Industrial Hygiene in The Pottery Studio

Understand the health risks in the pottery studio and learn best practices for making a comfortable space to create.
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Best Practices for Sculptors and Potters

I remember when my Mother gifted me an easel at a very young age. I entered my first oil painting of the eagle nebula in an art show when I was in elementary school. I have a similar relationship with musicianship. I continued to have a hobbyist’s interest and practice in art through high school and college, supplementing my biology and economics coursework, in true liberal arts fashion, with the history of impressionism and pottery. I found making mugs on the wheel strangely relaxing and intrinsically natural, and remember telling my very artistic mother, “you should try it.” At some point she did and started taking lessons. As I dove into my professional career of industrial hygiene, she eventually started her own pottery studio. From indoor air quality issue experiences in her own studio, she has prompted me to explore the indoor environmental quality of pottery studios. And so I write at the intersection of these things near and dear. I approach this writing as an industrial hygienist, but also as a hobbyist creator and son. 

My #1 advice is to understand each material in your studio, so you’re informed to manage your risks. The best way to do this is to examine each consumable’s Safety Data Sheet (SDS), even the clay. Beyond this, I will provide some recommendations and information regarding managing common environmental, health, and safety risks in your studio. Knowing that you have created a healthy environment for expression will maximize your comfort and ensure you have many more years to create in this enduring and prehistoric medium.

The information in this article is intended to address protecting your health in a home or hobbyist studio. This article does not address regulatory requirements of a pottery business. If you own or work in an industrial pottery facility, classroom studio, small business studio with employees, or anything beyond a home or hobbyist studio, you likely are subject to occupational health and safety regulatory requirements intended to keep your studio occupants healthy. In this case, I recommend contacting an industrial hygienist or other EHS professional for compliance guidance.

Clay and Mold 

There is an astounding diversity of clays available to the modern day potter. The main constituents of pottery clay include kaolinite, quartz, mica, feldspar, and water. There are various mixtures of aluminum oxides, silicon oxides, and many other minerals and constituents depending on the source and blend. 

Workable clay with a moisture content is a great substrate for mold growth. Mold spores are ubiquitous, and even the most tidy studio may have mold spores floating around. There are acceptable levels of mold spores in indoor air, but if you notice mold propagating on some of your clay, it is best practice to take care of it immediately. Occasional small amounts of visible mold growth is to be expected in a studio, and if you are reclaiming dry clay (slake) or have trimmings in containers with water, make sure to open them often to make sure they are not moldy. A small amount of visible mold can release large amounts of mold spores into the air. Many common mold species spores are considered allergens, and some contain mycotoxins and even emit volatile organic compounds (VOCs).

Dry Clay and Silicosis

When clay becomes dry, it creates respirable crystalline silica dust. Crystalline silica is an abundant earth mineral found in almost everything made from sand, stone, and soil. This dust can be generated from activities involving clay, plaster, and glaze. There are large amounts of public data relating silica exposure in industrial pottery to occupational disease. Working in an environment with unmanaged respirable crystalline silica dust puts you at an increased risk of silicosis, lung cancer, chronic obstructive pulmonary disease (COPD), and kidney disease. 

What makes this dust dangerous is its size. In modern industrial hygiene, we refer to three “fractions” of particulates; inhalable, thoracic, and respirable, which correspond to the particle size ranges and the depths that they can penetrate into our respiratory system.

The smaller the particle size, the deeper they can penetrate into our lungs. Respirable dust has a dynamic definition, but for simplicity we’ll say that about half the particles 4µm or less in diameter will be respired into the deepest recesses of our respiratory anatomy, where we do not have the capability to expel them.

Elevated concentrations of respirable crystalline silica dust can be released from various studio activities, and just because you can’t see it doesn’t mean it isn’t there! Fear not. I will provide some economical and efficient best practices to manage this dust in a later section.

Glaze Constituents

Most potters learn about food-safe glaze and toxic constituents of glaze early on. The first time I worked with glaze in college, we received a food-safe glaze lecture. The ASTM Standard ASTM D-4236 Standard Practice For Labeling Art Materials For Chronic Health Hazards is utilized to determine glaze toxicity, with classifications including AP Non-toxic. Some glazes contain highly toxic heavy metals including lead and cadmium, and it has been shown, aside from the standard, not all lead-free labeling is reliable. Also, you cannot assume that mixing two food safe glazes will result in a food safe glaze. Check out these DIY leaching tests, and keep in mind that standardized professional testing is best.

Be mindful that glazes can also contain low toxicity heavy metals including nickel, barium, selenium, cobalt, which, unlike lead and cadmium, may require a high dose to create health concern. Lead and cadmium containing glazes should be handled with various controls in place to make sure there are no mix ups, and a studio policy requiring labeling for pieces that do or do not contain lead is a good idea. Dry glazes are unsafe for inhalation. If your work requires you to mix dry glaze components, utilize PPE and mix outdoors if possible. 

Kiln Fumes, Heat, and Fire

When glazes are undergoing chemical reactions in the kiln that render your favorite glaze combinations, gases are released that must be properly vented from your studio. Follow your kiln manufacturer’s instructions, and a professional may be required for kiln installation. A fire extinguisher rated for electrical fires in an accessible location in the studio is a must.

Some other considerations for kiln safety include:

Vent kits are available to purchase for many kilns, consult with your warehouse or supplier for recommendations specific to your kiln brand and model.

Now that you are aware of potential risks, read on to learn about best practices you can implement to keep your studio a safe and healthy space to create.

Best Practices for the Pottery Studio

Eliminate or Limit These Practices:

Using Glaze That Isn’t Food Safe

If there is a glaze substitute that is food safe for a leaded glaze, use the safer glaze. This is especially important if you have children in the studio, as children are much more vulnerable to the health impacts of lead exposure. Any lead-containing and non food safe glazes should be stored in a secured area separate from other glazes and clearly labeled.

Dry Glaze vs. Liquid

Exercise your artistic freedom, but if there is a comparable liquid glaze, go that route. Here is a potter’s story of an acute inhalation exposure of dry glaze particulate. If dry glazes must be utilized, it’s prudent to utilize a P100 half face respirator, and do the work outdoors if possible. Be mindful about glaze dermal (skin) exposure, especially if you have any cuts or wounds.

Grinding, Cutting, and Sanding

When it is necessary to use abrasives on your clay or glaze finishes, use wet methods, increase ventilation, use a HEPA vacuum attachment, or do the work outdoors. Dry grinding, cutting, and sanding is likely to generate more silica dust than any other process in the studio, and is work during which it’s prudent to utilize a P100 half face respirator. Make sure you’re using eye protection, and other relevant PPE if you’re using power tools.

Dry Sweeping

A particle with a 3µm diameter in still air will take about an hour and a half to settle out of the air, and a 0.5 µm diameter particle, about two days! One sweep in a dusty room with a dry broom will resuspend (called re-entrainment) the dust particles that took some time to settle out of the air. Smaller particles may re-entrain from simply opening the door or walking by. 

Eating, Drinking, or Smoking in the Studio

Dedicated pottery artists spend many hours in the studio and it can be tempting to shorten breaks by eating and drinking in the studio, but it is best practice not to and strongly discouraged. Do not keep open food or beverage containers in the studio. Step outside the studio space before eating or drinking, remove your gloves and/or take care to thoroughly wash your hands before eating, drinking, or smoking.

Housekeeping

High Efficiency Particulate Air (HEPA) Vacuum

When it comes to maintaining great indoor air quality, a HEPA vacuum is a must. Keep in mind that “HEPA” is not a regulated statement. At a minimum you want to see “HEPA” on the label, but for the best performance you want the vacuum to be “Certified HEPA”. If you aren’t able to obtain a Certified HEPA vacuum, any HEPA vacuum is better than a non-HEPA vacuum. The two most economical certified HEPA vacuum cleaners I know of are the Vacmaster Pro 8 gallon Certified Hepa Filtration Wet/Dry Vac and the Atrix Omega Series. I personally use a Vacmaster and find it does a great job. Atrix also offers ULPA (Ultra-Low Particulate Air) filtration, which is even more efficient at capturing even smaller particles than HEPA filtration.

In the studio or home, your HEPA vacuum can be used whenever and wherever needed. 

A non-HEPA vacuum may actually be making your air quality worse! You may be circulating and reentraining more and more small particles that a normal filter is not capable of stopping. There are also cross contamination considerations. If you use a non-HEPA shop vac in the studio and then take it in to clean the living room, the air quality in your home may be worse after you vacuum. When you’re cleaning the studio, it is not a bad idea to utilize an N-95 dust mask or P100 half face respirator.

Cleaning Methods

When it comes to cleaning in the studio, water is the way. Wet sponges and rags can be utilized on horizontal surfaces, changing the water often (don’t forget a clay sink trap to protect your plumbing).

An entire sink system can be found here.

Mopping is the best approach for cleaning studio flooring, with frequent water changes. Following up your mopping, after the floors dry, with a thorough sweep using a certified HEPA vacuum with a brush broom attachment will help pick up any remaining dust.

Consider installing good quality casters on your tables, so that one person can move furniture easily for cleaning. Rugs can harbor dust particulates, so avoid them if possible or clean them regularly. Always take rugs outdoors to shake them out and vacuum.

HVAC

Seek to understand your HVAC system. Where are the vents and return air vents? How does the air flow through your studio? Maybe you have an air-source heat pump (ductless mini-split) or wood stove. Think about the path of the air flow, this is how the smallest dust particles will move. If you have a furnace or air handler, you can increase your filter’s MERV (13+) rating to better filter out small particles that may be recirculating otherwise. This is one of the easiest solutions, and upgrading your filter can make a significant impact in your studio (and home) particulate concentrations. Consult an HVAC professional for more improvement options. Larger studios may utilize local exhaust ventilation or fume hoods for mixing dry glaze and other dust generating processes.

If your studio is in your home, it is good to understand if your studio is under positive pressure. If the air pressure differential is moving out of your work area, that means that silica dust is migrating into other parts of your home. A crude way to check this is to crack the door slightly between the work area and the rest of your home while the HVAC system is in operation, and drop something light like a tissue, and see which way the air flows. If air is flowing out of your studio into the rest of your home, that should be addressed.

Air Filtration

I love HEPA air purifiers, and I recommend them to all my family members. From whisper-quiet desktop units to roaring hazardous material abatement air scrubbers, bluetooth and wifi connectivity, onboard air monitoring, and other air purification technologies, I recommend finding one that works for your home and your studio. Look for units with a total Air Changes per Hour (ACH) of 4 or more for your room size. My mother started operating a small HEPA filtration unit in her studio and saw immediate improvements in the studio air quality, prompting this article. These units also address most airborne mold spore issues. 

Air Monitoring

Air monitoring technologies for home indoor air quality have exploded in the last decade, and there are some great options for monitoring particulate matter, chemicals, and radon. A PM 2.5 indoor air quality monitor will allow you to analyze what activities in your studio practices need more care in controlling particulates. After cleaning the studio and operating a properly sized HEPA air purifier for 24 hours or more, use your monitor to establish a baseline value. Use that value to define what clean air is in your studio. Check out this article from Ceramics Weekly for more information and best practices.

These monitoring methods aren’t appropriate for direct comparison to occupational exposure limits for silica, but we can compare PM 2.5 our monitoring data to EPA Air Quality Standards for PM 2.5, which would include much respirable crystalline silica dust in your monitoring data. The EPA Annual PM2.5 standard is 12 micrograms per cubic meter (µg/m3) and with a 24-hour fine particle standard of 35 µg/m3. This means we want our air to be below 12 micrograms per cubic meter (µg/m3), but it’s ok if it is elevated up to 35 µg/m3 for short periods of time. 

For reference, occupational exposure limits for crystalline silica are an action level of 25 µg/m3, and a permissible exposure limit of 50 µg/m3 (NIOSH’s Carcinogen risk level) for an 8-hour Time-Weighted Average, meaning the average exposure over an 8 hour work shift. The methods for assessment of occupational exposure of silica dust use sample collection that isolates the respirable portion, and analytical methods that isolate the portion of the dust sample that is silica. If we observe the EPA Air Quality Standards in our studios, we should be minimizing chronic exposure risks to silica dust, and have some peace of mind.

PPE: Respiratory Protection

I’ve seen numerous pottery EHS posts suggesting respirators, but if you implement these previously discussed controls, there should be few processes in the studio that require a respirator. Self-monitoring your studio will show you which processes elevate the PM 2.5, and therefore crystalline silica dust, in your studio. If studio activities create PM 2.5 concentrations over the OSHA Action Level of 25 µg/m3 for respirable silica dust, consider utilizing an N95 respirator or P100 half face respirator for those activities.


I hope this article has helped you to think about making a healthier, more relaxing and productive pottery studio environment. If you have any questions or comments, please email me at peterson@windbornegroup.com.


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