1. What is a Major Accident Event?
A Major Accident Event (MAE) is defined in the UK Safety Case Regulations (SI 1992 No. 2885) as follows:
- A fire, explosion or the release of a dangerous substance involving death or serious personal injury to persons on the installation or engaged in an activity on, or in connection with it;
- Any event involving major damage to the structure of the installation or plant affixed thereto and any loss in stability of the installation;
- The collision of a helicopter with the installation;
- The failure of life support systems for diving operations in connection with the installation, the detachment of a diving bell used for such operations or the trapping of a diver in a diving bell or other subsea chamber used for such operations; or
- Any other event arising from a work activity involving death or serious personal injury to five or more persons on the installation or engaged in an activity in connection with it.
MAE was firstly defined in the offshore oil and gas industry. However, at the moment, MAE is widely applied in other industries where risk management of process incidents plays more and more important role in sustainable production.
2. The overall process of MAE identification
Identifying the MAEs is crucial in the development of the formal safety assessment for a safety case. All identified hazards must be subject to a screening process to determine if they can result in an MAE. Those hazards identified as having the potential to lead to an MAE must be considered in the formal safety assessment, whereas those not likely to result in an MAE, but are a hazard to health and safety must be addressed in the licensee’s or operator’s safety management system. The ultimate repository and record of the MAE identification process is within MAE register, a document contains both bowtie diagrams and MAE datasheet. MAE study ensures that the hazards and potential effects are fully evaluated and the mitigation and recovery preparedness measures put in place to reduce the consequences of any remaining risk to the installation.
3. Development of Bow-tie Diagram
“Bow Tie” diagram used in MAE study is a pictorial representation of how a hazard can be released and further developed into a number of consequences. Bowtie diagram is based on Bowtie XP software that is developed by CGE (Netherland) and distributed exclusively in Vietnam by SEN JSC. The left side of the diagram is constructed from the fault tree (causal) analysis and involves the following:
- Threats associated with the hazard;
- Controls associated with each threat; and
- Any escalation factor i.e. conditions that lead to increased risk due to loss of controls.
The right side of the diagram is constructed from the hazard event tree (consequence) analysis and involves the following:
- Consequences associated with the hazard;
- Recovery Preparedness Measures associated with each consequence; and
- Any escalation factor i.e. conditions that lead to increased risk due to loss of recovery capabilities.
A schematic “Bow Tie” diagram is presented in figure 1.
Figure 1 – Bowtie diagram for loss of containment in turret
4. The benefit of Bowtie Diagram
Bowties today are mainly used to make a decision about whether the current level of control is sufficient. This can be done to satisfy an organisation internally or an external regulator or customer. The bowtie has a helpful structure to brainstorm with a team on risks. It contains operational hardware barriers, behavioural barriers and organizational management systems, which makes it an ideal place to holistically look at where investing resources would have the greatest impact. The best reason for choosing the bowtie method is that it creates an easy picture to understand and communicate on multiple levels of the organisation. A complete bowtie diagram, linked to the management system, is like a graphical table of contents – a map, showing everything an organization does to controls its major risks.
An increasing number of regulators and companies are expanding their attention to include monitoring of barrier performance. There are already a lot of ways in which barriers are monitored implicitly. The challenge is to collect the available information from these sources and relate them to the barriers. This information can come from a number of sources like audits, inspections, permit to work systems, maintenance backlogs incidents- and near-miss investigations. After that, these data sources will be combined to create a regularly updated bowtie diagram that visualizes the current status of barriers. With regularly we mean fairly short term, compared to traditional risk assessment. As short as is feasible – updates can vary from monthly down to hourly. It enables more dynamic risk assessment that is embedded in daily operations.
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For further information about Bowtie XP software, please contact us at the email: info@senwork.com
