Unusual Cause of a fire

[jayjay]

See this link for an unusual  cause of fire

http://www.dailymail.co.uk/news/article-2229935/That-water-strong-stuff-Blaze-breaks-liquor-store-sunlight-ignites-vodka-bottles-shop-window.html

[SamFIRT]

Don't believe it ... there is another cause ... it just has not been discovered as yet. There is just not enough information in the sensational article to form an opinion as to what.

[Tom W]

Ok sensational headline but what they actually mean is that the sunlight through the bullet proof glass and the vodka bottles magnified the rays and burnt the cardboard. That seems a bit more likely right?

[Golden]

Another similar case in Hertfordshire recently as reported by the BBC.

http://www.bbc.co.uk/news/uk-england-beds-bucks-herts-20264972

[SamFIRT]

Whilst it is possible for sunlight to be focused to heat a point to the auto-ignition temperature of cardboard, (as we all know, as we have played with magnifying lenses as children), in my experience, it is not as prevalent as one would suppose. The sun has to be shining.... the rays have to be focused to a point and not diffused; this relates to the shape of the lens and the focal length of the lens. The item to be ignited has to have sufficient air supply.

In this case the gentleman in the article states:  'We have shades on the windows. We'll pull them down on sunny days to protect the wine on the shelves, never thinking it would ever start a fire...”.

It won’t.  Not if the shades are down it won’t. Does he mean the shades were not down on the day in question? Was it sunny? Where was the sun in the sky? What would be the focal length of a full bottle of vodka? Where would the ignition point be in relation to the above. How much does the window glass affect the above? What other ignition sources would there be at the point of ignition? What else does the CCTV show?

 I would be looking further myself. But then we don’t have all the evidence.

[Tom W]

Interesting points. I wonder how the business was doing financially.

[Midland Retty]

Piglet thats an incredibly sceptical outlook.... I don't how you could think that ! Someone torching their own property cos they need a few quid? as if!!!

Spoke to one of my fire investigation friends years back on the issue of direct sunlight as a source of ignition. He muttered something unpleasant, and asked if I wouldn't mind discussing something sensible!

[Mike Buckley]

Bear in mind that this incident did take place in America, (you know bigger, better, more outragious than anywhere else!) and their temperatures may be higher than our summer (what summer?). The other factor is that the owner drew the blinds on sunny days, however the store was closed the day of the fire therefore no owner to close blinds.

Two businees owners bewailing their losses, the first about the losses from the fire that burnt his place down. The second about the flood that ruined his place. First business owner to second, "Tell me, how do you arrange a flood?"

[kurnal]

One of the old manuals of firemanship or standard training books used to have a photo of a fire caused by a paperweight in a windowsill and the photos followed the scorched track along the wall. Thought it was 6A at first but on checking found it was not. Anyone remember which book it was?

And I hate to cast aspersions but I have seen this happen twice in my career. For definate. Absolutely certain. (Unless of course it was a passing steam locomotive that happend to go through the lounge)

[SamFIRT]

Kurnal......I did not say it could not happen. Just that it is not as prevalent as some may think. And I would say that if you only saw it twice in a long and distinguished career then ....QED.
 
In fact it happened only the other day in my FRS area. But this was only a scorch mark on a piece of timber furniture. I investigated one that destroyed a domestic property bedroom last year.  So, yes, it can happen; but not unless all the parameters are met. You see some people looking at plate glass, or a flat mirror and stating that could cause it. You see others looking at a convex mirror stating that could cause it, or a concave bull’s eye. But they won’t. Not unless the lens and or mirror can focus the light to a point. A convex mirror focuses the light to an imaginary point inside the mirror. A concave lens disperses the light rays. The opposite will focus EM energy (light) to a point and, provided the object to be heated is at the focal length, then heating may be sufficient to reach the auto ignition or smoulder temperature of the item on which the sun is focused and or start a smoulder possibly progressing to flame. Many times all that happens is the item is scorched.

It needs a bit of testing to prove the point. But firstly it has to be sunny and the blinds need to be up. 

Interestingly it does happen more often in the winter and spring seasons, when the sun is low in the sky. You sometimes see a scorch mark that describes an arc following the suns’ passage through the sky.

The link takes you to a Kent FRS example on the E Sussex FRS black museum. This time curtaining.

http://www.esfrs.org/blackmuseum/focusedLight.shtml

[Tom W]

I think a paperweights structure is more prone to magnifying sunlight than windows and a bottle of hooch though.

[Midland Retty]

Would have to agree Piglet.

My house is south facing and particularly in the summer when the sun is nice and hot and shining all day at the rear of the property, my lounge becomes something of a green house, infact it gets so hot that sometimes you can't comfortably sit in there.

I have glass ornaments on the window sill. They also get very hot. Never had any scorching though! Never had those ornaments or the odd empty wine bottle focus that light sufficiently to create a fire in my lounge.

So I won't say it can't happen, but I would have to say I remain rather sceptical.

[SamFIRT]

My point entirely

[Clevelandfire 3]

come on 8 extinguishers kurnal lets here about these two instances then in your career. i seam to be picking on you tonight. Not on purpose promise lol.

[nearlythere]

And I hate to cast aspersions but I have seen this happen twice in my career. For definate. Absolutely certain. (Unless of course it was a passing steam locomotive that happend to go through the lounge)

I don't think it would have been a passing steam locomotive going through your lounge K cos if it was you would have noticed a feckin great steam locomotive driving through your lounge belching steam and smoke and probably demolishing it and as I'm sure this did not happen you could probably rule out this theory.
I'm with you on this and not the members of the Forum's flat earth society who think that you can only light a fire with a match. I have heard of likelihoods as this as ignition sources from a fire forensic guy who I used for training Junior Officers in the Service.
I'm working with a similar type at the moment on a job and will ask him if he has come across such incidents or indeed any unusual ignition sources.