Fire safety in wooden constructions Trustful solutions? Ville Bexander

Truths(?) about timber buildings The starting point of the architect is that solid wood burns on the surface but then chars. The construction is therefore dimensioned to retain its load bearing capacity after a fire. Wood is also fireproof because 15% of its mass is composed of water that will evaporate before it catches fire. When solid wood is exposed to high temperatures it does ´t burn, it only gets charred on the surface. The load bearing capacity is kept intact. The only downside to timber houses - it sounds too good to be true.

Wood building of shops and apartments in Älvsbyn, 2012

It is too good to be true ... Wood burns also when it starts to char

Fire compartments Do fire compartments work in a timber building?

Terraced house fire, Trosa, 2006 Terraced house fire,Vällingby, 2010

Fire compartments Do fire compartments work in a timber building Fire compartments Do fire compartments work in a timber building? - Yes, but not as well as in a concrete building

Fire load EI60 and R60 means 60 minutes with a normal fire load

The fire load in homes is 750 MJ/m2 The fire load in homes is 750 MJ/m2. The fire load from the building material is to be added to this value

Fire load EI60 and R60 means 60 minutes with a normal fire load - On the verge of high fire load in homes and combustible building materials pushes the value from normal to high fire load

Structural fires The Fire brigades’ capabilities

“A common denominator in these fires is what I would call structural fires, namely, fires in crawl space attics, in roof construction, in walls, floor or joists which we desperately hunted through the building without getting a break through.” - - - “As long as we take care of the fires in fire compartments we succeed. If or when the fire runs away into the building structure it increases the risk of a total loss drastically.” Lasse Nelson, Swedish Civil Contingencies Agency

Structural fires The Fire brigades’ capabilities - Fires i fire compartments: Excellent - Structural fires: Poor

Load bearing capacity Timber and steel: Load bearing capacity is a critical fire design parameter Concrete and bricks: Load bearing capacity is excessive due to the sustained bearing capacity under fire conditions

After a fire in a school in Bagarmossen 2011 After a fire in a school in Bagarmossen 2011. The building still stands…

Load bearing capacity Timber and steel: Load bearing capacity is a critical fire design parameter Concrete and brick: Load bearing capacity is excessive due to the sustained bearing capacity under fire conditions - The bearing capacity of timber buildings under fire conditions is dimensioned near the stipulated limit

Other hazards - Arson - Threat from other external fires - Fire spread between buildings - Increased risk of outbreak of fire - Hazards during evacuation with fire brigade ladders

Automatic water sprinkler system verified in accordance with EN 12845 Reliable Robust Proven

Residential sprinklers Intended as an extra protection in housing - Attached to the building's normal water supply system - Generally less water quantities - Only required in living areas - Cheaper installation

Residential sprinklers Reliable? Robust? Proven?

Is it legal to design and build houses that, if they catch fire, will burn down?

The Swedish building act and ordinance Construction works must be designed and built in such a way that in the event of an outbreak of fire: (1) Load-bearing capacity for a specific period of time (2) Limited spread of fire and smoke within the building (3) Limited spread of the fire to neighbouring buildings (4) People can leave the building in case of fire (or be rescued) (5) The safety of rescue teams is taken into consideration

- There are fire hazards in timber high-rise buildings - Automatic water sprinkler system gives good fire protection - Legal demands in high–rises is not allways enough Ville Bexander