A Building in a Bag

Every year disasters and wars leave homes in ruins or drive people from them. One of the first tasks of emergency workers is to provide shelter--typically in the form of tents.

As anyone who has ever served time--er, spent time camping knows, however, a tent is not something you want to live in indefinitely. When you're camping you know you'll eventually get to go home. When you're a refugee, there may be no end in sight.

What's really needed is a more permanent structure that can be erected almost as easily as a tent--and as an article by Rowan Hooper in Wired News describes, that's just what a couple of London engineers, William Crawford and Peter Brewin, have come up.

Their "building in a bag," dubbed the Concrete Canvas, is a sack of fabric impregnated with cement. You add water to the bag, inflate it with air, and in 12 hours your shelter is dried out and ready for use. A 230-kilogram bag would inflate to a shelter with 16 square metres of floor space.

The shelter is described as Nissen-shaped, which means it's a half-cylinder. Lt. Col. P. N. Nissen invented the Nissen Hut during the First World War for much the same reason Crawford and Peter Brewin invented the Concrete Canvas: like refugees, military forces often need to throw up structures quickly.

The Nissen Hut is a form of prefabricated building--a building whose pieces are manufacture elsewhere, then fastened together on-site. The earliest prefabricated building may have been Nonesuch House, built on London Bridge in 1577: it was assembled in Flanders, then transported in pieces across to England and up the Thames to be re-erected on the bridge.

In the 19th century, corrugated iron became the material of choice for prefabricated buildings. Corrugating sheet iron increases its structural strength significantly, and it's easy to work with and light enough to be easily transported. The aforementioned Nissen Hut is made out of corrugated iron for that very reason, and almost every farm in Saskatchewan boasts a descendent of the Nissen Hut for one purpose or another.

More elaborate prefabricated buildings are often modular, made of pieces the same size as the shipping containers that the modern transportation system is designed to handle most efficiently. A simple pad foundation is laid, the modules are trucked into place, craned into position in whatever configuration is desired, then connected to each other and to services.

Both corrugated iron huts and modular buildings, however, while obviously superior to tents, are bulky, hard to transport, and relatively expensive. A modular bulding with 16 square meters of floor space costs more $9,000 Canadian. The same size tent costs around $1,400.

And the Concrete Canvas? Probably around $2,500--more than the tent, to be sure, but far less than a modular building.

Crawford and Bremin, who are pursuing master's degrees in industrial design engineering at the Royal College of Art in London, came up with the Concrete Canvas as their entry in an annual competition, sponsored by the British Cement Association, for new and innovative uses of concrete. They'd heard about inflatable structures built around broken gas pipes so repairs can be carried out, and, Crawford having worked for the Ministry of Defense and Brewin being a former British Army officer, were also familiar with the bandages impregnated with plaster-of-paris that military medics use to set broken bones. They combined the two ideas to create their "giant concrete eggshell."

Concrete Canvas comes folded in a sealed plastic sack. The sack's volume controls the water-to-cement ratio, so you don't have to measure anything--you just fill it up with water and you have the right amount. Not only that, but the fact it's in a sealed sack means it can be delivered sterile--blow it up, and you have an operating theatre ready to go.

Crawford and Bremin only won second prize in the cement association's competition, but they went on to win the British Standards Institute's Sustainable Design Award, which funded a trip to Uganda where they visited refugee camps and demonstrated their one-eighth-scale prototypes to U.N. agencies and non-governmental organizations.

The response has been extremely positive. Monica Castellarnau, the program head of Medicins Sans Frontieres in Uganda, said she would buy 10 of the shelters today if they were available.

They may be soon. The inventors have filed for a patent, and full-scale production is currently in the planning stages.

It can't come too soon. The need for emergency shelters, alas, will never go away.

These weekly columns on science appear in the Regina (Saskatchewan) Leader Post and Red Deer (Alberta) Advocate.  They are available for one-time publication or regular syndication to any interested newspapers, magazines or on-line publications.  E-mail me for details.