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Case Study: Small Fire in the Basement
A couple of years back we were dispatched to a structure fire at about 7:30 on a weekday morning. On arrival we found a house under construction with smoke showing. The house was completely framed and finished both inside and out, and in fact the owner was just about to receive his certificate of occupancy. The fire was discovered by a passerby who noticed light to medium gray smoke coming from the structure.
The house was constructed using lightweight materials – wooden I-joists with pressed wood-chip webs, and similar type material for the subfloor. However, we did not find this out until after the fire was extinguished.
The fire began in a plastic bucket of oily rags, which was placed on the bare first floor surface. Spontaneous ignition of the rags caused the fire, which apparently smoldered for quite some time before burning through the 5/8” chipboard floor sheathing and falling onto the basement floor. Once in the basement, the fire continued to burn and involved other materials that also fell onto the basement floor.
As seen in Photo 1, there was no fire showing on our arrival - only light to moderately gray smoke pushing from all cracks and crevices. The house was fully charged with smoke, and the initial hose team elected to make entry through a window on side 1. The first firefighter sounded the floor, then stepped in and immediately fell through the floor in the area seen above and behind the hanging light bulb in the picture. He had apparently sounded the floor above the block foundation wall, which projected about 18 inches into the room. A firm grip on the hose kept him from falling into the basement, and he was rescued by two other firefighters who heard his Mayday. Fortunately he was uninjured.
A second attack team entered the basement from the No. 2 side and carefully made their way to the seat of the fire. The fire was completely extinguished with about 100 gallons of water.
In Photo 2, what you’re looking at is the underside of the first floor as seen from the basement. In the upper center of the picture a saw horse is lying on its side, just about to fall through the roughly 4 x 6 foot hole in the floor. Just below the saw horse, in the background above the block wall, you can see the charred sill plate that bears the first floor outside wall. A deformed natural gas pipe to the left of center in the picture is holding up part of the floor sheathing. The I-joists ran parallel to the pipe and are completely gone in the fire area. The gas pipe probably impeded the firefighter’s fall into the basement.
Photos 2 and 3 really show the extent of the fire damage, an area not more than 15 x 15 feet. About 12 to 15 I-joists were damaged or destroyed, as well as a few sheets of the pressed board sheathing. Beyond the damaged joists, the heat was not enough to melt the 4 inch PVC waste pipe or the light bulbs. Damage to the rest of the house was mainly limited to smoke stains and broken windows; as the house was still under construction, no damage to carpets, furniture or personal belongings occurred.
Photo 3 shows the effects of fire on the I-joists. There isn’t much to burn to begin with, however it appears that heat melted the glue that holds the pressed wood materials together, causing a flaking effect which further weakened the structural member.
Notice the metal studs and the wall surface in the basement in photos 4 and 5: very little heat was present on the wall surface, indicating a relatively low intensity fire in the materials on the floor. Yet the fire continued to burn the underside of the first floor, generating enough heat to melt a light bulb (see photo 4) and drastically weakening the I-joists to the point of failure. It appears to me that the heat of the blazing pile of rags was enough to heat the lightweight materials to the point of vapor production, which sustained a fire within the web space of a few of the I-joists. The result was very little flame spread but complete disintegration of the joists that were involved.
Some people might call this a “good save,” however in reality it was not. There was enough damage to the lightweight first floor framing members that the house had to be completely razed and rebuilt - from the foundation up. From the insurance company’s point of view it was a total loss of about $300,000, so it didn’t really matter whether we made an aggressive interior attack or just stood back and let it burn.
The positive outcome of this fire was that our awareness of lightweight construction dangers has been heightened considerably. We are now marking high hazard structures with reflective red street address signs in place of our standard green ones. Our Chief has been to meetings with our county code enforcement officers to begin a push for a uniform county-wide marking system and database.
Also, by the time we get another fire in a similarly constructed building we will have rehearsed the answer to the questions: Should we, or should we not, make an interior attack on this structure? Is the risk to the interior firefighters worth it? Nope; not on my watch.
The house was constructed using lightweight materials – wooden I-joists with pressed wood-chip webs, and similar type material for the subfloor. However, we did not find this out until after the fire was extinguished.
The fire began in a plastic bucket of oily rags, which was placed on the bare first floor surface. Spontaneous ignition of the rags caused the fire, which apparently smoldered for quite some time before burning through the 5/8” chipboard floor sheathing and falling onto the basement floor. Once in the basement, the fire continued to burn and involved other materials that also fell onto the basement floor.
As seen in Photo 1, there was no fire showing on our arrival - only light to moderately gray smoke pushing from all cracks and crevices. The house was fully charged with smoke, and the initial hose team elected to make entry through a window on side 1. The first firefighter sounded the floor, then stepped in and immediately fell through the floor in the area seen above and behind the hanging light bulb in the picture. He had apparently sounded the floor above the block foundation wall, which projected about 18 inches into the room. A firm grip on the hose kept him from falling into the basement, and he was rescued by two other firefighters who heard his Mayday. Fortunately he was uninjured.
A second attack team entered the basement from the No. 2 side and carefully made their way to the seat of the fire. The fire was completely extinguished with about 100 gallons of water.
In Photo 2, what you’re looking at is the underside of the first floor as seen from the basement. In the upper center of the picture a saw horse is lying on its side, just about to fall through the roughly 4 x 6 foot hole in the floor. Just below the saw horse, in the background above the block wall, you can see the charred sill plate that bears the first floor outside wall. A deformed natural gas pipe to the left of center in the picture is holding up part of the floor sheathing. The I-joists ran parallel to the pipe and are completely gone in the fire area. The gas pipe probably impeded the firefighter’s fall into the basement.
Photos 2 and 3 really show the extent of the fire damage, an area not more than 15 x 15 feet. About 12 to 15 I-joists were damaged or destroyed, as well as a few sheets of the pressed board sheathing. Beyond the damaged joists, the heat was not enough to melt the 4 inch PVC waste pipe or the light bulbs. Damage to the rest of the house was mainly limited to smoke stains and broken windows; as the house was still under construction, no damage to carpets, furniture or personal belongings occurred.
Photo 3 shows the effects of fire on the I-joists. There isn’t much to burn to begin with, however it appears that heat melted the glue that holds the pressed wood materials together, causing a flaking effect which further weakened the structural member.
Notice the metal studs and the wall surface in the basement in photos 4 and 5: very little heat was present on the wall surface, indicating a relatively low intensity fire in the materials on the floor. Yet the fire continued to burn the underside of the first floor, generating enough heat to melt a light bulb (see photo 4) and drastically weakening the I-joists to the point of failure. It appears to me that the heat of the blazing pile of rags was enough to heat the lightweight materials to the point of vapor production, which sustained a fire within the web space of a few of the I-joists. The result was very little flame spread but complete disintegration of the joists that were involved.
Some people might call this a “good save,” however in reality it was not. There was enough damage to the lightweight first floor framing members that the house had to be completely razed and rebuilt - from the foundation up. From the insurance company’s point of view it was a total loss of about $300,000, so it didn’t really matter whether we made an aggressive interior attack or just stood back and let it burn.
The positive outcome of this fire was that our awareness of lightweight construction dangers has been heightened considerably. We are now marking high hazard structures with reflective red street address signs in place of our standard green ones. Our Chief has been to meetings with our county code enforcement officers to begin a push for a uniform county-wide marking system and database.
Also, by the time we get another fire in a similarly constructed building we will have rehearsed the answer to the questions: Should we, or should we not, make an interior attack on this structure? Is the risk to the interior firefighters worth it? Nope; not on my watch.
Replies to This Discussion
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Permalink Reply by Dave on
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Wooden I beams, Open truss flooring. We are seeing more and more of this. Did a little research thru a few old books I have, this is what I found
LAFD did a study a few years back. I'll just recap what they found and suggested
Here are a few considerations when working with light weight construction
1) Time required to failure
2)Speed/Rate of failure
3) Familiarity with building construction in your response area
they took 4 types of common construction and did live fire training on them. They spaced them and used the same deck material they had found used by contractors. Each test lasted no more then 6 minute, and if failure happened they would stop the test early. Each fire was of the same size and intensity and the test products would be suspened above the fire.
Wood I beams
Time to failure= 3minutes 20 seconds
Conclusions
Once the 3/8 plywood stems burned and weakened the entire structure weakens and fails. This wooden I beam is used for Floor joist and roof joists.
Metal gusset plate trusses
decking 3/4 CDX plywood, 16 inches on center spacing, Used for Floor system, Depth of penetration of gusset plates 3/8"
Time to failure= 1minute 20 seconds
Conclusion
Once the 2X4 charred to a depth of 1/4" the gusset Plates would pull out of the 2x4's. Because the ends of the 2x4 are butted together with the gusset plates there is no longer any structual integrity, leaving hte 2x4 to seperate and cause failure.
I have also heard that they have inspected some gusset plates to find that less then 50% of the gusset plates and placed correctly. I hope I didnt screw up the post, the book does have photos, but they are poor quality. -
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Oooopppss....A question for you on your attack. Why did they choose a window over a door to make entry??
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Permalink Reply by Kimberly A Bownas on
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It is like everything that we do in this job. We need to do proper size up and try to make informative decisions that keep us safe so that we all go home. Joe this is a great post and the pictures are fantastic. They show exactly what you were talking about. Great job..
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Permalink Reply by Joe Stoltz on
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Dave, the reason was that the building was giving every indication of a backdraft with smoke puffing from doors, windows and eaves. The entry team decided to take out the lower pane of glass, get in and cool off the fire before it blew.
I think the idea was to minimize the size of the opening and not let a lot of air in with the initial attack until ventilation could be accomplished up above.
That's what I was told; I didn't arrive on scene until 15 minutes or so into the incident. At the time of entry there were 3 members on the entry team, two pump operators and a whole bunch of people and equipment en route. -
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Permalink Reply by Christopher J. Naum, SFPE on
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Great example and the type of insights and knowledge we need to drive home to our personnel to better prepare them for the hazards on the job. We need toknow our buildings within our district and in our second and third dues and mutual aid areas, and understand how newer (engineered systems) work and can be affected by fire behavior.
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Here's some additional information regarding New York State's Truss Placarding law; 19 NYCRR Part 1264 - IDENTIFICATION OF BUILDINGS UTILIZING TRUSS TYPE CONSTRUCTION. Effective December 29, 2004 19 NYCRR Part 1264 Construction Type Designation
Floors= F
Roofs= R
Floor & Roofs=FR
Also, look at great report from - Attachments:
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19NYSRR1264.pdf, 13 KB -
CDC Truss Hazards.pdf, 1.4 MB
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This is good, but my understanding is that at the residential level the Code Enforcement officer can only "recommend" that the appropriate signage be placed in a prominent location on the house. At least in this part of New York State.
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Permalink Reply by ECB on
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The New York State Fire Code requires the placard on any new commercial building, or any commercial building that has had an addition made using wood or metal trusses in the roof and/or floor system of Group A, B, E, F, H, I, M, or S occupancy, and in hotels and motels classified as Group R-1 or R-2 occupancy. One and two family dwellings are exempt from this requirement. It is a safe bet, however, that a one or two family home that was built in the last few years does contain trusses in at least the roof, but more than likely in the floor system as well. The cost of lumber continues to climb, and the desire for larger "open areas" demands the use of the wood truss in the floor system. Also, keep in mind that the quality of the lumber being used today is not the same as it was 15 years ago. Measure the true dimensions of a 2" x 4".
The commercial buildings listed in the first paragraph that were built after December 2004 are required to have the placard at every exterior door, and at the fire department connections. The signs are reflective. Their only purpose is to identify the type and location of the truss to the incoming fire department to assist in making the offensive / defensive decision. Check with your local building department or fire marshal's office. -
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Permalink Reply by Steve Davis on
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In a similar case in my first due, we had a fire in the basement with similar smoke conditions. In this case, we were actually able to deploy AFFF and fill the basement with foam, effectively extinguishing the fire without putting a crew in the basement. Because new construction (to put in to plain words) sucks, we explorer our options before putting a crew in the basement.
With the signage, I think it is a great idea, however, I can also see the residents in the community not wanting to have the signs on the street and protesting to have them removed due to it reducing their property value. What we have done is increased our first due new construction inspections and started to conduct pre-incident plannings which can be input in to our CAD system and an alert can then be sent to each responding unit to notify them of any risks. This gives us the leg up and enables the residents to maintain their peice of mind with home values.
New laws have also helped us with a push for new homes to be constructed with sprinkler installations. -
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Permalink Reply by Ben Waller on
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Joe,
What is a "basement"?
My district has solid concrete 1st floors known as "slabs" on which the rest of the house sits.
Something to do with the water table being immediately on the dirt side of the grass, I think.
Just kidding of course, I grew up in a house that had a basement.
OSB I-beams are an increasingly common problem, even in non-residential construction.
I recently did some walkthroughs to get photos for an upcoming training session on big box fires.
I got photos of two big box stores with add-on mezzanines constructed from OSB I-beams.
They were not sprinklered (grandfathered construction) and had heavy product storage loads on one and newly-built offices on the other.
Good topic, and good photos. -
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Ben, you had me worried there for a minute. Thanks for the feedback.
Just a question to all - do the pictures show up vertically stretched or do they look OK? Some of the pics I've posted from home look distorted when I look at them from work. -
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