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So apart from the impact on our lives, why are fires in warehouse
so different to fire in other buildings?
Here we have the fire triangle which I’m sure we are all familiar
with. It highlights that in order to start and maintain a fire we need
Oxygen, fuel and heat. Remove one of these and the triangle
collapses and the fire will be extinguished. It is on this principle
that fire suppression systems are based. In the case of sprinklers
systems they work by cooling the fire with water droplets and by
reducing the available fuel by pre-wetting the goods stored.
Figure 3. Potential risk at side effect increase
What we sometimes forget is that if we increase one or more of the
three elements then the fire size will increase. If you have more
heat, add more fuel or if you make more oxygen available then you
will have a bigger fire.
Warehouses by their very nature have the potential to significantly
increase all three sides of the fire triangle, creating bigger fires than
you would expect in say an office or shopping centre. It is against
this unique challenge that sprinklers have proven themselves
robust enough to tackle these difficult fires and yet adaptable so
that they can cope with the ever changing demands of modern
day logistics.
Figure 4. Effect of fuel side on warehouse fires
The amount of fuel available to a fire will certainly influence its size
and no-one can deny that in today’s warehousing we have high
concentrations of flammable materials.
We only have to walk into any DIY store to see mixtures of
flammable liquids stored next to aerosols and wooden furniture, all
to great heights and with little space between the racks.
In commercial distribution centres the situation is further worsened
as more goods of more variety are stored. As land becomes harder
or more expensive to obtain the result is that we store higher and
higher – 20meters or more is not unheard of – further concentrating
BİLDİRİLER KİTABI TÜYAK
PROCEEDINGS BOOK 2009
the goods. As fire travels vertically very quickly, this can have a
dramatic impact on the size of fire.
Packaging nowadays is almost entirely made of flammable
materials, from expanded polystyrene around electrical goods
to cardboard sleeves around food we add a huge amount of
flammable materials to what we store – making the situation even
worse. Even the pallets alone used in warehouses constitute a
severe fire risk and unused pallets should ideally be stored outside
of the building. So even if what you store is a relatively low fire risk,
the packaging alone may create a major fire risk.
Clearly if you compare this to other risks such as hotels,
supermarkets or office developments then the fire loading – or
available material to burn – is much higher.
Figure 5. Effect of oxygen side on warehouse fires
Now no-one is suggesting that warehouses have a higher
percentage of oxygen in their atmospheres but what can vary is
the amount of AVAILABLE oxygen to the fire. In other words how
much air is able to get to the fire to feed it with oxygen.
This is affected by the type of storage that is used and here we
can see some common types of storage arrangements. The
arrangement on the left called block stacking or palletised storage
where boxes are simply stacked on top of one another. This
arrangement is used primarily when the goods being stored are all
the same and the user does not need to get to individual boxes.
For example if you were storing 100’s of the same type if TV. In
this type of arrangement the air can only really get to the outside
of the boxes meaning that the fire will grow primarily up the outside
of the stored goods, limiting both the size of the fire and it’s rate
of growth. Of course, if your boxes are storing goods with large
amounts of trapped air then that can be a different story.
The arrangement on the right is a racked storage arrangement
allowing the user to get to individual pallets when they need. This
is typical of modern distribution warehouses. Here we can see
that each pallet is surrounded on all sides by a plentiful supply of
oxygen. Ready to feed the fire once it starts.
So it is not only what we store but the way in which we store it
which can affect the size of fire and how fast it grows.
The type of goods we store in warehouse has changed dramatically
over the last 20 to 30 years. The amount of plastics has increased
and of particular concern to us is the amount of expanded plastics
TÜYAK 2009
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