Inherent safety index method

In the second method, the inherent safety index proposed by Heikkila [36] is appHed for safety analysis, which requires less information and covers lots of safety aspects [53]. Table 6.14 shows the results obtained from the inherent safety index method for both the technologies. In the inherent safety index method, the chemical inherent safety index and process inherent safety index are assigned to analyze the hazards caused by chemicals. 

Table 6.14 Results From Inherent Safety Index Method [36]...

Table 6.17 Results of the Modified Inherent Safety Index Method...

Edwards and Lawrence (1993) have developed a Prototype Index of Inherent Safety (PIIS) for process design. The inherent safety index is intended for analysing the choice of process route i.e. the raw materials used and the sequence of the reaction steps. This method is very reaction oriented and does not consider properly the other parts of the process even they usually represent the majority of equipment. 

In this thesis an index based method was selected since inherent safety in formed of many subfactors which are interrelated. Therefore it is more straightforward to represent these factors as subindices which are weighted by score means as discussed later in Chapter 9. 

The assessment and analysis of the inherent safety performance in the hydrogen system requires sound and appropriate metrics. Several valuable proposals for inherent safety metrics (Cozzani et al. 2007, Tugnoli et al. 2007) as well as the main issues needed for such assessment are well summarized in the literature (Roller ef a/. 2001, Khan eta/. 2003). Recently, a novel consequence-based approach for inherent safety key performance indicators (KPI) assessment was proposed (Tugnoli et al. 2007). The approach bases the calculation of safety indicators on the evaluation of the expected outcomes of the hazard present in the system, by runs of specific physical consequence models. The KPI method was preferred in the current assessment framework, since, unlike other approaches, it allows easily fitting the peculiarities of the analysed systems and does not require subjective judgment. Furthermore, the KPI method was newly reviewed to describe some particular features of the hydrogen chain. In particular the assessment of transport units was added and new index aggregation rules were defined. 

Several methods are available for identifying and assessing hazards (Kletz, 1990). Hazards can be identified through checklists, failure mode effect analysis (FMEA), fault tree analysis, event tree analysis, what-if analysis, and hazard and operability studies (HAZOP). Assessing hazards can be done through hazard analysis (HAZAN), codes of practice, the Dow Explosion Index, and prototype index of inherent safety (PIIS). 

The prototype index of inherent safety (PUS) (developed by Edwards and Lawrence, 1993) is a numerical score based on the nature of chemicals used and the type of process. The PUS was developed to compare processes based on raw materials and the sequence of reaction steps only. This method does not consider the other parts of the process. PUS is calculated as a total score and consists of two parts the chemical score and the process score. The first one is made up of inventory, flammability, explosiveness, and toxicity. The second one is made up of temperature, pressure, and yield. 

It can be summarized that the earlier studies focused more on health impact to humans in conjunction with the usage of biofuel and fossil fuel. Not until recently, the idea of inherent occupational health is being adopted into biomass processes. The works are actually done in a company with inherent safety assessment by Ng et al. (2013) and Liew et al. (2014) as described before in Section 14.6. Both used the Inherent Occupational Health Index (lOHI), an index-based method for inherent occupational health assessment of chemical synthesis processes. The method will be discussed in further detail in the next section. 

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