation to the fire, number and location of thermocouples, and pass/fail criteria.

More importantly, with both standards, NBC requires the testing agency measure the temperatures at the interface of the foam plastic and thermal barrier. There have been recorded situations where tests have been run with the thermocouples on the backside of the assembly or with the thermocouples buried in the foam. Neither of these conditions would meet the requirements of NBC or the test standards mentioned above. The code is very clear in this respect.


In the first category, NBC, in (titled “Combustible Insulation and its Protection”), allows for the use of a thermal barrier based on certain criteria. In a building required to be of noncombustible construction, foamed plastic insulation having a flame-spread rating not more than 25 is permitted, provided the insulation is protected from adjacent space in the building by a thermal barrier that meets the requirements of classification B when tested in conformance with CAN/ULC S124. As a general rule, if you can see foamed plastic insulation in the conditioned space of a building, it is a code violation.

This is a small-scale test, with an exposed surface area of 0.49 m2 (5.3 sf), requiring temperature measurements at the interface of the thermal barrier and the foamed plastic. Purely a thermal transmission test, it measures the effectiveness of the thermal barrier to insulate the foamed plastic from heat and fire. The test must be run in a horizontal orientation. The material is exposed to a fire that reaches 700 C (1290 F) after 10 minutes (Figure 1).

Despite its small size, it is accepted as a severe test and one that provides an accurate measure of a thermal barrier’s effectiveness. Organizations such as ULC and Intertek indicate if a material has a Classification B rating based on CAN/ULC-S124. For a Classification B rating, the temperature rise at the interface of the tested thermal barrier material and the foamed plastic insulation cannot exceed an average of 140 C (252 F) for all the thermocouples or a maximum rise of 180 C (324 F) at any single thermocouple for 10 minutes (Figure 2).

In the second and third categories, for buildings sprinklered throughout or 18 m (59 ft) or shorter (from grade to the floor level of the top storey), NBC requires a thermal barrier tested to CAN/ULC S124 for foamed plastic insulation having flame spread ratings between 25 and 500 if the building is sprinklered throughout, or not more than 18 m (59 ft) from grade to the floor level of the top storey. Otherwise, as in for taller buildings or those without sprinklers, thermal barriers must be tested to CAN/ULC-S101. This is a full-scale test, larger than CAN/ULC S124, requiring an exposed surface of 9.3 m2 (100 sf) that can be run in both horizontal and vertical orientations to evaluate the intended orientation of the thermal barrier. As per Section of the 2012 NBC, it establishes whether a material qualifies as a thermal barrier as follows:

2. Combustible insulation having a flame-spread rating of more than 25 but not more than 500 is permitted in the exterior walls of a building required to be of noncombustible construction, provided the insulation is protected by a thermal barrier that, when tested in conformance with CAN/ULC-S101 will not develop an average temperature rise of more than 140 C or a maximum temperature rise more than 180 C at any point on its unexposed face [(i.e. the unexposed face of the thermal barrier, which is the interface of the foam and the thermal barrier)] within 10 minutes.

3. Combustible insulation, having a flame-spread rating of more than 25 but not more than 500 on any exposed surface, or any surface that would be exposed by cutting through the material in any direction, is permitted in the interior walls, within ceilings and within roof assemblies of a building required to be of noncombustible construction, provided the insulation is protected from adjacent space in the building by a thermal barrier that, when tested in conformance with CAN/ULC-S101 will not develop an average temperature rise of more than 140 C or a maximum temperature rise of more than 180 C at any point on its unexposed face within 20 minutes, and will remain in place for not less than 40 minutes.

In addition to testing potential thermal barrier properties, CAN/ULC-S101 is primarily used to test the fire resistance of assemblies. However, for this type of testing, the thermocouples (and, therefore, temperature measurements) are located on the unexposed side of the assembly (Figure 3). This approach is different than what is used to assess a material’s effectiveness as a thermal barrier. The use of CAN/ULC-S101 in this fashion cannot be employed to approve thermal barriers because in this test procedure the thermocouples are not at the interface of the foam and thermal barrier as required by the National Building Code.

Preparing the foam for a CAN/ULC S101 wall test. Photo courtesy W.R.Grace and Co.

Current market situation
Until recently, thermal barriers have typically been one of two types—fibre-based or cementitious. These products protect the foamed plastic from fire, while also providing physical protection for the foam from abuse, allowing for longer in-place service life. Many of these materials have a long and successful track record, and are listed with testing agencies such as ULC, Intertek, and QAI, passing many CAN/ULC S124 or CAN/ULC-S101 tests as thermal barriers.

Recently, this author has seen unfounded claims by companies marketing paintable ignition barriers that are certified for use in Canada as thermal barriers. These products are often intumescents—typically, ammonium polyphosphate-based—which begin the intumescing process at 240 C (464 F), which is higher than the maximum allowable temperature limits of the code. (In other words, they begin their protective actions too late.) Unfortunately, in most cases, these companies have attempted to confuse the marketplace by intentionally running fire tests where the thermocouples were not properly located to comply with NBC.

For example, in some cases, a single material was tested using CAN/ULC-S101 with the thermocouples on the unexposed side of the assembly, behind the wallboard. This procedure is appropriate for qualifying a wall assembly, but cannot be used to qualify a material as a thermal barrier (i.e. because such a process requires the thermocouples to be at the interface of the thermal barrier and the foam).

Another inappropriate test had the thermocouples buried within the foam, which obviously does not meet the code. When this information was brought to the attention of one of the manufacturers that had run tests where thermocouples were not placed in accordance to the NBC requirements, the company stated it did not think the material would pass as a thermal barrier when using the required thermocouple placement.

In addition to erroneously promoting products with claims their products are certified for use in Canada, some companies have been supplying results from testing in the United States done in accordance to UL 1715, Fire Test of Interior Finish Material—a completely different and less severe test method that does not meet NBC requirements.

Thankfully, there has recently been the introduction of certain intumescent paints that do pass the CAN/ULC S124 test. By meeting the requirements of the test, these companies have negated the argument the CAN/ULC S124 test is too severe to act as a test method for intumescent thermal barriers.

Further, there exists in Canada a process whereby the developers of new and materials may use the Canadian Construction Materials Centre (CCMC) to demonstrate compliance with the requirements of NBC or provincial/territorial building codes. Regretfully, this author has seen engineering judgments appearing to ‘okay’ the use of intumescent thermal barriers. In some instances, the claims made have been factually incorrect; in others, the basis for approvals have been the alternate method for code compliance provisions, given in 1.2 of Division A of NBC where compliance with the code can be achieved by meeting a prescriptive test or by showing through performance testing a product meets the objectives of the prescriptive code section.

Considering the wide variety of thermal barriers choices now available, can one really state the alternate, but untested, product is as good as or better than those products currently available? This author does not believe such a claim can be made, especially when code-compliant test processes are available at a reasonable cost.

Contractor liability
Ultimately, it is the responsibility of the installer of the thermal barrier and the AHJ to provide and approve products conforming to the relevant provincial building code. Unfortunately, the contractor may also be held liable if he or she installs a product that does not conform to the applicable standard—even when the building inspector has incorrectly accepted products that do not meet the intent of the NBC. Architects and specifiers could also face legal liability, to say nothing of the moral issues for design professionals.

Canadian Construction Documents Committee (CCDC) documents suggest, it is the responsibility of the prime consultant to include in the contract documents the criteria required for the constructor to comply with the code requirements. It is the constructor’s responsibility to provide the work in compliance with the contract documents and the code. That said, the constructor is not responsible to verify the contract documents are in compliance with the code. The constructor may be liable if it installs a material not in compliance with the contract documents, or if it proposes a substitution material that does not meet the code requirements. The reality is all parties involved risk some legal liability, to say nothing of the moral issues.

To avoid any unnecessary liability, the specifications should request a submittal of a letter from the manufacturer stating the material being supplied has been tested in accordance with the requirements of the National Building Code (item and passed its criteria established for a thermal barrier. One should also ask for the test report that supports the requested letter. There are many products in the market that have successfully passed the NBC criteria as thermal barriers; selecting and using a product that has not met these criteria would be taking on unnecessary liability, and is a threat to life safety.

The fire protection industry (including manufacturers, engineers, architects, and the contractor community) has a duty to provide the public with a reasonable level of safety in buildings in compliance with the applicable building codes. It is the responsibility of all parties to perform their due diligence to ensure public safety is not put at undue risk. Accepting only code-conforming materials is an important aspect in the process.

Dalton[3]John A. Dalton is technical service manager for W. R. Grace & Co.’s fire protection products division. He is the task group chair of the ASTM E06.21 committee on serviceability and a principal member of the U.S. National Fire Protection Association (NFPA) 502, Standard for Road Tunnels, Bridges, and Other Limited Access Highways. Dalton has degrees in mathematics and industrial chemistry. He can be reached at[4].

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