The panel on the building's network. With everything that implies.

A fire panel is the cabinet that asks every detector and every call point several times a second and decides what happens. When there are several buildings there are several panels, and they have to be linked so that everything can be seen from one place. The usual thing is to link them with a cable belonging to the fire system.

This family links them over the network, the way anything else in the building is linked, and in a ring so that a break does not leave anybody on their own. That solves installations where running a cable of your own end to end is half the works: a hospital with ten buildings and service tunnels, a road tunnel, a network of stations.

You come across it mostly in healthcare, in infrastructure and in buildings with a lot of technical plant. In hospitals there is also a practical reason: the same firm makes the nurse call systems, so it is often already inside the building before fire is even discussed.

The cabinet is modular: processor, loop cards, outputs and power supplies with their batteries, and growing means adding cards. Each loop carries elements with their own address, and with isolators spread along it so that a short circuit eats a section and not the storey.

For detectors, the usual judgement: optical in rooms, corridors, offices and cabled voids; heat in kitchens, car parks and plant rooms; multi-criteria where you need sensitivity in an atmosphere that is not clean; flame outdoors and in tall industrial units; aspirating when you have to find out very early or the ceiling is twelve metres up. In tunnels and service tunnels, linear heat cable, which is the only thing that copes there.

The alerting side: call points beside the exits, sounders and beacons where there is noise, and voice evacuation when something more than «get out» has to be said — in a hospital that is normal, because a hospital is not evacuated, it is moved in stages. And the rest of the building goes with it: smoke doors that close, air conditioning that stops, dampers, lifts that come down, access control that releases the turnstiles.

If the panels talk over the building's network, the network is part of the fire system. That means the equipment it passes through has to be powered the way the rest of the system is powered, has to be in a locked cabinet and not in a corner, and cannot be reconfigured by somebody on a Tuesday afternoon without telling anyone.

So the project has to sit IT down and put three things in writing: which section belongs to the fire system and who answers for it, what happens if somebody touches a piece of equipment on that section, and how you test that the ring is still a ring. It is not bureaucracy: it is that when the network belongs to another department, the three-in-the-morning fault is picked up by somebody who does not know that was fire.

That said, when it is set up properly it solves things that otherwise do not get done: supervising ten buildings without laying kilometres of cable, or bringing what happens across a network of sites spread over a city to a single desk.

The known places are the usual ones and they are worth naming: kitchens, changing rooms and showers with steam, car parks with exhaust gases, stores with dust, building work inside the building with welding and sanding, and plant rooms. In all of them an optical detector is going to give false alerts, and the answer is not turning its sensitivity down: it is fitting the technology that belongs there.

The panel keeps the history of each sensor and warns about the one that is getting dirty before it starts being a nuisance, which allows a targeted inspection instead of a full round. That helps a lot and it does not replace the project: a badly placed detector will still be badly placed with the prettiest report in the world.

And there is one thing specific to hospitals that you only learn by being there: the zones that change use. A room that was a store and is now a technical space, a corridor where material is now parked, a floor under refurbishment with the ceiling void open for four months. That sets off systems that were well designed, and it is solved by reviewing the use of the zones and not the sensitivity of the detectors.

It suits large, spread-out sites, healthcare and infrastructure, and places where there is already a well run data network with people who answer for it. It does not suit —or it suits with care— where the network belongs to everybody and nobody: there it is more honest to use a cable belonging to the fire system, even if it costs more in works.

And there is a part that is not ours and is worth saying early, because in a hospital both halves are there: we are electronics people. Detection, alarm, evacuation, panel, integration and maintenance, yes. Sprinklers, hose reels, dry risers, pressure sets and tanks, no: another trade, another licence and other contractors. We say it in the first meeting so that the budget allows for both companies from the start.

Of gas suppression we do the electronic half —detection, timing, do-not-enter warnings, release, abort and the interlock that stops the air conditioning before discharge— and not the bank of cylinders or its pipework.

Your people have to be able to silence, reset after checking, read the log —at what time, which point, what happened before— and understand a fault alert. And in a hospital something more is needed: it has to be decided and rehearsed what happens to the affected floor, because what is ordered here is not going out into the street, it is moving people to the area next door.

Temporarily disabling a zone is your people's job too, because in a hospital there is always work going on somewhere. It is taught, with a written rule and a record of who disables and who puts back. A zone disabled during a four-month refurbishment that nobody put back is the classic hole in these buildings.

What is not your people's job: adding or moving elements, touching the programming, changing sensitivities, updating panels and touching the system's network section. That is not a preference of ours — the installation has to be in the hands of a licensed maintenance company, with a schedule and a signed file. And what decides whether they can operate it is the drawings, the one-page procedures and training given by role and by shift.