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About Bag Size:
AFC has introduced the reasonable and logical method for denoting the size of bags. In the past bags were assigned sizes based upon the maximal volume the bag could hold. This was a bad system for the following reasons:
1. That volume is uncertain. All plastic bags will stretch to some extent, depending on temperature, pressure, and relaxation time. Accordingly, the assigned volumes are completely arbitrary.
2. That "maximal" volume is virtually never used. Bags are seldom filled to maximal volume, they are generally used for purposes other than to carry a large volume.
3. The "maximal" volume gives little clue to the actual size of the bag. This makes it difficult for a user to select a bag for a given application.
The Afc Bag Size Standard:
The AFC standard size criteria is the number of milliliters of water that the bag will hold when the bag is restrained between two rigid plates spaced apart 1.0 centimeter when the water is permitted to fill the bag without head pressure for one minute at room temperature. We use that volume as the second portion of our catalog number. For reference purposes we also provide the maximum fill volume of water the bag will hold when suspended by its ports and filled to maximal extension after one minute with no head pressure. We also provide the surface area of the bag, both sides, for purposes of calculating gas exchange.
Why One Centimeter:
The selection of one centimeter thickness was based on research which indicated that human lymphocytes would expand at a maximal rate when the media fill was one centimeter thick. Greater thickness provided no greater expansion and is accordingly a waste of media. Lesser fill thickness resulted in lower expansion rates and is accordingly a waste of time.
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