Many potters are concerned about the safety aspect of gas ceramic pottery kilns and firing procedures. We will discuss some requirements of ventilation and flueing, but bear in mind that there are regulations which must be adhered to and you should check these with your local authorities before any installation. The most potentially dangerous aspect of gas kiln firing is insufficient fresh air, and inadequate exhausting of the combustion products. Never locate a kiln inside a sealed room, or where access to sufficient fresh air from outside is not available. Gas burners use enormous volumes of oxygen in order to complete combustion. Typically, a natural gas burner uses ten cubic meters of fresh air for every cubic meter of gas burned. L.P. type gas burners require 2 1/2 times the air volume. Fresh air should be available to the kiln by using fixed venting located at a low level in the wall or door or through a powered fan. The size of the vent is determined by the MJ/hour total burner rate. If air is drawn from the outside, the rate is 160 square mm per MJ/hour; thus a gas kiln with two burners and an input of 400 MJ/hour requires fixed ventilation of 250 x 256 mm. If the kiln draws air from an adjacent room, the area must be doubled. If using mesh, then the maximum hole size is 6 mm square. These figures are for natural gas burners; L.P. gas burners need 2.5 x the area. Note that all gasfitting and flueing work should be undertaken only by a licensed gasfitter.
Combustion in gas Amaco kilns produces hazardous gases which must be safely exhausted to the outside atmosphere. Natural gas burners which use one cubic meter of gas produce one cubic meter of carbon dioxide, eight cubic meters of nitrogen, and two cubic meters of water vapor. If the supply of fresh oxygen is restricted so that the combustion process is incomplete, then carbon monoxide gas will result. This gas is lethal, even in small quantities. Since this is a common occurrence in reduction firing, the need to make absolutely certain that the gases are removed from the work area safely is vital. The flue (chimney) should be of correct construction. While it is possible to build brick chimneys, it is more economical to use one of the metal types. A gas ceramic pottery kiln which is fitted with a venturi burner doesn't need an excessively long chimney. The flue on a modern, downdraft gas kiln is usually terminated near the kiln's top, and a canopy is fitted above this with a pipe going through the roof and a terminal connected to the outlet. The canopy helps to slow down draw from the kiln, since excessive draw will make the kiln operate inefficiently. The canopy pulls in air which helps to dilute the flue gases and cool them, thus ensuring that the chimney lasts longer, and is not as polluting to the environment.
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