Linear Heat Detection (LHD): Continuous, Low-Maintenance Fire Detection for Harsh Environments
Linear Heat Detection (LHD) provides continuous fire detection coverage using a heat-sensitive cable that acts as a “continuous run of spot detectors.” Designed for challenging environments, LHD systems deliver reliable, low-maintenance protection where traditional point sensors fail — including cold storage, industrial conveyors, and hazardous locations.
How Continuous Linear Heat Detection Works
Digital LHD (Protectowire) uses two conductors separated by a heat-sensitive polymer. When exposed to a preset temperature, the polymer melts, creating a short circuit and triggering an alarm — allowing for precise alarm location identification along the cable run.
Analog / Fiber-Optic LHD (Distributed Temperature Sensing, DTS) measures changes in electrical resistance or light reflection along the cable, providing rate-of-rise and pinpoint temperature readings. This enables programmable pre-alarms and detailed thermal mapping.
Applications: Where Linear Heat Detection Excels
Cold Storage & Freezers
Protectowire XLT LHD cables remain operational down to -60 °F and are UL & FM listed. They perform reliably in icing, condensation, or vapor environments where spot detectors are prone to failure.
Conveyor Belts & Cable Trays
LHD can be attached directly to moving equipment or electrical trays, detecting mechanical friction, belt slippage, or short circuits before ignition. Perfect for combustible dust-prone areas.
Hazardous & Corrosive Locations
Fluoropolymer-jacketed LHD cables (XCR series) are FM-approved for chemical plants and refineries. Operating on low voltage, they meet intrinsically safe standards for Class I and II Div 1 zones.
Tunnels & Large Facilities
Continuous coverage makes LHD ideal for tunnels, aircraft hangars, and large warehouses, where high airflow or inaccessible ceilings limit traditional smoke detection.
NFPA 72 Compliance & Low Total Cost of Ownership
Under NFPA 72, LHD cables are recognized as line-type heat detectors. Installed according to spacing guidelines, they deliver code-compliant protection in high-risk and remote environments.
Because the cable itself is the detector, installation and maintenance costs are drastically reduced — no calibration, no power supply to field devices, and fewer components to service. It’s the ultimate “fit-and-forget” fire detection solution.
SSI: Certified Installer for Protectowire & Fike LHD Systems
Suppression Systems, Inc. designs, installs, and maintains Protectowire and Advanced Detection solutions across the East Coast. We integrate clean-agent suppression and explosion protection systems to form a unified, NFPA-compliant safety strategy.
- Certified installation of Digital & Fiber-Optic LHD systems.
- Annual inspection and NFPA 72 maintenance service.
- Integration with alarm and suppression control panels.