BS 5839-1:2025 limits detector coverage by distance, not by area. On a flat ceiling, how far may any point in a protected area be from the nearest smoke detector?

Clause 21.2.1a): the horizontal distance between any point in a protected area and the nearest smoke detector should not exceed 7.5 m (21.2.1b) gives 5.3 m for a heat detector. BS 5839-1 sets no coverage area per detector at all, so any m² figure is a manufacturer or rule-of-thumb convention rather than a recommendation of the standard. 10.6 m is the related but different figure: it is the centre-to-centre spacing the 7.5 m radial limit works out at on a square grid.

Which type of detector is most suitable for detecting smouldering fires?

Optical smoke detectors are most effective at detecting smouldering fires that produce visible smoke particles.

A fixed-temperature heat detector

At what height should manual call points normally be mounted?

Clause 19.8: manual call points should be fixed at a height of 1.4 m +0.2/-0.3 m above finished floor level, measured to the centre of the operating face — so anywhere from 1.1 m to 1.6 m. The tolerance is asymmetric, not the ±0.1 m often quoted.

Free mock exam

Detectors & Devices — Fire Alarm Systems (BS 5839-1) Practice

Free topic-focused mock exam: all 25 questions on Detectors & Devices, drawn from the wider Fire Alarm Systems (BS 5839-1) bank. 35-minute timer, 70% to pass, worked explanation on every question. Use this when you've taken the full mock once and want to drill the topics you got wrong.

Questions: 25
Time limit: 35 min
Pass mark: 70% · 18/25
Question bank: 25

Free, no sign-up. Retake as many times as you like — the questions are reshuffled, with the answer order changed.

Sample questions

01BS 5839-1:2025 limits detector coverage by distance, not by area. On a flat ceiling, how far may any point in a protected area be from the nearest smoke detector?
- A10.6 m
- B5.3 m
- C84 m²
- D7.5 m
Why: Clause 21.2.1a): the horizontal distance between any point in a protected area and the nearest smoke detector should not exceed 7.5 m (21.2.1b) gives 5.3 m for a heat detector. BS 5839-1 sets no coverage area per detector at all, so any m² figure is a manufacturer or rule-of-thumb convention rather than a recommendation of the standard. 10.6 m is the related but different figure: it is the centre-to-centre spacing the 7.5 m radial limit works out at on a square grid.
02Which type of detector is most suitable for detecting smouldering fires?
- AA fixed-temperature heat detector
- BAn infrared flame detector
- CIonisation smoke detector
- DOptical smoke detector
Why: Optical smoke detectors are most effective at detecting smouldering fires that produce visible smoke particles.
03At what height should manual call points normally be mounted?
- A1.6m
- B1.2m
- C1.4m
- D1.0m
Why: Clause 19.8: manual call points should be fixed at a height of 1.4 m +0.2/-0.3 m above finished floor level, measured to the centre of the operating face — so anywhere from 1.1 m to 1.6 m. The tolerance is asymmetric, not the ±0.1 m often quoted.

Common questions

Is the Detectors & Devices mock exam free?

Yes — 100% free, no sign-up needed. Questions are pulled at random from a substantial bank, with a worked explanation on every question after you submit.

Can I retake the mock exam?

Yes. Every attempt picks a different random selection and reshuffles the options, so each retake gives you genuinely new questions. No limit on retakes.

Does this count towards the real qualification?

No — this is independent practice material. To gain the actual qualification you need to sit the official assessment through an approved provider.