BS 5839-8:2023, in our own words

Commentary on Clause 18: naming the fire

The commentary records that the old practice of keeping the cause of an evacuation from occupants, for fear of panic, is now deprecated. People given accurate information are less likely to panic, more likely to do what is asked, and less likely to lose time working out why they are being moved. On that basis the standard now regards using the word "fire" in the evacuation broadcast as likely to be advantageous.

Commentary explains a clause. It is not itself a recommendation.

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Clause 18.2: clear, concise, and repeated where it helps

An emergency message should be clear and concise, delivered in a calm and authoritative way, and repeated where repetition reinforces its meaning.

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Clause 18.5: how an emergency message should sound

Emergency messages should be spoken slowly and clearly, without raising the voice, in plain language, and without jargon, abbreviations or colloquial expressions. Item c) adds that they should be assertive and convey the need for immediate action.

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Clause 18.8: the broadcast sequence, and the examples in its notes

Sets out how a pre-recorded evacuate broadcast is built: an attention-drawing signal of 2 s to 10 s, a brief silence, the evacuate message, then a further silence, with no more than 30 s between the start of one message and the start of the next, repeating until someone silences it. Alert broadcasts follow a similar pattern with their own timings.

The example wordings printed with this clause, including the familiar evacuate message that opens with "Attention, please", sit in its notes. In a British Standard a note is informative: it illustrates the recommendation and adds nothing to it.

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Clause 19.1: how loud the attention-drawing signal should be

The attention-drawing signal and any non-speech alarm broadcast should reach at least 60 dBA throughout the accessible areas, with very small enclosures excepted (item a). Where the background noise is above 60 dBA, the signal should be 5 dB above that background (item b). Where the system is meant to rouse people from sleep, 70 dBA at the bedhead (item c). Nowhere that people can normally reach should it exceed 120 dBA (item d). Measurements are taken with all doors shut (Clause 19.2).

Clause 3.10: where the critical signal path ends

This is a definition, not a recommendation. The critical signal path is every component and connection that an emergency broadcast passes through on its way from wherever a fire broadcast can be started to the loudspeakers (or other alarm device, such as a voice sounder). It stops at each device's input terminals, wherever those sit on or inside its enclosure. The loudspeaker itself, and the wiring inside it beyond those terminals, are not part of the path as defined.

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Clause 10.1: what the panel should report, and how fast

Item 10.1.1 covers faults on the system's signal side. These should be indicated at the voice alarm control equipment within 100 s, even while the system is being used for something else, such as background music. They are: a loudspeaker circuit that is open, shorted or faulted to earth, with spur circuits expressly included (item a); a failed emergency microphone or its wiring (item b); a fuse, circuit breaker or other protective device in the critical signal path that has operated and could stop an emergency broadcast (item c); a failed transmission path between parts of a distributed system (item d); and a failure in any ambient noise sensing and compensation system that is fitted (item e).

Item 10.1.3 gives the power side longer. A failed standby supply should show within 15 min. Loss of the main supply, a charger failure, and the battery voltage falling below the fault level set in BS EN 54-4 should each be indicated within 30 min. Item 10.1.4 adds a 15 min indication where batteries are connected in parallel and one is disconnected or has a shorted cell.

None of these items names a monitoring method: they say what should be reported, not how to detect it. The six-monthly service under Clause 40.1 includes a check of the fault indicators, by simulation or by reviewing the panel's configuration, where practicable (item p).

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Clause 25.3.2: the battery type

The standby battery should be of a type expected to last at least four years in the conditions it will actually see in the system. Car starter batteries should not be used.

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Clause 25.3.4: recharge within 24 hours

The charger should be able to bring a battery that has been discharged to its final voltage back up to the capacity Clause 25.3.5 calls for within a 24 h charging period. A note warns that fitting a larger battery than the design assumed, for example to cover an unforeseen extra load, can stretch the recharge time beyond that.

Clause 25.3.5: how long the standby battery must last

a) Normally, the battery should keep the system running for at least 24 h and then still have enough capacity to broadcast the evacuate message in every alarm zone for at least 30 min.

b) Where the total evacuation time of the building is likely to exceed 20 min, that 30 min is extended by a safety margin agreed by all the interested parties.

c) Where an automatically started standby generator serves the system, the standby period drops to at least 6 h, still followed by the 30 min evacuate broadcast.

Cited in: Peukert's law oversizes your voice alarm batteries, What battery manufacturers should publish, but do not, Your next voice alarm battery quote should be smaller than your last

Annex C, C.1: the battery capacity calculation

Annex C is normative: it is part of what the standard recommends, not an illustration of it. C.1 gives the formula for the minimum battery capacity. It adds the standby load over the standby period to the alarm load over the alarm period, each multiplied by a derating factor, and multiplies the total by 1.25.

The derating factors are to be derived from the battery manufacturer's data. They describe how much less than its 20 h rated capacity a battery actually delivers when it is discharged faster, which for the 30 min alarm period is a great deal.

Cited in: What battery manufacturers should publish, but do not, Your next voice alarm battery quote should be smaller than your last

Annex C, C.1.2 and its notes: the 1.25 factor, heat, and missing data

The 1.25 multiplier allows for some variation in ambient temperature and for battery ageing.

Note 1 adds that heat shortens battery life sharply: at a continuous 35 °C a valve-regulated lead acid battery can expect only about 60 % of the life it is specified for at 20 °C.

Note 2 accepts that derating factors are not always available from manufacturers' data, and offers an approximation read from a manufacturer's 20 h rate battery selection chart instead.

Cited in: Voice alarm standby battery calculator, What battery manufacturers should publish, but do not, Your next voice alarm battery quote should be smaller than your last

Annex C, C.2.1: speech at one eighth

Where the system broadcasts speech messages, the alarm load current is taken as one eighth of the full load current, because a real emergency message is a mix of silence, attention-drawing signal and speech. A note records that the one-eighth value derives from tests in BS EN IEC 62368-1 and has been verified by experiment.

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Annex C, C.2.2: tone signals at a quarter

Where the system broadcasts signals imitating bells or sounders as its evacuate or alert signal, the alarm load is calculated as a continuous attention-drawing signal at 6 dB below full level, which is a quarter of full power.

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Annex C, C.3: the worked example

An example calculation for a small system on a valve-regulated lead acid battery. It uses a derating factor of 1.9 for the 30 min alarm period, a figure that belongs to the battery data it was taken from rather than to batteries in general.

As printed, one step of the example adds 8.4 and 4.22 and writes 14.72; the true sum is 12.62. The worked example that doesn't work follows the consequences.

Cited in: What battery manufacturers should publish, but do not, Your next voice alarm battery quote should be smaller than your last

Commentary on Clause 31: end-of-line devices

The commentary to Clause 31, the installer's responsibilities, notes that monitoring a loudspeaker circuit's integrity often relies on end-of-line devices. A circuit can need several of them, for instance where individual spurs are recommended to be monitored. It asks for each one to be clearly identified, its location recorded, and left accessible for servicing.

Commentary explains a clause. It is not itself a recommendation.

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Clause 33.1, Note: the margin for earth-fault sensing

The note is guidance, not a recommendation. Control equipment may sense earth faults against a set threshold of resistance to earth; the note's example is 1 MΩ. It points out that the whole installation's combined resistance to earth needs to sit well above that threshold, or the panel will report earth faults that are not there. On a large system, therefore, each cable needs to beat Clause 33.1's 2 MΩ minimum by a wide margin for the total to stay clear of 1 MΩ.

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Clause 33.4: the installation measurements, with every loudspeaker connected

Once the installation work is finished and every loudspeaker is connected, the installer should measure the impedance of every loudspeaker circuit at 1 kHz (item a), check polarity where it matters (item b), and carry out any other tests the equipment manufacturers specify (item c). By specific agreement, these tests can instead form part of commissioning. Clause 33.5 asks for the results to be recorded and passed to whoever commissions the system. That makes the figure taken with every loudspeaker connected the baseline that later impedance readings can be compared against.

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How often should a voice alarm be tested and serviced? Clauses 39 and 40

Weekly by the premises, and at intervals not exceeding six months by a competent servicing organisation, with further activities at least once a year.

Clause 39 places a routine testing duty on the premises: a test every week (39.1), at about the same time each week (39.2), with the results recorded in the system logbook (39.6, Clause 43). Occupants should hear the emergency messages during testing preferably monthly and at intervals not exceeding three months, the interval set by risk assessment (39.1).

Clause 40.1 recommends inspection and servicing at intervals not exceeding six months. Among the activities are a visual check for structural or occupancy changes that affect the design, functional tests, fault simulation, a check of the battery installation date against its recommended life, and a review of the logbook. Clause 40.2 adds activities at intervals not exceeding 12 months, including the manufacturer's recommended annual items, measurement of every loudspeaker circuit's impedance and comparison with the previous year's reading (item i), and subjective intelligibility testing in all loudspeaker zones (item j, new in the 2023 edition). Outstanding defects are reported to premises management (40.3) and an inspection and servicing certificate is issued on completion (40.4).

Six months is the code's maximum interval. A quarterly visit is an enhancement a maintainer may offer; it is not something BS 5839-8 recommends, and should not be described as one.

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Clause 40.1 a) and f): reading the fault record at every service

Two of the six-monthly activities in Clause 40.1 are about the record rather than the hardware. Item a) asks for the system logbook to be examined, to check that every fault recorded in it was properly dealt with. Item f) asks for the panel's electronic fault log, where it has one, to be examined for faults that appeared and later cleared, and for each to be reviewed in case it needs further attention. In practice we download a copy of the panel's fault log and configuration at each service and keep it safely off-site. Together they make the fault history part of the service, not just the faults present on the day.

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Clause 40.1 p): checking the fault monitoring itself

Among the six-monthly activities, item p) asks for every fault indicator and its circuit to be checked, where practicable. This is done either by simulating the fault or by reviewing how the control equipment is configured, to confirm that every fault monitoring function the code expects is switched on. It is the item that tests the watchman rather than the system it watches.

Clause 40.2 c): hearing every loudspeaker once a year

During the annual tests of the automatic and manual initiating inputs (items a and b), every loudspeaker should be checked, where practicable, to confirm that it works, and where it matters that it points the right way. Item d) adds a visual check of every loudspeaker for damage, again where practicable. In our reading, item c) is the one that catches a single dead loudspeaker that circuit monitoring cannot always see; the clause itself does not say so.

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Commentary on Clause 40: servicing is not a design review

The commentary to Clause 40 says that routine servicing confirms the functionality and serviceability of the existing system and does not constitute a fresh review of its design. It follows that a non-conformity with the design clauses will not necessarily be found at a service visit, and that where a maintainer does point one out, nobody can take that as meaning the whole design has been reviewed. The maintainer also needs to check whether an apparent non-conformity is in fact a variation agreed in the original contract before any corrective work starts.

Commentary explains a clause. It is not itself a recommendation. It is the paragraph to read when a maintainer is asked to vouch for a design, produce as-fitted drawings or reconstruct a zone schedule: the standard places those documents with the installer, the commissioning organisation and premises management (Clauses 31, 34 to 37 and 42). The maintainer reviews those records when it takes over (41.1 a)) and is expressly asked to supply only a logbook, where none exists (41.1 b) 7)).

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Clause 41.1: when a new maintainer takes over

On the appointment of a new maintenance organisation, a special inspection of the existing system and its records should be carried out to produce a maintenance plan. Non-conformities are documented and identified to premises management under seven headings: audibility (Clause 19), intelligibility (20.3), standby power (25.3), fire resistance of cables (Clause 26), fault monitoring (10.1), electrical safety (Clause 30), and the provision of a logbook where none exists. A note says that not every non-conformity need be rectified; that decision is the user's, on advice.

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Clauses 41.2 and 41.3: repair or modification?

Like-for-like replacement of a failed part is repair under 41.2: every fault or damage should be logged, and repair put in hand so that it is done as soon as possible (item c); the clause also recommends a call-out agreement with normal attendance within 8 h on a 24 h basis, and the maintainer's name and telephone number displayed at the main control equipment. A change to the system is a modification under 41.3, which recommends that it is made by someone competent in voice alarm design, agreed in writing by premises management, tested wherever it has an effect, recorded on updated drawings and covered by a modification certificate. Note 3 sets out when a certificate is generally needed; adding or removing more than 5 % of the loudspeakers is one of the triggers.

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Where these clauses are used

The battery clauses and Annex C are the basis of the voice alarm standby battery calculator. Clauses 39 to 41 are the basis of the three maintenance levels: what each level includes, and which of them meets the standard's servicing interval.

Clause numbers refer to BS 5839-8:2023. Where a later amendment or edition renumbers them, this page will be updated.