Taking Over Where Oven Manufacturers Leave Off
The 2003 edition of NFPA 86, a National Fire Protection Association standard, addresses the safety aspects of the design, construction and operation of gas- and oil-fired ovens and furnaces. It details the requirements for preventing fire and explosion hazards associated with the processing of materials in ovens, furnaces and related equipment. NFPA 86 states: The heat processing of materials involves serious fire and explosion hazards that can endanger the equipment, building or personnel.
When a new oven is installed, the oven manufacturer is expected to provide a piece of equipment designed in accordance with the latest edition of NFPA 86. Beyond the assembly of the oven, however, there are additional matters that need attention to make the operating oven fully compliant. End users, though, sometimes overlook important installation issues if they do not fully understand or carefully apply NFPA 86, which may jeopardize the safety of their workplaces.
Oven LocationIt would be ideal to install an oven in a detached building or separate fire-rated cut-off room so that other production equipment is not exposed to any fire or explosion hazards associated with the oven. While that would be ideal, it is not required and often not feasible. Industrial ovens typically are found in production areas near other process equipment such as paint spray booths and dipping or coating tanks. Ovens even may be located adjacent to storage areas. When locating an oven, NFPA 86 stipulates that the units must be placed in a way that minimizes exposure to:
- Building structural members.
- Combustible materials.
- Process equipment.
- Flammable vapors.
- Power equipment.
- Automatic fire-sprinkler risers.
Combustible stock and combustible building construction components should be separated from hot external surfaces of the oven, external heater boxes and associated ductwork. Insulation, area ventilation and enough distance should be provided so that combustible materials are not exposed to temperatures above 160oF (71oC).
Flammable vapors generated by painting and coating processes need to be controlled at their points of origin with appropriate exhaust ventilation. Ovens should be located so that they will not become sources of ignition to these flammable vapors. In general, ovens should be located outside of areas around flammable or combustible liquid processes that are classified for the use of explosionproof electrical equipment. For guidance, see NFPA 497, “Recommended Practice for the Classification of Flammable Liquids, Gases or Vapors and of Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas.”
The Oven OperatorNFPA 86 requires that there be an oven operator. The job of the operator is to monitor the oven and take appropriate action when needed. Often, the oven operator may be assigned other process tasks, but in the event of an off-normal condition, it is essential that the oven operator be available to promptly implement an emergency oven shutdown.
The standard describes the characteristics of an oven operator as alert, competent, trained, knowledgeable, proficient and effective. In other words, the oven operator is not just an attendant.
NFPA 86 directs the oven manufacturer to provide procedures for oven operations, including:
- Normal startup.
- Normal shutdown.
- Emergency shutdown.
The operating procedures are to be written and available at all times to oven operators, who should not be allowed to deviate from written procedures. Deviation is a typical cause or contributing factor to oven explosions.
Venting Fuel-Fired OvensWhen an oven manufacturer ships a “finished” oven to the customer, there still is more work to be done at the site before the oven is complete. For fuel-fired units, exhaust ductwork is needed to vent products of combustion, and for fuel-gas-fired units, a number of devices in the equipment's fuel-gas piping may need to be vented.
NFPA 86 stipulates that fuel-fired ovens must be equipped with an exhaust system and that no portion of the building shall be used as a part of that exhaust system. Ductwork is needed to carry exhaust outside of the building.
The devices on equipment fuel-gas piping that may require venting to an approved outside location include pressure regulators, fuel-gas pressure switches and relief valves. If a double valve-and-vent safety-shutoff valve assembly is used, that vent also will need to be extended to an approved outside location.
The vents from diaphragm-operated devices such as pressure regulators and fuel-gas pressure switches can be “manifolded” together. Vents from relief valves and double valve-and-vent assemblies also can be manifolded together. Guidance for sizing manifolded vent lines is contained in NFPA 86.
Typically, vents need to terminate to an approved outside location. However, there are conditions when vents can be terminated to an inside location. For guidance on selecting the termination point for vents, see Annex A.188.8.131.52.2 of NFPA 86.
Inspection and MaintenanceOnce a new oven has been installed and commissioning tests have been completed, an ongoing process of inspection, testing and maintenance should begin. Ovens have numerous safety controls, and periodic attention is essential to maintain overall system reliability.
NFPA 86 places the responsibility of establishing an inspection, testing and maintenance program on the oven user. To establish a program, the features requiring inspection or testing must be identified, and needed inspection frequencies must be establish based on the specific oven, control system and installed location (i.e., the environment). For guidance on inspection, testing and maintenance, see NFPA 86, Annex C.
Inspections are visual activities that identify conditions such as leaks, physical damage, tampering, corrosion or incorrect device settings. Testing is a physical activity that verifies device function, interlock setpoint, device calibration or alarm setpoint. Maintenance is a physical activity provided when needed, based on a manufacturer's schedule or as a result of inspection and testing.
The information in this publication was compiled by Zurich Services Corp. from sources believed to be reliable. We do not guarantee the accuracy of this information or any results and further assume no liability in connection with this publication, including any information, methods or safety suggestions contained herein. Moreover, Zurich Services Corp. reminds you that this publication cannot be assumed to contain every acceptable safety and compliance procedure or that additional procedures might not be appropriate under the circumstances. Accordingly, this publication is not intended to relieve any user or company from taking it upon himself or itself to gain a thorough understanding of NFPA codes and standards and the requirements for their own operation. The subject matter of this publication is not tied to any specific insurance product nor will adopting these procedures ensure coverage under any insurance policy.