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Tactical considerations for firefighting operations in lightweight construction
Battling the Hidden Danger
Tactical considerations for firefighting operations in lightweight construction
By James M. Dalton, Peter Van Dorpe, Robert G. Backstrom & Steve Kerber
Multiple firefighter fatalities at large commercial fires attract the attention and scrutiny they warrant. However, it’s also important to remember that many line-of-duty injuries and deaths occur in single- and multiple-family dwellings during routine, “bread and butter” residential fires. A review of 23 investigations conducted by the National Institute for Occupational Safety and Health (NIOSH) Fire Fighter Fatality Investigation and Prevention Program between 1997 and 2009 illustrates this issue: These incidents involved fires in residential buildings that resulted in 29 fatalities and numerous injuries. One common denominator in these incidents: rapidly spreading fire in areas of unprotected wood construction, the collapse of unprotected dimensional lumber or the collapse of lightweight engineered wood components.
In addition, departments nationwide have experienced numerous near-miss incidents involving lightweight structural components and truss construction; the National Fire Fighter Near-Miss Reporting System has documented more than 80 reports of such incidents.
The fire service has been aware of the hazards associated with lightweight construction for decades, but until recently, we lacked the scientific data to quantify the anecdotal evidence from the fireground. Furthermore, while manufacturers understandably submit for testing only those assemblies for which they expect to achieve the desired fire resistive ratings, building codes allow unrated, or unprotected, assemblies (i.e., wood covered with non-rated sheathing materials or exposed wood) to be used in residential construction, particularly in single-family homes.
Because the use of lightweight and engineered assemblies has become virtually the exclusive means of constructing floor and roof systems in residential buildings, it’s imperative that the fire service develops a better understanding of how these assemblies behave under fire conditions. It’s also imperative that we test these built assemblies in a scientifically valid and quantifiable way so that the results can be used to affect changes to building codes and construction practices.
In this article, we’ll share selected results of research conducted by Underwriters Laboratories (UL), the Chicago Fire Department, the International Association of Fire Chiefs and Michigan State University that highlight the dangers of lightweight construction. The findings of this research have also been developed into a Web-based training program for the fire service. This free interactive program is at www.ul.com/fire/structural.html. In addition, this article will also share some tactical recommendations for any firefighter responding to fires in buildings featuring lightweight construction.
THE EVIDENCE
UL and its partners were awarded funding from the Assistance to Firefighters Grant program to subject a representative group of floor and roof assemblies to the industry standard fire resistance testing method, ASTM E119: Fire Tests of Building and Construction Materials.
Following are some findings from the research:
• Residential fires may actually pose commercial fire risks. Many of today’s “typical” house fires are in buildings that, based on size and interior volume, can and should be categorized as commercial structures with commercial fuel loads. Combined with modern synthetic fuel loads, fires in large, unprotected and un-firestopped voids made of lightweight engineered building materials can be catastrophic. Today’s fireground operations must reflect this new reality.
• Thermal imaging cameras (TICs) don’t provide an adequate indication of a weakened floor or pending collapse. There’s a potentially dangerous misconception in the fire service that TICs can detect fire on the floors below or above a firefighter. TICs detect variations in surface temperatures for objects in the camera’s field of vision. They cannot detect temperatures in areas that are thermally shielded from the camera’s view by the finish materials of a floor or ceiling. During these tests, average temperatures below the assembly were in excess of 1,200 degrees F, while average temperatures on top of the carpet were less than 100 degrees F. The application of water during suppression operations will further mask or eliminate the thermal signatures available to the TIC’s sensor.
• Floor collapse can occur in 6 minutes. Engineered wood floor assemblies have the potential to collapse very quickly under well-ventilated fire conditions. When it comes to lightweight construction, there’s no margin of safety. There’s less wood to burn, and therefore less time before the assembly fails. During this research, the shortest failure time was noted during the unfinished/unprotected engineered wooden I-joist test. This assembly experienced a total structural collapse at 6 minutes.
• Tested assemblies significantly weaken well before they completely collapse. The ASTM E119 definition of collapse requires that the floor totally collapse. Several fire test standards recognized outside the United States, such as ISO 834:1: Fire-resistance tests, Elements of building construction, Part 1, look instead at how long a test sample is able to maintain its ability to support the applied load during the fire test, taking into account when a floor is progressively deflecting or failing prior to a complete structural collapse—clearly a critical piece of information for the fire service.
The bottom line: If the ISO standard was applied to the unprotected engineered wooden I-joist assembly, the accepted failure time would change from 6:03 to 4 minutes. All lightweight assemblies studied in this series of tests exhibited similar differences in time-to-failure based on the standard applied. Fire service instructors are encouraged to use these different criteria for time-to-failure or collapse to emphasize that test results can only be used for comparison and are not accurate indicators of operational time on the fireground.
• Plastic ridge vents can mask fire intensity. In the early stages of the modern roof assembly test, there was a significant amount of smoke emitting from the continuous plastic ridge vent. As the temperatures increased, the ridge vent melted and collapsed upon itself, sealing the natural opening. The heavy smoke emitting from the continuous ridge vent diminished to a light smoke trail, although the fire was still raging below. Temperatures in the attic space went from approximately 200 degrees F to 1,400 degrees F in less than 60 seconds. These are flashover conditions and can cause global failure of the ceiling. Firefighters conducting size-up and attempting to read smoke conditions from the exterior may be deceived by this change in the volume and velocity of the smoke venting from the roof, and roof teams may conclude that the roof is safe to operate on, when in fact it may be rapidly approaching the point of collapse.
TACTICAL CONSIDERATIONS
Over the last few decades, millions of single-family homes have been built with truss-constructed roofs that create large, undivided attic spaces and unfinished basements that have unprotected lightweight wood floor systems above them. This study established that while all unprotected wood floor assemblies are susceptible to early failure when exposed to fire, modern lightweight assemblies fail significantly sooner—and the failures are more global. Unprotected combustible wood construction also poses the threat of accelerated fire development.
Following are some tactical considerations for firefighting operations in lightweight constructed structures.
• Develop standard operating guidelines (SOGs) for lightweight construction. Francis Brannigan spent his life teaching the fire service the importance of “knowing your enemy.” Residential structures, and particularly “starter castle”-sized single-family homes made from lightweight engineered wood assemblies, are a very different enemy than legacy-constructed 1,500-square-foot homes. If your SOGs weren’t specifically developed for lightweight construction, they are inadequate.
• Collect and refer to standardized pre-fire planning information. Thorough pre-fire planning is an essential tool that highlights potential tactical considerations for responding companies approaching an unfamiliar structure. When possible, provide pre-fire planning information on mobile data terminals or via radio transmissions for responding units and incident commanders.
• Consider available department and mutual-aid resources. Review your department’s dispatch protocols to ensure that the assignment and staffing complement are sufficient for not only the occupancy but for the size and construction of the subject structure itself. Upgrade alarm response early and often. If you don’t have adequate resources to conduct an interior operation while protecting firefighter’s lives, consider a defensive operation.
• Adjust your initial size-up consideration. Assume this is a lightweight-constructed building unless/until you know otherwise. Start laying 2 ½" hoseline for your fire attack. Continually monitor the exterior of the building using a TIC, looking for signs of fire in the truss voids between floors. Consider the age of the structure, construction features, occupancy and the visual indicators of the fire’s progress, behavior and location. Follow Brannigan’s dictum and distinguish between a contents fire and a structure fire. Once fire is attacking the structural components of a lightweight constructed building, you’re out of time. Get out.
• Conduct a risk/benefit analysis. Continually assess potential victims’ survival profile. Aggressive interior attack should cease if and when the occupants are accounted for. Aggressive interior attack should also cease if and when fire conditions preclude victim survival. This does NOT mean we must always abandon the building and “surround and drown.” It DOES mean that we should identify when we’re the only viable life hazard within the building. Once established, tactical considerations should be based on the ability to conduct safe operations while protecting the fireground life hazards.
• When multiple “immediate” tasks must be accomplished sequentially, make fire control your first priority. Rescue of trapped occupants is the first strategic priority, but not necessarily the first tactical priority. More people are saved by a well-placed and advanced hoseline than by any other tactic. Controlling the fire removes the hazard from the victim, which is much more efficient than trying to locate and remove the victim from the hazard. Do not conduct unsupported or unprotected search and rescue operations, and support and protect the search and rescue operation sensibly.
• Open void spaces upon entry. Lightweight construction is balloon framing with lots of extra holes punched in the joists. Once fire enters the voids, it will travel anywhere and everywhere. Upon entering the fire floor, make an inspection hole in the ceiling above and the floor below. Inspection holes can help verify the conditions of structural framing members and uncover areas of hidden fire within the void spaces.
• Consider a transitional fire attack. Interior fire attacks can begin with a stream operated from the exterior of the building. A correctly applied solid stream from the exterior of a fire area with flames visible and venting from one or more openings will slow the fire’s growth and buy the necessary time to allow for a more considered and deliberate interior operation. Bring the nozzle as close as possible to the exterior opening and play the solid stream off the ceiling and walls. Shut down and reposition as soon as knockdown is achieved. This tactic works best with an adult-sized (i.e., 2 ½") hoseline.
• Check below your area of operation. Always check below the apparent fire location before committing to interior operations. Do not advance until conditions below the area of operation are verified.
• Aggressively ventilate all fire areas. We must verify the integrity of the lightweight structural components as soon as possible. To do this, we need to see; to see, we need to ventilate. This is especially true for basement fires. Once the fire is controlled, ventilation and opening of the ceiling voids has to happen now, not later.
• Vent attic fire areas from the exterior. With truss roofs, ventilate and attempt knockdown of attic fires from the exterior (aerial platforms, fire-protected areas or adjacent buildings) before committing personnel to the floor area below the attic. Interior extinguishment and search teams should remain below the landing of the stairs leading to the top floor. If a lightweight attic or cockloft area is so charged with smoke or fire that it’s truly in need of ventilation, it’s already at the point of collapse. No personnel should be allowed to operate above or below this structure.
• Follow the order of Vent, Enter and Search (VES). Monitoring crew locations is critically important during operations in lightweight constructed buildings. This search and rescue method has the advantage of always letting you know exactly where the search team is operating. The search team can also be sure of their means of egress; they brought it with them. VES can also be conducted on the ground floor with the appropriate-sized ladders or in a frame dwelling by making doors out of all the first-floor windows.
• Maintain operational flexibility. You don’t know when the “countdown to collapse” clock started. Conduct a continuous risk assessment and be prepared to revise the operational plan when necessary. Maintain awareness of operational progress and consistently monitor fireground communications. If little or no progress toward fire control is being made, interior occupants have been accounted for, interior occupants are no longer viable and/or primary search and rescue has been completed, consider moving to a defensive operation.
• Always use an adequately sized rapid intervention team (RIT). Deploy a dedicated handline with the RIT. Many RIT scenarios, especially those dealing with rapid flashover or structural collapse, can benefit greatly from the ability to control fire.
A FINAL WORD
Fires in today’s “modern” residential buildings pose greater risks than their “legacy” predecessors. These structures are subject to rapid fire spread through areas of unprotected wood construction, the collapse of unprotected dimensional lumber, and the collapse of lightweight engineered wood components. Understanding the testing methods employed and the results of this study, even on a basic level, will assist firefighters in conducting a safer fireground operation the next time the alarm bell sounds. A working knowledge of these results is also a critical step for all members of the fire service who are actively engaged in the growing movement to enhance firefighter safety by modifying the current code requirements for residential construction.
James Dalton is the coordinator of research and development for the Chicago (Ill.) Fire Department. Peter Van Dorpe is a battalion chief for the Chicago (Ill.) Fire Department. Bob Backstrom is a senior staff engineer with Underwriters Laboratories. Steve Kerber is a research engineer with Underwriters Laboratories and has 12 years of firefighting experience.
For More Information...
• For a complete interactive training program that explains the UL study in detail, including the motivation, methodology, testing and lessons learned, go to www.ul.com/fire/structural.html.
• For a chart showing the collapse time for different assemblies, go to http://tinyurl.com/collapsetimes.
• For further information, please e-mail Robert.G.Backstrom@us.ul.com, Stephen.Kerber@us.ul.com or James.Dalton@cityofchicago.org. To submit additional information and/or photos on local fire incidents within your area that may inform the issues discussed within this article, please contact James.Dalton@cityofchicago.org.
Tactical considerations for firefighting operations in lightweight construction
By James M. Dalton, Peter Van Dorpe, Robert G. Backstrom & Steve Kerber
Multiple firefighter fatalities at large commercial fires attract the attention and scrutiny they warrant. However, it’s also important to remember that many line-of-duty injuries and deaths occur in single- and multiple-family dwellings during routine, “bread and butter” residential fires. A review of 23 investigations conducted by the National Institute for Occupational Safety and Health (NIOSH) Fire Fighter Fatality Investigation and Prevention Program between 1997 and 2009 illustrates this issue: These incidents involved fires in residential buildings that resulted in 29 fatalities and numerous injuries. One common denominator in these incidents: rapidly spreading fire in areas of unprotected wood construction, the collapse of unprotected dimensional lumber or the collapse of lightweight engineered wood components.
The fire service has been aware of the hazards associated with lightweight construction for decades, but until recently, we lacked the scientific data to quantify the anecdotal evidence from the fireground. Furthermore, while manufacturers understandably submit for testing only those assemblies for which they expect to achieve the desired fire resistive ratings, building codes allow unrated, or unprotected, assemblies (i.e., wood covered with non-rated sheathing materials or exposed wood) to be used in residential construction, particularly in single-family homes.
Because the use of lightweight and engineered assemblies has become virtually the exclusive means of constructing floor and roof systems in residential buildings, it’s imperative that the fire service develops a better understanding of how these assemblies behave under fire conditions. It’s also imperative that we test these built assemblies in a scientifically valid and quantifiable way so that the results can be used to affect changes to building codes and construction practices.
In this article, we’ll share selected results of research conducted by Underwriters Laboratories (UL), the Chicago Fire Department, the International Association of Fire Chiefs and Michigan State University that highlight the dangers of lightweight construction. The findings of this research have also been developed into a Web-based training program for the fire service. This free interactive program is at www.ul.com/fire/structural.html. In addition, this article will also share some tactical recommendations for any firefighter responding to fires in buildings featuring lightweight construction.
THE EVIDENCE
UL and its partners were awarded funding from the Assistance to Firefighters Grant program to subject a representative group of floor and roof assemblies to the industry standard fire resistance testing method, ASTM E119: Fire Tests of Building and Construction Materials.
Following are some findings from the research:
• Residential fires may actually pose commercial fire risks. Many of today’s “typical” house fires are in buildings that, based on size and interior volume, can and should be categorized as commercial structures with commercial fuel loads. Combined with modern synthetic fuel loads, fires in large, unprotected and un-firestopped voids made of lightweight engineered building materials can be catastrophic. Today’s fireground operations must reflect this new reality.
• Thermal imaging cameras (TICs) don’t provide an adequate indication of a weakened floor or pending collapse. There’s a potentially dangerous misconception in the fire service that TICs can detect fire on the floors below or above a firefighter. TICs detect variations in surface temperatures for objects in the camera’s field of vision. They cannot detect temperatures in areas that are thermally shielded from the camera’s view by the finish materials of a floor or ceiling. During these tests, average temperatures below the assembly were in excess of 1,200 degrees F, while average temperatures on top of the carpet were less than 100 degrees F. The application of water during suppression operations will further mask or eliminate the thermal signatures available to the TIC’s sensor.
• Floor collapse can occur in 6 minutes. Engineered wood floor assemblies have the potential to collapse very quickly under well-ventilated fire conditions. When it comes to lightweight construction, there’s no margin of safety. There’s less wood to burn, and therefore less time before the assembly fails. During this research, the shortest failure time was noted during the unfinished/unprotected engineered wooden I-joist test. This assembly experienced a total structural collapse at 6 minutes.
• Tested assemblies significantly weaken well before they completely collapse. The ASTM E119 definition of collapse requires that the floor totally collapse. Several fire test standards recognized outside the United States, such as ISO 834:1: Fire-resistance tests, Elements of building construction, Part 1, look instead at how long a test sample is able to maintain its ability to support the applied load during the fire test, taking into account when a floor is progressively deflecting or failing prior to a complete structural collapse—clearly a critical piece of information for the fire service.
The bottom line: If the ISO standard was applied to the unprotected engineered wooden I-joist assembly, the accepted failure time would change from 6:03 to 4 minutes. All lightweight assemblies studied in this series of tests exhibited similar differences in time-to-failure based on the standard applied. Fire service instructors are encouraged to use these different criteria for time-to-failure or collapse to emphasize that test results can only be used for comparison and are not accurate indicators of operational time on the fireground.
• Plastic ridge vents can mask fire intensity. In the early stages of the modern roof assembly test, there was a significant amount of smoke emitting from the continuous plastic ridge vent. As the temperatures increased, the ridge vent melted and collapsed upon itself, sealing the natural opening. The heavy smoke emitting from the continuous ridge vent diminished to a light smoke trail, although the fire was still raging below. Temperatures in the attic space went from approximately 200 degrees F to 1,400 degrees F in less than 60 seconds. These are flashover conditions and can cause global failure of the ceiling. Firefighters conducting size-up and attempting to read smoke conditions from the exterior may be deceived by this change in the volume and velocity of the smoke venting from the roof, and roof teams may conclude that the roof is safe to operate on, when in fact it may be rapidly approaching the point of collapse.
TACTICAL CONSIDERATIONS
Over the last few decades, millions of single-family homes have been built with truss-constructed roofs that create large, undivided attic spaces and unfinished basements that have unprotected lightweight wood floor systems above them. This study established that while all unprotected wood floor assemblies are susceptible to early failure when exposed to fire, modern lightweight assemblies fail significantly sooner—and the failures are more global. Unprotected combustible wood construction also poses the threat of accelerated fire development.
Following are some tactical considerations for firefighting operations in lightweight constructed structures.
• Develop standard operating guidelines (SOGs) for lightweight construction. Francis Brannigan spent his life teaching the fire service the importance of “knowing your enemy.” Residential structures, and particularly “starter castle”-sized single-family homes made from lightweight engineered wood assemblies, are a very different enemy than legacy-constructed 1,500-square-foot homes. If your SOGs weren’t specifically developed for lightweight construction, they are inadequate.
• Collect and refer to standardized pre-fire planning information. Thorough pre-fire planning is an essential tool that highlights potential tactical considerations for responding companies approaching an unfamiliar structure. When possible, provide pre-fire planning information on mobile data terminals or via radio transmissions for responding units and incident commanders.
• Consider available department and mutual-aid resources. Review your department’s dispatch protocols to ensure that the assignment and staffing complement are sufficient for not only the occupancy but for the size and construction of the subject structure itself. Upgrade alarm response early and often. If you don’t have adequate resources to conduct an interior operation while protecting firefighter’s lives, consider a defensive operation.
• Adjust your initial size-up consideration. Assume this is a lightweight-constructed building unless/until you know otherwise. Start laying 2 ½" hoseline for your fire attack. Continually monitor the exterior of the building using a TIC, looking for signs of fire in the truss voids between floors. Consider the age of the structure, construction features, occupancy and the visual indicators of the fire’s progress, behavior and location. Follow Brannigan’s dictum and distinguish between a contents fire and a structure fire. Once fire is attacking the structural components of a lightweight constructed building, you’re out of time. Get out.
• Conduct a risk/benefit analysis. Continually assess potential victims’ survival profile. Aggressive interior attack should cease if and when the occupants are accounted for. Aggressive interior attack should also cease if and when fire conditions preclude victim survival. This does NOT mean we must always abandon the building and “surround and drown.” It DOES mean that we should identify when we’re the only viable life hazard within the building. Once established, tactical considerations should be based on the ability to conduct safe operations while protecting the fireground life hazards.
• When multiple “immediate” tasks must be accomplished sequentially, make fire control your first priority. Rescue of trapped occupants is the first strategic priority, but not necessarily the first tactical priority. More people are saved by a well-placed and advanced hoseline than by any other tactic. Controlling the fire removes the hazard from the victim, which is much more efficient than trying to locate and remove the victim from the hazard. Do not conduct unsupported or unprotected search and rescue operations, and support and protect the search and rescue operation sensibly.
• Open void spaces upon entry. Lightweight construction is balloon framing with lots of extra holes punched in the joists. Once fire enters the voids, it will travel anywhere and everywhere. Upon entering the fire floor, make an inspection hole in the ceiling above and the floor below. Inspection holes can help verify the conditions of structural framing members and uncover areas of hidden fire within the void spaces.
• Consider a transitional fire attack. Interior fire attacks can begin with a stream operated from the exterior of the building. A correctly applied solid stream from the exterior of a fire area with flames visible and venting from one or more openings will slow the fire’s growth and buy the necessary time to allow for a more considered and deliberate interior operation. Bring the nozzle as close as possible to the exterior opening and play the solid stream off the ceiling and walls. Shut down and reposition as soon as knockdown is achieved. This tactic works best with an adult-sized (i.e., 2 ½") hoseline.
• Check below your area of operation. Always check below the apparent fire location before committing to interior operations. Do not advance until conditions below the area of operation are verified.
• Aggressively ventilate all fire areas. We must verify the integrity of the lightweight structural components as soon as possible. To do this, we need to see; to see, we need to ventilate. This is especially true for basement fires. Once the fire is controlled, ventilation and opening of the ceiling voids has to happen now, not later.
• Vent attic fire areas from the exterior. With truss roofs, ventilate and attempt knockdown of attic fires from the exterior (aerial platforms, fire-protected areas or adjacent buildings) before committing personnel to the floor area below the attic. Interior extinguishment and search teams should remain below the landing of the stairs leading to the top floor. If a lightweight attic or cockloft area is so charged with smoke or fire that it’s truly in need of ventilation, it’s already at the point of collapse. No personnel should be allowed to operate above or below this structure.
• Follow the order of Vent, Enter and Search (VES). Monitoring crew locations is critically important during operations in lightweight constructed buildings. This search and rescue method has the advantage of always letting you know exactly where the search team is operating. The search team can also be sure of their means of egress; they brought it with them. VES can also be conducted on the ground floor with the appropriate-sized ladders or in a frame dwelling by making doors out of all the first-floor windows.
• Maintain operational flexibility. You don’t know when the “countdown to collapse” clock started. Conduct a continuous risk assessment and be prepared to revise the operational plan when necessary. Maintain awareness of operational progress and consistently monitor fireground communications. If little or no progress toward fire control is being made, interior occupants have been accounted for, interior occupants are no longer viable and/or primary search and rescue has been completed, consider moving to a defensive operation.
• Always use an adequately sized rapid intervention team (RIT). Deploy a dedicated handline with the RIT. Many RIT scenarios, especially those dealing with rapid flashover or structural collapse, can benefit greatly from the ability to control fire.
A FINAL WORD
Fires in today’s “modern” residential buildings pose greater risks than their “legacy” predecessors. These structures are subject to rapid fire spread through areas of unprotected wood construction, the collapse of unprotected dimensional lumber, and the collapse of lightweight engineered wood components. Understanding the testing methods employed and the results of this study, even on a basic level, will assist firefighters in conducting a safer fireground operation the next time the alarm bell sounds. A working knowledge of these results is also a critical step for all members of the fire service who are actively engaged in the growing movement to enhance firefighter safety by modifying the current code requirements for residential construction.
James Dalton is the coordinator of research and development for the Chicago (Ill.) Fire Department. Peter Van Dorpe is a battalion chief for the Chicago (Ill.) Fire Department. Bob Backstrom is a senior staff engineer with Underwriters Laboratories. Steve Kerber is a research engineer with Underwriters Laboratories and has 12 years of firefighting experience.
For More Information...
• For a complete interactive training program that explains the UL study in detail, including the motivation, methodology, testing and lessons learned, go to www.ul.com/fire/structural.html.
• For a chart showing the collapse time for different assemblies, go to http://tinyurl.com/collapsetimes.
• For further information, please e-mail Robert.G.Backstrom@us.ul.com, Stephen.Kerber@us.ul.com or James.Dalton@cityofchicago.org. To submit additional information and/or photos on local fire incidents within your area that may inform the issues discussed within this article, please contact James.Dalton@cityofchicago.org.
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