(68b) Facility Siting Rule Set for the TNO Multi-Energy Model for Congested Volumes (PES) and Severity Levels

Facility Siting has received considerable attention in recent years.  There are a number of generally accepted simplified methods for the prediction of vapor cloud explosion (VCE) blast loads, one of which is the TNO Multi-Energy Model (MEM).  TNO has provided guidance for the application of the MEM, however, the guidance involves physical parameters which can be hard to estimate, and to which the blast load predictions are fairly sensitive.  The consistency with which different analysts can estimate these parameters is therefore a significant issue. 

A major oil company commissioned a study by three consulting companies to develop better guidance on the application of the TNO MEM blast load assessments by reference to several refinery and chemical plant units.  Initially without a clear rule set the differences in TNO results were large and reinforced the need for better consistency.  In Phase 1 of the work, a rule set was developed to define how to apply the MEM for Facility Siting Purposes.   The rule set created had explicit separation distances and heights to be used in defining PES congested areas.  It also addressed special items such as isolated equipment within PES, cooling towers, pits, furnaces, parking areas, etc.  Phase 2 of the work addressed assessing and selecting the appropriate TNO Severity Levels.  While the team used different methods – rules of thumb, the BST method and GAMES – after careful review a consistent view of severity level was also obtained.  This is best captured using photographs and a selection of typical congested plant photos was created defining severity levels 4, 5, 5.5, and 6.  These are the most critical for facility siting purposes.