You may have noticed that we are on a *bit* of a mission to raise awareness of Linear Heat Detection as a cost effective, easy to maintain, and highly accurate piece of fire safety equipment.

(If you haven’t, we obviously aren’t talking about it enough…)

Last month, we welcomed almost 1700 individuals to our webinar, “Ensuring Fire Safety in Car Parks and Other Challenging Environments”. We were overwhelmed by the interest in such an important topic, and we are proud to have introduced linear heat detection (LHD) technology to so many people (apparently 517, according to the poll results)!

But there’s still some way to go.

Out of the 160 questions asked by our audience, there were a few that cropped up several times, so we thought it made sense to turn this into an article (trackable, Googleable…profile raising. Plus, informative. Win-win)!

Linear Heat Detection: You Asked, We Answered

“Do I have to replace the whole LHD cable after a fire?”

The short answer is no, you do not.

Two core, fixed activation (or digital) LHD cable is non-resettable, this means an irreversible change occurs within the cable when it alarms. However, only the section that has alarmed (and we recommend 3 metres either side of that due to heat transfer along the cable) needs to be replaced – not the whole zone length. This type of LHD is triggered at specific temperatures, and is best for higher activation climates, hazardous applications, and areas that experience rapid or extreme temperature changes. It’s also possible to pinpoint whereabouts along the cable the alarm is with fixed activation LHD cable.

Four core, programmable temperature (or analogue) LHD cable is resettable, so does not need to be replaced following an alarm or fire, as long as the sensor cable has not been exposed to a temperature above 125 degrees C.

Our Programmable Temperature Sensing product is the first cable-based resettable linear heat detector approved to EN54-22. It’s also the only type of cable-based linear heat detector that has automatic ambient temperature adjustments, rate of rise detection and pre-alarm functionality.

“What are the associated costs versus a traditional spot detection system?”

We love answering this one!

For like for like comparison of coverage, linear heat tends to be significantly cheaper. This is because LHD provides continuous coverage with a single installation, while typical spot detection systems require cabling in multiple spot detectors. It is important to factor in the cost of the fire rated cable as well as installation time. Wireless spot detection avoids this cost, but the devices themselves are much more expensive.

On top of being more expensive, spot detection can also be less effective and more prone to issues, such as false alarming or blocking in dusty, dirty and damp environments.

“Is there any requirement to maintain the cable in dirty or dusty environments?”

One of the key benefits of LHD in comparison to alternative means of detection, is that it is commonly referred to as ‘fit and forget’. It doesn’t expire, and unless it has cause to activate, it can function for decades with no interference – even in the harshest of climates.

LHD cables are suitable for use in the majority of dirty, dusty and hard to maintain environments – including damp, humid and unforgiving conditions. This is because they are unaffected by airflow, dangerous chemicals or toxins, removing the risk of reactive failure and false alarms – potentially leading to huge cost savings. Thermocable also provides the option for the LHD cable to be coated in different materials to thrive in particularly challenging applications.

Finally, with each of our reels and control units already being tested in our state-of-the-art lab before exportation, they exceed the most stringent of regulations.

“Can linear heat detection be used on the top deck of a multi storey which is open to the air?”

This is a good question, as open air environments are generally subject to higher airflow and more adverse weather conditions. But put simply, yes, open air environments are completely fine for LHD systems.

Coated in different materials to suit specific applications, LHD cables are appropriate for use in the majority of hard to maintain environments – including damp, humid and unforgiving conditions. This is because they are unaffected by airflow, dangerous chemicals or toxins, removing the risk of reactive failure and false alarms – potentially leading to huge cost (and time) savings.

In fact, we often do installations on floating roof oil tanks in the Middle East which, on top of the open-air factor, are some of the most difficult environments to protect from fire.

“Okay, so…in an open sided multi storey, what – if any impact – will car exteriors directly exposed to the sun have on detection temperatures seen at the detector? Would the radiated / convection trigger the alarm?”

This is another common problem in applications that are exposed to constant temperature increases – such as solar PV.

Thermocable’s programmable temperature sensing system (formerly analogue) combats this issue through ambient temperature compensation.

Measuring the environment’s ‘rate of rise’ in temperature, our smart system can tell the difference between a small increase of temperature over a more prolonged period of time, and an actual fire, which heats much faster.

“How about hazardous environments?”

Yes. Linear heat detection cable can be installed and used in hazardous areas as it is regarded as a ‘simple apparatus’ given its low voltage and that it does not contain an ignition source.

The monitor module or conventional fire alarm control panel should be installed in the safe area and the intrinsically safe (I.S.) barriers separate the safe area and the hazardous area as shown in Thermocable’s hazardous area installation guide.

“Is there any indication where on the cable run the alarm is triggered?”

Yes – our ProReact Fixed Temperature product range can identify the trigger point on the control panel to the nearest metre. This is exceptionally useful for large spaces and cable runs.

For our programmable systems, each control unit comes with a Modbus RS-485 output and an inbuilt test feature as standard, so every feature – including rate of rise and abnormal temperature points – can be accessed remotely via a laptop or smart phone.

“How do these cables operate (ref Lifetime cycle) to exposure to UV degradation?”

With multiple coating options which are specific to every environment, Thermocable tackled this issue by developing a nylon sheath for the cable. This nylon coating is extremely resistant to UV degradation, with an expected exposure resistance of lifetime 10+ years.

“Is there any limitation for how many metres we can lay the LHD?”

Theoretically, you can lay as much cable as you want, providing you install the recommended control panels at stipulated intervals per ‘zone length’.

Zone lengths:

  • 1000m for fixed temperature cable per zone (with 2 zones per controller)
  • 500m per zone for programmable

You can find out more here.

How do you test (without damaging) – and deal with any damage that does occur (including detecting this)?

Testing is extremely simple, and non-invasive, so no damage has ever been incurred (that we know of)!

For fixed temperature products, we have designed in a test switch on our End of Line (EoL) unit. All you do, is press it! While the cable may be installed in roof cavities, etc., the EoL unit is always easily accessible, so there is no requirement for invasive procedures.

For programmable products, you can do direct stimulus testing using the test kit we provide. There’s also a printed circuit board (PCB) that can be placed into the controller to simulate different ambient temperatures and alarm temperatures for pre-tests.

So, now we’ve answered the most common questions, is there anything you’d like to ask? We’d love to hear from you – you can get in touch on [email protected] or fill in our enquiry form here.