How are cleanroom garments validated as sterile for use in an aseptic cleanroom?

Sterilization is a process that is intended to destroy viable forms of microbial life including bacteria, molds, yeasts, viruses, protozoa, and algae (including bacterial spores) to an acceptable sterility assurance level (SAL). SALs were first used in the food canning industry and refer to the degree to which an item is expected to be non-sterile after exposure to a sterilization process. While we use phrases like “terminal sterilization,” we must remember that sterilization is a matter of degree or probability. In a sterilization process, the nature of microbiological death is therefore described by an exponential function, an expression of probability. For instance, a SAL of 10-6means that there is a one in a million chance (probability) that a microorganism will remain after the sterilization process. However, while this probability can be reduced to a very low number, it can never be reduced to zero. ANSI/AAMI ST67:2003 contains a decision tree to be used to determine the SAL for medicaldevices to be terminally sterilized.

Sterilization is necessary when microorganisms are a contaminant. Such cases would include surgery, the implantation of medical devices, or the injection of solutions into the body. Sometimes, the device, instrument, or solution can be sterilized and packaged until it is ready for use. Often, however, sterilization, regardless of method, has a deleterious effect on the product. In such cases, the alternative is asepsis, the prevention of contact with microorganisms. Aseptic processing or manufacturing generally requires the use of a cleanroom and cleanroom apparel. A sterile cleanroom is often called a sterile suite or aseptic cleanroom. These rooms are meticulously maintained in a sterile condition by rigorous housekeeping and special decontamination procedures governed by the FDA and detailed in the Federal Guidelines to Good Manufacturing Practice (GMP). Note: If you see cGMP, the small case “c” stands for “current.”

Cleanroom garments used in aseptic cleanrooms must be sterile. ANSI/AAMI ST67:2003 identifies the sterility assurance levels for terminally sterilized products. Many companies manufacturing products in an aseptic clean-room require all components used in aseptic processing, including cleanroom garments, to be terminally sterilized to 10-6SAL.

There are three typical methods of sterilizing clean-room garments: steam autoclaving, ethylene oxide (EtO), and ionizing radiation (gamma or electron beam). While each has advantages and disadvantages, gamma irradiation is the most popular method used today.

STEAM AUTOCLAVING
Steam autoclaving is the process of attaining sterility by means of saturated steam and pressure. Usually, the object to be sterilized is wrapped in a vapor-permeable (Tyvek™ paper or cloth) bag and subjected to a high temperature and pressure (121 °C at 15 psi for 15 minutes is common). Unlike dry heat sterilization, steam is much more efficient in penetrating and carrying heat to every surface of the object being sterilized. Steam auto-claving is reasonably convenient, fairly efficient, and widely used for general sterilization of materials that aren’t heat, pressure, or moisture sensitive. Surgical instruments and bed linens are examples of materials that are autoclave compatible. Many injectible solutions and plastic implantable devices are examples of materials that would boil away, cook, or melt if subjected to autoclave sterilization. Historically, steam autoclaving was the primary method of sterilizing cleanroom garments. This was something that the customer did on site. There are quite a number of disadvantages associated with this method, however. For instance, auto-claving causes most cleanroom garments to shrink, often up to two full sizes. This is especially true of the older (and now nearly obsolete) taffeta and herringbone garments. Shrinking, aside from the obvious fit problems this would cause, causes puckering and deformation around zippers and seams sufficient to allow viable and non-viable particle excursions. Steam autoclaving also tends to set in wrinkles, making the garment very unsightly, degrade the fabric prematurely, and affect filtration characteristics. It should be noted that there are some cases yet today where autoclaving can hardly be avoided. This is when the garments must be sterilized before being returned to the garment service provider.