In areas where flammable gases or other hazardous materials exist in the atmosphere, it’s crucial to mitigate the risk of ignition or explosion by investing in hazardous location motors. While standard electric motors cause catastrophic damage in these environments, flame-proof and explosion-proof motors are designed to keep explosions contained within a sealed environment and cool escaping gases so that they don’t ignite surrounding materials in the atmosphere.
While the end-products are similar in many respects, it’s important to understand the distinctions between flame-proof and explosion-proof motors to ensure that you get the right product for your application and geographic location. Using the wrong type of motor could create easily avoided financial and safety risks in your operation.
Flame-proof Motors
By design, flame-proof motors contain sparks, flares, and other internal ignition elements to allow for safe operation in environments where explosive materials exist. Flame-proof is the term used for motors that are certified for compliance with international standard International Electrotechnical Commission (IEC) 60079-1, Equipment Protection by Flame Proof Enclosures.
IEC standards define specific methods for constructing and testing flame-proof equipment. Construction standards include specific guidance for flame path width, cooling, and internal/external temperature tolerances to ensure that no part of the motor can ignite atmospheric threats.
IEC testing standards examine the following:
- Service/class temperatures
- Reference pressure – waveform smoothing at 5kHz
- Flame path width and gaps
- Ignition tests with variety of explosive gas mixtures, five tests per mixture
- Flame transmission
- Enclosure strength
- Enclosure must contain explosions at 1.5 times standard explosive pressure
Flameproof motors are required in any application that contains gas, dust, vapor, or any other flammable material that could be accidentally ignited. Risks posed by improper motor usage in hazardous areas range from fines and minor injuries to severe facility damage and death.
Explosion-proof Motors
Explosion-proof motors also have a special enclosure to prevent internal ignition elements from interacting with flammable external material. When explosions do occur, they must be contained within the motor, and the elements must be cooled below the flashpoint of the external material before being expelled from the motor.
The differences between explosion-proof and flame-proof motors largely have to do with the agencies that regulate them. While flame-proof motors adhere to IEC regulations, explosion-proof motors are subject to rules established by the American National Standards Institute (ANSI) and the Underwriters Laboratories (UL). Specifically, explosion-proof motors must adhere to ANSI/UL 1203, Explosion-Proof and Dust-Ignition-Proof Electrical Equipment for Use in Hazardous (Classified) Locations.
While much overlap exists between IEC flame-proof standards and ANSI/UL explosion-proof standards, notable construction differences in ANSI/UL regulations include:
- Weatherproofing for outdoor enclosures
- Minimum allowed wall thickness in enclosures
- More detailed gasket requirements
- Differing flame path width and gap requirements broken down by intended use
- More stringent standards for valves, plugs, fittings, and other components
- Rust/corrosion protection
- Additional standards for non-metallic enclosures
Testing guidelines for ANSI/UL-based explosion-proof certification also differ from IEC flame-proof standards:
- More lax reference pressure standards on gas mixtures
- Enclosure must contain explosions at four times the standard explosive pressure for 10 seconds
- Waveform smoothing at 2KHz
- Stricter flame path testing tolerances
- Ignition tests with variety of explosive gas mixtures, 10 tests per mixture
Similar to flame-proof motors, explosion-proof motors must be used in any hazardous environment where explosive materials such as dust or gases are present in the atmosphere. What type of explosion-proof motor is required depends entirely on the Class and Division of the hazardous work area.
Key Differences
The terms “flame-proof” and “explosion-proof” refer to very similar products that adhere to two different sets of standards. Flame-proof is the preferred international term, while explosion-proof is the term commonly used in North America. The primary differences are as follows:
- Differing flame path tolerances based on application/intended environment
- Explosion-proof motors undergo more intense explosion testing than flame-proof motors
- Explosion-proof motors tend to be more heavily constructed than flame-proof motors
- Flame-proof motors usually require special tools to open the flame-proof enclosure
- Explosion-proof motors can be safely field drilled, while flame-proof motors cannot
Even with these subtle differences, both types of hazardous location motors vary widely within their own categories based on the ANSI/UL and IEC Division, Class, and/or Zone classifications that define their operating environments. If you’re unsure exactly what type of motor you need to operate safely in a hazardous environment, it’s best to consult an expert or your vendor to ensure that you acquire the appropriate equipment.
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