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Does Your Process Require a Class A Oven?

Industrial Class A Ovens

Do you process flammable products or remove combustible materials in an industrial oven? If you do, you need a Class A oven that meets NFPA® 86 requirements. Flammable volatiles posing a potential explosion or fire hazard can come from paints, powders, inks, and adhesives. Potential threats can also come from finishing processes, such as dipped, coated, sprayed, impregnated materials, and polymerization or other molecular rearrangements. Combustible materials that can pose threats include substrates, wood, paper, plastic pallets, spacers, and packaging materials.

It doesn’t take much for a serious injury to occur when processing flammable products or combustible materials. Inadequate operator training, poor maintenance, and improper equipment application can all cause serious injuries. According to the Operational Health and Safety Administration (OSHA), there were 2,654,700 workplace injuries in 2020, with 4,764 fatal. Industrial accidents like these can cost companies a bundle.

Training operators to understand equipment ratings and how they impact product processing helps prevent workplace injuries. So, does complying with the latest safeguards minimize explosion hazards. Complying with existing safeguards should be a priority at your company, with no discounts or deviations. Put another way, ignoring industrial oven safety features or removing safeguards is courting disaster, the fallout of which could threaten your company’s existence.

NFPA 86 Standard for Ovens and Furnaces

Understanding and complying with the NFPA 86 standard for industrial ovens and furnaces safeguards the operation of direct fuel-fired ovens used to process flammable solvents or combustible materials. NFPA 86 covers all possible application requirements. That includes everything from material suitability comprising an oven, to the safety and precautionary interlocks serving as fail-safes, and everything in between. NFPA 86 also provides a dedicated section covering the full spectrum of an oven’s specialized functionality and specific role depending on oven type. (Despatch Class A ovens—whether benchtop, walk-in, or conveyor—all meet NFPA 86 requirements.)

Consult a copy of NFPA 86 Standard for Ovens and Furnaces from the National Fire Protection Association (NFPA) to learn the latest safeguards to minimize explosion hazards.

Class A Oven Requirements

Three rating classifications of ovens exist—Class A, Class B, and explosion-proof. Class B ovens are more straightforward and basic than Class A ovens. Class B ovens support clean processes, which include no flammable volatiles or combustible materials being heated. Electrically-heated Class B ovens must have an airflow safety switch, a manual reset excess temperature control, and backup contactors as fail safes.

The explosion-proof rating can be expensive compared to Class A and B. This rating isn’t the same as Class A requirements and shouldn’t be confused with it. Explosion-proof industrial ovens are complex thermal processing units with requirements far too extensive to cover in detail in an article like this. NFPA 70 addresses this rating if you want to learn more. NFPA upgraded the standard for 2023.

Requirements for Class A Ovens (gas-fired)

Class A applications require specially designed ovens for processing direct, gas-fired equipment or products involving flammable volatiles or combustible materials. These critical features include:

  • Explosion relief area: Incorporating a panel or special doors provides some form of a pathway to allow a controlled release of pressure from inside the oven in case of an explosion. The required explosion-relief area must be equivalent to at least one-fifteenth of the oven’s interior volume or a 15:1 volume-to-venting-area ratio (cu ft/sq. ft).
  • Positive forced ventilation: Class A ovens must have positively forced ventilation sized to accommodate the amount of combustible product in the maximum oven load. That means the oven needs an exhaust fan separate from the current recirculation fan.
  • Airflow safety switch: Class A ovens need an exhaust fan motor starter and airflow switch interlocked to prevent operation of the heating units unless the exhaust fans are running.
  • Purge timer — A purge timer ensures that the oven purges flammable vapors and gases from the chamber before the oven activates the heating elements. Failure to maintain the minimum required pre-ignition purge airflow stops the pre-ignition purge and resets the purge timer.
  • Manual Reset Excess Temperature Controller This controller is set at approximately 50°F higher than the oven setpoint or maximum rated temperature. If the industrial oven or furnace exceeds the temperature setting, the hi-limit shuts down the burner.
  • Flame Safety/Spark Ignition Control Direct gas-fired industrial ovens feature a flame supervision device. The control sends a high-voltage signal to the spark plug for ignition at startup by opening the pilot gas valve. That allows the oven to ignite the pilot flame. Once the control detects a pilot flame, the high-voltage signal stops and the main gas valves open. That permits ovens to go to high fire and start operations. If the oven fails to detect a pilot flame, the flame safety stops the ignition attempt.
  • High-Low Gas Pressure Switch If a sensor detects that the gas flow is too high or too low, the switch automatically shuts the oven down. The oven must supply even gas pressure to maintain the correct air-to-fuel ratio for proper flame characteristics and prevent combustible vapor build-up.

In addition, companies must attach a completed safety design data form for Class A ovens or ovens if solvent atmospheres are present. This safety form must include the solvent quantity per hour or batch, purge time, operating temperature, and exhaust rating.

Requirements for Class A Ovens (electrically-heated)

Electrically-heated Class A industrial ovens need some additional unique features not found in direct-fired Class A ovens, including:

  • Additional kilowatts (if needed)– These Class A ovens often require additional kilowatts. The added kilowatts help the oven forcibly remove heat from work areas using an exhaust fan. Class A ovens may also require more heaters to maintain process temperatures, which depend on heat-up time and maximum operating temperature. If you add more kilowatts, the industrial oven’s response time may be poor, or the oven may not be able to reach the operating temperature necessary to run the load.
  • Extra backup contactors — If the industrial oven comes with extra kilowatts, you need to add additional backup contactors as adequate oven safeguards. Backup contractors will ensure that the heaters shut off should the primary contractors become fouled or fused. A contactor is an electromechanical controller used to make or break the connection between the load and power supply. 

Additional Class A Oven Considerations

The oven’s environment impacts all the above requirements, which you must consider when buying Class A ovens. Class A ovens used in hazardous atmosphere areas, such as those requiring Class 1, Group D electrical construction, require additional modifications. They must also meet additional safety precautions spelled out by the National Electric Code. Many NFPA guidelines and specifications for Class A ovens are temperature-dependent thanks to the rate of evolution. So, never load Class A ovens when hot.

You also need to understand the process or solvent type and the amount of solvent released per batch or hour when buying Class A ovens. That ensures your process is compatible with the solvent rating being specified. Keep in mind that the user is responsible for the safe operation of their Class A oven. Reference the safety sheet (SDS) of the process material to understand how the temperature profile affects the rate of solvent release.

Another consideration is the manufacturer’s services and service response time. What other services does the oven manufacturer offer and how fast do they respond to service and support requests.? How quickly do they respond to parts requests?  

Class A Oven Maintenance

Inspecting your Class A oven should be routine to ensures its proper and safe to operate at all times. Implementing an oven maintenance program may seem like an unnecessary expense or a waste of time, but it’s not. Compared to the cost of a single untimely accident, the cost of implementing a maintenance program is a bargain. When it comes to handling flammable volatiles or combustible materials, safety always comes first.

Despatch incorporates all pertinent NFPA-required safety testing, visual inspection, and required documentation in all Preventative Maintenance and Calibration Service Agreements for its Class A ovens. NFPA 86 also requires Class A oven owners to do annual inspections, operational testing, documentation of testing, and visual inspection of specific oven components such as:

  1. Safety interlocks
  2. Set point of temperature, pressure, and flow devices used as safety interlocks.
  3. Pressure and explosion relief panels.
  4. Gas heater components.

Remember that troubleshooting gas-fired ovens differs from troubleshooting electrically heated Class A ovens. Know the difference before addressing issues with your Class A oven. Savvy companies establish maintenance schedules to achieve maximum efficiency and high performance for their industrial ovens.

Safety is Good Business

This article is a simple overview of Class A Oven requirements and safety guidelines. Please consult the full NFPA 86 standard for all the specifications and additional details. The consistent review of code updates, qualified testing and inspection of operation of safety devices, and training of operations and maintenance personnel is simply good business. It’s also smart business. It can save your company from a costly disaster.

Safety is a high priority at Despatch when using our ovens and furnaces. It should be at your company, too. For more information about Despatch Class A Ovens, or to find out more about our training courses and high-value subscription programs, contact us today. You can also download our guide “Understanding Class A Ovens”. The battle for safety is won by doing the little things.