(64l) Considering Overfilling to be a Non-Applicable Overpressure Scenario

The consequences associated with liquid overfilling are serious for plant safety, as illustrated by many recent incidents (2009, Bayamón, Puerto Rico; 2008, Chesapeake, VA; 2005 Hertfordshire, England; 2005 Texas City, Texas).  In many cases,  providing overpressure protection solely with pressure relief devices may not protect the facility.  Preventing the uncontrolled release of liquid may be the only viable safe option.  This paper will present an abbreviated analysis of several incidents that could have been avoided with proper preventive measures.  Engineering methods will be presented to eliminate the need to release liquids from a closed system.  For instance, the system can be designed such that upstream pressure sources are limited below the allowable downstream pressure. A designer can provide a safety instrumented system with an appropriate Safety Integrity Level (SIL) rating to reduce or eliminate the credibility of overfilling.  Alternatively, consideration may be taken for alarms and operator response, with consideration for RAGAGEP, to reduce the credibility of overfilling to an acceptable risk.  Systems can be redesigned to be inherently safer by minimizing contained liquids.  This paper then gives a few examples of the use of system design, shutdown systems, alarms/operator response combination and inventory controls to eliminate or reduce the potential for liquid release scenarios.