Guidance Notes on Kiln Safety for Users of Electric Kilns.

Electric kilns are designed to contain heat; even in extreme situations where a kiln malfunctions and overfires the heat will be contained within the kiln. Electric kilns are therefore not a fire hazard and are safe to operate providing common sense working practices are followed. We hope that the following notes will allay any worries, if you have any concerns please do not hesitate to contact our technical staff at the above address.

Legal Requirements

Electricity at work Regulations 1989 apply to both employed and self-employed persons. In essence the following statuary obligations apply.

  1. The kiln must be capable of being isolated from the electrical supply by fuses or circuit breaker.
  2. Control panels to be arranged so as to prevent access to live conductors.
  3. Kiln doors must be incapable of being opened while power on to the kiln, i.e. through interlock or failsafe switch system.
  4. Doors on control panels and electrical connection chambers must not be left off during kiln operation.
  5. Ideally kilns should be sited in a separate room with sufficient ventilation to remove heat and fumes.
  6. It is recommended that at least two persons should be trained to operate kiln.

What is an electric pottery kiln?

Kilns are chambers designed to contain heat so that temperatures can be achieved sufficient for clay to be converted to ceramic. The source of heat in electric kilns is the heating elements, wire coils that produce heat as a result of resistance to the flow of electricity. They are similar to the elements in an electric fire. The kiln chamber is constructed from insulation materials that contain the heat reflecting it back into the kiln. A kiln is really a box full of electric fires.

Cromartie Kilns have the following safety features.

  1. Over-temperature safety cut-off devices with all kilns.
  2. Anti-spike electrical surge protection with all controllers.
  3. Power On light - red warning light illuminated when the kiln powered up.
  4. Element On Lights - white lights that illuminate when power supplied to elements.
  5. Fuses - 3amp controller fuses fitted behind front panel of front loaders kilns
  6. Interlock - switches off power to elements before opening the door, essential safety equipment. Kiln won’t work if not in place.
  7. Energy Regulators - controls power to each bank of elements for fine-tuning.

Safe Practice

  1. Interlocks and Lid Safety switches prevent power from reaching elements when the door is opened, these should never be over-ridden or tampered with.
  2. Door opening - opening when hot, i.e. in excess of 100°C may cause brickwork to crack. Front loaders have taper fit doors that are held fast by expansion when hot, if forced open serious damage can be done to the brickwork.
  3. Ventilation - essential to have moving air for heat and fumes, see below.
  4. Supervision of firing – always supervise kiln firing whenever possible. It is essential to supervise the first few firings of any new kiln.
  5. All current Cromartie kilns are fitted with over-temperature cut-off devices, which shut down the kiln in the event of a component failure causing the kiln to reach 20°C hotter than the target temperature.
  6. All current Cromartie controllers are fitted with anti-spike devices to help prevent damage caused by electrical surges.
  7. Despite the safety features, damage can still occur through poor programming, for example, earthenware fired to a stoneware temperature will melt and could destroy kiln bricks and elements.
  8. Electrical Work – must only be carried out by a qualified electrician.

Maintenance

Kilns do not require very much maintenance, it is important that element grooves are kept clean by gently vacuuming up the accumulated dust. Take care not to chip oxide layer on the surface of the elements. Wiring Inspection should be carried out once or twice a year. After isolating the power open the inspection panel and look for blackened wires that might indicate loose connections. Ensure all element connections are tight and that the porcelain isolators are not cracked. Glaze spots should be removed by gently scraping or digging out; if left glaze will melt on each firing and will eat into brickwork and elements.

Positioning the Kiln

For front loaders preferred distance from walls 30cm side, 45cm rear to give access for servicing. If walls are of non-combustible material and space is tight, 10-15cm would suffice. Cromartie Top loading kilns are all fitted with castors so can easily be moved for maintenance. Castors must be locked during firing. Floors should be of non-combustible material, a paving slab or similar will suffice over a wooden floor. At least 1m clearance should be allowed between the top of the kiln and the ceiling.

Ventilation

Kiln rooms should have sufficient ventilation to prevent heat building to uncomfortable levels and to exhaust any fumes generated by clay and glazes being fired. An open window is usually sufficient, but a domestic fan extractor will ensure fumes and excess heat are removed more efficiently. Always ensure that there is a source of air to the room to replace air extracted by the fan. Cromartie can supply flexible metal ducting with fan and accessories to attach direct to the workhorse top loading range allowing fumes to be exhausted to atmosphere.

Ken Shelton