WORPLACE HEALTH & SAFETY IN KILN OPERATIONS

Transcription

1 WORPLACE HEALTH & SAFETY IN KILN OPERATIONS David Coggins INDEX Section 1. Section 2. Section 3. Section 3.1 Section Section Section 3.2 Section 3.3 Section 3.4 Section 3.5 Section 4. Section 4.1 Section 4.2 Section Section Section Section Section 4.3 Section Section Section Section Section 5. Section 5.1 Section 5.2 Section 5.3 Section 5.4 Section 5.5 Section 5.6 Section 5.7 Section 6. Section 7. Introduction Definitions Hazards Fume Emissions Electric Kilns Gas Kilns Hot Surfaces Dust Emissions Electrical Hazards Gas Hazards Location General Requirements Electric Kilns Electric Kilns Inside Electric Kilns Outside Clearance Kiln Instructions Gas Kilns Enclosure Flue Clearance Kiln Instructions Kiln Operation - General Notes RCF Lined Kilns Responsibility Protective Clothing Kiln Ventilation Door/lid Lock Kiln Supervision Gas Burners - Lighting Maintenance References

2 1. INTRODUCTION. This document covers procedures for location and operation of pottery kilns. 2. DEFINITIONS Pottery kilns refer to the ovens used to fire ceramic and glass wares. The use of kilns involves the loading, programming, firing and unloading of the kiln. Safety guidelines are included for electric and gas fired kilns. Kilns are constructed of two main insulating materials as follows:- a. Refractory ceramic fibre (RCF) materials. These are produced from molten silica/alumina mixtures and formed into blanket, board or other forms. RCF is white in colour and flexible. b. Refractory insulating (RI) brick. These are produced from aerated and fired clay mixtures, cut to various shapes. RI bricks are white to buff in colour and rigid. 3. HAZARDS 3.1 FUME EMISSIONS Kiln emissions can include sulphur oxides, nitrogen oxide, carbon dioxide, carbon monoxide, flourine, chlorine, metal oxides, etc Electric Kilns. Electric kilns operate by radiation from elements and produce no fumes themselves during operation - all fumes emitted are produced from the products fired in the kiln. The most common emission is oxides of sulphur from the clays used, followed by metal oxides from glazes. These emissions are totally under the control of the kiln operator. Electric kilns need to be ventilated only if enclosed in a room space - see LOCATION.

3 Positive ventilation units for small electric kilns are available. These operate by creating a negative pressure inside the kiln and extracting the fumes. These are then mixed with the cooler air, and exhausted to the atmosphere Gas Kilns Gas kilns operate by the combustion of Liquid Petroleum Gas (LPG) or similar. These kilns produce carbon monoxide and carbon dioxide as by-products of the combustion process and must have a suitable flue installed to carry these gases away from the operator - see LOCATION. Other gases are produced from the ware such as sulphur oxide and metal oxides will be carried away with the by-products of combustion. 3.2 HOT SURFACES Pottery kilns may operate at internal temperatures exceeding 1300 degrees centrigrade. Depending on the quality of wall insulation, the temperature of the external surface may exceed 150 degrees centigrade. It is essential that contact with all kiln surfaces are avoided during firing, unless protective equipment is worn. Refer to the LOCATION and OPERATION sections for further details. 3.3 DUST EMISSIONS Silica/Alumina (clay) dust is produced by all operations associated with ceramics, from original production to finishing and firing. The dangers of microfine particles of silica are well documented and these particles are produced at all stages of ceramic production. Electric kilns produce silica dust emissions because of abrasive actions of the expanding and contracting elements on the bricks or element supports, dust produced during firing explosions and eruptions, and dust falling from ware. This can be reduced or eliminated from the kiln by good house-keeping, ie. regular vacuum cleaning of the kiln interior. Refer to MAINTENANCE. In addition to the above, electric and gas kilns insulated by RCF are capable of producing microfine fibre particles. Worksafe Australia in their National Standard for Synthetic Mineral Fibres recommend an exposure standard for ceramic fibres of 0.5 fibres per millilitre of air (f/ml). Tests by the Qld Govt Division of Workplace Health and Safety have produced a concentration of only 1.03 f/ml DURING INSTALLATION of ceramic fibre during manufacture. Normal loading and unloading of kilns insulated by RCF offer no greater risk than any other operation in the production of ceramics. HOWEVER - if the surface of the fibre insulation is damaged in any way, care should be taken during loading or unloading to avoid disturbing the surface and action should be taken to have the kiln relined as soon as possible. 3.4 ELECTRICAL HAZARDS

4 Electric kilns must meet the appropriate Australian Standard AS 3100, and be fitted with a door/lid power cut off switch, so that all power is removed from the kiln when the door/lid is opened. Installation of the kiln must be according to AS 3000, by properly licenced persons, and the kiln must be serviced by properly qualified persons. A main power switch (isolating switch) must be located adjacent to the electric kiln, capable of removing all power to the kiln. It is advisable to switch the main power off to the electric kiln while loading or unloading, to avoid any possible shock hazards, should any fault condition occur. 3.5 GAS HAZARDS Gas kilns must be installed in accordance with the Petroleum and Gas (Production and Safety) Act 2004 by properly licenced gasfitter. Under no circumstances are unauthorised persond to interfere with, alter or adjust any LP Gas installation. All gas control equipment must be regularly maintained and tested by qualified persons. Flame failure gas cut-off devices MUST be fitted to all burners, and MUST always be in good operating condition. 4. LOCATION 4.1 General Requirements for kiln location:- Access to location for kiln delivery, ie. access for delivery vehicle, access through doorways, Access from pottery rooms to kiln - carrying wares over long distances presents risks. Access to power or gas supplies. 4.2 Electric Kilns Electric kilns located inside a building must be in a separate room with a lockable shutter or door. An exhaust fan capable of exhausting the volume of the air within the room in approx. 5 minutes must be installed, with a facility for the inlet of a similar volume of air. For example, a room 4 metres wide by 2 metres deep by 3 metres high, which is a standard size for kiln rooms in schools, has a volume of 24 cubic metres. Thus a fan of capacity of 5 cubic metres per minute or 80 litres per second at least should be installed Electric kilns located outside a building must have cross ventilation of the location, with no nearby windows into occupied spaces. The area must be covered by a waterproof roof, wide enough to prevent water entry onto the kiln entry during storms. The area must be securely enclosed by a mesh or wire fence, with a lockable gate to prevent unauthorised entry, and to prevent risk of burns or interference with the kiln controls An electric kiln should always be located at least 200mm clear of any vertical wall surface, and should be installed on a concrete floor. If concrete is not available, the wooden floor must be protected with

5 sheeting such as Hardiflex or with ceramic tiles. Free access to all control panels or wiring must be allowed for servicing Refer to kiln instructions or the manufacturer for specific instructions for each kiln Gas Kilns Enclosure. Gas kilns should be located in an area separate from any normally occupied locations, preferably in a separate free-standing lockable shed or enclosure, constructed of non flammable materials. Security must be provided to prevent unauthorised access to the kiln, to prevent possible injury from burning, or interference with kiln controls Flue. Gas kilns must be provided with a suitable flue to carry away the gases produced. Consultation with the manufacturer of the kiln may be necessary to ascertain the required design and area of the flue for complete exhaustion of the fumes. Flues should always be manufactured from stainless steel for long life Clearance must be available to allow access to all burners and dampers Refer to kiln instructions or the manufacturer for specific instructions for each kiln. 5. KILN OPERATION - GENERAL NOTES 5.1 Refractory Ceramic Fibre (RCF) Lined Kilns. a. Do not allow any person to prod, poke or damage the surface of the RCF in any way. b. Care must be taken to avoid brushing against the fibre surface during loading/unloading. c. If any skin irritation is noticed during loading/unloading, disposable sleeving should be worn. d. If any throat irritation is noted during loading/unloading, a disposable mask should be worn. e. If excessive dust is observed during loading/unloading, the kiln should be relined. 5.2 Responsibility a. One trained person should be responsible for the kiln operation. b. Children and students must never be allowed near an operating kiln. c. Kiln controls must be set correctly according to the kiln operating instructions. d. Always check that the correct temperature settings have been made. 5.3 Protective Clothing a. When removing bungs from a kiln during firing, protective gloves must be worn. b. When looking into a hot kiln through a spyhole, protective tinted glasses must be worn. c. Safety glasses must conform to Australian Standards (refer AS ). 5.4 Electric Kiln Ventilation

6 An electric kiln should be ventilated up to 600 degrees C during a bisque firing to ensure that the gases produced from the clay can escape. Failure to properly ventilate a kiln will cause premature failure of the frame and/or casing. 5.5 Door/lid Lock The kiln door/lid must be locked if equipped, or the kiln enclosure locked, to avoid accidental opening of the hot kiln. 5.6 Kiln Supervision Kilns must not be left unattended for long periods of time during firing. An electric kiln should be checked at least once each hour, a gas kiln should be checked every half hour. If the kiln is fitted with an automatic controller, these periods may be extended. In all cases arrangements should always be made to check that the kiln is switched off at the completion of firing, whether automatically or manually. Automatic controllers are not fool-proof, and many kilns and loads of pottery have been destroyed by overfiring. 5.7 Gas Burners - Lighting When lighting gas burners, the kiln door/lid must always be open, to avoid any possible build up of unburnt gas in the kiln causing an explosion. 6. MAINTENANCE Kiln maintenance consists of regular vacuum cleaning to remove dust and pot shards, particularly around the elements. Lid/door locks should be lubricated regularly, and door seals must be checked for tightness and adjusted if necessary. Great care must be taken when cleaning RCF lined kilns to avoid damage to the surface. Use ONLY a vacuum cleaner to clean RCF kilns - NEVER use brushes. If the RCF appears to be dusty and flaking, it should be replaced as soon as possible. Any change to regular firing times or results should be referred to qualified repairers for attention. Maintenance to gas or electrical equipment must never be attempted by unauthorised persons. 7. REFERENCES 7.1 Qld Dept of Education WHS document HS-10/ National Standard for Ceramic Fibres, Worksafe Australia 7.3 Australian Standard AS Welding filters