BY PETER McBRIDE
A challenge I regularly pose to firefighters is to ask them to explain the difference between preincident surveys and preplans. The responses I get are varied and generally evolve during the ensuing discussion to establish that preplans describe the agreed-on tactics needed to control the identified fire problems and hazards in the work.
Over the course of my fire service career, I have attended fires in mercantile, industrial, and storage facilities that represented significant social and economic loss to my community (photo 1). Because of the generally infrequent nature of and operational experience with these fires, I began to evaluate the tactical approaches being applied in other jurisdictions and their degree of success. In meeting the challenges of this class of building, I have reviewed literature, post-incident analyses, and operational trials; this research has led me to offer guidance in alternative tactics that have been demonstrated to be effective but that are not fully documented in the literature.
 (1) This strip mall represents a $30 million loss when replacement and business continuity costs are considered. (Photos by Scott Stilborn unless otherwise noted.) |
This article presents a brief overview of construction features to help develop a better understanding of the hazards and tactical guidance associated with the noncombustible class of buildings and its roofing variants and, through that understanding, proposed plans for tactical action.
PRACTICAL CONSTRUCTION CHARACTERISTICS
National Fire Protection Association (NFPA) 220, Standard on Types of Building Construction, 2009 edition, describes the type of construction used for various occupancy types as well as the requirements for fire resistance in separation of occupancies. Noncombustible, or Type II construction, is characterized by structural elements that are of approved non-combustible, or limited combustible, materials.
Use, occupancy, and modern fire codes dictate the degree of fire protection to structural elements offered in the design of a noncombustible structure. North American codes have adopted the concept of Performance Based Design (PBD). The use of PBD allows fire protection solutions where the equivalency of an assembly or assumptions about the local fire service provided may be considered in the design performance when systems or structural elements are exposed to real fire conditions. PBD codes require maintenance of the design features (assemblies/protective features passive and active) and may assume local fire service response will be available to enhance or support the assumptions fire protection engineers have made.
If the fire service thinks the truss is scary and is only now gaining tactical relevancy because of recent studies supporting our long-standing operational experiences and anecdotal reporting, it should understand that the truss is only the tip of the PBD iceberg (photo 2).
 (2) Intumescent paint and sprinklers provide fire protection in this Performance Based Design. (Photo by author.) |
For the purposes of this article, the term “noncombustible construction” means that the structural elements add no fuel to the fire; Performance Based Code elements are not considered as part of this basic overview.
MATERIALS
Noncombustible construction as previously characterized can use a number of materials to achieve the classification, but it is best to view the structure in two basic forms: wall-bearing structures and skeletal frame.
Wall-Bearing Structures
Wall-bearing structures may be composed of individual masonry units, monolithic concrete, and site or precast panels. The wall systems will have varying degrees of reinforcement appropriate for the expected design loads (e.g., wind and seismic) through the use of reinforcing rods, wire screens, metal plates, buttresses, or pilasters. Regardless of the wall system used, roof assemblies are critical to wall stability.
During construction, wall-bearing systems require by code or regulation some form of rake shoring or temporary support to stabilize the walls to ensure construction workers are not injured or killed by a collapse while assembling the building. If the roof system is threatened in a fire or other destructive event, the potential for collapse can be quite high (photo 3).
 (3) Plan and position for collapse in a well-involved building. |
Skeletal Frame Structures
Skeletal frame structures are composed of a steel frame of columns and beams of various profiles (H-, I-, T-, or C-beams, or hollow steel shapes) that are bolted or welded together to support an arrangement of girder beams to suit engineering or architectural needs. The frame then supports the roof beams consisting of open web steel joists (bar joists) and a variety of exterior and interior finishes.
Like the construction rules for bearing-wall systems, there are safety standards for erecting steel. In particular, the Occupational Safety and Health Administration (OSHA) has determined that some of the most serious risks facing ironworkers are those encountered during the erection of bar joists. More than half of the 40 fatalities suffered by ironworkers from 1984 to 1990 were related to the erection of the open web steel joist and its inherent instability when not bridged, supported, or braced against movement.1
Roof System Structure
Both wall-bearing and skeletal frame structures use bar joists in a parallel array (size, spacing, and bracing) designed to carry the roof and anticipated loads. The joists are tack-welded or bolted at their ends to stabilize the walls or frame and joist. The tack welding only serves to hold the joist in place and offers no lateral stability to the joist. It is not until the metal roof deck has bridged the joists and been tack-welded to the top chord and braced along the bottom chord that lateral stability of the joist is achieved. The lateral stability of the joist is critical to its structural performance as a beam (photos 4, 5).
 (4) The bar joist, metal deck, and cross bracing form an interdependent structural system. |
 (5) Note the common burn-through holes at the tack welds. This feature allows convective flow in either direction. |
Roof System Finishes
The roof system is finished with insulation and a waterproof cover that may or may not be surfaced with stone or granular ballast or roll-on coating. The waterproof covers (membranes) that dominate the roofing finishes are the built-up roof (BUR), polymer-modified bitumen sheet (MB), single-ply thermoplastic (PVC), or thermoset (EPDM) membranes. Surfacing is not applied to most single-ply systems. This fact may aid the roof team with identification, as these membranes tend to “bleed” oil at their edges when burning, and this can lead to a rapid running roof fire that can threaten operating positions. Always plan for multiple paths of escape when working on a roof.
Regardless of the type of waterproof cover used, the finishes are all highly problematic when exposed to heat or fire in that they rapidly melt, decompose (pyrolyze), and ignite. For example, the BUR uses rigid foam insulation that has a decomposition temperature of 585°F (285°C) and, because of being in an underventilated state because of its location, produces toxic styrene and ethyl benzene.
Mechanical fasteners adhere the foam to the deck, or it may be glued with hot asphalt. Over the top of the insulation, asphalt is used again to glue mechanical protection in the form of ½-inch (11 mm) fiberboard sheathing. The fiberboard is then overlaid in three to four plies of roofing felt that is saturated between plies with hot asphalt to form the waterproof barrier (photo 6).
 (6) The BUR and its tremendous fuel load. (Photo by author.) |
Roofing asphalt has a melting point of 525°F (274°C) and an ignition temperature ranging from 698°F to 867°F (378°C to 480°C). Given that fire temperatures well exceed the identified temperature characteristics of asphalt and foam, the presence of these materials means rapid involvement and contribution to fire growth. Based on a 2000 review of health effects literature, NIOSH concluded that roofing asphalt fumes are a potential occupational carcinogen.2 Many firefighters are unaware that asbestos is still permitted in roofing materials.
Both asphalt and foam have decomposition products that are toxic; firefighters must be disciplined and use their SCBA during all phases of the fire.
The roof structure and its finishes form a system that is incredibly strong and flexible in managing the static and dynamic loads imposed on it. Our understanding of the features, performance, and hazards of this roof under fire conditions defines the primary tactical challengescollapse, rapid fire spread, and toxic smoke.
TACTICS
History
My review was focused on the top-vent or no-top-vent proponents of tactical guidance and the reasons for the polarization in tactical approach. The no-vent proponents appeared to derive from experiences of near misses or firefighter fatalities associated with attempts to operate on this style of roof. The vent proponents, in contrast, had no near-miss/fatality experiences. Equally inconsistent within the top-vent proponents were those who advocated trench cutting as a tactical control and those who dismissed the trench because of its resource requirements and implementation time.
In my evaluation of this conflicting tactical guidance, it became clear that the positions taken were a function of tactical history based on training, experiential learning, staffing, and equipment. The approaches reflected local variants of the oral and written history of firefighting and, in some cases, represented misapplication, interpretation, or experimentation with tactics evolved to deal with the fire problems typically encountered in Type V (wood frame) and Type III (ordinary) construction.
Review
Tactically, applying water from master streams or 2½-inch (65 mm) handlines to the underside of the deck to cool steel is a proven and effective control, as related by the late Francis Brannigan in the first edition of Building Construction for the Fire Service (National Fire Protection Association) and subsequent iterations. The water thus applied cools the roof system and thereby arrests the deformation of steel that threatens the lateral stability of joists, columns, and walls. Equally as important, the hose stream acts as a giant sprinkler head raining water down on the burning commodities and slowsand may even arrestthe fire within the roofing finishes (photo 7).
 (7) Focus the first line on the steel over the fire. |
In my experience, unobstructed access to the underside of the deck and other steel elements is not always possible, or the self-sustaining fire in the roofing finishes can easily pass the point of access/application and continue to spread and threaten the structure.
Dealing with the fire’s spreading in multiple directions within the surfacing materials severely challenges any fire departmentmore so those departments constrained by their tactical history (training, experiential learning, staffing, and equipment). My developing understanding of the problems and the potential tactical limitations and, in some cases, misapplication of tactics led me to advocate for tactical change directed at the specific problems I have observed and believe can be controlled more effectively.
In the third edition of Building Construction for the Fire Service, Brannigan updated the section on fighting metal deck roof fires by offering a different view. Battalion Chief (Ret.) John Mittendorf, of the Los Angeles City (CA) Fire Department, and Brannigan coauthored the article “The Metal Deck Debate” in the March 1988 issue of Fire Engineering. Mittendorf proposed a two-stage process for strip ventilation (trench cutting) of the metal deck roof against the construction (at right angles to the bar joists). The first stage of the procedure involves removing the built-up elements with saws with wood-cutting blades. The second stage details the steps for cutting the metal deck using a metal-cutting blade.
A variant of the tactic is to remove the built-up elements only and allow the gases evolved through decomposition of roofing finishes to vent and not propagate fire farther along the deck. Then, consider using a hoseline to cool the deck and knock down the fire that crosses the strip. The tactics are outlined in detail on page 358 of Mittendorf’s book Truck Company Operations (Fire Engineering, 1998).
Another source of sound tactical guidance on the metal deck roof fire can be found within the third edition of the Fire Officer’s Handbook of Tactics (Fire Engineering, 2006) by Deputy Assistant Chief (Ret.) John Norman of the Fire Department of New York. Norman details his concern for cutting the metal deck and the potential to plunge through the roof but advocates for roof operations when steel deformation has been controlled by hoselines from below, and particularly when operating from defensive positions in adjoining exposures, to ensure a tenable position for operating firefighters.
Norman offers no guidance for trenching in the metal deck roof, although he does offer extensive history and defines the use of the trench in buildings with large common cocklofts. He further identifies concerns about using the term “strip ventilation” to mean a trench cut. The distinction he makes is that the trench cut is strictly a defensive measure and that strip ventilation implies offensive action or first vent. The use of strip ventilation as a defensive position has become problematic in some jurisdictions because it is confused with the tactical objectives of the trench cut, and this can lead to rapid fire growth and almost certain loss of the structure if misapplied.
The differences in tactical guidance and terminology do not on the surface appear significant, but they can pose extreme dangers for a firefighter who does not understand the tactical history or does not have established written guidelines based on local factors relative to the tactics that should be employed when operating in, on, or around the noncombustible class and its metal roof deck hazards.
Cutting a vent over a fire is predominantly a wood frame/ordinary construction tactic, and the opening size is based on a structure constructed of materials with considerably different properties, joist spans and spacing, and volume. Why does Norman have to warn us not to work over the fire in this class? I believe it is because he recognizes that wood frame tactical approaches are being applied to the metal deck in some jurisdictions and that doing this can cause firefighters to become seriously injured or killed. Why do Norman and Mittendorf differ in their advocacy of a trench and their terminology? I believe it is because of their built environment and tactical history (training, experiential learning, staffing, and equipment).
I don’t believe the guidance of either author is incorrect within the context in which it is given. However, a problem can arise if the reader of such guidance fails to understand the authors’ context and its implications for local use.
PREPLAN
I offer the following tested approaches that rely on the excellent guidance offered by Brannigan, Norman, and Mittendorfwith a local twist.
Large handlines or master streams (straight tips) must be put into position quickly and be directed at the underside of the metal deck and any supporting steel elements. Use a thermal imaging camera to direct the streams under heavy smoke conditions to ensure maximum cooling benefit. When visibility conditions are good, focus on areas where there is no carbon depositioncarbon does not adhere to steel with a temperature higher than 700°F (370°C), and the roof finishes above are already pyrolyzed or burning and being driven under pressure along the deck channels and any gaps in the foam insulation (photos 8-10). Consider unstaffed lines if collapse is a concern.
 (8) No carbon on the steel means the steel temperature is higher than 700°F (370°C). |
 (9) Roof finishes are rapidly decomposed and drive a self-sustaining fire. (Photo by author.) |
 (10) Gases move in all directions within the roof finishes. (Photo by author.) |
Adjoining occupancies should have lines deployed and directed at the roof structure. Even under a no-smoke condition, consider washing the metal decking, which will delay fuel development in the roof finishes and may stop fire growth in its tracks.
Departments that do not have properly staffed truck companies should consider using portable hydraulic extrication spreaders for rapidly opening the rear doors or doors that have been hardened against burglary. It may be a problem to make the triangle cut for overhead doors in some jurisdictions because the insulated doors and U-shaped metal reinforcement struts attached to the inside of the door panel are too thick for the rotary saw blade. The chain saw with hardened blade may be a better choice for a clean cut. Consider that opened overhead doors can block the application of hose streams to the deck and they may sag and fall on firefighters positioned in a doorway. Always use caution around overhead doors and their systems when in the opened position.
Depending on the compartmentation of the building, consider using positive-pressure ventilation to pressurize uninvolved stores two or three units away; this will counteract the pressure that developed in the roof finishes that is driving fuel into the uninvolved area.
Get to the roof and assess where to make a stand in the roofing finishes. Look for distortions in the roofing finishespillows or troughs. Pillows show a buildup of gas; troughs show an area that has decomposed or been melted under the heat of the gases and pressure buildup within the roofing finishes. These distortions help you to establish the location for a defensive line or to fall back to a known separation or fire wall. Cut the roofing materials only, as outlined by Mittendorf, and have 13⁄4-inch (45 mm) handlines ready to wash water back down the channels of the deck. Don’t wait for fire to come to you. This is not a defensive position (photo 11). This serves to cool the deck and knock down the fire brewing in the roofing finishes.
 (11) Cut the roofing finishes and wash back to the fire area. |
It is very important when cutting the roofing finishes that you don’t neglect to remove the beveled wooden cant strips at the edges of the roof and any facia/soffit elements that can allow fire to flank your position (photo 12). Also watch for any power supply cables that may lie at or under flashings or along the cut line. Respect the roof; position yourself away from collapse hazards, and remember to control all utilities. Gas supplies may feed a roof fire, and electrical supplies may energize the metal roof, creating an electrocution hazard (photo 13).
 (12) Cutting through the cant strips or facia/soffit elements is important in controlling fire spread. Roof modifications may offer unexpected holes. Sound ahead of your position. |
 (13) Controlling utilities is a high tactical priority. |
I am in Norman’s camp with respect to the trench. Cutting a trench is a defensive tactic to be implemented after the preliminary vents have relieved pressure. The trench represents a cutoff point for containing the fire in a portion of a larger wood-frame/ordinary constructed structure, by virtue of removing fuels and operating handlines from above and below the trench. Using the trench before a primary vent just draws flame to the trench, and fire can bypass the position while the cut is in progress.
 (14) This is a failed trench; it took five saws out of service. |
The trench is a labor-intensive tactic that requires a level of coordination many fire departments may not be able to achieve because of a lack of knowledge (training, experiences), skills (limited multicompany events), or ability (resource starved). Although the tactic was developed for wood-frame or ordinary constructed buildings, its use and evolution as a method of creating a primary vent opening is not an unacceptable tactic; it just ceases to be a defensive trench and more accurately should be called a strip vent (photo 14). Mittendorf’s stripping of the roofing finishes is a better solution and has proven very effective in my experience (photo 15).
 (15) This cools the deck and shuts down the fire in the finishes. (Photo by author.) |
My variation on the Mittendorf ventilation strip and the Norman defensive trench is to have the roof team introduce a single kerf cut in the decking where the roofing finishes have been cut out to thermally decouple the deck. The deck by virtue of its thinness and surface area is highly thermally conductive relative to other larger-mass steel elements and drives fire growth in the roof finishes.
The kerf cut is a virtual trench and is ideal if it is parallel to the run of the bar joists, since there is no thermal bridging of the cut by the bar joist. It is critical that the cut be made with the saw operator’s working on the joist and supported side of the deckthe correct side of the tree branch, if you willand that the unsupported area is identified as a no-go collapse zone.
The cut is safer when made at right angles to the joist, but the joists act as a thermal bridge that can allow conducted heat to bypass the kerf cut. You can control for this bridging by washing both sides of the kerf cut with hoselines and concentrating on cooling joist contact points in the uninvolved deck area you are trying to protect, because you have no unsupported deck to worry about (photos 16, 17). In both instances, cooling from below must continue until the fire is out and surfaces are well cooled. In many instances, the kerf cut may be unnecessary because of quick knockdown of source fires and the efficiency of the stripping area’s being washed by the hoseline. The virtual trench/kerf cut is best suited for a well-developed fire under collapsed roof elements that hoselines are shielded from reaching and cooling. Your control strategy is to give up part of the structure and eliminate or reduce the conductive threat in fire propagation.
 (16) This area could not be kerf cut because of electrical hazards; water cooling stopped the thermal bridging. |
 (17) There are no guarantees: The decking may not span from joist to joist. Look for tack welds at seams to ensure bearing. (Photo by author.) |
Of course, the next question is, what do we do when we are totally unable to get at the deck from below because of ceiling finishes? Many of the same strategies can be applied, except that we may invest in the true trench operation or consider stripping roof finishes and the kerf cut to delay/reduce the fire spread and use the rotary nozzles and piercing applicators to put out the fire in the void space and cool the steel. Alternatively, consider ventilation openings or applying large-caliber streams from an elevating device into the void area by breaching nonbearing exterior walls or finishes (photo 18).
 (18) Finishes may facilitate better opportunities for ventilation, fire attack, or cooling. (Photo by author.) |
Any plan should include having a hydraulic shovel on call and a developed understanding that, because of fire involvement, resources, or reflex time, your only tactical objective is to slow down the fire using any combination of tactics so that part of the building can be ripped down to save another part. Weather can play a significant role in fire growth. Canadian winters can stop a running roof deck fire in its tracks when melting ice and snow quell the volcano brewing in the deck (photo 19).
 (19) Read the building and truck signs, and understand the problem. You need a plan. |
Our tactical history is rich with lessons, and it is incumbent on the fire service to test and adapt those lessons for local conditions and give context to what we do in the form of written tactical guidance. If your fire department does not have written tactical guidelines, you don’t have a plan for tactical action. In fact, in many jurisdictions, it would be against the law to have workers undertake work or work plans they didn’t understand and in which they haven’t been trained. Why is this allowed in the fire service?
Endnotes
1. Hazard Alerts: Lateral Supports for Open Web Steel Joists – http://www.lni.wa.gov/Safety/Basics/HazAlerts/steeljoists0301, asp.
2. Owens Corning Corporation, MSDS Number: 23124-NAM, May 2007.
PETER McBRIDE is an incident safety officer (ISO) with the Ottawa (Canada) Fire Services. He has an extensive operational knowledge of the health and safety officer and the ISO positions and has assisted in developing numerous safety programs across North America. McBride recently sat on the Project Technical Panel, evaluating tactics for wind-driven fires, and on the NFPA 1521 Task Group. He has also contributed to NFPA 1500 and 1584.
