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09/08/2018 / Graham Lowe

Bold Claims Over Multi-Sensors; But What’s All the Fuss About?

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Multi-sensors are the topic of conversation at the moment, but do we really understand them? This blog has been written to demystify multi-sensors and help you make a more informed decision when selecting the best detector for the environment.


What is a multi-sensor?

BS 5839 Part 1 2017 defines a multi-sensor as a “fire detector that monitors more than one physical and/ or chemical phenomenon associated with fire”. The standard acknowledges that a multi-sensor could be;

  • Optical and heat
  • Carbon Monoxide (CO) and heat
  • Smoke, heat and CO

The standard, does however, accept that a multi-sensor can also be used in a single sensor state. Which poses the question; if a sensor has the ability to detect smoke and heat, but can only operate in one state or the other, is it a true multi-sensor? Arguably not, however some manufacturers still label them as multi-sensors.


Why does it matter?

Smoke, heat and CO detectors are each designed to respond to different characteristics of a fire, and whilst there are environments that will benefit from using a single state sensor, in most environments, these technologies used in combination will provide a more accurate and reliable indication of a real fire.

In fact, the Building Research Establishment (BRE) recently conducted research in conjunction with the Fire Industry Association (FIA), which tested 35 different multi-sensors. The study concluded that ‘advanced’ multi-sensors far outstripped other multi-sensors in false alarm testing. The report defined an ‘advanced’ detector as “A detector that contains significant design features that allow it to identify and reject false alarms, e.g. devices that have dual sensor detectors, backward and forward scatter optics, or advanced algorithms that enable it to perform complex background monitoring/pattern recognition”.


How do I know if I am looking at a true multi-sensor?

A sensor that meets the requirements for smoke detection will be approved to EN54-5, a sensor that meets the requirements for heat detection will be approved to EN54-7 and a sensor that can monitor CO to determine a fire condition will be approved to EN54-26. A sensor might be certified to one or more of these approvals, but this does not mean that the sensor is capable of using these states in combination.

A true multi-sensor is likely to be certified to one or more of the following approvals; EN54-29, EN54-30 or EN54-31. A sensor that can monitor both smoke and heat simultaneously will be approved to EN54-29, a sensor that can monitor heat and CO simultaneously will be approved under EN54-30, and a sensor that can monitor smoke, heat and CO simultaneously will be approved under EN54-31.


What do Hochiki offer?

Hochiki offer two true multi-sensors; the ACC and the ACD.

The ACC offers three modes of operation; optical detection, heat detection, or optical and heat detection used in combination.

Hochiki’s newest offering is the ACD; offering 24 EN approved modes of operation. This multi-sensor offers combinations of smoke, heat, CO and COHb detection and is approved under EN54-5, EN54-7, EN54-26, EN54-29, EN54-30 and EN54-31. Furthermore, the ACD has an extra feature called “+RFA”.  This sophisticated algorithm monitors the environment over time and automatically adjusts the sensor’s sensitivity up or down based on the conditions of the environment, thereby reducing the possibility of false alarms even further. The ACD will be available in Q4 2018.


Learn more at


Leave a Comment
  1. Daniel / Aug 29 2018 11:01 am

    According to Google, COHb is shorthand for Carboxyhemoglobin which is the result of CO bonding with haemoglobin in red blood cells after inhalation. I do not see how it would be possible or beneficial for your ACD detectors to have sensors or algorithms designed to monitor this factor as it is highly unlikely to be present in the air, at least not in significant amounts or quickly enough after a fire begins to make a difference when the system makes a fire decision. I have looked through your product page, overview PDF and product specification PDF but I cannot find any real description of what you mean by COHb or how the ACD actually detects it – even though the term is mentioned a lot. Can you please provide clarification on this matter?

    • Graham Lowe / Aug 30 2018 3:31 pm

      Hi Daniel, thanks for your comment! In terms of CO detection the ACD has two functions; to monitor CO levels in order to detect and alert occupants to a smouldering fire, but separate to this, the COHb mode will monitor for dangerous concentrations of CO as defined in EN50291 (which might be caused by a faulty boiler for example). Therefore, the COHb mode is not designed to help determine a fire condition, it is designed to alert building occupants to possible toxic poisoning (COHb detection); which is useful for nurseries, care homes, hotels etc. The ACD allows the installer to choose whether to have both of these modes switched on, one of these modes switched on, or neither! Hope that helps!

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