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Ceramic Kilns

I. The Issue:

The operation of a ceramic kiln may pose a risk to indoor air quality if the unit is not properly maintained and mechanically ventilated to the outdoors. In addition, the introduction of certain synthetic materials during the firing process may create unusual and hazardous emissions. As a result, it is prudent to review the use of all kilns as well as the ventilation system provided to each unit. Failure to maintain and safely operate ceramic kilns located indoors may degrade indoor air quality and result in the accumulation of harmful concentrations of carbon monoxide, ozone, volatile organic compounds, and metallic vapors.

II. The approach taken:

As part of a comprehensive indoor air quality assessment of the local school system, we endeavored to identify potential sources of indoor air pollutants. During this process, we identified five ceramic kilns operated inside local schools. Each kiln was then inspected for concerns related to its use and operation.

III. Observations made:

The most significant observation noted was that initially all the kilns vented directly into the schools where they were located. Three of the units had not been provided with any type of mechanical ventilation and were allowed to freely vent into the building. Two of the units had been provided with mechanical ventilation, unfortunately, several design flaws existed in the existing mechanical ventilation system which rendered the system ineffective. As a result, the operation of these units may have adversely impacted the indoor air quality at each school.

Another concern noted was the practice of introducing synthetic materials such as plastic or mothballs during the firing process as a means to create a new or unique lustre on the ceramic piece. Mothballs and stryofoam are examples of some of the synthetic materials that may be introduced during the firing process to develop a unique lustre. This is reported to be a common practice among ceramic artisans as a means to develop and express an artistic signature. The problem is that these synthetic materials tend to produce hazardous and/or carcinogenic emissions when fired.

A hazard associated with ceramics but unrelated to the operation of kilns is the generation of free silica. A review of the clays used by our schools indicated that these materials contain between 20% to 90% free silica. Free silica is a concern because it is physically similar to asbestos. In addition, free silica is a severe respiratory hazard. As a result, efforts should be made to minimize the amount of dust generated while preparing ceramic pieces. Furthermore, all dust generated by these activities should be assumed to contain free silica and should only be cleaned up via damp mopping. Sweeping or vacuuming could re-suspend the free silica and increase the respiratory hazard posed by this material.

IV. Problems or concerns noted:

V. Actions taken:

The high school art department maintains two kilns which area located in an interior room lacking a window. Proper venting of the kilns is critical in order to prevent the degradation of indoor air quality. The operation of a ceramic kiln commonly results in the generation of carbon monoxide, volatile organic compounds, and metallic vapors. Initially, the kiln room was vented to the outdoors via a manually operated ceiling mounted exhaust fan which was ducted thirty feet to the outdoors. The discharge for this ductwork was 10 feet below the roof line within a partially enclosed area and adjacent to the discharge was an inoperative louver fan for the ceramics studio. The following problems existed with this design. First, the kiln exhaust was not ducted to the exhaust fan but allowed to be passively drawn to the fan. This approach allowed the kiln emissions to escape the kiln room via two door ways or via the building heating and ventilation system which also serviced the kiln room. In addition, the operation of the exhaust fan was manually operated by the staff and students and due to its noisy operation most individuals preferred not to use the fan. Furthermore, it was questionable that the exhaust fan was capable of transporting captured emissions the required thirty feet and discharging the material via the louvered opening. Finally, it is likely that a portion of those materials that were discharged by the exhaust system probably reentered the building via the louvered fan located adjacent to the kiln exhaust discharge.

We addressed these problems by installing bottom mounted exhaust fans on both kilns. The kiln exhausts were also ducted directly to the existing exhaust system which was equipped with two quieter booster fans. The exhaust system was also modified to discharge above the roof line. The exhaust system has also been hard wired to operate whenever the kilns are in operation.

While reviewing the art supplies in the middle and elementary school, I noted that all the kilns located at these schools vented directly into the schools. As a result, carbon monoxide, volatile organic materials and other emissions were being released into the schools whenever the units were fired. This resulted in a degradation of the indoor air quality of these schools. This problem was addressed by installing the appropriate ductwork and exhaust fans to vent the units outside.

The potential hazards associated with introducing synthetic materials into the kiln during the firing practice have also been discussed with the staff. We have requested that the staff and students refrain from this activity. We are concerned that the ventilation systems may not be able to remove all of the hazardous byproducts generated by this activity.

Tips and suggestions:

1. Use a smoke bomb to test mechanical ventilation: This simple and inexpensive test can provide you with a quick and easy qualitative assessment of the function of a chemical fume hood or kiln exhaust. The use of brightly colored smoke will enable you to easily determine if exhaust may be escaping from the test unit, the ductwork associated with the unit, or if the exhaust is reentering other portions of your ventilation system. This is only a quick and dirty analysis designed to check for major problems. This approach does not replace the need to have a trained professional inspect, maintain and calibrate these units.

2. Seek assistance from local resources: We are all in this together. Tap into the assistance that is available from federal, state and local environmental, and health and safety agencies. Do not overlook local residents, corporations, and medical facilities. These groups have a vested interest as parents and tax payers, and are frequently willing to provide technical expertise and assistance.


I utilized the services and expertise of the following groups and agencies while reviewing the health and safety concerns associated with ceramic kilns.

Massachusetts Office of Technical Assistance
Attn: Lisa Dufresne
100 Cambridge Street, Room 2109
Boston, Massachusetts 02202
Telephone: (617)727-3260
Fax: (617)-727-3827

This agency provides free, non-regulatory technical assistance to schools located in the Commonwealth of Massachusetts. This agency also maintains a large database of technical information describing the investigation and resolution of a broad variety of potential environmental, health and safety issues that are commonly found in schools.

Massachusetts Dept. of Labor & Workforce Development
Division of Occupational Safety
Attn: Nancy Comeau
1001 Watertown Street
West Newton, Massachusetts 02165
(617) 969-7177
fax: (617)727-4581

This agency provides free technical assistance to schools located in the Commonwealth of Massachusetts. This agency also maintains a large database of technical information describing the investigation and resolution of a broad variety of potential environmental, health and safety issues that are commonly found in schools.

Center for Safety in the Arts
5 Beekman Street, Suite 820
New York, New York 10038
internet: http://www.nyfa.org/ Exit EPA Click for Disclaimer

The Center for Safety in the Arts monitors and evaluates a broad range of health and safety concerns involving the arts and theater. This group has also published a large volume of health and safety guidance. They also offer a variety pollution prevention information.

Maryland Department of Education
Office of Administration and Finance
Office of School Facilities
200 West Baltimore Street
Baltimore, Maryland 21201

The Maryland Department of Education has published a number of helpful technical bulletins describing potential EHS issues in schools as well as potential corrective action.

prepared by Todd H. Dresser, Environmental Engineer
(formerly of)
Burlington Board of Health, 29 Center Street, Burlington, MA 01803

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