The Edward Orton Jr. Ceramic Foundation has developed a direct kiln venting system that is an alternative to standard over-head canopy-type exhaust systems for multi-sided electric kilns of less than 12 cubic feet capacity.
Sold under the names Orton Kiln Vent and Skutt EnviroVent, this kiln ventilation system works by directly exhausting fumes and gases from the kiln rather than from the air around the kiln. This vent system also has the advantage of providing a more uniform kiln temperature.
To install the vent system, a specified number of holes are drilled in the top and bottom of the kiln. A stainless steel plenum and 60 cubic feet/minute blower is installed underneath the kiln and the ducting that leads from the blower to the outside. The blower pulls cool air from outside the kiln into the plenum, causing a venturi effect which creates a downdraft inside the kiln. This downdraft pulls air from the top holes through the bottom of the kiln, carrying with it any gases and fumes generated inside the kiln. These gases are then exhausted to the outside.
The vent system has to be installed and operated as specified in order to work properly. During operation, the lid and all peepholes should be closed. Older kilns (especially those with excessive wear that could result in leakage of excess air into the kiln) might require patching first. To test the system, hold a lit match directly over one of the kiln holes. The flame from the match should be pulled into the hole.
Another concern is the ducting. Although the manual states that flexible vinyl dryer hose with gentle bends is acceptable in many cases, we would only recommend rigid or flexible aluminum ducting. Sharp 90 degree bends should be avoided.
Can you provide any specifics of why down drafting ventilation systems are to be avoided? (I've talked with one kiln manufacturer, not Orton, who said they corrode from kiln emissions so they're a short-term solution).
Have you had any experience with metal fumes settling on surfaces around an unvented electric kiln where lead-based glazes have been fired? If paper and other school supplies are stored in the vicinity could they be contaminated? Do you think metal fume could spread throughout a school, if it could gain access to a heating/cooling system? If you could point me in the direction of any articles/studies I'd appreciate it. Thanks!
LC, Studio Safety Resources British Columbia, Canada
Basically the sulfur oxides and water vapor corrode the fan so you have to replace the fan after a few years, depending on the sulfur content of the clay. However, I think that is a reasonable tradeoff since the direct vent kilns are more effective than canopy hoods.
The air sampling results we have seen don't indicate that metal fumes (at least lead) escape from the kiln. However, they do vaporize and settle down on objects inside the kiln (even non-leaded ones) and on the kiln surfaces, thus contaminating the inside of the kiln. They can then contaminate non-lead firings. A direct vent kiln would help this problem since it is removing the lead fumes (although they might contaminate the duct).
As for contaminating paper and school supplies in the vicinity, they shouldn't be stored near the kiln because of the fire hazard due to the high surface temperatures of electric kilns. -Ed.