The elderly occupier of the house would use a microwavable wheat bag as a replacement for a hot water bottle.
She would regularly get up in the night to re-heat the wheat bag in the microwave and return to bed with the heated wheat bag.
On investigation a smouldering fire had been confined to the bed within the front ground floor bedroom.
On examining the bedding, a large quantity of what appeared to be small beans or grains was discovered within the bedding.
They appeared charred and blackened and were contained within one area.
Research was carried out for HM Coroner and the results showed that, the wheat contained in the tested microwavable personal warmers produced an exothermic reaction and thermal runaway at temperatures above 225oC.
These temperatures can be produced in reasonably short periods of time in a microwave oven which is working normally.
The time is significantly reduced if the turntable is either defective or obstructed in any way, if the turntable is in-operative it can produce high temperature "hot spots" within the bag.
There was no heating information directly on the products tested.
The lack of information on the product appears to be a major contributory factor to the overheating of the wheat.
The British Standard clearly states that the product itself should be permanently and legibly marked.
Like any product, wheat bags should only be used in accordance with manufacturers instructions and must not be placed in a microwave at either too high a power setting and / or for too long a time.
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Latest Update : 01 October 2020