Fire safety in woodenconstructions

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.

The only downside to timber houses - it sounds too good to

be true.

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.

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 compartmentsDo fire compartments work in a timber building?

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

Fire compartmentsDo 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 from the building material is to be added

to this value

Fire loadEI60 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 firesThe 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 capacityTimber 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. 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

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

Other hazards

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?

Construction works must be designed and built in such away 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

The Swedish building act and ordinance

- 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