Q&A | Co-Location

Question: If two independent ammonia refrigeration systems share a water diffusion tank should they be considered one (1) or two (2) processes under RMP and PSM?

Answer: This is a great question that addresses the issue of “co-location“. In order to correctly answer this question, we must first consider the definition of a Process.

Title 40 §68.3
Process means any activity involving a regulated substance including any use, storage, manufacturing, handling, or on-site movement of such substances, or combination of these activities. For the purposes of this definition, any group of vessels that are interconnected, or separate vessels that are located such that a regulated substance could be involved in a potential release, shall be considered a single process.

Title 29 §1910.119(b)
Process means any activity involving a highly hazardous chemical including any use, storage, manufacturing, handling, or the on-site movement of such chemicals, or combination of these activities. For purposes of this definition, any group of vessels which are interconnected and separate vessels which are located such that a highly hazardous chemical could be involved in a potential release shall be considered a single process.

While the definitions vary slightly in word selection, the intent of their meanings are the same. Clearly, interconnected vessels would represent a single process, but per the definition, circumstances could also cause vessels that are not interconnected to be “involved in a potential release” if a nearby process was impacted.

Confused? Join the club, because this issue has caused many people to scratch their heads.

Thankfully, both USEPA and CalARP have written helpful interpretations on this subject.

In the EPA’s General Risk Management Program Guidance, Chapter 2 Applicability of Program Levels, six (6) example sources are described in Section 2.8 and then clarification is provided as to whether or not the processes are subject to RMP. Of the six (6) example sources, four (4) address the issue of co-location (Source A, C, E, and F).

The CalARP Program Administering Agency Guidance Document used the information from EPA’s General Risk Management Guidance Document and produced a schematic representation of the concept of co-location. The result (Exhibit 1-2) can be seen below:

Considering the definition of a process and the written interpretations of both the EPA and CalARP regulations, two (2) ammonia systems which share a water diffusion tank would be considered co-located because of the close proximity of the relief valve discharge piping. Should the diffusion tank be accidentally impacted the resultant relief valve discharge pipe movement could certainly affect both systems simultaneously.

Two (2) helpful Safety Engineering Network blog posts on the topic of co-location can be read here and here.