...burst the cement matrix that holds the aggregate together. The temperature at which spalling occurs depends on the amount of free water in the concrete mix. Water content depends on age and other factors.

Thermal differential also is a major factor in concrete failure, say sources. The outer layer of a member heats up first and expands, causing the inner layer’s shear stresses to rise dramatically.

By month’s end, Canada’s National Research Council expects to publish results of tests done with the Portland Cement Association that determined fire resistance performance of high-strength concrete columns. That will add to what some say is limited new data about concrete in fire loads.

Debating The Best Balance Of Passive And Active Fire Protection

DOUSED Reductions for containment allowed with sprinklers. (Photo courtesy of ©Factory Mutual Insurance Company. Used with permission. All rights reserved)

Groups representing suppliers of smoke and fire-protected materials have been duking it out with the automatic sprinkler suppliers for years. The big fight has been over the correct balance of active and passive fire protection in buildings.

“A steady erosion of building code provisions concerning fire-resistant construction in commercial buildings has placed firefighters and the general public at greater risk than ever,” says The Alliance for Fire Safety, a Falls Church, Va., group that represents suppliers of passive protection, such as sprayed-on fireproofing.

AFS is “motivated by the realization it is losing market share,” says Roland Huggins, vice president of engineering for the American Fire Sprinkler Association, Dallas.

“Many building codes...are based upon the mistaken assumption that sprinklers virtually never fail and that fire-resistant construction materials can therefore be minimized or eliminated,” says W. Gene Corley, senior vice president of Construction Technology Laboratories, Skokie, Ill., and a paid consultant to AFS.

National Fire Protection Association data show that sprinklers do not operate about one time in six. In some cases, the fire was too small or originated in an area without sprinkler coverage, says NFPA. It cautions that passive protection also can fail due to poor installation, maintenance, poke through and blocked-open doors.

Corley notes that Seven WTC and a portion of Five WTC collapsed before burnout even though they were sprinklered. NFPA says there was a structural and fire challenge “well beyond anything contemplated by the designers of sprinklers or passive protection.” The message that the right passive protection makes collapse impossible is misleading, says John R. Hall Jr., assistant vice president.

AFS calls for “balanced protection” that includes active and passive protection. But AFS has not defined its performance objective, says NFPA’s Robert E. Solomon. Should performance be based on a total burnout of a floor without structural damage? he asks. Does the scenario assume total failure of active systems and 100% performance of passive? Neither assumption is reasonable, he says.

NFPA says sprinklers reduce chances of dying in a fire and average property loss by one-half to two-thirds. NFPA has no record of a fire killing more than two people in a fully sprinklered building where the system was operating. “We can not make any similar statement for...other systems,” says Solomon.