The title alone is open to discussion. We are really talking about films displaying anti-static properties of which there are 3 basic types:
- Incorporating a conductive component in the extruded or cast film (rarely seen)
- Incorporating an agency approved (FDA and/or EMA) anti-static component which acts by attracting a homogenous moisture film to the surface which becomes the conductive component (most common).
- A graphitic component painted on the surface of the film in a small hexagonal pattern which renders every point on the surface within a few millimeters of a conductive pathway (found in S. America).
The conductive surface requirement is a carryover from the days of open processing. The use of a flexible film isolator reduces the volume of the open space surrounding a vessel opening which can be effectively both purged to vessel headspace conditions, and collapsed to a small volume to minimize venting and purging.
There are 2 primary benefits:
- Elimination of an ignition source in the event of a solvent build-up to above the solvent Lower Limit of Explosion (LEL). Flammable solvents are commonly used which requires the headspace of vessels to be inerted to <4% oxygen (the LEL for hydrogen which is usually present during hydrogenation reactions).
- Prevention of a powder explosion. Powder explosions are in a different realm entirely. Relatively few dry powders exhibit static sparking between individual particles but those that do demand use of an inerted atmosphere. It is a fearsome sight to see sparks flying between particles when falling out of a dryer down a drop chute into a receiver.
Whether it is necessary to provide a large grounded surface of anti-static conductive film or merely rely on the inherent nature of an unconditioned film is a vexed discussion outside the scope of this message, I.e. does an anti-stat actually render a situation worse than a mechanically stronger film without additives, especially in light of the new regulatory residual contaminant demands.
The industry has yet to update thinking on the relevance of conductive and non-conductive (dielectric) surfaces because flexible film surfaces are a relatively new addition to the API manufacturing armory. The considerations is whether it is better to provide an enclosure that promotes charge generation by acting as a homogeneous grounding surface or allow a nonconductive surface to equilibrate with its environment in a passive way. The answer probably depends on the presence of a flammable vapor or a static generating powder. In either case a flexible enclosure can be quickly converted to an inert atmosphere containing volume which will render a non-explosive condition. The ability to purge the enclosure rapidly by flexing it (expanding and contracting it) using an inert purge gas flow and vacuum exhaust far surpasses the unknown attributes of ‘conductive’ or ‘passive’ film surfaces.
The processing engineer is the best person to weigh the facts operating in his work environment.
Current EMA and FDA Regulatory expectations are for the use of anti-stat films when in intimate contact of an API yet common sense suggests this to be a worst case for contaminant transfer in the event of film additive migration.
Material Data Sheets (MDS) can be found on our website for additional context about our selected conductive anti-static flexible film.
FabOhio, Inc. is experienced in design and manufacturing flexible isolator containment systems with conductive films. Contact us today to get started on your next containment project.
Written by Brian Ward, PhD, CSci, CChem, FRSC