This is a tough situation and you're right to be concerned. Here's a breakdown of the issues, potential solutions, and things to consider

Understanding the Problem:
Vibration and Rigid Conduit

Vibration is the core issue. Rigid conduit, while strong, can still transmit vibration, causing conductors to rub against the conduit walls, eventually wearing down insulation and leading to short circuits (ground faults).

Class I, Division 2 Area

This classification means ignitable concentrations of flammable gases, vapors, or liquids are not normally present, but may exist accidentally. While less strict than Division 1, the potential for explosion is still a real concern.

No Seals Due to Entire Run Being Within CID2

This is code-compliant

if the terminations are suitable for CID2 and the internal volume and spark-producing device requirements are met. However, it doesn't address the mechanical issue of conductor abrasion. Arcing

The visible arcing confirms that the fault is indeed creating a potential ignition source.

Downtime vs. Safety

This is the classic conflict. Preventing faults minimizes downtime in the long run, even if the initial repair might take slightly longer.

Lack of Detailed Specs

This gives you some leeway to advocate for safer solutions, but it also means you'll need to build a strong case.

Why Sealing is a Good Idea (Despite Potential Pushback)



Containment of Explosion

If an arc ignites a flammable atmosphere within the conduit system, seals can help contain the explosion to a smaller area, potentially preventing a larger catastrophe. This is the primary goal of seals in hazardous locations.

Prevention of Flame Propagation

Seals prevent the propagation of flames and hot gases through the conduit system.

Reduced Oxygen/Ignition

By containing the possible ignition source, the probability of an event is lowered.

Peace of Mind

Knowing you've taken extra precautions is valuable, especially in safety-critical environments.

Why Sealing Might Meet Resistance



Downtime

Replacing a sealed fitting in a hazardous location after a fault takes longer because of the need to re-seal it properly.

Cost

Seals and their associated installation labor add to the project's cost.

Other Solutions and Considerations



Hardened Cable (e.g., MC-HL)

This is an excellent alternative to standard conductors in conduit.

Advantages

Resistant to abrasion. The metallic jacket provides an additional layer of protection and grounding. Flexible and easier to install in some situations. Available with various insulation types to withstand specific chemical exposures.

Disadvantages

More expensive than standard conductors. Requires appropriate fittings rated for hazardous locations and cable type.

Cable Tray with Approved Cable

If possible, explore using cable tray instead of conduit. Ensure the cable is suitable for hazardous locations and the cable tray is properly grounded and supported.

Vibration Isolation



Elastomeric Conduit Hangers

These hangers absorb vibration before it reaches the conduit system.

Flexible Conduit Sections

Strategically placed flexible conduit sections can help dampen vibration. Ensure these are explosion-proof and suitable for the hazardous location.

Regular Inspection and Maintenance

Implement a routine inspection program to identify and address potential issues before they lead to failures. This is especially important with vibration.

Proper Conduit Installation



Support Spacing

Adhere to the recommended support spacing for rigid conduit to minimize flexing and vibration.

Tight Joints

Ensure all conduit joints are properly tightened to prevent loosening due to vibration.

Conductor Selection

Use conductors with insulation rated for the operating temperature and environment. Some insulations are more abrasion-resistant than others (e.g., cross-linked polyethylene (XLPE) vs. PVC).

Oversized Conduit

Slightly increasing the conduit size can provide more space for conductors to move without rubbing against the walls.

Document Everything

Keep detailed records of your design decisions, materials used, and installation procedures. This documentation is crucial for future maintenance and troubleshooting and can protect you if something goes wrong.

Consider a Variance

If you feel strongly about sealing the conduits but anticipate significant resistance, explore the possibility of requesting a variance from the local Authority Having Jurisdiction (AHJ). You'll need to present a well-reasoned argument and demonstrate how the proposed solution improves safety.

How to Push for Seals/Better Solutions


Present Data

Show your history and photos (even if only to internal management, as you are concerned about broader distribution) of failures related to vibration and conduit. Quantify the cost of downtime and repairs.2.

Focus on Safety

Emphasize the potential consequences of an explosion and how seals or hardened cable can mitigate the risk.3.

Cost-Benefit Analysis

Compare the initial cost of sealing or using hardened cable to the long-term cost of downtime, repairs, and potential safety incidents. Factor in the cost of inspections.4.

Code Compliance

Clearly explain how the proposed solution meets or exceeds code requirements. Refer to relevant sections of the NEC (National Electrical Code) and any applicable local codes.5.

Offer Alternatives

Present multiple options, each with its pros and cons, allowing decision-makers to choose the best solution for the specific situation. (e.g., seals everywhere vs seals at these critical points)6.

Involve Experts

Consult with a qualified electrical engineer or hazardous location specialist to get their input and support for your recommendations.7.

Document Your Concerns

If your recommendations are rejected, document your concerns in writing. This protects you in case of a future incident.

Example Argument for Seals

"While sealing the entire conduit run is not strictly required by code because the terminations are suitable for Class I, Division 2, the historical data shows a high incidence of conductor failures due to vibration-induced abrasion. These failures create a significant risk of arcing, which could ignite a flammable atmosphere within the conduit system. Installing seals at strategic locations (e.g., entry points to enclosures) will contain any potential explosions and prevent flame propagation, significantly improving safety. While the initial cost of the seals is higher, the long-term cost of downtime, repairs, and potential safety incidents outweighs the initial investment. Furthermore, seals will reduce the opportunity for oxygen to enter the conduit, lowering the probability of ignition."

Important Considerations



AHJ (Authority Having Jurisdiction)

The AHJ has the final say on what is acceptable. Communicate with them early in the process.

Manufacturer's Instructions

Always follow the manufacturer's instructions for installing seals, cable, and fittings.

Grounding

Ensure proper grounding of all components, including conduit, cable jackets, and enclosures.*

Training: Ensure that all personnel involved in the installation and maintenance of the electrical system are properly trained on hazardous location requirements.This is a complex situation, and there's no single "right" answer. Your goal should be to advocate for the safest and most reliable solution possible, while considering the practical constraints of the project. Good luck! Flag for review