Forensics

Brick Kiln Collapses

Forensic Services Newsletter

Bricks are one of the first building blocks of civilisation. Because they are heavy, low cost, and the raw materials are to be found almost everywhere, brick kilns are commonplace and near to most population centres. They have their share of failures, for a variety of reasons, some of which are described in this newsletter.

The earliest kilns were chambers that had to be dismantled after firing to recover the bricks, but modern ones are designed as tunnels. There are typically two tunnels, one for drying and the second for firing. Bricks from the drying kiln enter the firing kiln, where they pass through three zones as follows.

  1. Preheating zone, where there are no burners, the bricks being heated by hot gases flowing along the tunnel from the firing zone.
  2. Firing zone, where the burners are located, heating the bricks until they vitrify.
  3. Cooling zone, where cool air is introduced.

On the left below is a kiln with the cars removed. The bricks are placed on cars that run on steel tracks, like a rail car, designed so the sides of the car are close to the kiln wall and keep the underside of the car cool (see below right). Above the car, the wall and roof bricks are subject to a temperature of over 1000oC, so all the modes of failure associated with high temperature can occur.

Once a kiln is started up it can run for years without cooling down and indeed this is desirable. Despite the inclusion of thermal expansion joints, the cooling of a structure over 100m long from high temperature will always cause damage to some extent, particularly if the cooling is unplanned and faster then normal. The photographs below show the wall and roof of a kiln that cooled quickly when a flood interrupted production and water entered.



Roof and wall bricks can deteriorate over time and this will partly depend upon the fuel used, with some producing aggressive atmospheres. The photograph on the left shows bricks that have deteriorated over time.

Sometimes collapses can occur in an inordinately short time after a kiln begins service, and the photograph above left shows a long section of missing wall in a kiln only months old. This was a result of a number of causes, with one being the accelerated deterioration of supporting bricks low down, below the level of the car floor.

The remaining portion of wall is shown in the photograph above right.






The photograph shows a cross-section through a deteriorated brick, which had even glazed on the furnace side, where arrowed.

A fact that may interest insurers is the developing practice in the brick industry of using sawdust to lower fuel costs. Kilns are retrofitted so that sawdust can be injected directly into the combustion zone. Increasing complexity of industrial processes often means increasing diversity of failure mechanisms and we have just encountered our first instance of a sawdust explosion in a brick kiln.

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