August 1, 2003
Editor’s note: The Canadian Electrical Code and the National Building Code regulate the fire safety aspects of buildings. These codes are periodically revised to reflect our best understanding of the causes of fire as well as possible minimization and/or prevention strategies. Of interest is the current revision of the Building Code where a more stringent requirement for cables and raceways in the plenum has been recommended — primarily the addition of limitations on production of smoke from telecom cables and raceways. This is a good time to reflect on one of the key debates taking place within the Code change process: To what degree can conventional “passive” approaches to fire protection, like cable flame and smoke ratings, be traded-off against “active” approaches, like sprinkler deployment? The following is an abridged version of a more in-depth article by the author.
Since the development and publication of the first building codes in Canada in 1941, it has been recognized that the design feature that plays the greatest part in reducing the over-all fire risk in a building is the extent to which fire-resisting construction is used to divide a building into fire-resisting compartments.
This fire protection technique is known as “compartmentalization” and is now generally referred to as “passive fire protection”.
Over the past 50 years or so, one of the most significant technological advancements to the protection of buildings has been the automatic sprinkler. The ability of sprinkler systems, to control an unshielded fire is well known.
Although sprinklers are generally not designed to extinguish fires, there are certainly documented cases where this occurs. However, just as with passive fire protection, successful sprinkler activation does not necessarily prevent the continued production of smoke, toxic gases, and heat, nor necessarily extinguish a fire.
In passive fire protection, barriers such as walls, floors and ceilings and supporting elements such as columns, and beams are constructed or protected with fire resistant materials which when installed and tested to a prescribed time-temperature exposure, will provide a level of fire resistance that is measured in a period of time such as one or two hours.
The building code requires that compartments be constructed to provide a defined level of fire performance referred to as a fire resistance rating. In order for the wall, floor or ceiling to maintain the prescribed fire resistance rating, all openings must be protected.
Openings are protected in a number of ways: Rated fire doors and windows in wall openings, rated fire dampers for use in ducts that penetrate fire resistant barriers and penetration seals used around service openings such as pipes, cables and cable trays.
Even joints and gaps at the top of walls and at edges of floor slabs are fire stopped with materials tested to provide the required fire resistance rating. Along with these items, the traditional passive fire protection approach in building codes have required interior finishes, fabrics, cabling, pipes, and a host of other components of the building to achieve prescribed levels of performance in respect, for example, to a materials contribution to fire growth and production of smoke.
These levels are typically identified in a National Standard, and referenced by the Codes. All of these methods of protection are referred to as “passive” because they are present and ready to operate as part of the material or building design, without the need to “activate” in the event of a fire. There is a very large inventory of existing buildings in Canada that are protected solely by traditional passive fire protection methods.
As trends in construction continually evolve, varying philosophies on how best to contain and control fire are often debated. Recently, one trend, particularly has been toward a drastic reduction in passive fire protection features when active fire protection features such as sprinklers are present.
Given North America’s comparatively poor fire safety performance record against other regions of the world, is this the direction we should continue to head?
Sprinkler system efficiency
For years, every time automatic sprinklers were being considered in a prospective building code change, it has often been in conjunction with a corresponding reduction in the passive fire protection requirements already in place.
This is largely because it was generally accepted that sprinklers operate as designed in excess of 96 per cent of the instances where they are called on to operate.
However, more recently published information from the National Fire Protection Agency (NFPA) indicates that sprinklers operate in 74 to 91 per cent of the properties where they are installed in the U.S. based on the 1989-1998 (National Fire Incident Reporting System) NFIRS and NFPA study. Table 1, right, indicates the presence and operation of sprinklers in structural fires, by property use.
Clearly, a drop in efficiency from 96 per cent in the period 1897 to 1969 to 83 per cent in the period 1989 to 1998 is an indication of declining sprinkler performance, when advances in technology would suggest that at the very least, equivalent or improved performance would be expected. What are the causes of unsatisfactory sprinkler performance when it occurs?
NFPA maintained a database tracking sprinkler performance from 1925 to 1969. (See Table 2, next page.) It was discontinued in 1970 because it was felt that the data collection was focused on cases of poor sprinkler performance. However, the database is still useful in analyzing those failures and gives valid results on why unsatisfactory performance occurs when it does.
In more recent years, sprinkler head design and their affect on performance has been of substantial concern in the U.S. and Canada.
Between 1961 and 2001 44 million sprinkler heads were recalled in the U.S. and Canada. In a number of fires in which these sprinklers were installed, the heads failed to operate in areas directly over the fire.
While it can be argued that most of the data on sprinkler failures relate predominately to U.S. installations, fire losses in the U.S. and Canada are remarkably similar. Civilian fire death rates per million population have long been higher in both the U.S. and Canada than in almost any other industrialized country outside of the former Soviet bloc.
In all references to automatic sprinkler protection in the National Building Code of Canada, it states explicitly that sprinklers when used must be monitored. Sprinkler system monitoring is normally performed by alarm system monitoring and installation companies.
Surprisingly, information provided by Underwriters’ Laboratories of Canada, the only certification organization in Canada, of the total sprinklered building inventory in all of Canada, less than 2,400 sprinkler installations are actually monitored by a Central Station, which is certified by an independent third-party certification organization.
Passive protection methods
In addition to the normal construction elements forming compartments, and limitations on the flammability of interior finishes, the whole concept of passive fire protection has evolved to the point where many other elements of fire protection such as cables which supply power to fire alarm systems in fire detection systems or fire pumps in fire suppression systems such as automatic sprinklers, must have a fire resistance rating consistent with the barriers in the fire compartment.
Unlike active fire protection systems such as sprinklers, passive fire protection systems generally require very little maintenance after their initial installation in order for them to provide their protection. Some exceptions include fire dampers, whose mechanical or electrical components require ongoing service.
Fire protection balance
Sprinkler systems are clearly an important and valuable life safety asset for all buildings. Nevertheless, sprinklers can and do fail to provide the expected level of life and property protection for a number of reasons.
is clear that there needs to be a balance between the use of passive fire protection techniques and active fire protection (automatic sprinkler systems) in all buildings.
The recorded decline in fire death rates in the U.S. and Canada over the last 25 years can be attributed to a number of factors, one of which is the effective use of both active and passive fire protection.
The two techniques of fire protection do complement each other.
In Vancouver, where mandatory automatic sprinklers for residential construction was first introduced in Canada, there is an appreciation of the role of passive fire protection to maintain the needed balance in fire protection.
A bulletin issued by the city three years ago on sprinkler-based equivalences, performance and reliability issues, stated that there are already over 60 “trade-offs” or relaxations permitted for sprinklered buildings in the Vancouver building by-law and that designers need to be aware of the potential risks in placing total reliance on the operation of sprinkler systems to control fire.
The bulletin stated the following: “Many of the conditions that can lead to failure of a sprinkler system are also likely to affect fire rated glazing systems and water curtains. Care needs to be taken in designing building fire protection systems to ensure that some balance between active and passive fire protection is maintained in case of sprinkler or water supply failure.”
A balanced design incorporates into the total fire protection package the essential, complementary fire protection features that support suppression and containment: fire rated floors, walls and ceiling assemblies, fire rated doors, fire rated glazed openings, protection of joints and penetrations, structural fire protection, smoke control, fire and smoke dampers, fire extinguishers, standpipe outlets, hose racks and similar passive, containment and control features.
Passive and active systems are interdependent and corresponding. The combination of the two provide a better fire safety environment than either one alone.
A balanced fire protection design enables a safer egress for building occupants and fire fighters, and a reduction in property damage during successful sprinkler activation or in the event of a sprinkler failure, or failure of any component of the active fire protection system.
The issue is not one of a conflict between active and passive approaches to fire protection, but rather the overriding question of life safety.
Our fire experience record clearly demonstrates that a careful balance of fire protection techniques will save lives, help control property losses and enable us to continue to reduce fire death rates in Canada and the U.S.CS
Tony Crimi is president of A.C. Consulting Solutions Inc. and has over 14 years of experience in the areas of Standards, Testing and Conformity Assessment with Underwriters Laboratories of Canada. He can be reached at (905) 508-7256 or via e-mail at firstname.lastname@example.org