Does Your Process Require a Class A Oven?

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Industrial Class A Ovens

If you process a flammable product or remove combustible vapors from a product in an oven, you will need a Class A oven that meets NFPA 86 requirements. Flammable volatiles that pose a potential explosion or fire hazard can originate from paints, powders, inks, and adhesives. Potential threats may also originate from finishing processes, such as dipped, coated, sprayed, and impregnated materials as well as from polymerization or other molecular rearrangements. Combustible materials include substrate material, wood, paper, plastic pallets, spacers and packaging materials.

If you have more than one oven in your facility and are processing materials that require Class A, you may want to have all the ovens be Class A. This will remove the risk of someone using a non-Class A oven for a material that requires it.

Inadequate training of operators, lack of proper maintenance, and improper application of equipment can cause serious injury. Operators must be trained to understand the ratings of the equipment and how they relate to the processing of the product. Complying with the latest safeguards required to minimize explosion hazards is an absolute priority and an area where no discounts or deviations should be made. An industrial oven explosion inside a facility could potentially mean catastrophic damages and life-threatening risks. Such incidents can impact all aspects of the operation of a company, and in the end, its very existence in business.

The NFPA 86 Standard for Ovens and Furnaces

Understanding and complying with these National Fire Protection 86 standards is the best way to ensure long-term safe operation of ovens that are either fuel-fired or that process flammable solvents or combustible materials. For the latest safeguards required to minimize explosion hazards, get a copy of NFPA 86 Standard for Ovens and Furnaces, from the National Fire Protection Association (

As there is a wide range of industrial ovens to cover all possible application requirements out there, the NFPA 86 standard has grown to take everything into account, from the suitability of the materials that are used to comprise an oven, to the safety and precautionary interlocks that will serve as fail-safes in case things go wrong. Depending on the oven type, there’s a dedicated section of the standard that covers the full spectrum of its specialized functionality, and its specific role.

Class A Oven Requirements

Explosion relief area: Through the incorporation of a panel or special doors, there must be some form of a pressure-relief passage 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 force ventilation: Class A ovens must have positively forced ventilation sized to accommodate the amount of combustible product in the maximum oven load. This means that an exhaust fan separate from the recirculation fan must be installed.

Airflow Safety Switch: All ovens shall have the 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 is required to ensure that all flammable vapors and gases are purged out of the chamber before the heating elements are activated. Failure to maintain the minimum required pre-ignition purge airflow shall stop the pre-ignition purge and reset the purge timer.

Safety-design data form: A safety-design data form must be completed and attached to the oven if solvent atmospheres are present. This form must include the solvent in quantity per hour or batch, purge time, operating temperature, and exhaust rating.

Other considerations

The environment in which the oven resides tempers all the above requirements. Class A ovens without additional modification are not usable in hazardous atmosphere areas such as those requiring Class 1, Group D electrical construction. If they are to be utilized in hazardous areas, additional safety precautions spelled out by the National Electric Code must be met.

Many of the NFPA guidelines and specifications are temperature dependent due to the rate of evolution so it is important that a Class A rated oven never be loaded hot.

Purchasing a Class A Oven

When purchasing a Class A oven, you will need to understand; the process or solvent type and the amount of solvent released per batch or per hour to ensure your process is compatible with the solvent rating of the oven being specified. The user is responsible for the safe operation of their Class A oven. It is important to reference the safety sheet (SDS) of the material being processed and understand how the process temperature profile can affect the rate of solvent release.

Class A Oven Maintenance

Despatch incorporates all pertinent NFPA required safety testing, visual inspection and required documentation in all Preventative Maintenance and Calibration Service Agreements. NFPA 86 has requirements for annual inspection, operational testing, documentation of testing, and visual inspection of certain 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.


As you can see, NFPA compliance does not end with the delivery of the oven. Instead, as the oven user, there are many actions required for oven compliance during selection, setup and use.

This is a simple overview of Class A Oven Safety guidelines. Please consult the full NFPA 86 standard for all 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.

At Despatch your safety is a high priority when it comes to using our ovens and furnaces, for more information about Despatch direct gas-fired and electrically heated ovens, or to find out more about our training courses and high value subscription programs, contact us today. You can also download “Understanding Class A Ovens” from our website.