Jun 27, 2023
Firefighting in Wood Frame Three
By Joseph T. Berry Photos by author except where indicated A well-known quote
By Joseph T. Berry
Photos by author except where indicated
A well-known quote from Frank Brannigan advises firefighters to "know the enemy." That includes different types of building construction and how their structural components hold up to a raging fire.
Anatomy is the science that studies the structure of the body, and a doctor or nurse who is not familiar with the anatomy of the body could not make life-and-death decisions for the patient. Anatomy analogously also applies to the fire service in terms of building anatomy. Without knowing the type of building construction and the structural components within, firefighters’ lives would be in jeopardy.
New and renovated building construction sites should be visited during the different phases of construction by fire companies in that response area. This is the time to put an awareness prefire plan together on the type of construction, apparatus access, difficulty in laddering, anticipated long hose stretches, and building irregularities that could affect fire department operations.
The demand and dwindling supply of dimensional lumber has created a multibillion industry in engineered lumber. Today's wood frame building construction is dominated with engineered lumber products. Douglas fir dimensional lumber is expensive and in short supply. Spruce and yellow pine make up the majority of the lumber used in wood frame residential construction.
Structural components comprised of open web 2×4 wood with metal gusset plate floor trusses, large peaked roof trusses, truss joist I-beams (TJI), and laminated beams used as a support girder are the norm in today's wood frame construction.
Firefighters operating above or below a floor system that is constructed with open web 2×4 trusses must be aware that the floor platform structural stability can and will be compromised when fire extends and travels through this closed voided floor area. There is only a short window of time to operate on this floor platform.
Operations on the floor above should be delayed until the fire is knocked down and the structural stability of the floor is checked. Operational time is a critical factor—the incident commander must keep track of accumulative interior firefighting operational time. Remember, the floor trusses could have already been weakened and compromised prior to the arrival of the fire department.
The advantage of using open web trusses is twofold: structural floor support and for easier installation of HVAC duct work, plumbing feed lines, and risers, electrical supply lines, to each apartment. There's no boring of holes, as would be the case in using TJI.
The main disadvantage is the creation of a voided common cockloft area on each floor, with an additional lumberyard fire load from the trusses itself.
Depending on fire code requirements, horizontal and vertical fire stopping must be installed to prevent fire extension between apartments and areas above. The quantity and quality of fire stopping should not be compromised by substandard installation.
Sprinkler systems are required in most new residential apartment buildings. Sprinkler head locations may be found in the hallways and/or apartment units. Interior smoke and carbon monoxide (CO) detectors are mandatory today in all rentals, apartments, and private dwellings. The floor truss loft area should also be protected with a sprinkler head and hardwired smoke/CO detectors. Ceiling vents for the heating and air conditioning are an avenue for fire extension into the truss loft ceiling.
One of the most destructive and difficult type of fire to extinguish is in a roof cockloft or a closed voided area. The definition of a cockloft is an enclosed open spaced void between the ceiling and the roof. This definition would also describe a peaked truss roof area. The only difference is the shape of the cockloft—rectangular versus triangular, as in a peaked truss roof. The height of these cocklofts can range from one foot to several feet in height. Cocklofts are found in residential and commercial buildings alike.
When fire consumes the volume area of a cockloft, the oxygen level will gradually become depleted. This smoldering decaying stage is still producing hot, convected gases. There is enough O2 due to area leakage from vents or other areas to sustain continuing combustion. The size and depth of the cockloft determines how fast smoke pressurization can occur. This hot, pressurized smoke starts pushing out from vents, cracks, and crevices. As this process continues ,the visibility of the areas below become obscured from the smoke cloud.
Oxygen being introduced from a distance source, such as from forcibly entry or the venting of windows, can cause violent smoke explosion/backdraft to occur. The only way to relieve this pressure is through vertical ventilation.
The same fire scenario could occur from a raging fire that extending in a voided truss floor or roof truss loft area. An unchecked fire traveling horizontally and vertically through this voided area will eventually extend into the roof (cockloft) truss area.
Vertical ventilation cannot be performed on an open web floor truss. To put it bluntly, cutting a hole on the floor above would be a death wish.
Firefighters do not operate on roof trusses. If a truss roof has to be vented, the only safe way is operating on the platform bucket of a tower ladder. I cannot emphasize how important floor compartmentation and adequate horizontal and vertical fire stopping will slow down the fire path.
(1) Open web truss floor collapse. Photo by FDNY Ladder 55.
To illustrate the point, I present a fire from the Fire Department of New York (FDNY). This was a single-line fire that extended into the truss loft area and resulted in floor truss failure. Numerous floor trusses collapsed in this one bedroom fire.
The second-due truck was operating on the floor above, conducting a search under a heavy smoke condition. The officer felt a noticeable sag on the floor area and aborted further entry.
After the fire below was knocked down and visibility was clearer, the carpet on the floor above had large downward bow. What prevented further collapse was the weight of furniture on one end of the carpet floor area and a widescreen TV on the opposite end, which held the carpet in place.
The key to learning in the fire service is reviewing past fires. As an engine officer, I responded on the third alarm to a rapidly escalating fire in an occupied multiple dwelling. This provided a significant learning opportunity about a structural fire in voided cockloft floor areas.
The building in question was a Class 3 non-fireproof, five-story renovated apartment building with an existing 2×10 floor joist. On arrival, three 1 ¾-inch hoselines were stretched on the first, second, and third floors. There was a heavy smoke condition in three apartments on the first and second floor with no visible fire. Firefighters were employing masks, and encountered a medium smoke condition on two apartments on the third and fourth floor and yet no visible fire. There was a heavy smoke condition throughout the top floor in all apartments.
The fourth and fifth alarm were transmitted, and crews reported a heavy fire condition in the cockloft.
The problem was that when the building was renovated, the contractor lowered the height of the ceiling more than a foot from the original ceiling height, thereby creating a common cockloft void on all floors.
New replacement windows were installed to the existing rough brick exterior opening. This lowered ceiling height had to be addressed on the outside, also. To adjust the appearance on the outside of the existing brick opening, a non-operable, small, sealed transom window was installed above the new replacement windows.
As smoke conditions worsened, exterior ventilation to the second-floor windows was performed from a tower ladder bucket. Heavy smoke vented out from the apartment window, with no visible fire. As firefighters continued ventilation of the small transom window above the main window, a ball of fire vented out. This was the dropped ceiling voided cockloft that was created on each floor from the renovation.
It's very difficult to find the exact path of fire extension under a heavy smoke condition. Using a thermal imaging camera and opening an inspection hole in the ceiling with heated smoke pushing out becomes a labor-intensive operation. The path of the fire may already have traveled beyond your location. The soil pipe and risers are the vertical path where the fire is traveling.
In this case, the fire originated in the cellar above the heating system. It was a well-advanced fire brewing for some time before a smoke condition was reported. The fire traveled up a pipe recess chase and extended horizontally and vertically into the dropped ceiling voided areas throughout the height of the building into the roof cockloft. A common cockloft after drywall is installed enabled fire extension, as fire could travel horizontally and vertically.
(2) Long hallway corridor open web 2×4 gang plate open web floor trusses. The entire apartment floor area throughout is comprised of open web metal gang plate trusses.
(3) OSB exterior wood sheathing, vinyl siding, open web 2×4 metal gang plate floor trusses, and peaked roof trusses.
(4) Exterior of a three-story apartment building.
(5) A four-story apartment building with wood frame open web floor trusses. The exterior balconies have open web floor trusses.
Consumers’ desire for open concept floor areas has made such layouts the norm in today's apartment building. The spans for open floor areas can be increased by the overall height of the floor truss or by incorporating a support laminated girder beam.
Exterior apartment balcony decks provide a relaxing area to the outside. One of the leading causes from fires on exterior decks/ balconies have been smoking materials used on combustible furniture and barbeque grills. Exterior siding using a fire-resistant-type hardy board siding provides excellent panel wall protection versus vinyl siding.
(6) Five-story open web floor trusses with exterior balcony exits.
Another potential for floor truss collapse is from the added weight of accumulating water run-off from a hoseline or high-caliber stream. One gallon of water is 8.35 lbs. per gallon. Content soaked furniture, carpet, and water runoff can become the straw the broke the camel's back.
Floor areas are calculated at 40 lbs. per square foot for live loads and 10 to 15 lbs. for dead loads, but they do not take into consideration the additional weight of water accumulation. Lower floor apartments that did not sustain fire damage could have significant water accumulating throughout the apartment. No one should be allowed to return to apartments affected by water runoff until floor area has been inspected by a building structural engineer.
The first priority operating at every fire is the saving of life. An early morning fire within this type of heavily occupied, multistory apartment building creates the potential for multiple simultaneously rescues upon arrival by first on the scene units. This could cause a delay in suppression operations due to numerous imminent rescues.
Raising portable extension ladders for immediate rescues, occupants on numerous exterior balconies unable to exit via the interior, lifesaving evacuations, can and will use all fire personnel on first-arriving units operating on the scene. Multiple alarms must be transmitted for additional resources, but time is of essence for additional personnel to arrive on the scene.
The FDNY's critical information dispatch system (CIDS) provides valuable information that is forwarded to units upon response to an address location.
This vital information could relate to the building construction, layout topography, access for apparatus or a required number of units to respond for a confirmed structural fire for a particular building complex (as would be the case recommended in these multistory apartment buildings.)
In an apartment fire, checking for fire extension is crucial. After the fire has been knock down, check for extension as soon as possible. Start with inspection holes in conjunction with thermal imaging camera around the ceiling HVAC vents and light fixtures. If fire has extended into the floor truss void area, continue to open up so water can be directed into this voided area.
Smoke accumulating in this ceiling voided area must be vented, otherwise a smoke condition callback will occur. The presence of CO in this voided area must be checked and continually monitored.
Depending on the quality and quantity of adequate fire stopping, a well-advanced fire originating within this floor truss loft area could already have extended to the floors above. It could be difficult confine and control fire extension at that point.
A charged hoseline must always be readiness before opening up any ceiling.
Create a small inspection hole by the interior door before entering. Smoke under pressure is a telltale sign for a potential violent flashover or smoke explosion.
The structural stability of the floor trusses must be checked before operating above. Any deep charring or sagging is a sign of truss failure.
As mentioned before, the only way to relieve smoke pressurization in a cockloft is vertical ventilation. There's no way to provide vertical ventilation on this truss floor platform without putting firefighters’ lives at risk. Follow the cardinal rule that there are six sides to a fire area.
The FDNY has used this cockloft nozzle at fires with great success. The shutoff from the 1 ¾-inch solid bore nozzle controls the water flow. It has two open bore 15/16 tips with ½ tips attached and is lightweight, about 9 lbs. This is just another tool in the toolbox.
Operating this nozzle in floor trusses void will be a little tight. Firefighters must always be aware of the weakened state of these trusses.
Key fire safety takeaways:
Affordable housing is in demand, and these apartment complexes are popular, particularly with their added amenities. The life safety of firefighters and civilians must be taken into account when building wood frame structures. Strict building code requirements in conjunction with a fire protection engineer recommendations must be enforced during all construction phrases.
This should include the mandate that all voided truss areas be fully sprinklered, in addition to hallways and apartments, as well as four-hour fireproof enclosed interior stairs. It should also the maintenance of areas clear of parking for adequate fire apparatus access.
Most importantly for firefighters, continue to pass on information learned from past fire incidents and stay familiar with your enemy.
This article is dedicated to the memory of Bobby Halton.
JOSEPH T. BERRY, a 31-year veteran of the Fire Department of New York (FDNY), retired as a lieutenant in 2002. He was a firefighter with Engine 1 and Ladder Company 24. Promoted to lieutenant in 1983, he served with Engine 73 and then Ladder 42 until his retirement. Berry served on an FDNY committee that revised the probationary firefighter's manual and the standard operating procedures for firefighting in tenements, brownstones, wood-frame buildings, and lightweight residential construction. He has written numerous articles on building construction and firefighting. Berry was a consultant for Titan Corporation/Department of Homeland Security.By Joseph T. Berry Construction Concerns for Firefighters: Trusses Firefighters and Construction: Bowstring/Arched Rib Truss Roof Systems Construction Concerns: Truss Failure The Great Vertical Ventilation Debate Rekindled: Lightweight Construction and Vertical Ventilation Firefighters and Construction: The Cockloft Main Street Memo: Cocklofts Attic vs. Cockloft: What's the Difference? Concealed Spaces and Fire Spread metal gusset plates failed 1 minute and 20 seconds. Wooden trusses can fail after five to 10 minutes of exposure Key fire safety takeaways: This article is dedicated to the memory of Bobby Halton. JOSEPH T. BERRY