When firing with forest wood chips, the risk of fire is lesser than by firing with dry fuels. However, certain safety regulations must be complied with.
The fuel system should be equipped with an airtight dividing wall, thereby preventing fire from spreading backwards from the combustion chamber to the storage.
At most plants, the feeding systems are designed with an airtight “plug” of wood chips and a sprinkler system located just before the combustion chamber.
Attention should be paid to the risk of flue gas explosions. Unburned gases in an incorrect mixture with atmospheric air may cause extremely violent explosions if gases, e.g. due to a positive pressure in the combustion chamber leaking into the boiler room or the feeding system. Flue gas explosions may also occur in the combustion chamber if, e.g. the fuel due to suspension of operations has been smouldering with too little atmospheric air,
and air is suddenly introduced.
In the wood chip storage one should beware of the risk of spontaneous combustion. Here storage height, wood chip storage time, moisture content, and the
access to air will be a decisive parameter.
During firing with wood pellets and dry wood waste, there is a risk of dust explosion in the storage and the feeding system. Here fire extinguishing equipment should be built in just before the boiler. The risk of fire in the fuel storage also applies to pellets.