Explosion Isolation in Chemicals

Chemical plants combine explosible dusts with solvents, inert atmospheres and classified areas, so isolation has to fit into a safety concept that already exists.

The materials also vary between campaigns: a device sized for one dust can be inadequate for the next, and the connections between vessels are often more numerous than in a single-product plant.

Propagation stopped at every connection, with devices that are compatible with the area classification, the materials and any inerting already in place.

A protection case that survives a campaign change, which means it is written against the most severe material the plant may run rather than the one it is running, and reviewed when a new product is introduced.

Where inerting is part of the basis of safety, devices whose sealing performance is good enough to maintain the atmosphere as well as to stop a flame, with oxygen monitored downstream rather than inferred from the purge flow.

In a food powder plant the deciding document is the connection map, and the gap is almost always the short duct nobody drew.

The connection map comes first, as everywhere, and in a chemical plant it includes the nitrogen and vent systems as well as the product lines.

Where inerting is used, isolation serves a different role: it maintains the inert atmosphere as well as stopping flame, and a device that leaks defeats both. Where inerting is not used, the device has to handle the most severe dust on the material list.

Area classification decides what equipment may be installed at all, and the detection method follows from it. Optical detectors and pressure detectors have different requirements and different failure modes in a dusty line.

Material compatibility decides the wetted parts, including the suppressant in a chemical barrier, which must not react with the product it lands in.

The suppressant question is settled first because it determines everything else. A chemical barrier is effective, it works over a wide range of duct geometries, and the agent ends up in the product. If quality cannot accept that, the answer is a mechanical device, and a mechanical device needs a distance window that the duct layout has to provide.

That makes duct geometry a safety decision rather than a piping detail. A metre of straight run added between two vessels can be the difference between a certified option and none at all, and it is far cheaper to add at design than to retrofit into a congested plant.

• Map product, vent and inert systems together.
• Design for the most severe material, not the current one.
• Check suppressant compatibility with every product.
• Suppressant acceptability confirmed with quality before any device is specified.
• Duct geometry designed to provide the distance window a mechanical device needs.
• Protection case written against the most severe material in the campaign plan.

• The material list and its most severe member.
• Area classification, which constrains the device and the detection.
• Inerting, where present, and the sealing performance required to maintain it.
• Suppressant compatibility with every product in the line.
• Campaign changes, and whether the protection remains valid across them.
• Duct geometry available, which decides whether a mechanical device is an option at all.
• Maintenance access under permit, which limits the achievable testing interval.
• Review trigger for a new campaign product, so the case does not quietly expire.