What is Linear Heat Detection - and How Does it Work?

When thinking about fire safety, many people picture traditional devices, such as fire extinguishers on the wall, sprinkler systems above, or smoke detectors mounted on ceilings. These are all important elements of fire protection but relying solely on them doesn't offer complete protection.

The question isn't whether these devices are useful, it's whether they're comprehensive enough for the specific risks your environment faces.

Fires pose serious threats to business and critical infrastructure, which can result in significant human, economic, and environmental consequences. In the UK alone, Fire and Rescue Services attended over 133,000 fires in the year ending September 2024, a stark reminder of the ongoing risk fires pose.

Early detection is vital to minimise risk, protect lives, safeguard assets, and ensure continuity of operations. At Thermocable, we specialise in Linear Heat Detection (LHD), offering advanced solutions specifically designed for rapid, accurate fire detection.

With decades of industry expertise and a track record of protecting critical infrastructure globally, Thermocable is recognised as a trusted provider in fire detection solutions. Our linear heat detection products are crafted specifically to address complex environmental challenges, ensuring protection, peace of mind and making them ideal for fire detection in hard-to-maintain environments.

What is Linear Heat Detection (LHD)?

Often referred to as line type heat detection, LHD is a cable-based type of early fire detection, designed to generate either an alarm, or automatically activate a fire suppression system. 

The cable is engineered to recognise abnormal temperature rises anywhere along the length of the cable. Unlike discrete point sensors (e.g., smoke detectors), LHD provides continuous monitoring across large or difficult to reach areas, offering early detection of overheating or fire before incidents escalate.

LHD systems are suited to large, complex, or hard to access areas i.e., cable trays, conveyors, tunnels, floating roof tanks and more, where conventional spot detectors are impractical or unreliable. The sensing cable performs reliably in dusty, humid, or harsh environments, with the capability to resist false alarms, making linear heat detection a reliable, low-maintenance 'fit and forget' solution.

Applications: Where LHD Shines

Linear Heat Detection is most practical where early temperature rise detection and continuous coverage are essential. Some of the applications where LHD thrives are:

• Industrial and Manufacturing Facilities - protection of machinery and conveyors from overheating
• Infrastructure and Tunnels - coverage for confined spaces where access and visibility are limited
• Oil, Gas, and Chemical Storage - rapid response to temperature increases on tank roofs or critical infrastructure
• Solar PV - resistant to environmental stresses like UV, wind, rain, and dust, maintaining performance outdoors. Read our solar press release to learn more about LHD supports photovoltaic system safety.

With a variety of coatings, Thermocable's LHD solutions can be adapted specifically to environmental conditions, ensuring maximum protection and reliability for your needs.

Two Technologies: Fixed Temperature Activation vs Programmable Temperature Sensing

Linear Heat Detection solution come in two types: Fixed Activation and Programmable Temperature Sensing. Each solution has distinct capabilities tailored for your specific applications.

Fixed Temperature Activation (Digital)

This solution operates using a two-core cable with a special polymer designed to melt at a specific temperature (ranging from 68 to 185⁰C). When the cable reaches the pre-set temperature threshold, the polymer melts, causing the two cores to touch which triggers an alarm. Some distinct features of this solution are:

• Non-resettable: After an alarm is triggered, the affected area of cable must be replaced
• Long Cable Length: Supports up to 3,000 metres per detection zone, ideal for areas where extended coverage is needed
• Alarm Location: Thermocable's interface modules can pinpoint exactly where the activation occured along the cable length
• Practical For: High-risk, long-distance applications where cable replacement after activation is acceptable, such as long conveyor systems, tunnels, storage tanks

Programmable Temperature Sensing (Analogue)

The solution uses a four-core cable continuously monitoring resistance changes along its length. The changes in resistance correspond to temperature changes, allowing the control unit to identify both rapid and gradual temperature increases. It gives the users the ability to programme the exact temperature thresholds, providing customised protection and early warning capabilities. Some distinct features are:

• Resettable: If the cable hasn't experienced excessive heat (approximately 125⁰C), it can be reset and reused
• Early Detection Warning: Capable of detecting gradual temperature increases and rapid rate-of-rise scenarios, allowing intervention before a disastrous event
• Shorter Detection Zones: Typically covers distance up to 500 metres per detection zone
• Practical For: Sensitive environments requiring precision, adjustable detection, and flexibility, including escalators and car parks

So, Ultimately, the Benefits are..?

As well as the obvious benefit of providing extra protection against the impacts of fire, one of the main advantages of linear heat detection cable is its versatility. It can be installed in both indoor and outdoor environments and in hazardous areas if required. And more importantly, it is unaffected by dirt, dust, debris, damp and time – which means it’s both cost effective, and low maintenance.

Performance and Reliability

• Continuous detection along the entire cable length, eliminating blind spots across large or complex areas
• Reliable operation in dusty, humid, or polluted environments where point detectors can struggle

Cost and Lifecycle Value

• Lower installation and maintenance costs compared to point-based technologies
• No routine maintenance required on the detection cable itself
• Low total cost of ownership over a system life
• Programmable options allow system reset without cable replacement, while fixed-temperature variants support longer zone lengths, reducing overall cable requirements

System Integration and Response

• Direct integration with conventional and addressable fire alarm control panels
• Supports automated activation of sprinklers, preaction system, or suppresion valves as part of a coordinated fire response

Installation Flexibility

• Multiple cable constructions available, including PVC, nylon, and stainless steel, to suit different mechanical, UV, or chemical exposure conditions
• Wide operating temperature range, allowing installations at temperatures to -40⁰C and reliable performance at ambient temperatures up to 170⁰C

Although it is perfect for multiple applications, and can be a hugely effective part of your fire strategy, linear heat detection is often overlooked when considering the safety of your buildings/apparatus, and that is because it isn’t spoken about enough. People simply aren’t aware of its existence.

We are here to change that.

Conclusion

Linear Heat Detection provides unparalled fire detection capability, with the ability to safeguard critical infrastructure, people, and business operations across diverse environments. With Thermocable's ProReact range of fixed and programmable LHD products, your business can rely on robust, continuous, and reliable fire detection that meets your operational and environmental demands. 

Want to learn more? Read our 10 Frequently Asked Questions About LHD to get quick answers to common customer queries or check out our YouTube channel to see how the system works in action!