(131a) Facility Siting, a Practical Approach

Under Process Safety Management Regulation, every facility is required to acknowledge or considering “facility siting” in the process hazard analysis (i.e. HAZOP), but does not provide a clear guidance on what is a proper approach to consideration and what is adequate. This requirement can be easily overlooked during the design, leading to decisions considered during late project stages, even after the intended permanently occupied buildings are already in place and mitigation measures are extemporaneous or budget prohibitive.

The American Petroleum Institute (API) and the Center for Chemical Process Safety (CCPS) has invested significant effort in develop API RP-752/753 guidelines and literature. Although these resources provide a good starting point and a sound process via practical flowcharts, the recommended practices leave a lot of room in the selection of adequate technical methods needed to complete the assessment; this is a gap particularly when required answers call for quantitative event simulation and frequency calculation. Some challenges medium and small operators face are for example, once the API screening flowchart is applied, and qualitative assessment is completed; but the building does not meet siting criteria for explosion or toxic, what next? How detailed should the detailed analysis be? Can radiation and blast loads be determined without a full blown quantitative risk analysis (QRA) that is in most cases budget prohibitive? How much of sound analysis can be can be done with a constrained budget? In absence of benchmark public industrial development individual/risk criteria, are there local/corporate siting decision criteria for decision making?

An overall practical quantitative method is discussed in this paper including four stages:

1. Stage 1: Defining building occupancy, building functionality, identifying buildings of concern and conducting spacing review
2. Stage 2: Review the hazard sources in more detail to identify potential impact to target buildings, by using recognized risk index methodologies to classify the sources in accordance with their risk: for example Dow’s Fire & Explosion Index (F&EI). Screen out buildings outside Intermediate-Heavy-Severe Radius of Exposure
3. Stage 3: Perform optimized QRA only for the sources and targets affecting the buildings that were not screened-out during Stage II, this is process blocks with a risk greater than intermediate
4. Stage 4: Demonstrate Risk-based or As Low as Reasonably Practicable (ALARP)
   1. Tolerability verification: occupied buildings risk is below tolerable frequency for workers (as dictated by client or suggested by best practice)
   2. Risk-based/ALARP verification: All options to reduce risk to occupied buildings identified and assessed and every option not grossly disproportionate was discussed, assessed in terms of cost-benefit, and implemented
   3. This 4-staged approach is flexible: Can be applied for a variety of process and multiple facilities and scope can be managed (i.e. when to stop and what to evaluate). This approach is cost-effective: A staged process allows screening-out what does not contribute to risk. It also strengthens qualitative assessment and reduces the scope of Stage 3.