The LWF Blog
Fire Safety Engineering for Design – Gaseous Fixed Fire Extinguishing Systems – Part 312
November 9, 2026 9:47 amLWF’s Fire Safety Engineering blog series is written for Architects, building designers and others in the construction industry to highlight and promote discussion on all topics around fire engineering. In part 311, LWF talked about gaseous fixed fire extinguishing systems by discussing the types of extinguishing agents used. In part 312, we turn our attention to halocarbon and fluoroketone extinguishing agents in particular.
Halocarbon fire suppression systems provide a method of protecting sensitive environments where conventional water-based extinguishing systems may be unsuitable. Used in applications such as equipment rooms and other enclosed spaces, these systems rely on chemically formulated agents designed to extinguish fires while limiting damage to protected equipment.
Halocarbon extinguishing agents are classed as synthetic agents because they are formulated specifically for their fire-extinguishing properties. The principal agents covered are HFC-227ea, HFC-125, HFC-23 and the fluoroketone FK-5-1-12. Each has distinct characteristics that influence how a suppression system is designed, stored and discharged. The Fire Industry Association’s Guidance Document on Recycled Halocarbon Extinguishing Agents provides further technical information on these agents. (PDF)
HCFC Blend A was developed as an alternative to halon, but it is excluded from this group because its use is now banned in the context described by the source material. Its ozone depletion potential was a key factor in that decision. UK requirements governing ozone-depleting substances are explained in the government’s official guidance. The regulatory status of an agent should always be checked against current legislation before specifying it for a new installation.
Halocarbon agents are stored as liquids under pressure and discharged as gases. Most have very low vapour pressures, so a nitrogen pressurising medium is used to provide the pressure needed to deliver the agent through the system. HFC-23 is the exception to the low-vapour-pressure characteristic.
The pressure selected for a system affects its design and installation. A fill pressure of 25 bar is common, while systems operating at 42 bar and 70 bar are becoming more prevalent. Higher-pressure arrangements can offer greater flexibility in pipework design, helping engineers position storage cylinders further from the protected area.
Cylinder capacity also varies considerably, typically ranging from 5 litres to 343 litres. Selecting an appropriate cylinder requires consideration of the agent type, storage temperature and fill ratio. These factors influence the quantity of agent a cylinder can hold and how effectively the system can deliver it during discharge.
Discharge performance is a central consideration in the design of a halocarbon suppression system. The agent must be discharged within 10 seconds, placing specific demands on cylinder placement and pipework. The applicable system standard and manufacturer’s design requirements should be checked to confirm the criteria for each installation.
BS EN 15004-1 covers the design, installation and maintenance of gas extinguishing systems, providing a key reference for engineers planning and assessing these installations.
In a typical 25 bar system, meeting this requirement can restrict cylinder locations to within, or immediately adjacent to, the protected risk. Longer pipe runs can make it more difficult to achieve the required discharge time, limiting the options available to the building designer.
Higher-pressure systems can help overcome some of these constraints. Operating at 42 bar or 70 bar can extend the practical distance between the cylinders and the protected area, giving designers more freedom when allocating plant space and planning installation routes. The final arrangement still needs to satisfy the system’s applicable design and performance requirements.
Selecting a halocarbon fire suppression system involves balancing agent characteristics, cylinder capacity, storage conditions, operating pressure and the layout of the protected space. A configuration that works well in one building may not suit another, particularly where cylinder storage is remote from the hazard or pipework routes are restricted.
Understanding the relationship between pressure and discharge time helps engineers assess these constraints early in the design process. Careful consideration of the agent and storage arrangement can support a system that meets its required performance criteria while accommodating the practical limitations of the building.
In part 313 of LWF’s series on fire engineering we will continue discussing halocarbon and fluoroketone extinguishing agents. In the meantime, if you have any questions about this blog, or wish to discuss your own project with one of our fire engineers, please contact us.
Lawrence Webster Forrest has been working with their clients since 1986 to produce innovative and exciting building projects. If you would like further information on how LWF and fire strategies could assist you, please contact the LWF office on 0800 410 1130.
While care has been taken to ensure that information contained in LWF’s publications is true and correct at the time of publication, changes in circumstances after the time of publication may impact on the accuracy of this information.