As intense heat scorches the UK, the Met Office has issued the UK’s first extreme heat weather warning in history. It follows record temperatures over the weekend, with temperatures reaching 31.6 °C (88.9 °F) in some areas – but that is only expected to get hotter. An amber warning for extreme heat is still in place in Northern Ireland, and some places in the UK have been expected to hit 33 °C.
However, the extreme heat is leading to some unlikely (and disastrous) events. On July 19, the powerful sun bearing down on an unsuspecting bus stop in Solihull reportedly caused it to spontaneously burst into flames. West Midlands Fire Service quickly attended the scene and doused the flames, but the fire had melted away a noticeable portion of the bus stop.
“Thank you to our colleagues @WestMidsFire service for attending this bus stop in Chelmsley wood within minutes of the call today after it self-combusted due to the intense heat, flames were doused and the stop made safe.” wrote Chelmsley Wood Police on Twitter.
It appears no one was hurt in the incident, but it certainly calls to question how well plexiglass shelters will fare versus the unprecedented heatwaves.
So, how did a solid plexiglass shelter suddenly ignite from just sunlight? No one can know for sure, but physicists have some ideas. The most likely explanation is an abnormally high ambient temperature, combined with the angle of light hitting the plexiglass became too much for the acrylic pane, which is flammable. Plexigas, the original acrylic safety pane manufacturer, claims their version can withstand up to 70 °C (158 °F), but it should be able to take much higher temperatures before bursting into flames. It fuses at a more reasonable temperature of 200 °C – so to erupt into flames and melt so readily, something else must be happening.
If the angle of the sunlight hits at the right point, it is possible to get an effect similar to total internal reflection. The rays would be reflected along the inside of the plexiglass, which under specific conditions could result in the metal frame increasing in temperature rapidly and melting the pane. Of course, this is only a guess, and if you have a better explanation feel free to get in touch with IFLScience – we would love to hear theories!
For now, the UK must continue to bear the intense heatwave. Owing to a recent series of drownings in rivers, the Met Office also warns UK citizens to be careful around open water as people head out to enjoy the sun.