Advances in Explosion Protection: How Advanced Solutions Open New Doors

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While venting is a reliable, cost-effective method of preventing damage from pressure, it does not affect flame. One consequence can be a residual fire in the dust collector, silo, etc. Often, these vessels are equipped with fire extinguishing system utilizing inert gases such as CO₂ or N₂. However, the vent opening allows the extinguishing gases to escape and oxygen to enter, making it more difficult and costly to control the fire. A recent advance has been the inventing of a reclosing low mass vent.

The vent closure behaves normally during the release of pressure, but once it has passed, the nature of the closure material returns it to its original position. The residual opening is about 5 per cent which now permits fire suppression to be effective. The figures below show the vent position as it begins to open, when it is open and after the flame and pressure have been released (approx. 500 milliseconds) when it has returned to its original position.

Isolation Devices

A non-technological advance in isolation that should be mentioned first is the increased recognition of the need for isolation in conjunction with suppression, venting or even containment. A process without interconnections is rare and any process with interconnections is subject to flame propagation through the ductwork. This is recognised in the ATEX directives and the latest revisions of the NFPA Standards. For example, NFPA 654 states in 7.1.4.1 “Where an explosion hazard exists, isolation devices shall be provided to prevent deflagration propagation between pieces of equipment connected by ductwork”. Some of the technical isolation options are listed in Table 4.

Only a few technical advances have happened in recent years. Gas generators described above are now being used as the primary closing force for several types of mechanical valves, replacing pressurized gas containers. An increased interest in passive valves and diverters has been seen and a CEN standard for Flame Diverters/Explosion Decouplers or Diverters has been drafted.

Standards and Guidelines

Significant changes have been made in the past decade in the development of industry standards and guidelines. The standards provide a clear definition of responsibilities, emphasizing the requirements for record keeping, inspection, maintenance, and training, management of change, and the role of performance based designs. In general the industry standards have greatly expanded technical sections with specific performance requirements.

But the real decisive criteria for explosion protection is something different: awareness and communications....

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