Detecting and releasing is ours. The cylinder and its pipework, no.

The second is the one that puts it in a place of its own: this house is designed to command a fire suppression system. It does not only report that there is a fire, it also runs the sequence that ends in a discharge of extinguishing agent, with everything that drags along with it: confirming before releasing, warning whoever is inside, giving them time to get out, allowing somebody to stop the discharge, and releasing nothing if the room is not in a condition to receive it.

You come across it where water is not an option because getting wet is as bad as burning: server rooms and communications rooms, electrical and transformer rooms, archives and document stores, control rooms, battery banks, machine cabins. Also in industry, where on top of fire there is a risk of explosion and the protection has other rules.

In a room protected by gas the detection is built differently from an office, and for a physical reason: you have to detect in the three places the smoke can travel through. At the ceiling, in the raised floor if there is one, and in the air conditioning return, which is where the smoke will pass first because that is where the airflow is. A server room with detectors only at the ceiling and the air moving can take a long time to find out.

And it is built with double confirmation: two detectors from different groups are needed for the system to accept that there is a fire. That adds a few seconds to the detection and avoids the one thing you cannot allow in a room with gas, which is a discharge caused by a wrong detector. An unnecessary discharge costs the agent, the refill, the shutdown of the room and everybody's confidence in the system.

Ours is everything that carries current and logic. The detectors and where they go. The control panel and its programming. The double confirmation. The pre-warning timer, which is the time given for people to get out. The sounders and the illuminated signs inside and outside the room, which are the ones that say «do not enter». The manual release call point and the abort call point. The interlock with the door and with the air conditioning, because the discharge is no use if the air is still moving or if the door is open. The electrical command that goes out to the cylinder actuator. The supervision that this release circuit is still connected. And the integration with the building's main panel, so that what happens in that room is seen at reception.

What is not ours is everything mechanical. The cylinder bank and its bracketry. The agent inside them and its refill. The pipework, the nozzles and the calculation of how much agent is needed and where it comes out. The actuator fitted on the valve. And two things that are building work and not installation: the airtightness of the room, because a gas escaping through the cable penetrations does not hold the concentration for as long as it has to, and the overpressure relief, because discharging puts a lot of volume into a closed space all at once and that pushes.

And what really helps is somebody saying this: the weak point of these installations is not in either half, it is in the join. The panel programmed and tested on one side, the mechanical part fitted and tested on the other, and nobody who has checked the two together to see that the command goes out, arrives, and does what it has to do. We ask for that joint test with both companies present, with the discharge inhibited, and for the result to be recorded on the certificate with both signatures.

Sprinklers, dry risers, fire hose reels, pump sets, tanks and all their pipework: we do not do it. It is the same reasoning as with the cylinders and with more reason, because there you have hydraulic calculations, pressures and a licence that is not ours.

What makes it release when it shouldn't is nearly always a design fault, not an equipment fault. A single detection group instead of two. A smoke detector put where there is steam or dust. The sensitivity inherited from another project. Or the most usual trap in technical rooms: a room that filled up with cabinets after commissioning, so the air no longer circulates the way it did and the detectors are looking where nothing happens any more.

And there is a failure mode that is not technical and is the most frequent one: the abort call point used as if it were a silence button. Somebody presses it because the sounder is annoying, and keeps the discharge inhibited. That is not fixed with electronics: it is fixed with training and with a procedure on the wall of the room.

It fits where there is a closed space, with something inside that cannot be got wet and cannot be stopped, and with few people normally inside. A technical room, an electrical room, an archive. And it fits when you want the detection and the release governed by the same head end instead of by two systems tied together with a relay.

It does not fit as the general detection system of an office building if there is nothing to suppress: there you are paying for a capability that is not going to be used. And it does not fit —this matters— in a space that cannot be sealed. If the room has open cable penetrations, a suspended ceiling shared with the corridor or a door that does not close, the gas goes and the protection is decorative. That has to be resolved beforehand with building work, or another strategy chosen. Saying it after installing is too late.

The fire suppression part, no. Here there is one function the client does have to know how to use and only one: inhibiting the release when there is going to be work in the room, and putting it back at the end, both of them noted in a record with a name and a date. Everything else —changing times, touching detection groups, modifying the sequence— is not touched from inside, because a change made badly here does not show until the day it matters.

And the maintenance has two schedules, not one. The detection one, which is the one for any panel, and the one for the mechanical part: checking the weight or the pressure of the cylinders, the state of the actuator, and the verification that the room is still airtight, which is the one most often skipped and the one that creates the most false security. It costs money every year and it is worth knowing that before signing.