The Definition of Kiln Safety

Definition of Kiln Safety

Kiln safety is the set of practices, equipment and controls used to protect people from the hazards of operating, loading, unloading and maintaining kilns. A kiln is an insulated chamber that heats materials to very high temperatures to fire pottery, fuse glass, cure ceramics, dry lumber or produce materials such as brick, lime and cement.

Kilns range from small electric units in schools, art studios and dental labs to large gas-fired, wood-fired and industrial rotary kilns. Even a small electric kiln can reach temperatures well above 2,000 degrees Fahrenheit, and its outer surfaces, the air around it and the gases it releases can all injure workers.

Good kiln safety combines proper installation and ventilation, safe operating procedures, control of dust and fumes, electrical and fire safety and the right personal protective equipment. Because many kilns run for hours with little supervision, procedures for monitoring and shutting down the firing are just as important as controls at the kiln itself.

Kiln Hazards

Heat and burns

• Hot surfaces: kiln walls, lids, doors and peepholes stay hot during firing and for hours afterward. Touching them can cause a serious burn injury.
• Hot air and ware: opening a lid or door releases a blast of hot air, and fired pieces can stay hot long after the kiln is switched off.
• Heat stress: large gas or industrial kilns can raise room temperatures significantly, adding to the risk of heat stress for workers who load, monitor or unload them.

Fumes and gases

As clay and glazes are fired, organic matter burns off and some minerals and metals break down or vaporize. Depending on the materials and fuel, kiln emissions can include:

• Carbon monoxide: produced by fuel-burning kilns and by organic matter in clay, especially during reduction firings. Poor venting can lead to carbon monoxide poisoning.
• Sulfur dioxide and other irritant gases: clays and glaze materials may release sulfur oxides, fluorine and chlorine compounds and nitrogen oxides.
• Metal fumes: metals in glazes and colorants, such as lead, can vaporize at high temperatures.
• Smoke: raku and other reduction processes produce large amounts of smoke and carbon monoxide and are best done outdoors, away from building air intakes.

Dust hazards

• Crystalline silica: clay, glaze materials and kiln wash contain silica. Dry sweeping, sanding greenware or scraping kiln shelves can release respirable dust that causes silicosis. See silica exposure.
• Refractory ceramic fibers (RCF): many kilns use ceramic fiber blankets, boards or seals as insulation. RCF is classified by the International Agency for Research on Cancer (IARC) as possibly carcinogenic to humans. Fibers that have been heated to high temperatures over time can also form crystalline silica, so removing old insulation calls for dust control and respiratory protection.

Radiation, electrical and fire hazards

• Infrared radiation: looking into a glowing kiln through a peephole exposes the eyes to intense infrared light. Repeated, unprotected viewing has been linked to cataracts.
• Electrical shock: electric kilns draw large currents. Touching elements with metal tools during firing, or working on wiring without disconnecting power, can cause shock or electrocution.
• Fire: combustible materials stored near a kiln can ignite, and a kiln that fails to shut off can overheat, melt elements and start a fire.
• Gas leaks: fuel lines, valves and burners on gas kilns can leak and create fire and explosion risks.

Kiln Safety Controls

Installation and ventilation

• Install kilns according to the manufacturer's instructions, with required clearances from walls and combustible materials.
• Vent fuel-fired kilns to the outdoors. For electric kilns, use a kiln vent system or a local exhaust hood that removes fumes at the source.
• Place kilns in a separate room or area away from classrooms, offices and break areas when possible.
• Install carbon monoxide detection in kiln rooms, especially where fuel-fired kilns are used.
• Have a qualified electrician install dedicated circuits and disconnects for electric kilns.

Safe work practices

• Never leave a firing kiln unattended for long periods, and confirm that it has shut off at the end of the firing.
• Unplug or lock out the kiln before repairing elements or wiring, following lockout/tagout procedures.
• Keep paper, wood, solvents and other combustibles away from the kiln.
• Clean dust with wet methods or a HEPA vacuum instead of dry sweeping.
• Avoid glazes that contain lead and other toxic metals where possible, and follow the safety data sheet for each material.
• Check gas kilns for leaks with soapy water or an approved leak detection solution, never with a flame.

Personal protective equipment

• Eye protection: use infrared-filtering glasses or welding-type lenses when looking into an operating kiln. Some university safety guides recommend a shade between 1.7 and 3.0.
• Hand protection: heat-resistant gloves for opening lids and handling hot ware.
• Clothing: natural-fiber clothing and closed-toe shoes, since synthetic fabrics can melt onto skin.
• Respiratory protection: a properly fitted respirator when mixing dry materials or handling ceramic fiber insulation, as part of a respiratory protection program.

Example of Kiln Safety

A university art department ran three electric kilns in a small room next to a classroom. Students began complaining of headaches and a sharp odor during glaze firings, and an instructor noticed scorch marks on a cardboard box stored beside one kiln. The department asked its environmental health and safety team to review the room.

The review found that the kilns had no exhaust system, combustible supplies were stored within a few inches of the kiln walls and students viewed firings through peepholes without eye protection. The department installed a downdraft vent on each kiln, moved storage outside the kiln room, posted clearance markings on the floor, provided infrared-filtering glasses and trained students to check that kilns had shut off before leaving. Complaints stopped after the changes.

Frequently Asked Questions: Kiln Safety

Do electric kilns need ventilation?

Yes. Electric kilns do not burn fuel, but the clay and glazes inside them still release gases and fumes during firing. A kiln vent or local exhaust system that sends these emissions outdoors is recommended.

What eye protection should I wear when looking into a kiln?

Use glasses or goggles that filter infrared radiation, such as welding-type lenses in a light shade. Ordinary sunglasses are not designed for this purpose.

Is kiln insulation hazardous?

Some kilns use refractory ceramic fiber insulation, which can release fibers when handled or removed. Old insulation that has been heated many times may also contain crystalline silica. Use wet methods, dust control and respiratory protection when working with it.

Can a kiln cause carbon monoxide poisoning?

Yes. Fuel-fired kilns and reduction firings can produce carbon monoxide. Venting kilns outdoors, using carbon monoxide detectors and doing raku firings outside reduce this risk.