dryers

[potter 2]

Ive noticed a big upturn in the amount of fires in domestic dryers.A common point has been where the owner has pets and dried the cat/dog blanket in the dryer.The normal fluff filter hasnt become overly blocked,and the owners regulary empty it.The coarse hairs have been found inside the actual metal casing.They have built up a significant amount on all ledges and around the heating element at the rear.A lot of the hairs show signs of singieng and burning.They then appear to get drawn into the drum  and ignite or have come out of the back,especially where the vent tube hasnt been used and in some cases ignited debris on the floor.I visualised it like a Ray Mears programme  a handful of hair heated to a smoulder then a nice warm breeze passing over the fluff and it goes to flame easily.So I was wondering if any of you investigators had noticed this or if it has been looked at before.After any replies I intend to take it to our FARS regional meeting for their thoughts..Comments please

[Midland Retty]

Fires in tumble dryers are quite common.  The normal culprit is a blocked filter, or drying fabric which isn't designed to be tumble dried.

Ive never heard of cases where debris has gotten into the workings of the machine but clearly it is not beyond the realms of possibility for it to occur.

You may find little information exists on the phenomena you describe. This is because Fire Investigators don't normally get called out to fires involving tumble driers. They only tend to be called out if the cause of the fire is unknown or when there is reason to believe a criminal offence or act has been commited. Instead the officer in charge of the fire crew will write a report.

[kurnal]

These things tend to have air inlet, fan and heater element ducted together bit like a fan heater inside an outer box in which the drum turns, the hot air forced into the drum from the outside and exhausted through the centre at the front. Inevitably lint builds not only in the filter on the exhaust side but also some falls through the holes in the drum into the outer box.

Some how, if your theory is correct, dog hair hair is coming into close contact with the heating element to the extent that ignition is taking place, or the temperature of the air coming from the element is sufficient to ignite the residue dog hair and lint in close proximity, or there could be spontaneous ignition taking place as a result of biological, or chemical action in proximity to a heat source,  and oxygen from the air flowing by. Humidity could be another factor.

Air flow in the drum will be dependent on the size of the load, the nature of the materials in the drum, the availability of a good flow of inlet and exhaust air, the amount of water in the materials in the drum. The fan performance will be optimised for a certain combination of these. There will be a positive pressure in the cabinet and some leakage around joints etc is inevitable.

Here are some thoughts.
1- I would guess dog hair due to its mass compared to a fragment of lint may be more likely to remain in the drum and pass into the cabinet than a fragment of lint. There will be a factor as to the nature of the hair itself as to whether it iis likely to pass through the filter or the percentage that will do so.
2- If the lint filter or exhaust hose are obstructed then the fan will speed up, temperature and humidity in the drum may increase depending on the stage in the cycle. As the air flow drops the heating element temperature will increase, the radiated heat in the vicinity of the element will become a much more significant factor.
3- As the fan is then outside its optimum rating could turbulence  arise inside  the cabinet close to the fan itself which could cause air from the drum side of the fan impellor  to pass back to the inlet side taking with it any lint and hair which will be deposited on and near the heating element, rather like our fire pumps slipping water against a closed delivery?

It may be worth a FINDS message to see if this is a common occurrence.

[Clevelandfire 3]

Hair of any sort wouldnt cause a massive fire unless we are talking huge quantities of it. Hair would most likely frazzle into nothing when heat is applied to it. I cant see it starting a blaze myself. Have you got any reports or fdr1s or anything to back this up, hair on its own wouldnt cause a fire unless  there was a lot of it.

MR is correct in saying little study would have been done into this by fire investigators, unless their respective brigades have asked them to undertake case studies.

[potter 2]

thanks for replies.
Midland thats exactly how I came across it doing FI on strange fire.no obvious cause for kitchen fire.tracked down to extract from dryer.(no vent tube used)so i took it apart and found loads of burnt hairs.directly on the element which has little actual cover/protection.got some photos if you want a look or if anyone does.
Kurnal.good summary of possible events,dont think spon comb came into it.definateley build up of coarse hair
cleavland.quite a few examples now ive highlited it to ops crews.Its possible that  decent kitchen fires are being recorded as dryer/electrical when the damage is great,but ive found some with little damage that show the common traits ive mentioned.I also found ,very recently 2 severe public house fires in dryers where the licensee is using a domestic dryer to dry fluffy bar drip towels,so again a lot of coarse fibres were evident.going to try and find if any common makes are showing up on fire data bases.

[Clevelandfire 3]

Not being funny Potter but you are probably more qualified than most of us on here. Why didn't you tell us you were a fire investigator in the first place. We would have tailored our answers to suit. To be perfectly honest rightly or wrongly as an officer in charge I wouldnt have called out an investigator to a burnt out tumble dryer at all unless I felt there was something very funny about it. My gaffers would have thought I was taking the mickey to trouble you lot with something like that.I see from your response that this is commonplace. So educate your watches to ensure they make you aware of similar instances. I am genuinely suprised at your findings. Im sure others would be too.