By Arthur J. Parker, PE and Jesse J. Beitel
The use of plastic building materials in commercial and residential construction has dramatically increased due to improved plastic material performance, efficient use of technologies in new applications, and the need for lightweight, durable materials for insulating and construction purposes.
Plastics, like all organic materials, will burn. As such, those plastic materials used in construction contain fire-retarding compounds to increase the temperature necessary before ignition and/or to lower the rate of burning.
The various building codes typically have sections that deal with plastic building materials. These regulations require specific fire performance characteristics (both in general and for the application into which the plastic material is to be used). These characteristics are for fire/flame retardation and safety. In the International Building Code (IBC), provisions governing plastic building materials, design, application, construction, and installation of plastic materials are provided in a dedicated chapter, Chapter 26, Plastics. In the International Residential Code (IRC) the provisions are in Section R314.
In commercial buildings, where the most stringent fire performance is required, fire performance requirements are provided for a wide range of plastic building applications, including:
- insulation materials;
- interior finish and trim;
- light-transmitting plastic products (e.g. light covers);
- light-transmitting plastic wall panels;
- light-transmitting plastic roof panels; and
- light-transmitting interior signs.
Due to their versatility, plastic building materials may be found in the walls, roof, plenums, doors, attics, crawlspaces, walk-in coolers/freezers, and in (or on) masonry. The myriad of applications has resulted in the development of specific fire performance requirements and tests so in the event of a fire, the plastic product does not significantly contribute to fire growth based on the anticipated use and the potential impact on building occupants. Thus, while specific tests may be required for a type of plastic building material, additional tests can also be required for the specific application in which it will be used.
Today’s plastic products, when used in the proper application and correctly installed, can meet or exceed the fire performance characteristics required by most codes and standards, and can help provide a nice living environment for homes and offices by performing their intended function. A brief review of the requirements for a few of the more common applications of plastic building products in some commercial buildings is provided below.
Foam plastic insulation building materials
A foam plastic insulation building material is defined in the building code as:
A plastic product that is intentionally expanded by use of a foaming agent to produce a reduced-density plastic containing voids consisting of open or closed cells distributed throughout the plastic for thermal insulation or acoustical purposes and has a density of less than 20 pounds per cubic foot (pcf ).
The most common types of foam plastic insulation building materials are:
- extruded polystyrenes (XPS);
- expanded polystyrenes (EPS);
- rigid polyurethanes;
- sprayed-applied polyurethanes (SPF); and
- polyisocyanurates (polyiso).
Three general requirements usually exist in building codes for the use of foam plastic building materials in buildings and structures.
- Foam plastic building materials are required to be listed and labeled by an independent third-party approval agency to:
- ensure the end-use complies with the building code requirements; and
- verify its composition remains unchanged from what was initially tested;
- Foam plastic building materials shall have a flame spread index of not more than 75 and a smoke developed index of not more than 450 when tested in accordance with the Tunnel Test (ASTM International E 84, Standard Test Method for Surface Burning Characteristics of Building Materials), unless other more stringent requirements are mandated by the building code.
- Foam plastic building materials shall be separated from the interior of a building by an approved thermal barrier. A 12.7-mm (0.5-in.) thick layer of regular gypsum wallboard, or an equivalent material, is usually considered by the building codes to be an adequate thermal barrier.
The thermal barrier material must be capable of limiting the heat transfer through to foam plastic insulation and remain in place for a minimum period when subjected to a standard fire exposure.
This thermal barrier requirement may be waived in some applications based on additional testing or construction. For instance, the thermal barrier can be eliminated when the foam plastic is:
- covered by a minimum of 25.4 mm (1 in.) of masonry or concrete;
- installed in a roof assembly which passes an underdeck flame spread test; or
- installed in doors with a metal facing of minimum thickness. In these instances, some means of delaying or preventing ignition is an integral component of the assembly, or a standard fire test has been conducted to demonstrate its performance.
When foam plastic building materials are installed on the exterior of buildings, different performance requirements are specified. Additional specialized tests are also specified so the foam plastic insulation material does not significantly contribute to upward flame spread over the surface or within the exterior wall. When applied to the exterior walls of certain types of buildings, foam plastics:
- cannot reduce the fire resistance rating of the wall assemblies;
- must be separated from the interior of the building by an approved thermal barrier;
- must not have a potential heat—expressed as BTU/sf—exceeding specified limits (thereby controlling the amount of foam plastic that can be applied to the wall); and
- must have a flame spread of not greater than 25 (thereby providing some control on the flammability of the foam plastic insulation by itself).
Additionally, the complete wall assembly must meet the acceptance criteria specified in National Fire Protection Association (NFPA) 285, Flammability Characteristics of Exterior Non-load-bearing Wall Assemblies Containing Combustible Components Using th Intermediate Scale Multi-Story Test Apparatus (ISMA), which evaluates the upward flame propagation potential of the foam plastic insulation. As well, the complete wall assembly must not exhibit sustained flaming when tested in accordance with the Radiant Heat Test (NFPA 268, Standard Test Method for Determining Ignitibility of Exterior Wall Assemblies Using a Radiant Heat Energy Source), which evaluates the ignition potential of the wall assembly by a fire in an adjacent structure.
Due to the uniqueness of foam plastic building products and their continually changing applications, the codes have allowed testing which represents the actual end-use configuration and evaluates the finished manufactured foam plastic product assembly in the maximum thickness intended for use. Successfully conducting and passing a full-scale fire test is considered to be equivalent to meeting the individual prescriptive requirements because the full-scale fire tests are more representative of the assembly performance during a fire event.
Light-transmitting plastic building materials
Light-transmitting plastic building materials are commonly used in building construction as covers for interior lighting, decorative accent pieces, skylights, exterior wall and roof panels, etc. Their function, as the name implies, is to permit natural light to filter into a building to result in a more open, friendly environment. When plastic building products are used in these light-transmitting applications, they are required to have a self-ignition temperature of 343 C (650 F) or greater.
Each light-transmitting unit or package must also be identified by a mark that categorizes the material combustibility classification as CC1 or CC2—this provides a means to evaluate the fire propagation performance of the materials in a small-scale test. It should be noted while the small-scale tests may be less severe than other tests, light-transmitting plastic building materials are also regulated based on area allowed (square footage), separation distance between units, and, in some cases, what type of building (or portion thereof) in which they are allowed.
A specific example of a requirement based on a plastic building material’s application is when lighttransmitting plastic diffusers (e.g. those on fluorescent lighting), are used in a room or space. In this application, the lighttransmitting plastic products must be capable of remaining in place at an ambient room temperature of 79.4 C (175 F) for 15 minutes or more. This requirement demonstrates the light-transmitting plastic building product does not fall out prematurely under normal conditions (i.e. non-fire situations), potentially injuring building occupants or causing undo panic. To demonstrate the light-transmitting plastics do not burn in place, the plastic panels must fall from their mountings before igniting at a temperature at least 93 C (200 F) below their ignition temperature. By falling out below their ignition temperature, surface flame spread requirements are eliminated from being imposed on these plastic materials. To further limit the potential for obstruction or injury due to the plastic panels falling from their mounts, length and area restriction are also imposed on the final installation.
Significant amounts of research, development, and testing into the flammability of plastic building materials have resulted in specific building code regulations governing their performance, application, and installation. Developed by industry, these regulations have provided the building code official with valuable tools to demonstrate the increased use of plastic building materials will not inadvertently raise the hazards to building occupants. As new types of plastic building products are produced, and new applications developed, the building codes requirements will be modified and improved to regulate the flammability of plastic construction materials, maintaining a codified acceptable level of safety for building occupants through requirements that emphasize safety and performance.
About the Authors
Arthur J. Parker, PE, is a senior fire protection engineer with Hughes Associates Inc. (www.haifire.com). He has conducted research, testing, design, and analysis of passive fire protection systems and materials, evaluated the performance of plastic materials through small- and full-scale testing, and is active in the building code development process. Jesse J. Beitel is a senior scientist, and principal with Hughes Associates. He is a recognized industry expert with regards to the fire performance of plastic materials and has conducted various research and analysis projects for many plastics industry clients and trade associations.