Walkie-Talkie Skyscraper Designers Didn’t Understand This Basic Survival Skill

by Paul Kirtley

Bushcraft instructor holding parabolic mirror focussing light onto smouldering tinder

Frontier Bushcraft Instructor James Bath demonstrating the use of a parabolic mirror. Photo: Duane Yates.

You may have heard of the so-called 'Walkie-Talkie' skyscraper. The £200 million building is situated at 20 Fenchurch Street in the City of London. The 37-storey glass-covered tower hit national and international news headlines due to it creating a beam of light that "melted cars". In a late summer spell of clear skies and warm sunshine, the curved surface of the building was found to be reflecting sunlight into a concentrated spot on the street below. This phenomenon is similar to that of focusing sunlight with a magnifying glass - a concept that many people are familiar with. The effect at work here, though, is that of a parabolic reflector. The reflective properties of a parabolic mirror have been understood since at least the 3rd Century BC, when the Greek mathematician Diocles wrote about them in his book On Burning Mirrors. Unfortunately the architects of 20 Fenchurch Street are not up on their classical geometry. Nor do they seem to be versed in basic survival skills. Focusing solar energy is an important method of ignition when it comes to fire-lighting. Indeed, using a parabolic mirror (or a magnifying glass) is a very reliable - and quick - method of gaining ignition in sunny climes where dry tinder is available. In Africa a classic tinder for this is a piece of dried elephant dung. In the photo above the tinder is a dried rabbit dropping. Jumping back to the City of London, the beam from 20 Fenchurch Street was sufficiently powerful to cause damage to at least one parked car and start a doormat in a shop on Eastcheap smouldering. A resourceful City AM reporter even used the concentrated heat emanating from the building, which has been quickly re-dubbed the "Walkie Scorchie", to fry an egg. On the hottest September day in 7 years, the beam of light - up to six times brighter than direct sunlight - was measured at a temperature of 110 degrees Celsius (230 Fahrenheit).

 

As mentioned in the above video, the property developers quickly produced a statement, which included "The phenomenon is caused by the current elevation of the sun in the sky. It currently lasts for approximately two hours per day, with initial modelling suggesting that it will be present for approximately 2-3 weeks." Hmmm, that's alright then, it'll go away in a couple of weeks. Very reassuring. I'm assuming, however, they've realised the Sun has a very predictable cycle and it will pass through this range of elevations again for the same amount of time next year? In fact, they don't even have to wait that long. Given the symmetry of the annual cycle around the Solstices, City workers should expect to be able to fry eggs in Eastcheap every April too. Let us know what you think in the comments below. Have you used parabolic mirrors to light fires? Or have you cooked an egg in an unusual way or location? We'd love to know...

Online News Articles:

Walkie-Talkie Skyscraper Beam 'Melts Cars' - Sky News; The Walkie Talkie melted my Jag! - Daily Mail; Eggsclusive: We use the Walkie Scorchie light beam to fry an egg - City AM.
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Paul Kirtley is owner and Chief Instructor of Frontier Bushcraft. He has had a lifelong passion for the great outdoors and gains great satisfaction from helping others enjoy it too. Paul writes the UK's leading bushcraft blog as well as for various publications including Bushcraft and Survival Skills Magazine.

 

{ 18 comments… read them below or add one }

Ray H

I imagine some coating can be applied to the windows that will scatter the light instead of focusing it in a single spot.

Or they can employ someone to demonstrate solar firelighting on sunny days?

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Stewart Lomax

I have a reflector like the one James is demonstrating. It’s incredible how effective it is at starting a fire but he really should be wearing sunglasses as the light is very intense.

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Paul Kirtley

Yes, now that you mention it Stewart, it’s strange that James isn’t wearing his shades. He doesn’t normally need much excuse…. 😉

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Paul Shakesby

Someone in the city of London had time to boil an egg using the sun’s rays from a skyscraper! If that is not the coolest thing I have heard this year, I don’t know what is.

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Paul Kirtley

I know, amazing. Those City boys will be inventing fire next….

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Sean

Yep, done that successfully using ‘roo poo as tinder. As Stewart says, you could really do with wearing sunnies.

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Paul Kirtley

Hi Sean,

Good to hear from you. Point taken about the sunnies.

It’s good to know that there are poo-tinder options in Australia too.

All the best,

Paul

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Craig

This sort of energy technology / science could be used to create FREE energy for the world…so why hasnt it been??? Cos the rich elite need to control us and keep us in servitude!! Nature always has the answer – man always hides the answer

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Paul Kirtley

Hi Craig,

I’ve stayed in camps with solar water heaters in Africa.

Here’s a site dedicated to making them:

http://www.reuk.co.uk/Build-a-Concentrated-Solar-Water-Heater.htm

Cheers,

Paul

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Will Northcote

Can the same be done with a reflector from a torch lamp?

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Paul Kirtley

Hi Will,

Yes. It’s the same principle which is being used – with a torch or car headlight reflector designed to have a single bulb in the middle – of creating a parallel beam from a point source.

Cheers,

Paul

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paul nicholls

Trust Henry to design a building that can be used to a light fire.Bushcrafters these days, there every where lol.On a serious note,i find cramp balls (Daldinia concentrica) very good tinder for this method.On a good sunny day it takes hold in seconds.Another benefit is they burn/smoulder for a long time.

All the best

Paul

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Paul Kirtley

Yep agreed Paul – that’s a good tip 🙂

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Steve Bayley

+1 for Paul’s suggestion of Crampball / King Alfred’s Cake Fungus as tinder for use with fire-lighting techniques using the sun. On a sunny weekend in Wales a few years ago (I know it’s rare!) Paul and Sue were practicing hand-drill fire-lighting and getting pretty good results fairly quickly. I thought I’d have a go with an alternative method and had a crampball burning within literally a couple of seconds using the magnifying lens on my compass. Sea-grass growing nearby could be lit with equal ease. My point here is to emphasise that we are sometimes use a ‘Bushcraft technique’ when something else might be easier. If I’m out somewhere wild I’ll have my compass with me so this is not as unlikely a method as it may seem and some people carry a swiss army knife with a magnifying glass giving another practical alternative to a parabolic mirror. Plainly this is unlikely to be a suitable method year-round in Northern Europe but it works and takes virtually no effort so it is something well worth keeping in mind. What other tinders work well with this technique?

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Paul Kirtley

Hi Steve,

It’s a good tip to remember that many baseplate compasses also contain a magnifying glass.

Flexibility of mind is certainly an asset in the outdoors. In some ways it’s the flip side of Malcolm’s comment regarding cheating on this fire-lighting article.

Sure, we should restrict ourselves when training; if we only ever use the techniques we are good at, then we won’t become proficient in others. Avoid the comfort ruts, if you want to become well-rounded in your abilities.

But equally, when you need a fire, be flexibile enough to use what you have available.

Horse’s Hoof fungus, Fomes fomentarius, also works well with this technique.

Cheers,

Paul

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James Harris

I’ve just come back from Turkey and all the hot water is heated by the sun in special heating tanks mounted on the rooftops, it was very efficient and good for the environment too.

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rman

Where can I get a reflector like the one on the first picture?

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Paul Kirtley

Hi there,

Am I right in thinking you are in Hungary?

The reflector is called a Sundance Solar Spark Lighter and is made in the USA.

In Europe it is available here on Amazon amongst other places.

I hope this helps.

Warm regards,

Paul

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