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According to the United States Fire Administration, a fire occurs in a residential structure every 79 seconds. On average there are approximately 100 firefighters who die in the line of duty every year. Many of these deaths are attributed to structural collapse during firefighting operations. This paper will examine the data and statistics pertaining to firefighter fatalities associated with structural collapse, as well as construction features contributing to the increased life safety risk for structural firefighters. This paper will also identify recommendations to potentially decrease or mitigate the effects of these construction features and increase the safety of firefighters in the United States.
Background and Significance
Firefighting is inherently dangerous by virtue of the hazards encountered. Firefighters are asked and expected to put themselves in harms way to save the lives of others, and they do so willingly and with full understanding of the potential consequences. However, this expectation has led to a historical trend in strategies and tactics which are significantly aggressive, particularly when determining defensive vs. offensive operations.
Residential structure fires of today are significantly different and more dangerous than the residential fires of years past. There are numerous factors that contribute to the increase in severity of residential fires which will be discussed in this paper. However, even with the increased severity and dangers associated with residential fires, fire service personnel continue to employ aggressive offensive tactics which have led to firefighter fatalities.
Residential Features Increasing Hazards
Over the last three decades, there have been numerous changes in residential construction and furnishings that have significantly increased the severity and intensity of residential structure fires.
In the 1970s residential furnishings were predominantly manufactured utilizing natural materials such as wood, cotton, wool and leather. Today, furnishings are constructed primarily of synthetic materials like polyurethane that weren't widely used or even available. Testing by various agencies (UL University, NIST) has demonstrated that these materials ignite more readily, contribute to rapid flame spread, burn at a much higher temperature & release more toxic or poisonous gases. One comparative test conducted by UL University with similarly furnished rooms of natural vs. synthetic materials demonstrated that the same fire started in both rooms would have very different results. In the room furnished with natural materials, the flame had only reached a height of approximately 6" at four minutes and 25 seconds. Conversely, the room furnished with synthetic materials was almost fully engulfed and reaching the flashover stage at four minutes.
Another factor contributing to the high hazards associated with residential structure fires is the energy efficiency of modern construction. Fires that have reached the free burning stage take longer to be identified in unoccupied dwellings due to the lack of exterior ventilation. Hidden fires may be burning for a substantial period of time prior to Fire Department notification and response. Additionally, the high heat and gases are not vented to the outside, but rather trapped on the interior leading to increased risk to firefighters and greater potential for flashover and backdraft situations.
Residences of today are much larger with much more open floor plans. These open expanses allow for rapid spread of heat and product of combustion. Residential construction of the past was typically much smaller and more segmented which facilitated a better ability to isolate areas of fire origin for longer periods of time. The smaller size of residential structures facilitates rapid search and rescue evolutions which decreases the amount of time and personnel required to accomplish this task. Basements of modern homes are typically large open spans. Fires originating in this setting can expose structural members to heat and flame resulting in significant potential for structural collapse when firefighters make entry on upper level floors.
The final construction feature that has increased the hazards associated with residential structure fires is the introduction and predominant use of lightweight construction components. In the late 1980's and early 1990's, builders in the United States began using lightweight construction components in residential construction. According to a report published by the National Institute of Standards and Technology and data provided by the National Fire Association, there have been 180 firefighter fatalities associated with structural collapse between 1979 and 2002. Although the overall trend in the number of fatalities associated with structural collapse in general has decreased since 1979, the number of firefighter fatalities associated with residential structural collapse has increased significantly. From 1979 to 1992, the number of firefighter fatalities resulting from residential collapse remained relatively consistent at approximately 14%. However, from 1994 to 2002, the firefighter fatalities due to collapse in a residential structure increased to 51%.
Lightweight Construction Components
As societal demands for lower cost "greener" construction alternatives increases, the use of lower cost lightweight construction components become more predominate. These lightweight construction components offer several advantages for builders and homeowners, but when exposed to direct flame contact pose serious life safety risks to fire service personnel.
According to the National Institute for Occupational Safety and Health, engineered wood I-joists have grown in use since the early 1990s, and by 2005 were estimated to be used in more than half of all wood-frame construction. These I-joists have several advantages over traditional structural supports for builders and homeowners. Prefabricated engineered I-joists are lighter and stiffer, and will not warp, twist or shrink like solid wood framing materials. These, easier to use / install I-joists reduce construction time and labor costs. Additionally, homeowners and builders considering the conservation of natural resources are turning to engineered lightweight trusses and structural components because they are manufactured using significantly less wood than traditional structural components. They allow for longer spans and have much less waste during the manufacturing process.
Although these technologically advanced structural members are advantageous to builders and homeowners, there are enormous disadvantages and life safety hazards that these materials pose for fire service personnel. Engineered wood I-joists normally consist of a top and bottom flange made of 1 Â½" to 3 Â½" wide composite or sawn lumber with a vertical web made of plywood or oriented strand board (OSB) which is typically 3/8" to 7/16" thick. If this vertical web burns through there is minimal structural integrity to support the weight of not only the flooring materials from the floor above, but fire service personnel who enter the structure.
Several organizations have conducted comparative performance testing on these structural members, most recently (2008) UL University. This testing compared the performance of traditional legacy construction with 2 x 10 structural members to the performance of engineered I-joist structural members described above. These components were compared using identical fire conditions in a simulated basement fire. Testing indicated that 2 x 10 joists unprotected by gypsum wall board failed and collapsed at 18 minutes and 35 seconds when exposed to direct flame contact. Similar testing conducted on engineered lightweight I-joists unprotected by gypsum wall board failed and collapsed in only 6 minutes. This collapse allowed firefighter mannequins positioned on the floor above to fall through the floor into the fire below. Additional testing was conducted on the same structural members under the same conditions, however gypsum wallboard was added as a barrier between the structural members and the fire below as would be seen with a finished basement with a ceiling. The 2 x 10 joists protected with gypsum wallboard failed and collapsed at 44 minutes and 40 seconds. Comparatively, the engineered lightweight I-joist protected with gypsum wallboard failed and collapsed at 26 minutes and 43 seconds. These results not only indicate the extreme safety hazards associated with engineered I-joists exposed to direct flame contact, but also the significant benefit of requiring protection for exposed structural members.
As discussed earlier in this paper, fires in unoccupied residential structures may not be easily identifiable. This delay in recognizing the fire as well as making fire department notification and response times may easily exceed the six minute timeframe identified in performance testing. This may result in firefighters falling through fire damaged floors as they make entry. Structural members exposed to fire conditions underneath may significantly degrade causing the floor system to easily fail with the added weight of firefighters. This failure may occur with little indication prior to the catastrophic event. Testing indicated that floor coverings such as carpeting, carpet padding and subflooring all inhibited heat transmission to personnel operating above. Additionally, the weight of alternate flooring materials such as ceramic tile and lightweight concrete may actually decrease the amount of time to failure and increase the risk to personnel operating above or below the weakened structural members.
Similar structural members are being used to fabricate roof truss systems. Similar testing being conducted on these roof trusses are having similar results. Failures of these roof trusses have significant potential for trapping firefighters under falling debris as well as allowing personnel performing ventilation operations to fall through to the fire floor below. Lightweight construction features not only involve wood or composite structural members. Commercial structures may also be constructed using lightweight steel structural members which can pose a significant potential for collapse when exposed to fire conditions.
In addition to engineered lightweight trusses discussed above, there are several other lightweight construction components / techniques utilized by builders that pose significant life safety hazards to fire service personnel. Metal gusset plates and finger joints are methods used to form joints. Gusset plates are thin metal plates with small points or teeth that are utilized to join one piece of lumber to another to form a truss. A finger joint is a technique where two pieces of lumber are notched to fit together and held in place by adhesive / glue to form a truss. Neither of these techniques are as structurally durable as traditional construction techniques when subjected to fire conditions.
As technology changes and societal needs change, it is incumbent upon the fire service to change and keep up with these advances. There are numerous ways that departments and individuals can better meet these challenges.
It is imperative that fire service personnel stay educated on changes in industry standards and practices. Incident Commanders should base strategies and tactics at residential structure fires on current information. In determining whether operations will be offensive or defensive, Incident Commanders should be largely based on a carefully considered risk vs. benefit analysis. Staying educated and aware of changes is possibly the most important technique fire service personnel can employ to help reduce life safety hazards to firefighters.
There are several code changes that would significantly reduce the potential danger to firefighters engaged in structural firefighting operations. As discussed earlier in this paper, it has been proven that structural assemblies protected by either gypsum wallboard or lath and plaster maintained their structural integrity much longer than unprotected assemblies. If this were incorporated as a change to the building code, it would allow occupants additional time to escape from a residential fire. Additionally, it would allow firefighters who enter a structure additional time to complete suppression and search and rescue operations.
Another code change that was proposed and passed on September 21, 2008 at the International Code Council's annual conference was the residential sprinkler resolution RB64-07/08. This code change would require that all new residential construction after January 1, 2011 be equipped with a residential sprinkler system. Opponents of this resolution are making efforts through state legislature to prevent this change to the building code. Arguments against residential sprinkler systems have been broad and varied and have been voiced predominantly by the building community, but these concerns have been considered and debated and found to be inconsequential in comparison to the risk associated with unsprinklered residences. One of the primary concerns voiced by the opposition is the cost associated with the installation of a system. As of April 2009, the estimated cost for a residential sprinkler system in a new home was $1.00 to $1.50 or 1% to 1.5% of the total building price. In comparison to the amount of dollar loss associated with property damage from a residential structure fire, the cost of a residential sprinkler system is relatively insignificant.
Opponents have also voiced concerns pertaining to the potential water damage associated with the activation of a residential sprinkler head, and concerns regarding the activation of multiple heads in the event of a single head activation. It has been demonstrated that the water damage associated with advancing and utilizing an attack line for fire suppression in a residential structure fire would result in significantly more damage than an activated sprinkler head. Additionally, sprinkler system manufacturers have clarified the fact that if a single sprinkler head were to activate, that did not result in multiple heads activating unless the fire was extending.
Another code change that would be beneficial to fire service personnel is the Firefighter Safety Building Marking System. This code is planned to be implemented in the 2009 edition of the National Fire Protection Association code as an annex to the code. The Firefighter Safety Building Marking System is a method localities can utilize to placard or mark structures with lightweight truss floor or roof assemblies. By identifying and marking these structures in the construction or pre-incident planning phase, Incident Commanders can carefully consider strategic and tactical decisions based on an educated risk vs. benefit analysis. Even prior to an official code change, which can be a lengthy and in-depth process, localities can implement similar programs by local ordinance. Jurisdictions can utilize frameworks / programs established by other departments around the nation.
Pre-incident planning in residential structures can be done on established homes on a voluntary basis, by contacting homeowners associations or individual homeowners and expressing the purpose of residential construction pre-plans for the purpose of firefighter safety. Most residential construction in a subdivision will have similar characteristics as far as materials and techniques utilized. For this reason, even a few structures evaluated within a subdivision may give a good indication of lightweight construction to other residences in the same area. However, in the absence of residential pre-planning or marking, fire service personnel should always maintain a high index of suspicion for lightweight construction components in structures built after the early 1990s.
With technological advances in the construction industry, comes significant challenges for fire service personnel. It is imperative that personnel and departments stay abreast of changes and meet these challenges head on. Through education, training, and modification of standard practices, the lives of countless personnel may be saved. Fire departments should carefully examine current practices, and identify areas where alternative tactics could be employed for structures constructed with lightweight construction features. Utilizing techniques such as defensive overhaul operations in structures with damaged floor or roof assemblies, or ventilation techniques that do not require personnel to be supported by roof assemblies, significantly reduce the life safety hazard faced by suppression personnel. Fire service personnel should consider becoming actively involved in the code process and affiliating with organizations that campaign for codes that reflect safe practices and requirements for firefighters.