Explosion Isolation in Pharmaceuticals

A mill, a dryer and a collector sit within a few metres of each other, joined by short ducts. If a deflagration starts in the mill it reaches the collector through that duct as a flame front in an atmosphere the pressure wave has already compressed and stirred. The collector's vent was sized for ignition inside the collector, not for that.

Isolation is the answer, and in a pharmaceutical plant it immediately runs into two things.

The first is containment. The ducts belong to a closed system that keeps an active ingredient away from the operator, and most isolation hardware wants to be opened, inspected and reset by hand. The second is the product itself. A chemical suppressant barrier fires a powder or an agent into the duct, and whatever it touches is in contact with the batch.

The equipment is also small. A micronizer and its receiver can be a metre apart, which is shorter than the distance most certified devices need to work.

Every connection between protected vessels either carries a tested isolation device within its certified distance range, or is shown by assessment not to need one.

Shown, not assumed. The assessment that says a duct does not need isolation is part of the documentation, with the same status as a device certificate.

The arrangement holds the containment band the process was designed around, and the whole package reads as a qualification document rather than a drawing with notes on it.

A power or biomass plant certifies against a fuel envelope rather than a product: isolation valid for the commissioning fuel says nothing about the blend burning today.

The sequence starts earlier than most plants expect. The isolation concept is written while the containment concept is still open, because the two of them share the same ducts and the second one to arrive loses.

Where the product cannot tolerate suppressant, which is the normal case for an active ingredient, the choice narrows to mechanical devices and to geometry. A rotary valve certified as an isolation device can serve where the process already needs a valve. A fast acting gate or a flap valve needs a minimum distance from the ignition source to close in time and a maximum distance beyond which the flame has already passed.

That is where the duct layout becomes a safety decision. A metre of straight duct added between two vessels is not a detail of the piping drawing; it is what makes a certified option available at all.

Detection, if the chosen method needs it, lives inside the duct and therefore inside the containment boundary. The detector, its seals and its cleaning route are part of the cleaning validation, not an afterthought bolted to the outside.

• Isolation method chosen together with the containment concept, not after it.
• Duct geometry designed to give the device the distance its certificate requires.
• Device internals included in cleaning validation and the product contact list.
• Certificates, test basis and distance ranges collected for the qualification package.
• Maintenance, testing and reset held under the same change control as the process equipment.

• Product compatibility with suppressant, which for an active ingredient usually rules out chemical barriers before anything else is discussed.
• Duct geometry between protected vessels: length, diameter and bends decide which certified devices are even eligible.
• Containment band the line is designed to, and what the device does to it when it is reset or inspected.
• Explosion characteristics of the active and of the blend, which are not the same; a blend can be milder or sharper than its components.
• Cleaning and changeover: whether the device internals can be cleaned to the validated standard in the time available.
• Documentation required for qualification, including the certified distance range and the test basis behind it.