Until 2006, there were no requirements for pure steam in the pharmacopeias (e.g., USP, Ph. Eur.). However, starting with USP 29, the USP has included a monograph which describes the quality attributes for Pure Steam. The introduction to the monograph acknowledges that it is difficult to directly measure the quality attributes of steam. Therefore, the monograph directs to perform the prescribed tests on the steam condensate. The pure steam monograph and General Chapter <1231>, Water for Pharmaceutical Purposes, stress the importance of maintaining cleanliness during the condensate collection process so as not to impact on the quality of the condensate. USP General Chapter <1231> also discusses the potential sources of undesirable contaminants in Pure Steam, which include anti-corrosion steam additives, entrained water droplets or residues from the steam production and distribution system. It is USP's opinion that the requirements in the Pure Steam monograph will be able to detect most of the potential contaminants. However, the presence of non-condensable gases (see chapter 5.F.3.1 Degassing) in steam or the existence of a superheated or dry state is not addressed by the USP Pure Steam monograph, even though the presence of these attributes could negatively impact the effectiveness of the steam. These attributes are not controlled in the Pure Steam monograph because they are use-specific.
The tests and requirements specified in the USP monograph are summarized in Figure 5.F-2.
Figure 5.F-2 USP Tests and Requirements for Pure Steam
In addition to the requirements in Figure 5.F-2, the monograph also refers to General Chapter <1231>, Water for Pharmaceutical Purposes, for microbiological guidance for Pure Steam.
The USP also points out that plant steam, which is less pure then Pure Steam, may be utilized for non-product contact uses, such as:
Other specifications regarding steam quality are defined in several standards, including the following:
DIN EN 285 (1997-2)
This standard and the steam quality described in it are applicable for large steam sterilizers used in the sterilization of packed products (instruments etc. and porous goods) in the health industry. It can also be used in the commercial manufacturing of medical devices. This standard cannot be applied for sterilizers used in the sterilization of pharmaceutical products.
The standard contains comprehensive detailed specifications for the execution of sterilization using large steam sterilizers. It also describes the technical equipment and procedures for controlling and monitoring the sterilization process and the sterilizer. It provides details of steam composition, dryness (not below 0.9), overheating (must not exceed 25 K in the case of steam that flows freely in the atmosphere), and non-condensable gases. It also specifies a maximum speed of pressure change in the sterilizer of 10 bar/min. The annex of DIN EN 285 provides concrete suggestions for the quality of feed water and steam (for information purposes).
DIN 58950 part 7 (April 2003)
This standard is applicable for the sterilization of pharmaceutical products in contact and non-contact sterilization. This standard specifies three qualities of steam depending on the relevant sterilization products.
Example assignment of the sterilization products to different steam qualities.
Figure 5.F-3 Assignment of sterilization products to different steam qualities (DIN 58950)
This standard distinguishes between two steam qualities (Figure 5.F-4):
Figure 5.F-4 Steam qualities according to DIN 58950
The DIN standards also define more detailed specifications regarding humidity, overheating, pressure fluctuations, mechanical filtering, non-condensable gases, etc. The steam quality to be used in a particular situation depends on the manufacturing process and the product itself. The pharmaceutical manufacturer is responsible for ensuring that steam used in the manufacturing process is suitable for the product.
Pure steam is used for a wide variety of applications in manufacturing operations as well as laboratories. Typical application areas for pure steam are as follows:
According to USP General Chapter <1231>, "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".