Process failures creating, 55 described

The process of applying mathematical constructs to describe experimental results often reveals patterns in the agent s pharmacokinetics or dynamics that might not otherwise be discernible. Failure of a model s simulations to predict experimental measurements sometimes prompts questioning of the data, such as the reliability of the quantitative methods, or sample collection or exposure techniques. More often, it may indicate that greater complexity in the model s structure is required to capture the data s behavior. This is another primary reason for developing models to create hypotheses (model structures) that are falsifiable, leading to improved models and improved predictions in an iterative process. 

In process plant, it had become normal practice to subject new, large pressure vessels to hydraulic proof pressure tests. The distinction between hydraulic and pneumatic pressure tests is an important one. Water is essentially incompressible - its volume barely changes when it is pressurized. Gas (or steam) is, however, highly compressible. Hence, in a hydraulic pressure test, the pressure vessel is filled with water, and if any failure should occur, as soon as the enclosed volume begins to increase because of the developing failure, the pressure immediately collapses. This means there is no explosion - just a bang as the metal fails, followed by a flood of water. By contrast, if a pressure vessel fails when pressurized with gas or steam, as in the boiler explosions described above, the energy of the compressed gas/steam drives the failure to create a violent explosion, and pieces of the failed pressure vessel become missiles. 

ZSA is an HA technique that identifies hazards that are created by failures that cross system zones and violate design safety independence requirements. ZSA is part of a comprehensive CCF analysis. It was developed for analysis of aircraft systems and is described in SAE/ARP-4761, Guidelines and Methods for Conducting the Safety Assessment Process on Civil Airborne Systems and Equipment, 1996. 

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