RICHARD AMBROSE V/O: Now it's time to look at an everyday object using an infrared camera. Hot things give off lots of infrared whilst cold things give off less. And this camera can actually do what our eyes can't. It can see the variations in temperature. There are about 30 million fridges in the UK alone. What will the infrared camera reveal about this one?
JONNY PHILLIPS: Are you ready Rich?
RICHARD AMBROSE: I'm ready.
JONNY PHILLIPS: So what do you see?
RICHARD AMBROSE: Black, and very dark blue.
RICHARD AMBROSE V/O: Most of the fridge is at plus 4 degrees Celsius. But because heat rises, the top section is at double that.
JONNY PHILLIPS: Do you want to look at the freezer? See if there's any difference?
RICHARD AMBROSE: You can't see any definition in there at all. It's very cold.
RICHARD AMBROSE V/O: Well that's a shock revelation. The freezer is cold.
Inside it's around minus 18 degrees Celsius.
RICHARD AMBROSE V/O: So it's no wonder that after just seconds, Jonny's fingers have halved in temperature. Another few minutes and he'd officially have frostbite.
RICHARD AMBROSE V/O: Until 1929 fridges used toxic gases including ammonia and sulphur dioxide as coolant. Unfortunately, several fatal accidents occurred.
RICHARD AMBROSE V/O: Today, fridges use refrigerant. A man-made chemical which absorbs heat. It's circulated by this compressor, which is the hottest part of the fridge. The refrigerant travels in the walls of the compartment, absorbing heat from the food. When it comes out at the back of the fridge, the liquid coolant is warm. As it travels down through these tubes it cools down. The change from red to green represents a massive temperature drop. By the time it gets to the bottom it's cool enough to pass inside the fridge again.