by Marc Ward
Clay Times June 1997
Well, last issue I promised to delve into the subject of ceramic fiber. Here goes a walk in the mine field.....
Refractory Ceramic Fiber (RCF) is a mainstay of ceramic industry. Many engineers, factory owners, and studio potters think it's the best thing since sliced bread. Others think it's death incarnate. What's going on here?
RCF is basically spun brick. Alumina and silica, the main components of brick and clay, are melted at very high temperatures. This molten mass has water injected into it, at temperature, causing it to be forced, under pressure, through nozzles which turn the molten material into fibers that are laid down on a bed, compressed and needled into a blanket. This creates a soft pliable blanket that can be formed into many shapes. Quite a bit of air is trapped in the matrix of the fiber which makes it a great high temperature insulator. So great, in fact, that fuel bills can be cut in half or more over brick kilns. The problem lies in the fact that these fibers can become airborne during construction and tear down and enter the lungs.
The danger from RCF is from the free silica. Because RCF is alumina and silica, installation is not as dangerous as tearing out used fiber. Once RCF is exposed to temperatures over 1600 degrees F, it begins to form cristobalite, a form of free silica. Free silica is known to cause silicosis, a lung disease. No matter if you are building or tearing down a fiber kiln, you need to take some precautions. You should wear long sleeves, head covering, eye protection, and use a NIOSH approved respirator for mineral dust. Now comes the rub.... These are the same precautions you should take when making glazes. Honestly now, how many of you out there dress up like astronauts to make glazes? Should you? That's your decision and responsibility.
I build 75 or so Raku kilns a year using RCF. I'm on the front line of this battle. I wear long sleeves and a respirator. I have a top of the line vacuum system that I use on a regular basis. I find fiber irritating and potentially dangerous. I also have a 120 cubic foot fiber car kiln for stoneware use. I don't give a second thought about it when I'm loading, firing, and unloading. These are two different situations that, I believe, warrant different procedures.
I've spoken with professors that have insisted on tearing out all the RCF kilns in their schools because of the danger of silicosis and cancer, but all their students are still making glazes without respirators, they have no vacuum system, and they don't wet mop. This is "Chicken Little" thinking. I also know kiln manufacturers that have removed RCF from their line of kilns. I believe this has more to do with insurance underwriters and lawyers than it has to do with actual test results.
RFC is now classified as a Class 2A carcinogen. This means that there is sufficient evidence for carcinogenicity in experimental animals and that limited evidence for carcinogenicity exists in humans. Other long term studies of factory workers in the RCF industry have not shown a link between cancers and exposure. Living in the 20th century in Western civilization is dangerous. Brick dust is the same danger....sweeping the studio floor is the same danger.....making glazes is the same danger....making clay is the same....driving down a gravel driveway with the windows open is the same..... All these things expose us to free silica and silicates. Living in a technological society presents all of us with choices. If you truly want to be safe, there is one thing you can do that will make a huge difference; Give Up Your Car! Encased in metal boxes, we hurtle down the road, sometimes at speeds of 70 miles per hour. We go around corners, trusting that the other drivers won't cross the center line, trusting that our tie rods don't break, trusting that their tie rods don't break. Trusting that everyone's tires don't blow out. All this while missing each other by mere feet! A basic understanding of physics would lead you to believe that driving is pure lunacy. But, drive we do. We've made our 20th century choice.
I've chosen to use RFC. It has enhanced my life in clay, but it's not for everyone.
Pay attention to the appropriate uses for RFC and how to handle the material. Raku kilns are one of the best uses of ceramic fiber. It's light weight and low thermal storage, make it ideal for Raku drum kilns. They are easy to lift and cycle quickly. Stoneware kilns are very efficient, but cool down quickly. This can be a plus or a minus. Once RFC's are in place, dust is not really a problem. In 15 years of using ceramic fiber, I've NEVER had a glob of fiber in the bottom of a bowl or a platter. I've also taken precautions that I haven't gotten a glob of fiber in the bottom of my lungs.
Ceramic fiber offers great fuel savings. It never ceases to amaze me that potters that are vigilant about recycling, composting, etc.., will use fossil fuels to gas fire hard brick kilns and claim a life of minimal environmental impact. Come on... who are ya kidding?
If you're thinking about building a fiber kiln, know something about the material and the proper precautions to take while handling RCF. It's a great material that deserves respect and proper use.
NOTE: Since writting the above article new, safer RCFs have come onto the market, We carry Unifrax's new IsoFrax™ which does not carry the health warnings associated with more conventional forms of ceramic fiber.