The risk increases with exposure time and with the type of surface that makes contact with the product or the size of a container opening that exposes the product to the environment. The place where microbes most likely would enter the product is called a critical site. A critical site is any opening providing a direct pathway for microbes into the product or any surface that comes in direct contact with both the environment and the product.
Products can come in contact with contaminating particles from the air, surfaces and operators.
One example is the exposed tip of a sterile syringe. The larger the critical site and the longer it is exposed to the environment, the greater the risk of contamination. Besides the information you find in this guide, an extensive technical report by the Parenteral Drug Association on the principles, practices and methods of environmental testing is also available. An environmental control program must take into consideration the nature of a particular workspace. The larger the workspace, the greater the risk of contamination.