Failure of a Freeze Dryer Slot Door
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CASE HISTORY—PEER-REVIEWED
Failure of a Freeze Dryer Slot Door Clint J. Grafelman
Submitted: 2 July 2008 / Published online: 1 October 2008 ASM International 2008
Abstract Freeze-drying is utilized in the biopharmaceutical industry to give higher stability, broader temperature tolerance, and longer shelf-life to formulations that are unstable in aqueous solution (Green and Perry, Perry’s Chemical Engineers’ Handbook, 1997). Freeze-drying equipment consists of a drying chamber, condensers, a cooling system, and a vacuum system. The drying chamber is where the product is placed to undergo the lyophilization process. The chamber has two access points: a maintenance door, located in a mechanical room, and a slot door, located in a sterile clean room. The maintenance door permits entry into the chamber. The slot door facilitates tray loading and unloading from the clean room using an automatic tray handling system. At 9:26 AM on March 2, 2008, a freezedryer failed during the steam-in-place (SIP) cycle. As a result of the failure, the slot door was plastically deformed. Several items in the proximity of the slot door sustained damage. Fortunately, no personnel were inside the clean room when the event occurred; there were no injuries or loss of life. The impact to production was severe. The event removed the freeze dryer from service for approximately 2 months, reducing bulk powder production capacity by 33% during the time it was down. The failure occurred because the slot door was not closed properly when the SIP cycle began. Instead of being completely restrained, it was allowed to become simply-supported, seriously compromising its pressure-containing ability. Keywords Plastic deformation Failure Pressure vessel Pharmaceutical
C. J. Grafelman (&) Monsanto, 1788 Lovers Lane, Augusta, GA, USA e-mail: [email protected]
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Introduction Lyophilization, or freeze-drying, is a process where an aqueous solution is frozen and its water content is largely removed by sublimation of water vapor under reduced pressure and temperature. There are three primary steps in a typical lyophilization process beginning with the freezing of the aqueous solution, followed by a primary drying step that removes water through sublimation, and finally a secondary drying step where residual water is removed through heating. Freeze-drying is utilized in the biopharmaceutical industry to give higher stability, broader temperature tolerance, and longer shelf-life to formulations that are unstable in aqueous solution [1]. The freeze dryer discussed in this case is used for this purpose. Water is removed from slurry to form a dry, stable bulk powder suitable for long-term storage and formulation. Freeze-drying equipment consists of a drying chamber, condensers, a cooling system, and a vacuum system. The drying chamber is where the product is placed to undergo the lyophilization process.
Drying Chamber Slot Door The drying chamber is a rectangular-shaped pressure vessel constructed of SA 240-316L stainless steel. It is rated
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