Clay products contain carbon and organics. These react with oxygen in the air to form carbon monoxide in the firing. During firing, gases in the kiln expand. These gases are forced out through cracks and holes, making it difficult for new air to enter the kiln. Only a downdraft vent system pulls out the fumes, allowing fresh air to enter the kiln.
Carbon monoxide can produce headaches, fatigue, sore throats and nausea.
Testing has shown that carbon monoxide produced during firing can be higher than accepted government standards. Fumes may also contain organics, volatile metals, flourides and sulphur oxides, which should be removed. Virtually eliminates odors from lusters, metallics and sulphur. Kiln stays under negative pressure to provide complete fume removal. Hoods can't do this.