Putting the Edge Pieces in Place – Managing Risk at the Boundaries of a Batch Process

Hazard Identification and Risk Analysis (HIRA) is one of the key building blocks of process safety management (PSM). If a facility is unaware of the hazards and risks presented by a process, it will be unable to adequately manage those risks. For many continuous chemical processes, the physical boundaries of the process being studied are clear, with the production unit defined from raw material tanks through the process unit operations to the product tanks. The implications of what should be included in a process hazard analysis (PHA) have recently been further illuminated by the Wynnewood court decision. In batch processes, the boundaries of the process are often less physical and more temporal. The approach used in batch PHAs may be shifted to focus more on procedure steps and their order – what is being added and when, when is heating or cooling applied to the unit, how fast changes occur in the unit, etc. – than on continuous equipment units and their functionality.

This paper will explore some of the potential blind spots that could occur when conducting PHAs on batch processes. Conducting a batch process PHA based on the batch procedure is considered a best practice, but a procedure-only approach could miss potential concerns with auxiliary equipment, such as scrubbers or utility systems, that may operate in the background of the batch process. Often in batch processes, quantities of chemicals contained within the process and even in raw material or product storage may be much smaller than PSM regulatory threshold quantities, however significant risks could still exist. A PHA program focused solely on regulatory compliance could miss potentially serious risks, particularly around reactivity or toxicity issues. Similarly, in a PHA focused only on the procedure used for the batch, risks associated with storing and handling the chemicals prior to their introduction to the batch unit could remain hidden. These risks may be exacerbated if the batch sizes or campaign lengths are changed over time, and the quantities of chemicals being handled or stored changes without recognition of the change in risk. Could the facility’s risk tolerance change if the shipment amount or container type is changed or if a “short term” project becomes a stable, long-term product? Examples of how these concerns could manifest themselves in a batch chemical facility will be presented, and this paper will discuss ways to potentially address them in the HIRA process.