Building collapse dangers
PHOTO AP/Stephen Morton
Federal investigators look over the scene after the Charleston fire.
The loss of nine brothers in Charleston, S.C., in June forced me to recall and review structural collapse indicators in the size-ups and ongoing structural assessments during fireground operations.
This article is not meant to point fingers at any department or individual. But the horrific tragedy in Charleston requires that we learn as many lessons as possible from it, and train our personnel in the hope of reducing the odds of this type of event from occurring again.
Structural collapse in a fire-based scenario is impacted by numerous possible causes. Being aware of these causes can assist the interior officer or acting officer in cataloguing a factors to consider when fighting fire inside or outside the structure.
While the following list is in no way complete, it serves as a prompt when evaluating the stability of a burning structure you are working in or around.
1. Building construction type
2. Occupancy type
3. Age of building
4. Known structural remodeling
5. Walls out of plumb/bulging/bowing
6. Deteriorated mortar joints and masonry
7. Cracks in exterior or interior walls
8. Water/Smoke coming out of cracks in masonry
9. Sagging floors
10. Truss construction
11. Fire impinging on the dead load support structure of the building
12. Significant volume of fire
13. Significant fuel load
14. Impact of suppression activities on structure
15. Length of interior operations
16. Sound made by a moving building: groans, cracks, etc.
17. Multiple fires in the same building or damage from previous fires.
All of these factors will assist the initial fire officer when making the offensive versus defensive attack decision. If there is no known rescue impact on the fireground and the fire is of a significant enough size at the onset, the officer must question whether or not to initiate a defensive attack.
This decision should be made when considering total on-scene resources, the time required to control the fire and the ability to match resources with tasks. It should be based on:
• The projection of the fire involvement
• Resources required to match tasks
• Projection of the time the crews are able to deploy hoselines into areas for suppression versus the amount of extension the fire will move in the same timeline.
Remember, anyone can make the decision to make an interior attack because "that's what we always do." As officers, we must make fireground decisions based on reality, not tradition or repetition.
The company officer should ensure that a best "guess" is applied to the time window for total fire involvement. This is primarily critical in any structure that utilizes a truss system to support floors or roofs.
Recent research shows that fires in wood truss systems may last anywhere from five to 15 minutes of direct flame contact. Metal truss systems don't fare much better — while they can hold up for a little longer than wood truss systems, they tend to lose their tensile strength quickly or expand to push support walls out and collapse. In addition, remember trusses are built as systems and generally collapse as systems.
The incident commander must keep total fire times at the forefront of their mind to ensure minimal interior time for crews.
If the company officer decides to initiate an interior attack, some primary acts should be taken to ensure the safety of the crew is paramount. Thermal imaging cameras (TIC's) should be utilized if they are on the fireground. Get a good feel for where the heat lies within the structure before entering. Bring pike poles to enable initial crews to "pop" ceiling tiles to ensure they don't have fire doubling back over their heads and possibly cutting them off from their primary egress point.
Once you are able to visualize the roof / floor construction, advise command that you can confirm the presence of a truss system. Use extreme caution and follow standard operating procedures when operating on or under truss systems. When possible, open ceilings and other concealed spaces whenever a fire is suspected of being in them, but remember that opening concealed spaces may result in a backdraft.
Have a hose line available to assist in reducing pre-flashover temperatures and to assist with immediate suppression if needed. Try to position your crew between the nearest exit and the concealed space to be opened and advise other crews in the area you are working in of your actions. Finally, understand that fire ratings for truss systems may not be truly representative of real-time fire conditions and that truss systems' performance may be affected by fire severity.
During the incident, you should continue utilizing the TIC to track the progress of the fire. Using interior and exterior TIC's can assist interior crews with confining and/or extinguishment of an interior fire.
Don't hesitate to utilize fog patterns to assist with reducing ceiling temperatures below that point where rollover is visible. While know that this may disturb the thermal balance, it's better a little warm than caught in a flashover.
Crews can also utilize nozzles to assist in "freezing" metal trusses in place. While this may not prevent a truss system from eventually collapsing, they can assist in locking it in place until crews can evacuate from a hazardous environment.
This maneuver should not be utilized as a standard procedure but only as an emergency process while facilitating the evacuation of your crews. In addition, when possible, coordinate exterior ventilation activities with interior suppression and rescue operations, although ventilation for the sake of ventilation can cause more problems than it solves.
The primary thing to remember is to evacuate firefighters performing operations under or above trusses as soon as possible if it's determined that the trusses are exposed to fire. An immediate operational shift to a defensive attack should be strongly considered.
Defensive operations are the safest way to extinguish fires in truss-constructed buildings. Once the fire is out, and in an effort to keep firefighters safe after evacuation, use defensive overhauling procedures and. use outside master streams to soak the smoldering truss and prevent rekindles.
Remember that we have a responsibility to ensure anyone operating in the post-fire environment is kept safe from collapse when investigating the fire. If you are unsure whether or not the structure is unsafe, contact an engineer from your local building department, or even better, a structural collapse engineer from a local FEMA/USAR resource.
NIOSH also recommends that fire departments take the following steps to protect firefighters:
- Conduct pre-incident planning and inspections to identify structures that contain truss construction.
- Ensure that firefighters are trained to identify roof and floor truss systems and that they use extreme caution when operating on or under truss systems.
- Develop and implement standard operating procedures to safely combat fires in buildings with truss construction.
- Ensure that the incident commander conducts an initial size-up and risk assessment of the incident scene before beginning interior fire fighting.
- Use a thermal imaging camera as part of the size-up to help locate fires in concealed spaces
Fighting fires in truss-constructed occupancies is now the rule and non-truss buildings are the exception. We will be fighting fires in these structures for the rest of our careers. If we fight fires in as a professional manner as we say to the public, we should become practiced and educated regarding fires in truss systems.
Take time to learn all you can from various articles and books available for your education. Firefighters can find a rapid checklist for these details regarding fires in truss constructed buildings at NIOSH's website. We owe it to ourselves, our personnel and their families to be as safe as possible.
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