Different Types of
Fire Detector Heads (Sensors)

Choosing the Right Fire Alarms: A Comprehensive Guide for Optimal Safety

When it comes to fire safety, having the right fire alarm system in place is crucial. Different types of fire alarms use various sensors to detect different fire types. Understanding the distinctions between heat and smoke detectors is essential for selecting the most suitable alarm for any application. In this article, we will explore the four primary types of fire detectors, discuss their detection mechanisms, and provide expert guidance on choosing the ideal alarm system for your premises.

The Four Types of Fire Detectors

The four most common detectors are ionisation, photoelectric, combination ionisation/photoelectric, and heat. All smoke detectors sound an alarm, when they identify smoke, to notify a building’s occupants. What differentiates these detectors from one another is the way that they detect smoke.

Ionisation Smoke Alarms

These detectors are excellent at detecting fast-burning fires. These are the cheapest and cost very little to purchase. They are very sensitive to small particles of smoke produced by fast flaming fires, such as paper and wood, and will detect this type of fire before the smoke gets too thick.

Ionisation Smoke Alarm

Photoelectric (Optical) Alarms

These detectors are effective at detecting larger particles of smoke from slow-burning, ‘smouldering’ fires. They’re extremely reliable and produce few false alarms. These are more expensive but more effective at detecting larger particles of smoke produced by slow-burning fires than an ionisation smoke detector.

Photoelectric (Optical) Alarms

Ionisation/Photoelectric (Multi-sensor) Alarms

They are designed to be sensitive to a wide range of fires and provide a faster reaction to both fast-flaming and slow-smouldering fires. As a result, BS 5839-6:2019+A1:2020 recommends the use of multi-sensor technology in all rooms except the kitchen. As the unit monitors for two different by-products of fires (smoke and temperature), its response to all types of fire is vastly improved over traditional single-sensor alarms. They are also less prone to false alarms associated with ionisation and optical-type alarms.

Multi-sensor detector

heat detectors

These can detect an increase in temperature and are insensitive to smoke. Heat detectors detect the presence of heat and an increase in air temperature. These detectors have few false alarms but, they take longer to identify a fire than a smoke detector. They are ideal in situations where smoke detectors may cause false alarms such as steamy, humid, or dusty environments and therefore best suited for kitchens, garages, and lofts.

Heat sensitive point detectors

Point detectors can again be subdivided into a further two types;

  1. Fixed temperature – which will operate when it is exposed to a pre-determined temperature. Normally fixed temperature detectors employ a fusible alloy element that must be replaced after the detector has operated. Different temperature-rated elements are available to take into account varying ambient air temperatures.
  2. The second type operates on the rate of temperature rise. The rate of rise temperature detector may also include a fusible element for fixed temperature operation.
Heat Detector

best practice for positioning cO and fire detectors

Smoke and Heat Detectors

BS 5839-6:2019+A1:2020 recommends that smoke and heat alarms be installed:

  1. On the ceiling, as central as possible in the
  2. Sited 300mm from walls and light fittings – this ensures the alarm is out of any ‘dead air’ spaces where the airflow may be blocked
  3. Placed within 3m of every escape door and bedroom door to ensure audibility
  4. Positioned between high-risk rooms and bedrooms
  5. For peaked and sloped ceilings – make sure there is a maximum of 600mm vertically down from the apex for smoke alarms, and 150mm vertically down for heat alarms

Carbon Monoxide Detectors

The Smoke and Carbon Monoxide Alarm (Amendment) Regulations 2022 came into force on 1 October 2022. From that date, all relevant landlords must:

  1. Ensure at least one smoke alarm is equipped on each storey of their homes where there is a room used as living accommodation. This has been a legal requirement in the private rented sector since 2015.
  2. Ensure a carbon monoxide alarm is equipped in any room used as living accommodation which contains a fixed combustion appliance (excluding gas cookers).
  3. Ensure smoke alarms and carbon monoxide alarms are repaired or replaced once informed and found that they are faulty.

The requirements are enforced by local authorities who can impose a fine of up to £5,000 where a landlord fails to comply with a remedial notice.

The BS EN 50292:2013 standard recommends that a CO alarm should be installed:

  1. Between 1m–3m from all potential sources of carbon monoxide (fuel-burning appliances)
  2. Sited 300mm from walls and light fittings – this is to ensure that they are outside of any ‘dead air’ spaces that occur in corners and spaces where the airflow may be blocked
  3. If the fuel-burning appliance is in a confined space (e.g. a boiler room) then the alarm should be sited on the ceiling just outside the room
  4. If there is no fuel-burning appliance, then place the alarm at breathing height e.g. bed’s head height in the bedroom

Selecting the appropriate fire alarm system is essential for safeguarding lives and property. By understanding the differences between heat and smoke detectors, as well as the various types of smoke detectors available, you can make an informed decision for your specific application. Following best practices for positioning CO and fire detectors, as outlined by industry standards, ensures optimal performance and enhances the overall safety of your premises. Remember, investing in a reliable fire alarm system is an investment in the protection and well-being of everyone within your building.

Fire Risk Consultancy Services have the knowledge and experience to assist your business to comply with all legal requirements surrounding Fire Safety including the legislation regarding Fire Alarms. Be sure to read our accompanying guides: British Standards Relating to Fire Alarms,  A Guide to Fire Alarm System Types, Categories of Fire Alarm Systems, Fire Alarms in the Home, AND Fire Extinguishers, Emergency Lighting, Fire Door Regulations, Fire Safety Signs, also published on this site. 

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