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Roof collapse – case study
The ‘Learning from incidents’ section of Brigade magazine includes case studies of major incidents researched by Fire & Emergency Management. Here, we analyse two roof collapse incidents.
A case study is an explanatory story based on a real-life incident that looks at what happened and why it happened. The aim is for people to learn from the case study so they improve their decision making in time-critical situations.
If you have any observations or initiatives you would like to submit from your own experiences in emergency management, visit the Observation Sharing Centre: http://www.surveygizmo.com/s3/1449131/observation-sharing-centre
Recently there have been a number of incidents where firefighters have entered burning buildings made from lightweight materials, either to fight the fire or carry out search and rescue. These buildings have then collapsed and exposed responding crews to a level of risk which may not have been anticipated.
Collapsed roof example
An Epping fire started in a bedroom of a single storey construction attached to the rear of a double-storey house. The fire spread horizontally through the roof void above the bedroom to where the single-storey pine roof trusses abutted a void between the ground and first floors of the dwelling. The void was created by the Posi-STRUT floor construction and allowed lateral fire spread above the kitchen. The first floor also contained a kitchen with heavy timber furniture.
Two crews fighting the fire had advanced lines to the centre of the home (the ground floor kitchen) using a thermal imaging camera due to a lack of visibility. The crews heard a crash one to two metres in front of them and crouched lower to the floor. The entire ground floor kitchen ceiling had collapsed on to the kitchen island bench with remains of the Posi-STRUTs still attached. The Posi-STRUTs had failed so only the sheet flooring (which was significantly deformed) was holding the first floor kitchen and heavy furniture. The failing of the Posi-STRUTs without warning in a low visibility environment was a near miss for crews.
Collapsed sub floor and walls example
A Torquay house fire started in the garage of a two-storey building and spread to the first storey through the ceiling/floor and wall cavities. The construction consisted of high-span ply I-beams which let the fire spread from one end of the structure to the other. The wall cavities allowed the fire to progress to the first floor ceiling space and the burning progressed via the ply inserts in the timber I-beams.
Firefighters were in danger when the internal walls and the floor of the master bedroom (shared by the ceiling of the garage) collapsed despite very little impact from fire. The main bedroom was completely unburnt. The collapse was caused by the lightweight construction beams and the gang nail fixtures becoming compromised and allowing the bedroom construction to fall apart. Following the collapse, the fire rapidly impacted the upstairs living area next to the master bedroom where two firefighters in breathing apparatus were conducting a primary search. Fortunately, the firefighters maintained their escape route and exited down the stairs to safety.
This incident was reported as a near miss and was investigated. As a result, several new initiatives are being developed by the Training and Community Safety teams.
There were also lessons learned about the ducted heating and cooling systems in this style of home. When the ceiling-mounted ducting (reinforcement wire) burns, it drops from the ceiling to the floor and can become tangled with firefighters’ breathing apparatus and clothing.
The main areas of concern in these two examples are:
- the integrity of high-span structural supports Posi-STRUT and ply I-beams in a fire)
- the lack of fire separation between an attached garage and the house
- the rapid fire spread through the walls, floors and ceiling space in concealed areas
- the unexpected building collapse
- the use of these construction materials puts occupants and firefighters in danger.
Signs of structural failure
Buildings and their individual structural elements can fail in a variety of ways. Structural collapse may be imminent when:
- cracks or bulges appear in brickwork
- a floor or roof moves
- ceilings are concave
- floors are concave
- walls are out of alignment
- unprotected steel distorts
- there is prolonged burning
- there is intense fire and loud noise.
Actions to take at structure fires
Firefighters attending incidents involving multi-storey domestic buildings should take into account the following:
- Refer to Dynamic Risk Assessment (DRA) to identify and manage risks associated with the intended ‘plan of operation’.
- Establish collapse zones (approximately 1.5 times the height of a wall) around areas in which wall collapse may occur. Barrier tape should be used to identify the collapse zone.
- Appointment of a safety Officer to monitor signs of building collapse and firefighter movements during the fire fight.
- Look for signs of fire or smoke issuing from points remote from the fire indicating rapid spread through internal voids.
- Assume that the pre-fabricated truss system has been compromised by the fire.
- Remain alert to the possibility of floor collapse (spongy or bouncy floors).
- Where possible use thermal imaging equipment to determine fire location and spread through a building.
- Restrict non-essential work and the number of firefighters entering the structure.
- Determine breathing apparatus control procedures early in the fire.
- Immediately withdraw to a safe location when any movement, sagging, cracking, spalling or any other signs of building or wall collapse are noticed.
- Conduct internal firefighting operations, where necessary, as close as possible to an exit and determine your escape routes.
- Always wear the appropriate protective clothing and equipment.
- Request expert advice such as from a municipal building surveyor.
Structural collapse is happening more often because of lightweight construction, so it’s vital that fightfighters are aware of the signs of structural failures and take appropriate action. Firefighters should keep up with modern designs of buildings and the potential impacts on their safety.
Firefighter safety must be given priority over all other fire suppression considerations and activities.