PPP: Clearing the Air

March 1, 2009
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At some point, we have all questioned the quality of the air we breathe while working in a pottery studio, and for good reason: Undetected and unknown airborne ceramic materials are potentially hazardous and worthy of our concern. The very nature of working with clay and glaze materials can propel micron-sized particles into the studio environment. The real questions are: How dangerous are these particles? How long do they remain in the environment? And how can they be safely removed?

Figure 1. Common raw materials used in clay body and glaze formulas can be released into the studio environment. From left: ball clay, talc, E.P.K., bentonite, feldspar and flint.

Are Potters at Risk?

The oral histories of potters over the past 60 years, along with a statistical survey sponsored by the National Council on Education for the Ceramics Arts (Health and Safety Questionnaire 2000 Report), do not indicate respiratory difficulties among potters. However, it is still the best course of action to reduce studio airborne particles as much as possible to increase safety margins.

The high concentration and prolonged inhalation effects of alumina and silica (contained in clays, flint, and other ceramic raw materials) are medically recognized as the cause of aluminosis, silicosis and other harmful lung diseases. Other materials, such as iron, manganese, chrome and cobalt (found in many glazes), can also cause respiratory distress (see Figure 1). Such cases are thoroughly documented in government and medical research statistics.

Unlike silica miners and industrial workers exposed to silica inhalation in their workplace, no potter would go into their closet, open a bag of flint and stay there for the entire workday, every day, for 10-20 years. Since potters are not exposed to airborne particles of flint or other raw materials in the same concentrations and durations as industrial workers or miners, are pottery studios imposing a health-related risk? Because there are no absolute answers to this question to date, potters should use all available means to keep the levels of airborne particles to a minimum.

Removing dry clay from a 50-lb bag.

Particle Size

The average diameter of clays-whether ball clays, stoneware clays, fireclays, kaolins, earthenwares or bentonites-can range from 100 to 0.01 microns* in size depending on the type of clay.1 As a point of reference, the diameter of a human hair is 100 to 150 microns, and the hair itself can remain airborne for 5 seconds. Cell debris from the human body can range from 0.01 to 1 micron in diameter and can remain airborne for hours or days in a studio environment, as can clay platelets of a similar size.

As it pertains to clay, the ratio of upper and lower planes in relation to the platelet’s thickness is 10:1, meaning it has greater surface areas on its planes than its width. The hexagonal flat shape of a clay platelet makes it similar to a lifting body or sail, causing it to be suspended and carried by air currents.

The flint or silica commonly found in clay body and glaze formulas can range from 44 microns to sub-1 micron size in a 325-mesh grind. Their shape is classified as fractioned and shattered. Feldspar typically runs from 1 to 100 microns in size, and its shape is irregular and blocky. For example, 270-mesh nepheline syenite (a feldspathic material used in clay body and glaze formulas) can have an angular particle shape and range from 9 to 11 microns in diameter. Other clay body and glaze materials, such as wollastonite, whiting, dolomite, zinc oxide and magnesium carbonate, are also very small in particle size and can remain on horizontal studio surfaces or in the air for long periods of time.

*1 micron = 1/24,500 of an inch, or 1 millionth of a meter.

Weighing dry glaze material.

Any potter who has mixed dry glaze materials can see particulates suspended in the air, which can eventually result in a thin film deposited on worktables. However, it is not the visible particles in the air that are the most significant health risk-it is the micron-sized invisible particles that can enter the lower respiratory tract.

The average adult breathes 3000 gal of air per day. While the human body is efficient at filtering airborne particles of greater than 10 microns, which get caught in the nose and throat and expelled through coughing or swallowing, particles of less than 10 microns are easily inhaled into the lungs and can impose health risks. Individuals who are overly sensitive, smoke, or have allergies or asthma are at even higher risk. Particles of less than 1 micron have the potential to enter the lower respiratory tract and are the most difficult for the body to remove.

Glazing operations in the studio.

Potential Sources

Almost any studio activity has the potential to release dry materials into the atmosphere. The simple act of walking into the studio, no matter how well it is maintained, sends small particles into the air. Worktables and shelves-all horizontal surfaces, really-have the capacity to trap particles until any draft lifts them into our breathable air.

Other activities-such as trimming pots, clay/glaze/plaster mixing, reprocessing clay scraps, sweeping, opening or moving raw material bags, spraying glaze, using clay-encrusted tools, or even touching raw glaze on bisque pots-can generate raw material residue.

Wiping dry raw materials off of a worktable.

Simple Precautions

Though definitive statistics are lacking regarding airborne health risks to potters working in studios, a conservative approach would be to simply accept that lowering any airborne particles in the studio environment is a desirable goal. To that end, following are several techniques, procedures and tools that can be easily incorporated into any studio to help ensure safe operation:

Dry glaze surfaces can release airborne particles.

  • Invest in a respirator. Use an approved respirator* during any operation that will release dry materials into the air.
  • Wear studio-specific clothing. Have a separate set of washable clothes for studio use only.
  • Wipe up spills immediately. Any liquid spill can dry into a fine dust that can be released into the studio atmosphere.
  • Clean your studio regularly. Employ a regular studio cleaning schedule.
  • Do not eat or drink in the studio. Reserve the studio for only ceramic-related activities.
  • Close all dry material containers. Open containers or bags of material have the potential to release dust particles.
  • Wet-wipe all work surfaces and floors. Use a wet mop or sponge to periodically clean all studio surfaces.
  • Design the studio to remove all horizontal surfaces, where possible. Horizontal surfaces capture dust. The ideal studio would let all particulates fall to the floor, where they can be wet-mopped.
  • Clean tools and equipment after use. Do not let dry clay and glaze materials adhere to tools. Wash all tools after use.
  • Ensure adequate ventilation for the studio. Air should be circulated throughout the studio, preferably through an effective filter system.
* Two respirators have been National Institute for Occupational Safety and Health (NIOSH)-approved to meet Occupational Safety and Health Administration (OSHA) requirements and Centers for Disease Control (CDC) guidelines: the 3M 8210 N95 particulate respirator and the 6000 series low-maintenance respirator with replacement cartridge filters.

Dry-sweeping the studio sends dust into the air.

Using common sense and good housekeeping procedures will reduce the amount of airborne particles in the studio, ensuring a safer work place. Simple procedures, such as cleaning the studio daily and wearing an appropriate respirator, often go a long way toward improving air quality.

Author's Note

The author would like to thank the following for providing information for this article: Jim Fineman, professional potter; Anthony Volpe, technical consultant; Tom Landon, technical services leader of Imerys North America Ceramics; Keryn Geho, technical services representative of U.S. Silica; and Unimin Corp.

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