Utilizing Mineral Fiber Insulation to Slow the Spread of Fire in Commercial Buildings

J.R. Babineau

J.R. Babineau is a Research Manager and the Principal Building Scientist for Johns Manville. For more than 20 years, he has been involved in research and development of building products, as well as providing education and consultation on building systems, with an emphasis on health, air, moisture, noise, and energy efficiency. He can be reached at francis.babineau@jm.com.

February 1, 2020

Many factors influence the resilience of a commercial building, especially as it relates to protection against fire. A building’s design and the materials it is designed with play a critical role in the safety of building occupants during a fire event. Buildings today are equipped with complex fire safety measures, all of which should be considered and carefully planned during the early stages of designing a new building.

Fire protection measures typically fall into 2 categories: active and passive. When these measures are well planned and implemented, they can work together to slow or even halt the spread of fire. Active fire protection would be systems that require action or motion in the event of a fire, such as fire extinguishers, smoke alarms, sprinklers, and even firefighters. Passive fire protection involves measures put in place to slow down the spread of fire from one space to the next through walls, ceilings, floors, or even up the side of a building.

Insulation can serve as an effective passive fire protection measure. While insulation will not prevent or necessarily stop a fire from occurring, it can delay the spread of fire in most rated wall and floor/ceiling assemblies. While there are several types of insulation that are available, depending on application, to slow the spread of fire, including perlite, vermiculite, cellulose, ceramic fiber, microporous, this article will focus on mineral fiber. When planning for insulation to fulfill this role, here are 2 considerations to keep in mind.

Hourly Rating and Required Codes

The standard test for fire resistance is typically measured in time, or the duration a passive fire protection system can withstand a standard fire resistance test. Most areas within a building fall into the 1- or 2-hour rating, though longer ratings may also be required. The required rating is dependent on the type of construction, the type of occupancy, any special hazards in the building, and the criticality of a particular area within a building for life safety. For example, walls in stairwells may be rated higher than in other areas to allow building occupants more time to evacuate. Buildings like hospitals or prisons often require higher ratings, at least for certain sections of those buildings, to allow more time for evacuation or to allow occupants to shelter in place.

Fire-resistance tests are primarily developed and maintained by the National Fire Protection Association (NFPA), ASTM International (formerly the American Society for Testing and Materials), and Underwriters Laboratories, Inc. (UL). Some of the most common test methods are ASTM E119, Standard Test Methods for Fire Tests of Building Construction and Materials; UL 263 (equivalent to ASTM E119); and NFPA 285, Standard Fire Test Method for Evaluation of Fire Propagation Characteristics of Exterior Wall Assemblies Containing Combustible Components. When a wall or floor/ceiling system is tested against fire code requirements, it is most often pass or fail; there is no gray area.

While many exterior wall assemblies must be designed to deliver an hourly rating from ASTM E119 (or UL 263), or also to pass NFPA 285, there are other codes to be aware of. For example, the Wildland-Urban Interface (WUI) is a zone of transition between wildland and human development, an area that may have an increased risk of wildfires. In WUI zones, the standard for noncombustible and fire-resistant construction is higher than in other areas, due to the increased fire hazard. Chapter 7A of the California Building Code and the International Wildland-Urban Interface Code contain additional standards and design parameters associated with construction in these areas.

Insulation Products to Delay the Spread of Fire

The delay of the spread of fire is when, during a fire, insulation stays in place within the wall assembly even after surrounding materials have deteriorated. Insulation materials made from rock wool, such as mineral wool, are more effective for fire protection when compared to others. It is noncombustible, meaning it will not ignite or burn when exposed to fire or extreme heat, and it typically has a melting point in excess of 2,000°F.

Fiber glass is another suitable insulation solution for slowing fire spread. While fiber glass will melt at a lower temperature than mineral wool, it is also noncombustible, and its typical melting point of 1,300°F is acceptable in most 1-hour rated assemblies.

There are other insulation products, including autoclaved aerated concrete (AAC) and spray-on materials—typically a combination of mineral wool, perlite, vermiculite, cellulose, ceramic fiber, microporous, and cement applied to structural steel—that meet the standards in helping delay the spread of fire.

How Mineral Wool and Fiber Glass Work in Different Wall Assemblies

Building insulation can be installed in a few different places, both interior and exterior. Depending on where the product is placed, it can serve a different function in delaying the spread of fire. Interior or cavity insulation is insulation placed in walls, ceilings, floors, or even the concealed spaces between floors.

  • Depending on the design and the building structure, mineral wool is commonly used for interior walls and ceilings, not only for its fire safety capabilities but also because it delivers excellent sound control, thermal performance, and moisture resistance, as does fiber glass. It is also relatively simple to install and can be placed directly into the wall cavity without any fasteners (depending on the manufacturer).
  • Fiber glass batts and rolls are simple to install, cost effective, and durable, while still meeting noncombustibility requirements. Depending on the manufacturer, fiber glass batts also can be used in the interstitial cavity between the ceilings and floors of commercial buildings in lieu of installing sprinkler systems in these concealed spaces.

An advantage of both mineral wool and fiber glass is they do not burn easily, and because they provide fire resistance by slowing the flow of heat between the hot side (fire exposed) and cool side of a wall or floor/ceiling assembly. Slowing heat transfer helps to protect the gypsum, concrete, or other components, so the assembly maintains its integrity longer and allows occupants time to evacuate.

Additionally, mineral wool as exterior continuous insulation (CI) can help protect against the spread of fire up the outside of a building. Combustible components, such as water-resistive barriers (WRBs) or air barriers, or combustible claddings, can provide fuel for a fire to spread up from one floor on the outside of the wall, especially when a window is breached. Rainscreen exterior wall systems with mineral wool CI can be a viable solution, as this combination has been shown to resist this type of fire spread in NFPA 285 tests. Some systems have even been tested to incorporate the use of combustible claddings, like high-pressure or metal laminates, because of the protection provided by the mineral wool CI.

While there is insufficient official data to back its sole effectiveness, when mineral wool is included as CI on a wall assembly, some studies suggest the assemblies can be effective in slowing the spread of fire through the exterior wall.

Importance of Installation

The quality of the installation of any insulation product is perhaps the most important consideration, because without it, goals are not met, and the assembly may not pass the requirements of commercial building codes. A high-quality installation has no gaps or voids—areas typically sealed with sealant or spray foam. If unattended, these spaces will allow a fire to penetrate more easily from space to space.

Insulation that is haphazardly installed by being overly compressed into the cavity, or bent or folded, also will underperform in delaying the spread of fire because its R-value has been compromised. In short, poorly installed insulation will not pass code requirements; therefore, it is important to consult an insulation contractor and eliminate the need for future repairs or rework.

Insulation can play an important role in slowing the spread of fire in commercial buildings, and many considerations are involved in the decision-making process when selecting materials. Each building and planning process is different, each with its own code requirements. No matter the project, the safety of the building occupants and those around it remains top priority, and passive fire protection is an essential part of this protection.

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