Control of Domino Effect Due to Fire in Chemical Process Industries handling propane:Evaluation of Effectiveness of Safe Distances Among Hazardous Units

Wherever propane is manufactured, stored or transported, the boiling liquid expanding vapor explosion (BLEVE) is an ever-present threat. The BLEVE is perhaps the most destructive of the forms of accidental explosions that can occur in a chemical process industry. A propane BLEVE will result in blast waves, missiles, and fire. On account of either or a combination of these outcomes, there is every possibility of triggering a domino effect’ or ‘chain of accidents’.In order to minimize the probability of damage to nearby equipment and buildings on account of a BLEVE; and to thereby minimize the probability of a domino effect occurring, one of the techniques used is to ensure a minimum safe distance between the containers carrying propane and other containers/building/equipment so that the consequence of a BLEVE due to one vessel do not impact other vessels; thus triggering a domino effect. There are several standards and codes which prescribe minimum safe distances to be maintained between different volumes of containers, such as NFPA (2008),OSHA (2007),OISD (2007),NSAI (2009), HSE (2002), CSA (2007), FM Global (2001),CCPS (2003), API (2001) and Gas cylinder rules (2004) to name a few.In this paper, the NFPA 58 codes prescribed for the minimum safe distances to be maintained between vessels containing propane and other vessels, buildings and equipments are examined for their effectiveness for protection against a domino on account of a fire resulting from a propane BLEVE. The NFPA 58 code has been chosen for this study because it prescribes separation distances which are equal to, or larger than the largest separation distances prescribed by the other codes. Using a special purpose software FORCIBLE earlier developed by us, the heat radiation generated due to fire resulting from propane BLEVEs are calculated for various quantities (volumes) of PLGs at the corresponding distances (between containers, buildings, equipment etc) mentioned in the standards. The heat radiation levels thus obtained are compared with the threshold values of radiation levels which can cause various forms of damage.