DNV Enhanced Approach to 3D Fire Mapping

Across the energy industry there is significant scope to improve fire mapping studies used to determine the number of flame detectors required for a process facility.

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Typically, such studies do not demonstrate ALARP, do not adequately explain assumptions, completely omit some assumptions, or do not consider the fundamental physics of fires or detectors.  However, such issues are not black and white and there is significant uncertainty in any fire detection mapping, or at least there should be. This is not acknowledged in typical studies which are not conservative enough to encompass all reasonable uncertainties.  Essentially, studies may follow a defined methodology, but they cannot be shown to drive the risk of non-detection to be ALARP.

To increase the confidence that flame detector layouts demonstrate ALARP and to reduce the uncertainty in fire mapping studies, DNV has developed an enhanced approach built upon existing 3D mapping techniques. This approach considers all of the deficiencies observed following more than three years of critical evaluation of multiple fire mapping studies for onshore and offshore facilities, reference documents and standards. 

The DNV enhanced approach considers and addresses the inherent uncertainty of common assumptions within typical fire mapping studies and the impact these have on the final detector layout/count. To address this uncertainty, DNV has developed three criteria that ensures that flame detectors add meaningful value to a layout, with conditions that must be satisfied for a detector to be included within a flame detector system. The approach:

· Demonstrates that only detectors that are providing coverage greater than the inherent uncertainty within the modelling are added to a facility.

· Prevents an overabundance of detectors.

· Simultaneously demonstrates that a system is ALARP, and critically.

· Gives the operator and designer better understanding of their fire detection system.

To demonstrate that the risk of non-detection is ALARP, the enhanced approach does not use arbitrary coverage targets. This is because if a commonly used target coverage (where coverage is the percentage of a given area/volume that a detector can ‘see’ after accounting for obstacles such as pipework/equipment) for a facility of 80% (2ooN) has already been achieved, but the addition of a further detector would increase the coverage to, say, 88% (2ooN), it would seem reasonable to add the extra detector. In this scenario, the addition of an extra detector increases coverage by 10%. The cost of the detector to achieve the additional 10% coverage is unlikely to be grossly disproportionate to the benefit achieved so, based on the principles of ALARP, the detector should be added. Conversely, if the benefit associated with an additional detector is low (the key aspect being how to define “low”), then it would not be warranted. However, as most fire mapping studies reference internal company documents and standards that provide prescriptive coverage targets, additional detectors would not normally be considered if the arbitrary coverage target is met. Therefore, the determined flame detector system cannot be ALARP in this case.

Although the coverage achieved using the enhanced approach broadly aligns with existing standards, to DNV’s knowledge the enhanced approach is the only approach that can robustly demonstrate a fire mapping study is ALARP.

Development of the enhanced approach to fire mapping

The high volume of assumptions that are either not fully explained or not considered in typical fire mapping studies, led DNV to consider the fundamental question of “what exactly are we trying to detect?”. Each assumption in typical fire mapping approaches was scrutinised to determine its impact on a detector layout. Such inputs and assumptions include:

     · Standards currently used within industry and use of prescriptive coverage targets.

     ·The various calculation methods within 3D modelling software used to determine coverage.

      ·The difference between reference fire size and critical fire size.

      · Sizing a flame detector field of view for the critical fire size based on the reference fire size.

      ·Critical jet/pool fire size and shape.

      ·Facility process conditions and the specific fire hazards related to these.

      ·Flame detector sensitivity.

      · Uncertainty within the modelling.

In the process of doing this, the enhanced approach was developed and is currently being developed into a DNV recommended practice (RP). To ensure accessibility to a wide range of users, the RP includes step by step instructions on how to use the enhanced methodology and includes a fully worked example.

Has the enhanced approach been used on existing facilities?

The enhanced approach to fire mapping has been used by DNV for both onshore and offshore facilities. The approach has been shown to mainly reduce detector count when compared to other approaches and makes it easier to demonstrate ALARP requirements where other approaches struggle.

DNV can demonstrate and offer a level of technical depth and knowledge not achieved by other methodologies. Following projects using the enhanced approach to fire mapping, DNV presented it to the OEUK control and instruments working group in summer 2024. With positive feedback on the level of technical depth and knowledge that is not inherent in other typically used methodologies.

Applicability

The enhanced approach is applicable to all liquid and gas fire types (including hydrogen). The approach can be used for new build systems and revalidation of existing flame detector layout systems both onshore and offshore.

Written by Luke Callaghan and Dr John Morgan. To find out more please contact Luke Callaghan using the contact information within the top right-hand side of your screen. 

2/14/2025 3:06:00 PM