The Fire Tetrahedron: The Science Behind Brookes Bell’s Marine Fire Investigations

Fuel, heat, oxygen, and an uninhibited chemical reaction comprise the fire tetrahedron — the four elements necessary for ignition and sustained combustion. Understanding how each variable interacts with the other and the circumstances that brought them together is critical when it comes to unravelling how a vessel fire originated and propagated, as well as identifying measures that may prevent recurrence or mitigate losses.

Despite improved safety regulations and onboard systems, the frequency and impact of commercial vessel fires remain a significant concern. According to the Allianz Safety & Shipping Review 2025, there had been a total of 250 fire and explosion incidents reported in the previous 12 months.  This represents a 20% year-on-year increase compared to the previous year and the highest annual total recorded in at least a decade.

Marine insurers are also highlighting how fire incidents are the most expensive type of insurance claim across all shipping sectors as a result of vessel damage, cargo destruction, and operational downtime.

“There are so many reasons why a fire can break out on a commercial vessel. It can stem from an issue at berth to problems that slowly develop while the vessel is in transit. That is why it is so important to understand the science behind vessel fires and why the service Brookes Bell provides after an incident is so important to the wider industry,” said Paul Ayres, a Forensic Fire and Explosion Investigator at Brookes Bell.

During any fire investigation, examining the fire tetrahedron is fundamental. The tetrahedron describes the four elements that must be present simultaneously for a fire to exist and develop.  Remove any one of these elements and the fire cannot continue. Understanding how these elements were introduced, removed or changed throughout the incident, and at what stage of the incident, is often the starting point for any fire investigation.

From a cargo fire perspective, identifying the ignition source requires consideration of whether sufficient energy was available in the form of electricity, mechanical friction, chemical reactions, electromagnetic radiation, or something other? When tracing the fuel source, investigators must consider what combustible materials were present, what is the material’s ignition characteristics or threshold, and how readily it can sustain flaming combustion? Finally, are oxygen concentrations higher or lower than ambient levels?  Are there any chemical oxidants that needs to be taken into consideration? Understanding the ventilation system of a cargo hold, from natural vents, mechanical vent and hatch covers, is vital to know how fires develop or stay active.

“Clients come to us looking for reliable information about what actually happened. They may want to know what the ignition was but that is only one part of the picture. Brookes Bell also examines why it developed the way it did, what factors influenced the extent of damage, whether fire protection systems operated as designed, what contributed to any injuries or fatalities, and what the likely outcome would have been had systems or safeguards functioned as intended,” he noted.

Paul noted that to deliver this outcome, Brookes Bell’s fire investigators leave no stone unturned during their assessment.

“For example, I have the ability to collect a material and send it to The Lab to help me determine the specific ignition threshold of the material. I can collect electrical components and have it analysed using a Scanning Electron Microscope (SEM) to identify electrical arcing or determine if a conductor experienced an overcurrent condition.”

All these variables mean Brookes Bell’s fire investigators have to wear several hats across any investigation.

“Fire investigations sit at the intersection of physics, materials science, chemistry, and investigative practice. We have to be experts in thermodynamics, fluid dynamics, material properties, thermal degradation of materials, combustion science, and oxidation-reduction chemical reactions. Then there is ensuring that we interview witnesses, review records, and handle and examine physical evidence.

“From all of this, we develop and test hypotheses to determine origin, cause, contributing factors, and ultimately issues of responsibility,” he noted.

“At the centre of it all remains the fire tetrahedron and the scientific method. Those two things make up the cornerstone of any fire investigation, guiding our approach from the moment we step onto a vessel to the final independent report we deliver,” Paul added.