Pure Steam— is also sometimes referred to as “clean steam”. It is used where the steam or its condensate would directly contact official articles or article-contact surfaces, such as during their preparation, sterilization, or cleaning where no subsequent processing step is used to remove any impurity residues.
These Pure Steam applications include but are not limited to porous load sterilization processes, product or cleaning solutions heated by direct steam injection, or humidification of processes where steam injection is used to control the humidity inside processing vessels where the official articles or their in-process forms are exposed.
The primary intent of using this quality of steam is to ensure that official articles or article-contact surfaces exposed to it are not contaminated by residues within the steam.
The minimal quality of source water for the production of Pure Steam is Drinking Water whose attributes are prescribed by the U.S. EPA, EU, Japan, or WHO, and which has been suitably treated.
The water is then vaporized with suitable mist elimination, and distributed under pressure. The sources of undesirable contaminants within Pure Steam could arise from entrained source water droplets, anticorrosion steam additives, or residues from the steam production and distribution system itself. The chemical tests in the Pure Steam monograph should detect most of the contaminants that could arise from these sources. If an official article is exposed to Pure Steam and it is intended for parenteral use or other applications where the pyrogenic content must be controlled, the Pure Steam must additionally meet the specification for Bacterial Endotoxins Test
These purity attributes are measured in the condensate of the article, rather than the article itself. This, of course, imparts great importance to the cleanliness of the process for Pure Steam condensate generation and collection, because it must not adversely impact the quality of the resulting condensed fluid.
Other steam attributes not detailed in the monograph, in particular, the presence of even small quantities of noncondensable gases or the existence of a superheated or dry state, may also be important for applications such as sterilization.
The large release of energy (latent heat of condensation) as water changes from the gaseous to the liquid state is the key to steam’s sterilization efficacy and its efficiency, in general, as a heat transfer agent.
If this phase change (condensation) is not allowed to happen because the steam is extremely hot and in a persistent superheated, dry state, then its usefulness could be seriously compromised.
Noncondensable gases in steam tend to stratify or collect in certain areas of a steam sterilization chamber or its load.
These surfaces would thereby be at least partially insulated from the steam condensation phenomenon, preventing them from experiencing the full energy of the sterilizing conditions.
Therefore, control of these kinds of steam attributes, in addition to its chemical purity, may also be important for certain Pure Steam applications.
However, because these additional attributes are use-specific, they are not mentioned in the Pure Steam monograph.
Note that lower-purity “plant steam” may be used in the following applications:
1) for steam sterilization of nonproduct-contact nonporous loads,
2) for general cleaning of nonproduct-contact equipment,
3) as a nonproduct-contact heat-exchange medium, and
4) in all compatible applications involved in bulk pharmaceutical chemical and API manufacture.
Finally, because Pure Steam is lethal to microbes, monitoring of microbial control within a steam system is unnecessary, as is microbial analysis of the steam condensate.
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