A reliable fire and gas detection system is vital for early detection of potential hazards and prevents escalation to catastrophic consequences by alerting the operator to take appropriate timely actions and initiating relevant automatic actions; it is more emphasized for relatively congested offshore facilities having limited means of safe personnel evacuation from toxic exposure/explosion hazards. To achieve a reliable fire and gas detection, it is essential to have a robust fire and gas detection system and strategic detectors placement.
There are industry standard guidelines which propose suitable types of fire and gas detectors and provide advice for selection and placement. In addition, fire and gas mapping tools are becoming popular means to justify the correct location of fire and gas detectors. Rapid evolution to fire and gas detection technology has further contributed to the design challenges impacting detector quantity and its associated downstream system design. Ambiguities in Codes & Standards and the approach adopted during various stages of the project often cause over design and burden to Company.
NPCC has experienced variety of challenges and lessons learned in fire and gas detectors selection and layout during EPC stage executed in the recent past. In one project, open path gas detectors suggested at FEED stage were changed to point type gas detectors during the EPC due to multiple cases of line of sight obstruction in the offshore platforms which resulted in a 4 fold increase to gas detector quantity. In another project, fusible plugs were considered during the FEED stage, to detect fire on unmanned well pads. However during EPC, fire and gas mapping study suggested using UV/IR type flame detectors as the fusible plugs cannot be considered for area coverage in the mapping study. This resulted in an additional 116 flame detectors besides the fusible plug type fire detectors. Finally, in another case, fire and gas mapping study during FEED stage suggested using HC detectors to monitor H2S leak at stoichiometric concentration. However, during EPC, it was recommended to use separate HC and H2S gas detectors resulting in doubling of the number of gas detectors.
In conclusion, careful use of available technology and finalization of F&G detection philosophy at early stage of project is the first step for cost-effective solutions. Secondly, close coordination with the Consultant performing the mapping study to avoid unnecessary detectors is required. This paper attempts to outline the challenges and ‘Lessons Learnt’ by EPC Contractor for fire and gas detectors selection and placement. Finally, the paper proposes a way forward for effectively handling the same.