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Fire caused by mirored glass

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  • Fire caused by mirored glass

    I am looking for any case studies or information regarding occurances regarding mirored type glass used in the construction on the roofs of sunrooms. I have had two fires in the last week at the same residence which may have been cased by these panels on the next door neighbors home. It is possible that these panels(which were installed two years ago) ignited the untreated cedar shingles on the neighbors home caused by the relection of the sun. It is obvious that the fires have started on the exterior of the structure and in the same place. There was no power to the structure at the time of the second fire due to renovation work being performed. No work crews were on site at the time of the second fire. Both days were very sunny with high temperatures. I am asking for your thoughtsd and opinions. I am sending a sample of the cedar shingle to the lab for anaysis of moisture content and setting up field tests to determine the rate of rise temp of the shingles and the maximum temp during the next sunny day. The fires started at the same time of day during the same type of atmospheric conditions in the same location. Any thoughts would be appriciated

  • #2
    Further to my above message. The field testing was done today and an analysis was done on the mirrored roof which produced a one inch depression which made it like a giant concave mirror concentrating the reflection of the sun to one specific area of the house and moving the reflection slowly as the sun moved. The readings had a very large varience and showed concentrated reading of 140 degrees F. Not enough to ignite the wood today due to cloud cover and the angle of the sun moving slightly.

    I have learned this has happened once before in the city but was not reported to the fire department as no fire occured but the reflection was strong enough to melt the vinyl siding off a house. Has any one else heard of this?


    • #3
      Now here is one that you can talk about for some time. I know that there is a discussion on this topic in Kirk's Fire Investigations. In those discussions, the speak of a simular incident with a bathroom mirror.

      My question would be what has changed since the panel was installed. If they have been there for two years, why is this the first occurrence? I guess the cedar could have lower moisture content as it ages. The sun will track the same path each year; however, will be at a different elevation on the horizon. If you do field tests, you better do them quick. To repeat the same results, you need to have the sun at the same angle.

      Keep us posted, this seems kinda cool if nothing else. What a great way to get rid of that neighbor you don't like. "I swear officer, I thought these large concaved mirrors were a great addition to my siding"


      • #4
        Further tests will be conducted after the same number of days after the summer solice. Lucky for me I only have to wait several weeks to get the same effect....Weather permitting


        • #5
          I would strongly suggest you stand back and take a very hard and objective look at the suggested hypothesis of mirrored glass panels suspected of causing the fires. While what is suggested can occur, there is usually far more plausible answers for fires to occur.

          Sound to me like you are well aware that you are dealing with simple Physics Principles here....In order for the sun rays to ignite an object from a reflection, they need to be focused, so that the heat flux (watts/m*2) is such that it can raise the temperature of the shingles above the ignition temperature. So your tests should be able to assist you in your quest for the answer.



          • #6
            The final testing has been completed. I made a false wall or target from some of the original shingles from the house ( The house now has new cedar shingles after renovations. The tests were conducted after the same amount of time had passed after the equinox so the sun would be in the same position. Temperatures were close to the same and all other conditions were as close to the original as I could manage.

            The results:

            The cedar shingles reached a temperature of 398 degrees F in a matter of seconds and smoke was visable from the wood target almost immediately. Also the reflection was very concentrated and melted a black hard plastic case used by one of the workman that was on the staging in a matter of a few moments. Standing on the staging proved a bit of a challenge as the reflection moved because it became extremly hot and I was unable to stand it for more than a moment or two. It felt like some was holding a lit match to my face.

            Something to think about as this was certanily a very unusual case. I would appreciate hearing from others who have had similiar experiences. Also if any one wishes to see video of pictures of the experiment they are available by e-mailing me at [email protected]


            • #7
              I am an investigator by trade but this fire occured at a friends house.This friend was going to install a window in a solid wall odf his house he removed a round convex window from this wall and placed at the exterior leaning against a picnic table. He then went to the hardware store for some supplies to install this window. upon his return approx. 20 minutes later he foubd that ther was a hole begining to burn through his cedar shingles.It was clearly the result of the sun reflecting of this convex mirror. if he had been gone for any length of time I doubt anyone would have identified this mirror as an ignition source.As you have stated it is certainly food for thought.Mike.H C.F.I


              • #8
                I had a similar situation in a way except that it was in an automobile. A man came in and asked for my help in figuring out how this burned streak happened. It was across the inside of the roof of his car starting on one side and going across to the other side with cloth, matting and plastic burned. To make a long story short, I finally figured out that he had had a make-up mirror belonging to his wife in the back floorboard. We reproduced the original scene here at the fire station and when the sun hit the mirror, sure enough it almost immediately started burning the headcloth with 1/16th of an inch of the original burn. It was btw, the magnified side. Very interesting!


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