Fire caused by a magnifying glass focussing sunlight on to a bed
How this fire happened
The fire occurred on a sunny winter’s day in a resident’s second floor bedroom of a care home.
The elderly resident was not in the room at the time of the fire. The alarm was raised by the automatic fire alarm system fitted in the premises and the closed bedroom door contained the fire damage to the one room. The fire was extinguished by fire crews.
In this instance there were three magnifying glasses placed in a pot on the bedside table. It only requires one glass or plastic concave lens with the correct focal length to concentrate the sun’s rays on to combustible materials for ignition to take place.
The same results can be produced by shaving (convex) mirrors, spectacles, metal bowls, chrome reflectors, glass containers filled with liquid as will some decorative window glass such as Bull’s eye (bullion) and Flemish glass.
The Fire Research Station has estimated that 150-200 fires occur annually in the UK due to focused sunlight (Vytenis Babrauskas, Ignition Handbook 2003, FSP).
The effect it had
Every year, the Fire & Rescue Service attends a number of fires caused by the solar rays focussing through or onto a lens.
This cause is more common during the winter months – when the sun is low in the sky.
Care should be taken when placing magnifying glass, mirrors, spectacles or any other glass or plastic object capable of focussing the sun’s rays, in a position adjacent to windows (especially those that are south facing) and close to combustible materials such as upholstery, curtains, paper etc.
Consider putting such objects away or covering them with a cloth when not in use.
Get into the habit of closing internal doors, not only as part of a bedtime routine, but also when you leave your home unattended. Even a light internal door will help prevent smoke and heat from damaging rooms and contents remote from the source of a fire.
Remember to regularly test your smoke alarm.
In one case a uPVC window frame started to burn. Fortunately it did not develop into a serious fire, probably due to a build up of cloud and also the fact that there were no curtains in close proximity.
In the second case a fire causing significant damage was started.
The final example shows a magnifying make-up mirror sitting on a dressing table which had focused the sun's rays on to a nearby curtain. In this case, luckily, the fire did not spread.
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Latest Update : 30 September 2020