In more controlled fashion, oxygen is fanned into embers to try and increase the burn. As a youngster, I remember bending near a budding fire. It usually required pressing a cheek near the ground and blowing sideways at mostly glowing cinders that lacked flames. It took a special knack to direct a stream of breath at the base, so that smoke did not blow back at my face. It also helped to control the jet so that is was lasting and steady. If administered properly, flames would pick up, Once established, I could back away and the fire would draw air to itself.
In this small way, I was using my lungs as a bellows.
The same effect can be produced to enhance the burn of a fire. Forcing air at a fire increases the burn rate and thereby the heat. One time I lived in a house that relied on a wood stove for heat. My job was to tend the fire. We had a tool that consisted of a long metal tube. At one end was a mouthpiece similar to that found on a wind instrument. The other end had a pointed nozzle that had two small holes side by side. This tool could be placed into the fire and by blowing on the mouthpiece a steady stream of air could be directed to a precise spot in the fire. I experimented with directed a sustained blast of air at the most internal part of the blaze. It was easy to detect I was making an incredible hot spot. I further experimented with placing bits of metal in a crucible in this hot spot. I was able to bring the temperature up to a point that metals I played with glowed red and became plastic and pliable. I was discovering the elements of forging.
Mechanical devices came to be used for the same effect. These could maintain an even steady stream of air at a fire and did not have to pause for inhalations and catching breath. They could work steady. Old-time forges had such a device and it consisted of an air bladder that when expanded sucked in air. When it was collapsed, air was forced out of a nozzle at the fire. Usually, an apprentice operated this device, pumping it up and down, while the master worked at the fire end handling red hot metal pieces. This is another form of bellows. The root of this word means blast bag. Furnaces that had similar devices were called blast furnaces. This is where fires were brought up to such heat that hard metals such as iron and steel could be melted and forged.
In a forging experiment, I devised a means to turn a used washing machine pump motor into a blower. Through a set of pipes I directed a slow steady stream of air at a coal fire, I had set up in an old tractor rim. The air would blow up through the pile of coals, setting them to a good glow. From the side I could place metals and crucibles in the coals. This produced a steady hot fire without the need to have someone constantly at work pumping an airbag up and down.
The last form of bellows I witnessed is that one found in nature. This is when a fresh breeze springs up while a fire is going outdoors. Here a strong wind acts counter productive to creating a hot fire, since it has more of a dispersing effect and can blow the fire out. But when the breeze is slow and steady it creates a blast furnace effect. Such fires have been known to melt metals and glass, at temperatures far exceeding those capable of being produced in ordinary wood fires. Again, it is the air blast that makes the difference. By working with fire in these conditions, I began to see why ancients regarded fire as a magical and transformational element.