Explosion Protection for Pharmaceutical Production

Pharmaceutical powders are explosible. Lactose, starch, many actives and most granulations form explosible clouds, and the equipment that handles them, mills, dryers, fluid bed units and collectors, is exactly the enclosed kind that concentrates them.

What makes this industry different is that every protection method interferes with something else. A vent discharges to somewhere, and in a contained facility there is no somewhere. A suppression system puts an agent into contact with the product, which quality has to accept. A containment design that makes the vessel strong enough to hold the pressure is attractive but expensive.

Solvents are present more often than people expect. Fluid bed drying, granulation and spray drying all involve organic solvents, and a hybrid atmosphere of solvent vapour and powder ignites at a fraction of the energy the powder alone needs. The ignition energy for the assessment then has to come from the hybrid case.

And the whole arrangement has to be documented for qualification, which means certificates, test bases and calculations in a form a reviewer can follow.

An explosion concept and a containment concept that were designed together, so neither one breaks the other.

Explosion characteristics measured on the material as handled, including the hybrid case wherever a solvent is used, with the data referenced in the qualification package.

A basis of safety per vessel, with inerting engineered as a safety system where it is chosen, and all certificates and calculations assembled for review.

A power or biomass plant has to cover a fuel envelope and self heating as well, and protection valid at commissioning expires when the fuel mix changes.

The two concepts are written together. That is the single most useful practice here, because an explosion protection concept retro fitted to a contained facility produces either a vent with nowhere to go or a suppression system quality will not accept.

Inerting is frequently the answer for solvent processes, and it fits a closed system well: nothing is opened, nothing is added to the product, and the equipment is already designed to hold an atmosphere. It becomes a safety system with oxygen monitoring, a trip action and a case for startup and maintenance.

Where inerting is not applicable, containment by vessel strength or flameless venting are the practical options, and both need the vessel strength established as a number rather than inferred.

Measurement then has to be honest about the material. Data on the excipient does not describe the granulation, and the hybrid ignition energy with the actual solvent is the figure the detection and avoidance measures have to work against.

Finally everything is assembled for qualification: measured data, calculations, device certificates, the basis of safety per vessel and the maintenance and testing regime under change control.

• Explosion and containment concepts developed together, before equipment is specified.
• Inerting preferred for solvent processes, engineered as a safety system with monitoring.
• Vessel strength established as a verified number where containment or venting is used.
• Explosion data measured on the granulation and the blend, not only the excipients.
• Hybrid ignition energy used wherever a solvent is present.
• Data, calculations, certificates and the basis of safety assembled for qualification.

• Containment band, which rules out some protection methods before they are evaluated.
• Solvent presence and the hybrid ignition energy that follows.
• Product compatibility with suppressant, which for an active is usually unacceptable.
• Vessel strength, verified, since containment and venting both depend on it.
• Measured characteristics of the granulation or blend as handled.
• Documentation requirements for qualification and change control.