In a world with millions of refugees, numerous war zones and huge areas devastated by natural disaster, aid agencies and militaries have long needed a way to quickly erect shelters on demand.

Soon, there will be such a method. A pair of engineers in London have come up with a "building in a bag" – a sack of cement-impregnated fabric. To erect the structure, all you have to do is add water to the bag and inflate it with air. Twelve hours later the Nissen-shaped shelter is dried out and ready for use.

The structure is intended to improve upon two current methods of providing emergency shelter: tents, which provide only poor protection, or prefabricated, portable buildings that are expensive and difficult to transport. Dubbed the Concrete Canvas, the shelter incorporates the best aspects of both forms. It is almost as easy to transport as a tent, but is as durable and secure as a portable building.

The inventors are engineers pursuing a master's degree in industrial design engineering at the Royal College of Art in London. William Crawford and Peter Brewin came up with the idea when they were thinking of an entry for the annual British Cement Association competition for new and innovative uses of concrete.

They thought of an inflatable concrete tent after hearing about inflatable structures that are built around broken gas pipes to carry out repairs.

"This gave us the idea of making a giant concrete eggshell for a shelter, using inflation to optimize the structure for a compressive load," said Brewin. "Eggs are entirely compressive structures with enormous strength for a very thin wall."

The idea won second prize in the cement association competition in 2004. Crawford and Brewin, who are both engineers and have worked, respectively, for the Ministry of Defense and as an officer in the British Army, were also inspired by the plaster-of paris-impregnated bandages used to set broken bones.

Crawford said he and Brewin have been developing the concept for 16 months and made eight full prototypes at one-eighth scale.

The inventors filed a patent, which covers the concept of creating structures using a cement-impregnated cloth bonded to an inflatable inner surface. Full-scale production is planned and could take off soon, as Concrete Canvas is short-listed for the New Business Challenge run by Imperial College London and the Tanaka Business School. The winner of the £25,000 ($48,000) prize will be announced next week.

The idea has already garnered several other awards, including the British Standards Institute Sustainable Design Award. This funded a trip to Uganda last year.

The pair spent a month meeting U.N. agencies and nongovernmental organizations, visiting refugee camps and demonstrating the prototype shelter. The response has been positive.

"If this was available now, we would buy 10 today," said Monica Castellarnau, program head for Medicins Sans Frontieres in Uganda.

Aid agency chiefs have been impressed by the simplicity and economy of the idea. A bag weighing 230 kilograms (approximately 500 pounds) inflates into a shelter with 16 square meters (172 square feet) of floor space. Cost is estimated at £1,100 ($2,100), while an equivalent-size Portakabin (a type of portable building widely used in the United Kingdom) costs about £4,000 ($7,700). The same-size tent costs about £600 ($1,150).

Concrete Canvas comes folded in a sealed plastic sack. The volume of the sack controls the water-to-cement ratio, eliminating the need for water measurement. You literally just add water.

"The shelter can also be delivered sterile," said Crawford. "This allows previously impossible surgical procedures to be performed in situ from day one of a crisis."

Markus Hohl, a lecturer on the Industrial Design Engineering course, praised the successful teamwork of Crawford and Brewin. "They've come up with a design that integrates plastic to inflate the structure and doubles as the inner skin; a wicking fabric that draws the water in and an external resin of concrete which holds the thing together: Concrete Canvas is triple clever."

Gareth Jones, former product development director of the award-winning vacuum-cleaner maker Dyson, admires the design simplicity and functionality of Concrete Canvas.

"The Concrete Canvas product tackles the key issues of portability, ease of assembly, durability and cost," he said. "The applications in the humanitarian field are immediate and obvious, but there are many other fields where this technology could successfully be deployed."

See related slideshow