“Sanitary” vs. “High Purity” Plumbing

Previous blogs have addressed what might be called the universal or common requirements for sanitary plumbing. Although obviously important, things like selecting the right materials and surface finishes are only the beginning of designing a system which is compliant with the requirements for a sanitary system as they may be defined by a particular user. As I stated earlier on, the requirements for a sanitary system are not well defined and certainly aren’t universal so let’s take a minute and review some of the requirements that are included in the specifications for some equipment that may not immediately even seem pertinent. Before proceeding, however, let’s briefly consider the history of “sanitary” plumbing.

The term “sanitary plumbing” first emerged in the 1920’s with the formation of the 3-A Sanitary Standards organization. This organization was a cooperative effort the International Association of Food Industry Suppliers, the International Association for Food Production and the Milk Industry Foundation. Clearly, the main interest of this organization was to promote and protect the safe processing of food hence the term “Sanitary Plumbing” with the term “sanitary” applying specifically to biological contamination. As other requirements for high purity processing came along – namely pharmaceutical and semiconductors – those industries also adopted the standards set forth by 3-A SSI because it already existed and, at the time, provided the required degree of purity in these applications. In the case of the semiconductor industry, however, the goal, instead of hygiene, was to maintain the purity of chemistry, prevent contaminating particulates, and prevent cross-contamination in the process of producing critical semiconductor components. As these industries grew and became more critical in their requirements for purity, meeting the requirements set forth by 3-A SSI was no longer adequate or, at least in part, not applicable in these new disciplines. By the late 1990’s the “sanitary” requirements appropriate for the food industry and the requirements for purity in the semiconductor and other growing industries diverged sufficiently to result in the expansion of ASME B31.3 to include sections dedicated to the semiconductor and bioprocessing industries. Because of the divergence of requirements for a variety of industries, the term “sanitary plumbing” is, at best, an historical reference, especially as applied in applications where biological contamination is either not a concern or is only one of a longer list of concerns which fall more in the realm of “high purity.”

ASME B31.3 and its new chapter X has now become the specification most defining the needs of the industry segments requiring “high purity” piping. Even so, the specification includes a disclaimer in its introduction which states: “The designer is cautioned that the code is not a design handbook; it does not do away with the need for the designer or for competent engineering judgment.” After this series of events, then, we don’t have a definitive specification for what many still call “sanitary plumbing.” As a result, those manufacturers who supply equipment to the industries requiring high purity plumbing are faced with the task of coming to an understanding with the buyers of equipment exactly what is meant by the term “sanitary plumbing” which seems to persist despite its lack of propriety.

Assuming that “sanitary” is a reference to biological purity, the requirement for sanitation can often be met by a sterilization procedure using steam, hot water or a sterilizing chemical followed by flushing with high purity water. Such procedures will not meet the needs of the semiconductor industry where contaminants will not be eliminated by sterilization procedures and cross-contamination is a critical issue. In the applications requiring high purity, the challenge is one of preventing sites within the plumbing where contaminants can collect and later be released with deleterious effect.

In the next blog, I will discuss some examples of the mechanical and other considerations for high purity plumbing.

– FJF –