You're right to be skeptical. The concept of a small Type X pressurized enclosure around a clamp-on gas flow meter with gas tubes entering and exiting the enclosure in a Class 1 Division 2 environment is highly problematic and likely not viable without significant engineered solutions and careful consideration. Here's a breakdown of why: Type X Purge Systems

Type X purge systems are designed to reduce the hazard within an enclosure from Class 1 Division 1 (or potentially even Unclassified) to a non-hazardous area as long as the purge system functions correctly. They typically use a non-hazardous gas (usually air or nitrogen) to dilute and remove any flammable gases or vapors. A key assumption for Type X to work is that the internal volume is well-ventilated by the purge gas and that flammable gases are not continuously leaking or being introduced.

The Problem with Gas Tubes

Your biggest issue is the gas tubes entering and exiting the enclosure. This creates several critical problems:

Continuous Source of Flammable Gas

The gas tubes are intended to carry a flammable gas, so there's a constant and deliberate introduction of a hazardous material inside the enclosure. This is almost directly contradictory to the whole concept of purging to eliminate the hazardous atmosphere. The Type X system would constantly be battling to dilute the leaking flammable gas.

Leakage Potential

Any fittings, connections, or even the tube material itself have a potential for leakage of the gas inside the enclosure. Even very small leaks are unacceptable because they would accumulate inside the enclosure and potentially cause a hazardous atmosphere.

Purge System Overload

The purge system is designed to deal with small leaks or residual vapors, not a continuous flow of flammable gas. The purge system would likely be incapable of maintaining the required pressure and non-hazardous atmosphere.

Flow Interruption and Purge Failure

If the flow through the tube is interrupted, the gas within the enclosure could bleed back into the gas line during a purge failure.

Alternatives and Considerations


Intrinsically Safe (IS) Instruments

This is the preferred and most common solution. Use a clamp-on flow meter that is specifically designed and certified as Intrinsically Safe (IS) for Class 1 Division 2 (or Division 1, for even more safety). IS devices are designed to limit energy levels to the point where they cannot ignite a flammable atmosphere, even under fault conditions. This eliminates the need for purging or other explosion protection methods.2.

Explosion-Proof Enclosures

Use an explosion-proof enclosure that houses the clamp-on flow meter's electronics (if necessary). Explosion-proof enclosures are designed to contain an internal explosion and prevent it from propagating outside the enclosure. The gas tubes would not pass through the explosion-proof enclosure. Care would need to be taken on how the signal is passed from the flow meter to the electronics in the explosion-proof enclosure.3.

Type Z Purge

A Type Z purge system is the lowest level of purge system. Type Z purges can be used to reduce an area from Class 1 Division 2 to Unclassified. However, the main concerns listed above about the gas tubes still apply.4.

Relocate the Electronics

If possible, relocate the electronics to a non-hazardous area and run the necessary cabling from the clamp-on flow meter to the electronics.5.

Engineered Solution (Highly Complex)

It might be possible to engineer a highly complex solution that includes: An incredibly robust, continuous gas leak detection system inside the enclosure. Redundant purge systems with extremely high flow rates. Automated shut-off valves on the gas lines in the event of a leak or purge failure. Comprehensive safety interlocks and alarms. Extensive documentation, training, and maintenance procedures. Independent review and approval by a qualified safety engineer.However, this would be very expensive, complex to maintain, and likely not cost-effective compared to using intrinsically safe instruments.

Code Compliance

Any solution you choose must be compliant with applicable codes and standards, including: NEC (National Electrical Code) - Article 500 and 505. ISA (International Society of Automation) standards - ISA-12.12.01 (Nonincendive Electrical Equipment), ISA-60079 Series (Explosive Atmospheres). Local regulations and authority having jurisdiction (AHJ).

In Conclusion

The idea of using a small Type X pressurized enclosure around a clamp-on gas flow meter with gas tubes entering and exiting the enclosure* in a Class 1 Division 2 environment is generally a

very bad idea due to the continuous introduction of flammable gas and the high risk of leakage. It is likely to be non-compliant with safety standards, and intrinsically safe instruments or other alternative solutions are almost always a better approach. If you are not sure, please consult with an engineer experienced in hazardous location installations. Flag for review