SUNS LIGHT / SOLAR RAYS CAUSING FIRES (Again)

[firstforensic]

Sorry to resurrect this again but it seems to be silly season this summer: I accept that you can’t always believe what you read in the paper but “no smoke without fire”? Three recent examples:

1) Sunlight shining through a glass barbecue table set fire to a fence and two adjacent heating oil tanks.
Has anyone seen these tables? What would their focal length be I wonder? Set fire to a fence an all; not just a piece of tissue paper.

2) Fire investigators believe the paperweight concentrated the sun's rays on to a pile of books and set them alight when it was left in the first floor conservatory during last month's mini-heatwave.  “I had a small, glass paperweight in the conservatory on the window ledge and it's the only thing that fire investigators have decided could possibly have caused it”.

(You’d be lucky to set a pile of books alight with a blowtorch much less a paperweight. No possibility of a deliberate ignition then?)

3) A spokeswoman for **** Fire and Rescue Service today confirmed the crystal ball was to blame for the fire. She said: "The homeowner had a crystal ball on the window sill and direct sunlight refracted through it into her living room. It then set light to the television near the sofa and caused the fire.”

(I’m sure someone could work it out; but assume the TV about a metre away from the windowsill so I’d guess to get this focal length would require a crystal ball about 6 feet diameter? More chance of being crushed to death?)

[kurnal]

Well I will hold my hand up and say I have attributed two fires to this. One was a due to a shaving mirror and the other to a paperweight. I never did the physics but the evidence was strong. The paperweight in particular had led to a whole series of scorch marks on the table nearby to its usual location. The lady of the house moved it to a new location on the window sill where it then set fire to curtains which burned, fell down and damaged the carpet.

[Clevelandfire 3]

Were you in fire investigation long?

[firstforensic]

Kurnal
I have no issues with this as a potential source of ignition which needs to be properly considered - it just appears to be used sometimes as an alternative to "unknown"

Cleveland 3
This seems like a new discussion thread?

[John Webb]

Re Item 2: The vertical surface of a stack of books will catch fire from such an intense source and the fire will spread up the face of the stack. If hardbacks, then further spread is relatively slow. If paperbacks (or magazines) the top of the top magazine will catch fire fairly quickly. If curtains are close then these can be set alight and the fire further spreads...... (Observations from various test fires for the British Library and for DoE.)

[firstforensic]

Thanks John

Can you give me the specific references to this. Who did these tests? When? Is it published anywhere?
Thanks

[John Webb]

The work for the British Library was for a film in the 1970s entitled "Keeping your words" about salvaging books affected by fire, flood etc. The work for DoE was part of a series of tests on various retail and other public place scenarios measuring the effectiveness of sprinkler protection and possible use for life safety. A summary of this latter work was published in the IFE Journal in an article by Penny Morgan around 1998/99 after I'd taken my early retirement from the Fire Research Station in 1997. I can't lay my hands on my copy at the moment, alas!

[firstforensic]

Thanks again John

The info I have from Penny Morgan indicates that this was used as a "what if" scenario and was not the result of any experimental work. So still no evidential/experimental work to suggest that piles of books can be ignited this way. Loads of anecdotal.

[Boat Safety Scheme]

Sorry to resurrect this again but it seems to be silly season this summer: I accept that you can’t always believe what you read in the paper but “no smoke without fire”? Three recent examples:

There have been several fires on boats started by rays being focussed and insified through domed decklights or bullseyes as the boating community call them. These look like giant magnifying glass lenses. They are used to introduce daylight into dark parts of boat interiors.

Checks for charring and heat damage have now been introduced as a part of the Boat Safety Scheme examination this year. A warning was put out in 2007 on the same subject http://www.boatsafetyscheme.com/downloads/NR0507%20Advice%20to%20check%20for%20heat%20damage%20near%20decklight%20FINAL.pdf

Futher guidance on fire protection on boats will be to not have any combustible materials within 300mm of any domed decklights.

We have no sources of any properly researched and documented mitigation measures to prevent the focussing of the rays at the given focal length of the magnifying glass

Rob
Boat Safety Scheme

[Midland Retty]

Interesting stuff Rob

Do you know if the Maritime and Coastguard Agency issue similar advice by chance?

[Boat Safety Scheme]

Do you know if the Maritime and Coastguard Agency issue similar advice by chance?

I'm not aware of anything from the MCA, but it does have a representative on our committee who will have been kept informed of our risk review and mitigation.

I have some photos available now and a copy of our latest news release by way of further illustration of the risk. In one photo you can see the tracking of the rays in the pyrolysis of the wooden surround.

We also have record of incidents where loose objects in the focal path have started to burn.



As a general plea to any FI in fire authorities or in the insurance industry, we are very interested in any boat fire information identifying root causes whether, behavioural (eg inadvisable use of petrol) or as in this case, inherent in the installed arrangements, or indeed a mixture of both.

Current topics of hot (scuse the pun) interest are solid fuel appliances, petrol fires, electrical fires. you can see our contact details in the press release. Either Dave Washer or I, Rob McLean are the best contacts for anyone with information.

Regards
Rob

[firstforensic]

Rob

Thanks for that interesting obsesrvation. We plan to do some tests on various items (often quoted as the culprit) to determine such things as focal length and hope to be able to offer a more scientific assessment of the risks. If you are able to get hold of any of these boat "bullseyes" we would be happy to test them and see if the 300 mm rule is sufficient. Likewise if anyone else has items they'd like tested we'd be delighted to include them in the research.

regards
Andy

[Boat Safety Scheme]

Rob

Thanks for that interesting obsesrvation. We plan to do some tests on various items (often quoted as the culprit) to determine such things as focal length and hope to be able to offer a more scientific assessment of the risks. If you are able to get hold of any of these boat "bullseyes" we would be happy to test them and see if the 300 mm rule is sufficient. Likewise if anyone else has items they'd like tested we'd be delighted to include them in the research.

regards
Andy

Andy,
That's a great offer which we would like to take up. We will arrange to have samples made available for you. There are various designs and sizes.

Would you like to call me on 07710 175478 or 01923 201278 to discuss details.
Regards
Rob

[SamFIRT]

Hi. I have read this thread with interest. Taking into account the fact we all know the sunlight can be focused to cause ignition in combustible material, the debate in our brigade has been whether this can occur once the light has already passed through glass. i.e. if the light has already been refracted before it is subsequently focused. I have just been doing a couple of experiments. Using a 10 x magnifying convex lens from our FI van I was able to ignite paper with ease using direct sunlight. Ignition occurring in seconds once the light was focused. I repeated the experiment with the sunlight passing through a double glazed kitchen window. Slower ignition but it still worked. So I repeated the experiment in some vehicles. Hummmmmmmmm didn’t work. Same strength of direct sunlight, same lens , same paper. Heat was generated but not enough to cause scorching of the paper let alone auto-ignition. I am of the opinion this may well be due to the polarising glass used in vehicle windscreens and side screens. Does anyone know of any research into this?

[Midland Retty]

Hi Sam

I cant point you in the direction of any definitive research, but if memory serves me right London Fire Brigade's FRIT team did some experiments with bullseyes and different types of glazing a few years back. Im sure that their tests demonstrated that the chance of ignition was reduced when polarising glazing was used.

.