FIRE DETECTORS-5
LINEAR HEAT FIRE DETECTORS
The FSIB introduces the fifth in a series, on types of detectors available for the many and varied applications one might face.
Linear Heat Fire detectors
Linear heat detection cables are specialized fire detection devices that detect heat continuously along their length. Each linear cable length is connected to a control panel that determines a temperature change has occurred. These cable systems are often well suited to environments where point-based detectors might not be ideal. They are highly versatile and effective in areas with challenging conditions or where large coverage is required.
Linear Heat detector types.
There are distinct types of linear heat detectors, tailored to meet various fire detection needs:
- Digital Linear Heat Detection Cables - Specialized fire detection that triggers an alarm when a specific temperature is reached determined by the length of cable.
- Analog Linear Heat Detection Cables - These monitor the actual temperature along the cable and can trigger alarms based on temperatures programmed from a range of levels within the controller. An alarm is raised before the cable is damaged.
Applications
Linear heat detection cables are ideal for locations where traditional fire detectors may not be best suited, such as:
- Cable trays in industrial environments.
- Tunnels and underground installations.
- Conveyor belts.
- Installed around items of plant.
Areas where high airflows, significant dust accumulation, or other environmental conditions occur and where standard point-type detectors may not be suited is where linear heat cables come into their own.
Linear heat detection is also used for monitoring certain items of plant. Cables are laid in close proximity to the machine or piece of equipment to monitor for overheating.
These systems are also used over long lengths such as cable runs in cellars and where the linear cable can be laid in close contact with the other cables.
How do they work?
Digital Linear Heat Detection Cable
The digital type of linear heat cable consists of two conductors within a plastic sheath. Several types of sheathing are available.
Digital linear heat detection cables are designed to trigger a response when a specific temperature is reached. If the temperature surrounding the cable reaches the alarm temperature, the two cores quickly come into contact and trigger an alarm. These cables are known as “digital” because they are “off” below the activation temperature and irreversibly switch “on” when the activation temperature is reached
The cable will be damaged at alarm temperatures and must be repaired or replaced.
Analog Linear Heat Detection Cables
Analogue linear heat detection systems comprise of a control or interface unit, a zone of a four core analogue linear heat detection cable and an end of line unit. The system identifies fires or overheat conditions by continuously measuring changes in electrical resistance along the detection cable. An alarm is triggered once the resistance along the cable falls below a set threshold, which is determined by the desired alarm temperature (chosen by the user).
Analogue systems can be reset after an alarm is generated, without damage to the cable.
Where should we NOT use it?
While linear heat detection cables are often dependable, they are not suitable for situations requiring detection of smoke rather than heat such as stairways, computer environments or for the operation of gas suppressions systems.
Where can it be installed?
Linear heat detection cables are perfect for areas where point-type detectors cannot provide adequate coverage. Examples include long conveyor belts, cable tunnels and industrial sites with extensive cable runs.
They are also invaluable for hazardous areas that require reliable, explosion-proof detection systems.
Installation Guidelines
When installing linear heat detection cables, consider the following general guidelines:
- Spacing: Adhere to manufacturer guidelines and national standards for spacing between runs and distance from walls or other structures.
- Testing: Perform regular testing to ensure the system is functioning as expected and clean the cables to remove dust or debris that could impact performance.
- Routing: The cables should not be installed where they are expected to be damaged.
- Environmental Considerations: Account for environmental factors such as temperature, humidity, and exposure to chemicals, and select cable types that are suitable for those conditions.
Advantages of Linear Heat Detectors
Linear heat detection cables can offer numerous benefits:
- Wide Coverage: They detect heat along their entire length, ensuring no "blind spots." Long lengths of coverage.
- Durability: Resistant to harsh environments, some including extreme temperatures and humidity.
- Early Detection: Advanced models offer early warnings, mitigating fire risks before they escalate.
- Localised detection: Linear heat cables can be mounted close to machinery, equipment, or cables for early detection of overheating.
False alarms and maintenance
While linear heat detection cables are less prone to false alarms, environmental factors like heavy dust accumulation or chemical exposure can impact their performance.
Mechanical damage to cables can occur if the cables are loosely slung. Ensure the cables are securely fixed in areas of limited traffic
Regular inspection, testing, and cleaning can help maintain their reliability.
Conclusion
Linear heat detection cables are a great tool in fire detection systems. Their adaptability, reliability, and ability to cover extensive areas make them a preferred choice for various applications. Whether protecting industrial sites, tunnels, or storage facilities, linear heat detection cables can provide dependable protection.