A dust explosion in the fuel station
A dust explosion in the fuel station of a power plant created
a serious event. Unfortunately, people suffered burns, but fatalities
A power plant, built next to an industrial plant supplies heat
and steam to the establishment and to the local district heating
network. The power plant’s maximum electricity output is
85 MW. The fuel used is mainly bio-fuel, such as cull lumber and
sawing waste. The plant has a fluidised-bed boiler which makes
it possible to use a variety of fuel types.
Since wood fuel contains branches and stumps, the fuel to be
used is crushed to an adequate consistency before transporting
it to the boilers. Along with stumps, big stones may end up in
the crushers, which can generate sparks.
Conveyor system on fire
One evening there was a dust explosion in the fuel crusher. The
explosion propagated along the partitioned conveyor tunnels and
caused a fire in the conveyor system while setting off secondary
explosions, which propagated a fire in the receiving hoppers and
in a parallel fuel network.
At the time of these events, an employee of the transportation
company was cleaning the fuel unloading station area according
to received instructions. Gases from the dust explosion were released
in the unloading station and caused burns to the driver. Car drivers
working at the parallel fuel station also suffered moderate burns.
Rapid action saves thousands
The power plant personnel immediately began initial extinguishing
action and extinguishing vapour was discharged through the fuel
conveyor system. The fire department arrived in 15 minutes, began
extensive extinguishing action and emptied the fuel conveyors.
The fire did not reach the fuel silos. Thanks to rapid extinguishing
action the property damage did not reach EUR 100,000. The greatest
damage was caused by a pressure wave which tore off walls, doors
and fuel conveyors.
Actions to prevent similar accidents
After the event, it appeared that the spark detectors in the crusher
had functioned properly. However, these detectors cannot prevent
dust explosions which occur immediately when a certain dust mixture
obtains sufficient ignition energy.
To identify the cause, the fuel side was closely examined. It
was soon discovered that, during the day, some non-compliant loads
of too-dry bio-fuel had arrived at the plant, which might have
caused the formation of potentially explosive dust. The following
actions were taken to prevent similar accidents:
1) The crushers were provided with explosion vents and channels.
2) The reception of fuel at a low humidity level was no longer
3) The use of extinguishing vapour was increased with extremely
dry fuel and during maintenance and repair work.
4) In the future, the entire workforce will receive training on
the functioning and location of extinguishing vapour valves.
Rapid fire protection may prevent the very worst consequences,
but it is always possible to learn from an accident and try to
anticipate dangerous situations.