BS 7827:2019, in our own words

Does a stadium follow BS 5839-8 or BS 7827? Clause 4.1

Both, zone by zone, and BS 7827 is the standard that says which. It's natural to read BS 5839-8, BS EN 50849 and BS 7827 as three options and pick one by building type, but they are not parallel choices. Whether a system is a voice alarm under BS 5839-8 or an emergency sound system under BS EN 50849 is decided by its connection to fire detection, not by the building; a stadium, an arena or a terminal can be either. BS 7827 sits above both: Clause 4.1 recommends a risk assessment that divides a large or complex venue into voice-alarm zones and emergency-sound-system zones, and that allocation decides which of the other two standards each zone follows. BS 7827 then adds its own venue-scale provisions around them: the Table 2 power model, tiered fault reporting and acceptance over public events.

Clause 15: back-up power, and why sports grounds differ

The discussion that opens this clause explains that the sources disagree on how long back-up power should last. The Green Guide works to 3 hours at sports grounds, so that an event can run to its end after a mains failure rather than be abandoned in front of a crowd. BS 5839-8:2013, PD CEN/TS 54-32:2015 and BS EN 50849:2017 work to 24 hours of quiescent operation followed by 30 minutes of emergency operation.

Table 2: recommended back-up power

For sports grounds, Table 2 recommends back-up power for 3 h whether or not a generator is fitted, with a duty cycle of 3 h rather than 30 min, because the duty cycle follows the expected length of the event, including getting the crowd in and out. For voice alarm coverage in general it keeps 24 h (6 h with generator back-up) and a 30 min duty cycle.

Cited in: Peukert's law oversizes your voice alarm batteries

Why 3 hours is a survival window, not 3 hours of broadcasting

The sports-ground row is easy to read as "three hours of broadcasting", and it is often repeated that way, but that isn't what it says. Footnote A to Table 2 defines the duty cycle by the expected length of the event, including entry and exit: it bounds how long the system must stay capable of operating, derived from how long people are on site. The rationale Clause 15 gives is continuing the event on secondary supplies so that a crowd is kept informed and orderly rather than sent out in the dark. So the battery is sized to that window, and 3 h is not something to specify, or sell, as event audio.

Clause 18: three tiers of fault reporting

Fault monitoring at a large venue should serve three different readers: a generic "system fault" to the fire system, zone-level faults to the venue control room, and component-level diagnostics to the servicing technician. The critical path is monitored at all times, and every fault is logged with the time it occurred and the time it cleared. Clause 18 applies across both kinds of zone from the Clause 4.1 assessment; only the first tier is a link to a fire system, and that describes how the system is connected, not what kind of system it is.

If you're looking for the familiar figure of 100 s for reporting a fault, it isn't in Clause 18. It appears in Clause 21, the site acceptance fault tests, which cites BS 5839-8:2013 for it.

Clause 25: acceptance over two public events

Acceptance has two stages. A technical demonstration covers the installation, broadcast routing and priorities, intelligibility, back-up power and network resilience. Final acceptance then follows satisfactory performance at two public events, so that quality is judged with the crowd present and the venue's real noise. Declaring acceptance after one event does not meet the code.

Where these clauses are used

The sports-ground power model and the Clause 4.1 allocation are the basis of how a stadium or arena system is maintained and reported: stadiums and arenas. The service visits that keep a voice-alarm zone to BS 5839-8 are set out in what each maintenance level includes.

Clause and table numbers refer to BS 7827:2019.