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Much has been made of tumble dryer fires in the news recently; a number of household fires and some fatalities have occurred as a result of defective tumble dryers or of users not cleaning their machines properly, however these are not the only causes of fires in the dried laundry.

If you don’t clean the filters of the tumble dryer or you continue to use the machine, even though you can detect an odd burning smell each time you use it, there is no surprise perhaps when the machine bursts in to flames at some point or incinerates the washing inside it. But what if you have taken the laundry out of the dryer and stacked it neatly in the airing cupboard or in a plastic laundry basket for putting away later? Or maybe you are drying someone else’s laundry and you have tied it up in a plastic bag for transporting? Would you expect it to suddenly burst in to flames perhaps hours later?

It happens, it is not that common thankfully but there is much evidence out there to support several studies of the possible causes of “spontaneous combustion” of laundered textiles.

It seems that whether it concerns commercial laundries that dry tea towels for restaurants, restaurants doing their own laundry or home launderers, a number of fires have occurred when the dried laundry is left in piles, trucks or bags ready for re-use. Researchers have dubbed this “Spontaneous Combustion”. It might be less frequent but there are instances where home laundry has burst in to flame or as some would describe it, exploded!

Auto Ignition

The researchers say this is caused by oxidation within the laundry when it is hot i.e. it begins whilst it is still in the dryer. If the laundry has not been allowed to cool down fully before folding or packing, then that oxidation continues and because of the packed nature of the materials, the heat from oxidation cannot escape or dissipate, so it builds up to a point when the internal temperature reaches the “auto-ignition temperature” for the material and a fire starts.

Auto ignition temperatures of some fibres

Fibre

Ignition Temperature (°C)

Cotton

255

Viscose

420

Nylon

575

Polyester

560

Wool

600

Oxidation

Oxidation is a decaying process; the reaction caused by the combination of materials in the laundry with oxygen, which then produces a chemical breakdown of the material and consequent heat generation.

In the case of fire, it is the reaction of combustible material with oxygen that produces heat release. As the temperature increases so does oxidation – a sort of chain reaction. When heat cannot be dissipated, as we have already said, it builds upon itself and because the bundle is insulating the heat inside, fire can result.

Fabrics, especially those with high cotton content, are combustible either as cloths, uniforms, rags or lint. The ignition point for these materials is referred to as the critical surface temperature. Cotton begins to oxidise at a surface temperature of 95 degrees centigrade.

Remember: the more flammable the material is and/or the denser the pile of the material is, the greater is the opportunity for fire.

Contamination

Another source of fuel and oxidation in laundry is contaminants even if only as traces left in the fabric after laundering. Described as “unsaturated fats”, these originate from cleaning products, cooking oils, sweat, animal fats or mixtures of plant oils and mineral oils (such as would be used in gymnasiums and health clubs). If the laundering process is not sufficient to remove these contaminants from the fabric, the opportunity for oxidation and therefore fire from spontaneous ignition increases.

Moisture

We have mentioned moisture in the above paragraphs; this too can cause heat to be generated, adding to the heat from the drying and that from oxidation. This is “heat of wetting”. This is not normally a property of great interest to textile people. It is mentioned to students in their early years, usually about wool, to demonstrate how interesting textiles are. It is said by way of an example that Scottish gentry wear wool plaid and Harris Tweed etc because of the Scottish climate in the Glens. The wetness of the atmosphere causes an exothermic reaction in the wool which then keeps the wearer warm. Wool however is not the only fibre to exhibit this property (see the table below). Of course in a case like a closely bound stack of hot, moist laundry, unlike the Laird’s tweed jacket, this heat is contained and cannot escape as we have shown above and simply adds to the rising temperature inside the bundle

Heat of Wetting

Fibre

Heat of wetting (joules/g)

Cotton

46

Viscose

106

Wool

113

Nylon

31

Polyester

5

Heat Sources in the Laundry that contribute to spontaneous ignition

1.    Heat from the dryer.

2.    Heat trapped in the items after drying and piled in carts or stacks without sufficient cool-down.

3.    Heat from external sources when stored in a constantly warm place as in a sunny area or airing cupboard thereby adding to heat contained in them from the drying process.

4.    Heat from the oxidation reaction.

5.    Heat of wetting

If the hot moist bundle is stored in a plastic basket, plastic bag or as with some commercial laundries, a plastic wheeled bin, the risk of fire is increased simply because the plastic e.g. polyethylene, is not only an insulator reducing air circulation, but may have a low “auto ignition temperature” itself making this a primary cause of initial ignition!

What to do to avoid fires in or around the dryer

1.    Ensure the dryer is well maintained and the exhausted air is not restricted in any way.

2.    Ensure there is no build up of lint in filters and ducting. Clean them regularly.

3.    Always allow the dryer to go through its “cool down” cycle fully before unloading the machine.

4.    Allow the laundry to air and cool properly before storage.

5.    Never store warm laundry in drawers, cupboards or airing cupboards until they are cool.

6.    Don’t leave warm laundry unattended in piles or stacks and especially not in plastic containers.

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