Linear Heat Detection: Where and How to Use It
Some fire risks are long, dirty, hot or awkward — a cable tunnel, a conveyor, a car stacker, a plant room full of pipework. Point detectors struggle in these places: too many would be needed, or they simply would not survive. Linear heat detection solves the problem with a continuous sensing line that responds to heat anywhere along its length. This guide covers what it is, where it belongs, the main types, and what to check.
The defining feature is a continuous sensing element that protects a route or a piece of plant end to end, in conditions that would defeat point detection.
Who this is for
This is for competent fire alarm engineers selecting, installing or maintaining linear heat detection. The experience level assumed is competent engineer. Use it for the principles; the specific type, routing and settings come from the fire risk assessment, BS 5839-1 and the manufacturer's data.
What linear heat detection is
Linear heat detection (LHD) uses a continuous sensing cable or line that responds to heat at any point along its run, instead of a detector at a single location. This makes it ideal for linear risks and for rugged environments, because the whole length senses heat and robust versions tolerate dirt, moisture and temperature extremes. Line-type heat detectors for fire alarm use are covered under the BS EN 54 series, and their application follows BS 5839-1 and the fire risk assessment.
Where it suits
LHD suits linear or awkward risks in harsh conditions: cable tunnels and trays, conveyors and escalators, car stacking systems, tank and plant areas, and cold or dirty spaces. Because the sensing element follows the risk, it protects that route or plant along its whole length, and rugged cable copes where a point detector would foul or fail. Whether LHD is the right solution, and where it should run, is a design decision from the fire risk assessment and BS 5839-1, matched to the specific risk.
Types of LHD
There are several technologies. Digital cable triggers at a fixed temperature when any point along it reaches that threshold. Analogue or integrating cable responds to temperature along its length and can allow more nuanced alarm criteria. Fibre-optic sensing reports temperature and, importantly, location along the fibre, which helps pinpoint where heat is developing. Each type differs in its ability to locate a fire and set alarm conditions, so the choice follows the risk, the manufacturer's data and the design.
Servicing LHD
Servicing focuses on the integrity and routing of the sensing element. Confirm the cable is intact, correctly routed and fixed along the risk, that the interface and any control unit are healthy, and that it is tested by the manufacturer's method. From field experience, physical damage, disturbed routing after other trades have worked nearby, and failed interface or end-of-line units are the recurring problems. Record the routing, test method and results, and re-check whenever work has taken place near the cable.
Common points to check
Recurring issues include physical damage to the sensing cable, routing disturbed by other work, and failed interface or control units. Confirming the sensing element is intact and correctly routed along the risk is the essential check.
When not to rely on this alone
When not to use this article: do not use it to select or route linear heat detection for a specific risk. That comes from the fire risk assessment, BS 5839-1, the relevant BS EN 54 parts and the manufacturer's data, applied by competent professionals.
Relevant standards
Line-type heat detectors are covered under the BS EN 54 series, and their application within a system by BS 5839-1, a code of practice, with the manufacturer's data authoritative for routing and settings. The legal duty for fire precautions in relevant premises sits under the Regulatory Reform (Fire Safety) Order 2005. Separate the legal duty from the recommended methods, and always work to current editions.
Professional disclaimer
This is an educational and workflow resource for competent engineers and does not replace the current British and European Standards, the manufacturer's data, the fire risk assessment, or competent judgement. Verify linear heat detection selection and routing against current documentation.
Related documentation
Use this with the current BS 5839-1 and the relevant BS EN 54 parts, the fire risk assessment, and the manufacturer's data. Record the cable routing, type, test method and results, and re-check after any nearby work.