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Special Section

 CSI:
Designing
with Masonry

Fire kills more Americans annually than all other natural disasters combined. Eighty-four percent of all fires occur in residences, resulting in nearly $5 billion worth of property loss in one- and two-family dwellings alone. Americans are still left with horrifying images of fire devastation from the 2003 California wildfires and the Rhode Island nightclub fire. Incidents like these have heightened Americans' concerns about fire safety, according to a survey commissioned by the National Concrete Masonry Association (NCMA).

Of the 1,000 adults surveyed, 61% are more worried about fire in public and commercial buildings because of what they've heard and read regarding recent fires.

What do they believe can be done to make buildings safer? According to the survey, 85% believe that stricter building codes for public and commercial buildings would improve fire safety. Those surveyed also indicated they are willing to pay more for fire safety. Seventy-nine percent want safer, less combustible materials used in buildings, even if it means increased construction costs and higher prices passed on to consumers.

The United States has one of the worst residential fire safety records among industrialized nations around the world, despite prevalent use of detection systems (alarms), tough code requirements for suppression systems (sprinklers), and some of the best trained and equipped fire service and emergency response teams. Existing building codes, standards and construction practices in the U.S. favor the use of light construction, a practice that is not typical in other countries where fire safety records are better.

While the nation's fire statistics have improved over the years, those gains have been limited by trade-offs made within building codes resulting in the reduction of containment requirements provided by passive fire-rated assemblies.

Comprehensive Fire Safety Design Approach
To provide the best protection and greatest opportunity for occupants to escape a fire, NCMA recommends that codes for buildings require a balanced design made up of three key elements: fire detection, fire suppression and fire containment. Fire detection includes the installation of smoke detectors and fire alarms. Active fire suppression includes the use of sprinkler systems. Fire containment includes fire barriers, fire-rated assemblies and exterior walls built of substantial, noncombustible, fire resistant materials such as concrete masonry.

"Unfortunately, today's new model of building codes and fire codes has strayed significantly from the balanced design approach to fire safety," says Gene Corley, senior vice president of Construction Technology Laboratories and head of the team that analyzed the design implications, damage and mechanics of the collapse of the World Trade Center. "Recent fire tragedies have raised a red flag about how well buildings are designed, constructed, operated and maintained to protect the lives of occupants. Noncombustible masonry construction can reduce or eliminate the spread of fire and provide additional protection and time for occupants to exit and for fire and emergency personnel to conduct rescue operations."

Corley encourages code officials across the nation to participate in making building codes more fire safe and recognize the importance of using noncombustible fire containment construction, such as masonry, as a strong foundation for a balanced design approach to fire safe buildings.

Fire Safety Testing Standards
Ongoing building code revisions may result in providing less protection from fires. Here's why: Until 2000, the Southeast, Northeast and West had separate organizations that created building codes for those regions. Recently, the three regions combined in order to create one building code, the International Building Code, for the entire country. This has resulted in less protection from fire in some cities and states where the old codes provided more protection.

Traditionally, assemblies are fire-rated in terms of "hours," which means that the product has passed a one-hour, two-hour, three-hour or four-hour test. Using "hours" to name these tests creates the false impression that the systems tested can withstand fire for the amounts of time indicated in the names of the test. The hourly rating system is merely a convenient term to define a wall's resistance to heat transfer when subjected to a single standardized temperature profile and impact resistance following heat exposure.

Some materials, like concrete masonry, endure the temperature and impact portions of the test using only one wall panel. Other materials are permitted to obtain an identical fire rating by testing two wall panels, one for each phase of the standardized test. Thus, some products are able to achieve the same fire rating as a concrete masonry wall without providing the same level of protection. This inequity is not general public knowledge.

With the poor fire performance statistics for the U.S., building codes should be working to increase protection for occupants. However, the general trend in building codes is an arguable over-reliance on sprinklers to provide protection in fire events. Thus, instead of promoting improved fire containment and overall balanced design for fire safety, the International Building Code has continued the practice of trading off the protection provided by fire-rated assemblies for increased use of sprinklers.

Attributes of Masonry in Relation to Fire Safety
Masonry walls provide the best option to designers seeking fire containment as an integral strategy to fire safety. Masonry is noncombustible and provides a minimum one-hour fire rating, as opposed to wood frame that can burn in 15 minutes even with immediate response from the local fire department.

Any four-inch masonry wall will provide a minimum of one hour of protection and can easily exceed four hours of protection, using thicker wall sections. Not only does concrete masonry resist heat transfer, it also provides more protection than most available systems from falling debris and other impacts that can threaten the barrier protection provided by the fire-rated assembly. Also, due to the noncombustible nature of masonry, it will not contribute to toxic smoke or provide more fuel to a conflagration.

Use smoke detectors and sprinklers, but also take into account the benefits that concrete masonry fire-rated assemblies can provide. The redundancy of a balanced design approach is needed to protect occupants and property.






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