Issue link: https://www.e-digitaleditions.com/i/1067339
Tablets & Capsules January 2019 29 or air-steam heat exchanger, as direct heating may lead to hot spots that can scorch or weaken fabrics. Use washing and drying machines that are appropri- ate for the size and geometry of the filter bags. No established correlations exist between washing-machine drum size and bag diameter, tube length, or number of tubes, but using the largest practical wash drum helps minimize how packed the bags will be in the machine and allows them to move more gently during agitation. Also, avoid tying the tubes together during washing, since it can lead to premature abrasion where the tubes rub together continuously. Some companies prefer to hang-dry the bags, in which case it's a good idea to have a drying room where the bags can be suspended using a rack and hangers with the same geometry as in the fluid-bed dryer. Other compa- nies reinstall the washed bags in the fluid-bed dryer and then dry them using unheated air at a high flowrate. Use a risk-based approach when considering either of these methods, as you need to think about validation and possi- ble cross contamination, especially when drying bags that are dedicated to one specific product. Fluid-bed filter bags will shrink over time with repeated use, washing, and drying. Innovative weaves and polymer choices in fabrics can help mitigate this, but some shrink- age is inevitable. Properly manufactured filter bags are sized large enough to allow for nominal shrinkage and will usually remain within the equipment's tolerances. Evaluate the fit during each installation. Bags with excessive shrink- age will be difficult to install over the mounting ring and/ or may become distorted at the caps once attached to the hanger. Either of these conditions can lead to mechanical stress and tearing. Also, if the tubes become too short and taut, they may fail prematurely from stress during shaking. Inspect the bags regularly. When the bags are dirty, it's easy to miss small holes that may have formed during operation. Current GMPs suggest thorough inspection after cleaning and again just prior to use. Once holes form, they tend to propagate with repeated use and during washing and drying cycles. It's important to closely inspect filter bags that contain stainless steel wires for conductivity because damaged wires can "pick" at the fabric, forming tears and causing yarns to unravel. Storage and handling Proper storage and handling are important to prevent environmental and mechanical influences from damaging the filter bags. Storage systems and handling methods are largely a personal preference, and there is a lot of devia- tion between sites. Some companies rely solely on plastic bags for storage, with the sealed plastic bags often stacked or crammed onto shelves or even into drawers to fit limited storage space. This can put unnecessary com- pression force on the filters at the bottom of the stack and may cause undue stress and result in stubborn creases or other damage, especially during long-term storage. A better practice is to store filter bags in robust plastic containers with lids, as shown in Photo 1. The plastic Photo 1: Sturdy plastic containers sealed with airtight lids prevent damage to spare bags, and a rolling shelf system keeps the bags organized and provides a convenient GMP-friendly storage solution.