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At the OCI Nitrogen ammonia plant, located at the Chemelot site in Geleen, The Netherlands, a project has been initiated to monitor major accident processes at the site. This contribution answers the question whether indicators can be derived from the barrier system status to provide information about the development and likelihood of the major accident processes in the ammonia production process. The accident processes are visualized as scenarios in bowties. This research focuses on the status of the preventive barriers on the so called 'left-hand side' of the bowtie, before a hazard becomes uncontrollable. Both the quality - expressed in reliability/availability and effectiveness - and the activation of the barrier system give an indication of the development of the accident scenarios and the likelihood of the central event. This likelihood is calculated as a loss of risk reduction compared to the original design. The calculation gives in an indicator called "preventive barrier indicator", which should initiate further action. Based on an example, it is demonstrated which actions should be taken and their urgency. [ABSTRACT FROM AUTHOR]

Hazardous events in process plants like the leakage of dangerous substances can result in severe damage, and such an event is often defined as the TOP event of a fault tree analysis (FTA) in a quantitative risk analysis. The TOP event probability can then be calculated if the basic events probabilities are provided. These probabilities are often determined based on generic reliability data which do not necessarily reflect the operational and environmental characteristics of a plant of interest. This paper presents an approach based on Bayesian network (BN) analysis to explicitly include experience data collected during the plant operation to make the generic probabilities more plant specific. The approach is illustrated via a pressure vessel containing a toxic substance in an Ammonia production plant. In this case study, the failure rate distribution in the BN is updated as the new information becomes available during plant operation. The results show that the suggested approach effectively reflects the operating experience of a specific plant. [ABSTRACT FROM AUTHOR]

Research was carried out in an ammonia plant of OCI Nitrogen, located at the Chemelot site in Geleen, The Netherlands. It focuses on the development of process safety accident processes in which loss of mechanical integrity is one of the root causes. A significant share of the mechanical integrity scenarios originate from corrosion mechanisms which develop over a relatively long time period, possibly taking months, years or even longer before turning into an event. Based on an example, a failure mechanism is worked out and visualized using a bow tie. Bow-ties have shown a good visual representation of the 'early warnings' and the barriers in place. The monitoring of the 'early warnings' and barriers can provide information about the current probability of the scenario in order to intervene prematurely. [ABSTRACT FROM AUTHOR]

Monitoring progress of accident scenarios, and effectiveness of control measures is a main goal of safety indicators. From an overview of scientific literature one may conclude that indicators do not logically relate to current safety theories and models, their relation with accident processes is far from perfect, and a 'silver bullet' has not been identified yet. Professional literature shows another picture, and divides indicators in leading and lagging. This distinction seems convincing. Not only companies, but also regulations adopted this division. Currently many indicators used in industry generate a number, while the relation with accident processes is questionable at least. In addition, it can be expected that regulators of major hazard companies will ask to identify and implement both lagging and leading indicators, and anchor these indicators in a safety management system. The subject 'safety indicators' will remain in the spotlight in the time to come. This presentation will focus on a review of scientific and professional literature. This article is written in 'praesens historicum', and based upon recent articles (Oostendorp et al., 2016, Swuste et al., 2010, 2014, 2016 a,b, 2018). [ABSTRACT FROM AUTHOR]

In order to control occupational accidents, it is crucial to have a clear view on the potential accident scenarios that are present in a company. The bow-tie method is a way to capture and visualise these accident processes in an integrative way. Included in the bow-tie are safety barriers (both technical as organisational and human) and management delivery systems that can intervene in these accident processes. Once bowties are composed, they are an excellent point of departure to assign indicators to the safety barriers and management delivery systems in order to control (i.e. prevent or mitigate) the accident scenarios. Two types of indicators can be distinguished. Firstly, there are general indicators that are linked to management delivery systems interrupting multiple accident scenarios, and which can yield a higher safety gain (as they intervene in multiple accident scenarios). Secondly, there are scenario-specific indicators targeting one specific accident scenario, and which can be valuable as they target a specific safety problem in the company. Some crucial aspects have to be taken into account when using indicators, such as sequentiality in follow-up and prioritization of indicators, and the focus on quality rather than quantity. [ABSTRACT FROM AUTHOR]