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Water Bottle Car Fire Warning

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Message warns that a water bottle left inside a car on a sunny day could ignite the upholstery and start a fire.

Water bottle focusing sun onto plastic

Brief Analysis

The information in the message is true. Given the right kind of plastic container and the right environmental conditions, sun shining through a water bottle can indeed lead to combustion. A round plastic bottle filled with clear water can act as a lens that concentrates the sun's energy on one point.



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Subject: Starting fire with water

Or how I nearly burnt my car down

It's simple really...we do it all the time

Water bottle car fire hazard 1
...and I'd encourage you to try this at drives home the message quite effectively when it is demonstrated!!

Paper doesn't burn that easily

Water bottle car fire hazard 2

But that doesn't mean it won't...

Water bottle car fire hazard 3

Car upholstery was another matter altogether...

Water bottle car fire hazard 4

Each of these burns took less than 7 seconds!

Water bottle car fire hazard 5

Contributing factors
. Angle of sunlight
. Shape and clarity of bottle
. Bottle full of water
. Readily inflammable material

What can you do?
. Don't leave bottles in vehicles (or near windows in buildings) – cover them up if you have to.
. Better still...use purpose-built water bottles which are not made of clear glass or plastic
. Share this within the business
. Share it with your family and friends
. PS – you now know another way to start a fire in a survival situation!

Detailed Analysis

According to this warning, which is currently circulating via email and social media, leaving a filled plastic water bottle in a vehicle on a sunny day has the potential to start a fire inside the car. The message includes several photographs depicting how sunlight shining through a water bottle could potentially generate enough heat to start combustion. The last photograph shows several upholstery burns allegedly caused by a water bottle.

Given the right kind of plastic container and the right environmental conditions it is true that sun shining through a water bottle can lead to combustion. A round plastic bottle filled with clear water can act as a lens that concentrates the sun's energy on one point. Basically, the bottle acts like a magnifying glass. This magnifying effect can be easily seen if one looks at an object through a full bottle. As many of us will recall from childhood experiments, it is not at all difficult to burn holes in paper or dry leaves using a magnifying glass.

Thus, if the sun's energy is concentrated through a water bottle on to combustible material, then it is possible that fire could result. I conducted experiments using the same kind of bottle featured in the above photographs and I found that, by focusing the sun's rays through the bottle onto a thin plastic sheet, I could quite easily burn holes. The following photographs illustrate the results of one of my experiments. A hole was burned through the plastic after around 30 to 40 seconds of placing the bottle. A small indentation was also melted into the hard plastic tool-case that I used to support the bottle and plastic sheet:

Water bottle focusing sun onto plastic

Hole burned into plastic sheet Indentation melted into tool case

The phenomenon has also been captured on video by the New Zealand television program Fair Go. The program discusses damage caused to the upholstery of a Jeep Cherokee. The owner of the vehicle, Mark Gillings, first noticed the potential danger when he left a full plastic water bottle in the Jeep's backseat bottle holder on a sunny day. He subsequently reported the issue to the media and motoring groups in New Zealand.

An April, 2007 article on the program's website notes:
Mark Gillings of Queenstown came back to his car after a few hours fishing to find a burn mark on the back seat of his Chrysler Jeep Cherokee. It turned out that a full 1.25-litre Pump water bottle, which was sitting in the rear seat centre drinks holder, had focused the sun's rays like a magnifying glass on the seat about three centimetres from the holder.
Further investigation revealed a number of other cases in New Zealand. Thus, it seems clear that the phenomenon is real and the warning message is valid.

That said, according to the New Zealand Motor Industry Association, none of the reported cases actually lead to a car fire. In every instance, the damage was limited to small burn marks on the upholstery. Moreover, the majority of plastic water bottles have a series of surface ridges or indentations that seem to effectively disperse the sun's rays so that no one point can become heated enough to ignite. I conducted experiments with several types of plastic bottles, but I could only burn holes using those with clear, smooth tops. However, it should be noted that the "Pump" brand and other clear-topped plastic bottles like the one shown in the photographs are available in many Australian supermarkets. Also, there is a very large range of bottle styles available and some styles may only be distributed in specific countries or regions. Due to these factors, I could only experiment on a relatively small selection of bottle styles. And of course, the range of styles is even larger if you factor in plastic containers that originally held other liquids that may be reused for water, glass bottles, and bottles that hold clear liquids other than water. It is therefore probably safest to assume that any bottle has the potential to become a burning lens given the right environmental conditions.

Although incidents like the one reported in the warning message are probably quite rare, the potential for a serious car fire caused by a plastic water bottle certainly cannot be dismissed. Thus, the warning is worth heeding. As a precaution, it is advisable to remove plastic water bottles from cars left in the sun or cover them so that they cannot act as lenses.

Last updated: June 26, 2015
First published: February 7, 2008
By Brett M. Christensen
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