OCI Nitrogen, one of Europe's largest fertilizer producers, is investigating the extent to which it is possible to take targeted measures at an early stage and stop the development of major hazard accident processes. An innovative model has been developed and recently explained and elaborated in a number of publications. This current paper contains a validation of the model by looking at the BP Texas City incident in 2005. The bowtie metaphor is used to visually present the BP Texas City refinery incident, showing the barrier system from different perspectives. Not only is the barrier system looked at from its trustworthiness on the day of the incident but also from the perspective of the control room operator, and from a design to current standards of best practice. The risk reductions of these different views are calculated and compared to their original design. In addition, evidence and findings from the investigations have been categorized as flaws and allocated to nine organizational factors. These flaws may affect the barrier system's quality or trustworthiness, or may act as ‘accident pathogens’ (see also Reason, 1990) creating latent, dangerous conditions. This paper sheds new light on the monitoring of accident processes and the barrier management to control them, and demonstrates that the BP Texas City refinery incident could have been foreseen using preventive barrier indicators and monitoring organizational factors.

OCI Nitrogen wants to gain knowledge of (leading) indicators regarding the process safety performance of their ammonia production process. This paper 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 left-hand side of the bowtie. 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 results 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 what their urgency is.

OCI Nitrogen seeks to gain knowledge of (leading) indicators regarding the process safety performance of their ammonia production process. The current research determines the most dangerous process equipment by calculating their effects resulting from a loss of containment using DNV GL's Phast™ dispersion model. In this paper, flammable and toxic effects from a release from the main equipment of an ammonia plant have been calculated. Such an encompassing approach, which can be carried out for an entire plant, is innovative and has never been conducted before. By using this model, it has been demonstrated that the effects arising from an event of failure are the largest in process equipment containing pressurized synthesis gas and ‘warm’ liquid ammonia, meaning the ammonia buffer tanks, ammonia product pumps, and the ammonia separator. Most importantly, this document substantiates that it is possible to rank the most hazardous process equipment of the ammonia production process based on an adverse impact on humans using the calculated effect distance as a starting point for a chance of death of at least 95%. The results from the effect calculations can be used for risk mapping of an entire chemical plant or be employed and applied in a layer of protection analysis (LOPA) to establish risk mitigation measures.

A Safety Research project was carried out in an ammonia plant of OCI Nitrogen, located at the Chemelot site in Geleen, The Netherlands. This research focused on the development of a method to monitor accident processes in the chemical industry mainly caused by mechanical integrity of static equipment like vessels, tanks and heat exchangers. A significant part of the mechanical integrity failure scenarios originates from material degradation and corrosion mechanisms which may develop over a relatively long-time period, possibly taking months, years or even longer. Mechanical failure scenarios from two process units have been worked out and visualized using a bowtie. The research project shows that the monitoring of early warnings can provide information about the current development of mechanical failure scenarios. In addition, early warnings can be used to initiate inspections if there is a likelihood that the mechanical failure scenario has been activated. Considering the shift from breakdown maintenance to preventive and predictive maintenance and risk-based inspection (RBI), inspections based on early warnings could also be a new step in the field of maintenance efficiency.

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).

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 bow-ties 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.

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.