Beware: A magnifying glass is a fire hazard

Be careful of free-standing magnifying mirrors, glass ornaments, magnifying glass or paperweights that may be exposed to direct light because they can catch fire in the sunlight. Do not leave mirrors or glass ornaments on window sills because they are a fire hazard. You will be surprised by the extent of fire damage and smoke they can cause.

This is an all year round risk, fires don’t just start when it’s hot in the summer because sunlight gets into the house all year around. Fires from magnifying glass or mirrors tend to start in the winter when the sun is low in the sky.

Do not place reflective items like a magnifying mirror or magnifying glass in direct sunlight because they are a fire hazard.

The reason they are a fire hazard and can cause a fire is because they intensify the sun’s rays. The sun’s rays bathe the Earth in a constant flow of thermal energy spread over each square metre of the planet. While this tends not to be strong enough to ignite paper, wood or other combustible substances, if the rays are focused, the flow of energy becomes concentrated enough to exceed the threshold for combustion. Fire damage can spread throughout the house or business very rapidly if the fire is not detected.

It’s the photons in the particles that carry visible light from the sun to the earth. They also contain energy in the form of heat. Through the use of a magnifying glass, the path of these photons are narrowed to a highly localized area (the dot of light that passes through the lens). This results in a concentration of heat that can reach incredibly high temperatures, approximately 450 degrees Fahrenheit. Then the glass will catch fire or objects nearby like curtains will begin to combust.

magnifying glass

The key to localizing photons is in the convex shape of the magnifying lens. This shape collects photons on one side of the lens and draws them to a single point as they enter out the other side. As such, any item with a convex lens can be a fire hazard. For example, a pair of glasses or a binocular lens can also be used but a magnifying glass or magnifying mirror is bigger.

The larger the lens, the easier it is to start a fire and cause significant fire damage.

The steepness of the convex shape also plays a part in achieving the extreme heat needed to achieve combustion.

Magnifying glasses concentrate the sunlight very effectively, refracting the rays and bringing them to a tight focus. But even fragments of glass can have some focusing effect – with potentially disastrous consequences.

The sun’s rays can be magnified by a lens or magnifying mirror and become focused on a nearby object such as curtains, clothing or even wooden or plastic furniture, fixtures or fittings.

This can cause scorching, or charring potentially leading to smoke, smouldering or an actual fire.

In the evening, morning and during the winter, when the sun is lower on the horizon, the shallower angle at which the sun’s rays hit the earth means that it is particularly important to be aware of objects that can cause a fire hazard. These can be magnifying mirrors, and glass ornaments or a magnifying glass, which may be left exposed to direct sunlight.

Most commonly this is because glass objects like magnifying glass and magnifying mirrors are placed on the top of shelves or drawers which are next to a window according to East Sussex Fire and Rescue Service.

While fire caused by everyday objects may seem like one of the more unusual cases, in principle it is the same as focussing the sun’s rays with a magnifying glass and everyday objects can be a fire hazard that set light to things like curtains in the home.

Keep your window sills clear to protect your home and its contents from fire damage.

In the last 5 years there have been 125 fires reported which have been caused by the sun’s rays. Every business and home owner also needs a smoke alarm fitted on each floor of their property to detect smoke so that fires can be prevented before they happen.

magnifying mirror

Charles Piton Ltd attended a fire in the last month which was started by a magnifying glass. If you raise the alarm quickly, a bad fire can be avoided but in the summer, a woman was out in her garden when a glass ornament caught fire in a living room window. In the end the whole house was gutted because the blaze spread very quickly. Keep doors closed to contain any fire that may catch you unawares.

Fire fighters said the ornament concentrated the sun’s rays like a magnifying glass would. The fire took place in Bognor Regis and spread so quickly that the occupants had to move out while fire restoration work was done. If you have a property that is fire or smoke damaged, call Charles Piton’s 24 hour emergency number day or night. Our team will inspect and record the damage for your insurers, store, refurbish and restore furniture and fittings, remove any fire hazards and the smell of smoke, cleaning away any trace of fire damage.

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