Fire and gas detection – as part of a structured process safety management system – plays an important role in the protection of people, the environment, assets and corporate reputation. Detection is dependent on both the hardware’s ability to function on demand and detectors being located in the ‘right’ place.

Historically, there has been a significant effort invested in ensuring detectors function on demand and less focus given to their positioning (termed fire and gas detector mapping). This is evidenced by data from the HSE Offshore Release Database which indicates that a large proportion of releases go undetected – 36% of major and 69% of significant gas releases. Should these releases ignite or be toxic the consequences can be devastating.

At present there is limited guidance on how many detectors you need and where they should go. ISA-TR84.00.07 gives detailed guidance on a fully quantitative method but limited guidance for toxics. So why is there such little guidance available? The answer is that the locating of detectors is not trivial and can be influenced by many factors such as ventilation conditions (both forced and natural), nature of the fluid being released, congestion, confinement, amongst others.

Despite limited guidance, there has been significant investment in recent times in Fire and Gas Detector mapping and with the development of parallel computing and machine learning techniques such as Computational Fluid Dynamics (CFD) and genetic algorithms, many commercial software packages are now available that can ‘aid’ the mapping process. However, even with the advances in technology, the age-old problem of ‘garbage in equals garbage out’ still remains and without guidance there is often little consistency or documentation that justifies the number and position of detectors.

The industry is addressing this issue through the development of a British Standard that is to be released in early 2020. The aim of the British Standard is to bring consistency to fire and gas mapping and give guidance on the key points to consider for the hazard against which you are trying to protect. The guidance will also cover toxic gases, a topic which is even less documented than flammable gas and fire detection.

This paper will take guidance from the British Standard and explain how we define good practice for Fire and Gas Detector Mapping and how it can differ dependent on the application and hazard you are protecting against.

Tim Jones

Tim Jones is a Chartered Mechanical Engineer, specialising in process safety and hazard modelling and has worked on projects around the world under a variety of different regulatory regimes. He is highly experienced in conducting consequence modelling using both empirical and Computational Fluid Dynamics (CFD) techniques. This covers gas, fire and explosion modelling for flammables and toxics.

Tim has applied his understanding of hazard modelling to fire and gas detector mapping and optimisation and is on the British Standards Committee covering this topic. He also sits on the IMechE Upstream O&G and North-West Process Division committees as well as the Oil and Gas UK (OGUK) flare and vent working group.

Tim has presented at numerous conferences, including the Global Congress on Process Safety (hosted by the Centre for Chemical Process Safety), Hazards (organised by the Institute of Chemical Engineers) and Fire and Blast Information Group (FABIG) events. Tim has covered a wide range of topics, including dispersion, explosions and gas detector optimisation.

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