Hot air hand driers are a spin off from the American space programme of  the mid 1960's. The problem facing NASA was how to handle the mundane hygiene issues of three astronauts confined in a tight space for the two weeks it took to get to the Moon and back. Everything had to be reusable or recycled, obviously there is no scope for doing the laundry so the concept of hand drying using a stream warm air was born.

The initial design consisted of a unit fitted to the back wall of the Command Module which tapped into the hot gasses from the rocket motors. The unit cooled the gas to a usable temperature and then via a heat exchanger, directed warm air into the cabin.

The problem is that tapping off even the smallest amount of exhaust from one rocket motor was  enough to alter the craft's course. The deviation was very slight but over the enormous distances of space it was enough to cause the flight to miss it's rendezvous with the Moon.

The solution was to reduce the time that the hand drier was used for. This was achieved by fitting it with a timer which shut a valve from the rocket after a fixed period. The amount of time allowed was a compromise between hand dryness and course deviation, which turned out to be 37 seconds.

NASA applied for world patents for it's invention and these days every commercially produced unit is manufactured under licence. The licence conditions still have the 37 second cut off stipulation.

Hand Drying Facts

• Hot air hand driers collect pathogens from the air and give them a nice warm place to breed. These, sometimes deadly, bugs are then deposited onto your hands as you dry them in the air stream.
• The the temperature of the air from a hot air hand drier is normally set to 30°C. In tropical countries it is increased to 40°C because otherwise the hot air would be cooler than the surrounding room temperature.