If your product must be marked for use in a Class I (Gas) Hazardous Location, it must comply with one or more protection methods suitable for Class I environments. Not all protection methods are practical for all product types, and the earlier in the design cycle these protection methods are considered the easier compliance will be.
Below is a list of protection methods suitable for Class I Locations (based on the 2017 Edition of the NEC). This list includes both Division and Zone scheme protection methods, as these can be considered interchangeable in terms of product compliance.
Explosionproof – Allows marking for Division 1. Enclosure which can withstand an internal explosion is used to house components not suitable for the Hazardous Location.

  • Pros: Provides an off-the-shelf option for otherwise unacceptable installations.
  • Cons: Expensive; installation requires the use of explosionproof fittings and sealing compound at wiring entry.

Flameproof – Allows marking for Zone 1. Enclosure which can withstand an internal explosion is used to house components not suitable for the Hazardous Location.

  • Pros: Typically provides an off-the-shelf option for otherwise unacceptable installations.
  • Cons: Expensive; installation requires the use of explosionproof fittings and sealing compound at wiring entry.

Purged & Pressurized – Allows marking for Divisions 1 or 2, or Zones 1 or 2. Enclosure housing components not suitable for the Hazardous Location are provided with a protective gas supply (typically compressed air) to prevent the ingress of flammable gas. A sealed enclosure that does not leak is “pressurized” with the gas. Whereas a “purged” enclosure leaks by design or by nature and an adequate flow rate of the gas must be maintained.

  • Pros: Provides an off-the-shelf option for otherwise unacceptable installations.
  • Cons: Requires air supply (typically compressed air) at equipment. May increase Pollution Degree inside equipment. Unexpected shutdown of equipment if air supply fails.

Intrinsic Safety – Allows marking for Divisions 1 or 2 or, Zones 0, 1 or 2. Equipment is inherently incapable of igniting the gas environment by limited energy.

  • Pros: Greatest flexibility for installation. Ordinary location wiring methods are permitted.
  • Cons: Expensive certification process. Very limited energy requirements (maximum 12W fault power, can require <0.5W fault power).

Encapsulation – Allows marking for Zones 0, 1 or 2. Equipment is encapsulated (potted) to prevent the electrical parts from exposure to the atmosphere.

  • Pros: Can be a simple means to comply with Hazardous Location requirements (just add potting compound).
  • Cons: Adds cost and time to manufacturing. Adds weight to product.

Nonincendive – Allows marking for Division 2. Equipment is inherently incapable of igniting the gas environment by limited energy and/or non-sparking/arcing parts and construction.

  • Pros: More flexibility for installation, ordinary location wiring methods are permitted (limited energy only). This is typically an easier compliance path for low power products with no moving parts and no electromechanical components (ex. electronic product using only solid state devices).
  • Cons: Only suitable for US and Canadian certifications. Not applicable to International markets.

Increased Safety – Allows marking for Zones 1 or 2. Equipment is protected by non-sparking/arcing construction.

  • Pros: Can be an easier compliance path for electrical products without sparking/arcing parts (ex. transformer, brushless motor).
  • Cons: Stricter construction requirements. Thermal protective devices need to be suitable for the Hazardous Location or located remotely.

Hermetically Sealed – Suitable for Division 2, not required to be marked.

  • Pros: Does not require to be marked for Division 2. A formal declaration by the manufacturer is acceptable (ex. Datasheet specifying a Helium Leak rate).
  • Cons: Practical only for components, not for end-products. Surface Temperatures still need to be considered.

Conclusion – Multiple Protection Methods: The more complex a product, the less likely it is that one protection method will be enough to bring the entire product into compliance. In many cases multiple protection methods may be needed, with different protection methods utilized for different parts of the product.

As an example, an Industrial Machine might use a “Purged” or “Pressurized” control panel, while integrating utilization equipment that is “Explosionproof” (motors or heaters). This is a fairly simple example considering that today’s industry requires an increasing amount of automation, which leads to more sensors and radio devices. It is common for sensors to be protected by various protection methods (explosionproof, encapsulation, intrinsic safety, etc.) – be aware that this may affect their installation requirements. Whereas radio device antennas may need to be installed exterior to the control panel enclosure and also be separately protected. It pays to know all the protection methods!

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