We carried out a fit-out of an addressable fire alarm system in Deansrath Community College. The fire alarm system was going to be the new option in the school in comparison to what originally was there, which was a conventional style system where the identification of fire was much poorer. It would be harder to identify a device that went into the fire because there’d be more than one device on that loop that could be up to 25 devices here, maybe on it.
So we started with wiring the school. We used a metal conduit and cable tray throughout the school. We then wired the fire alarm using Firetuff which has got protection against burn, which would be an hour rating. This cable must be secured in some sort of cable management, for example, conduit, Pyro clips or cable tray. If it’s on a cable tray, we need to secure the cable tray using steel cable ties rather than plastic, because the cable must be kept in position. Firetuff works by turning into a form of glass when it is burned, which protects the copper on the inside. If the cable was just left hanging above a ceiling and that ceiling collapsed and the cable fell, that glass would crack and then open the copper to the atmosphere and just probably destroy it hence why it’s secured into position. Then we wire a loop.
On the panel, you have “loop in” and “loop return”. The signal and voltage are sent out through the loop into one device, out and in and out and in and out to each device on the loop until eventually, it returns at the panel. If the cable is cut, the panel will send voltage from each side which would mean that you might still have full protection. Whereas if it were a radial circuit, and the radial got cut in half, then the fire alarm would only be to see possibly halfway or even less. You would lose a lot of devices, and that wouldn’t be good in a school or any public building so this ensures that the fire alarm has redundancy and will work even if the cable is damaged. If the cable is caught in two places, then you would lose whatever is in between the two cuts. But that’s rare. Usually, if it’s cut in one place will be called out and we can come back and fix it.
We can connect sounders on the loop. We screw a sounder base on the ceiling, wire it and then click on our smoke detector or heat detector. It gives us more room to choose where we want sounders fitted, whereas on an old conventional system we would have to wire, especially for the sounder circuit. The sounders then can also be programmed for different decibel levels.
In an area where maybe a disabled toilet or in a very loud room where there’s a lot of machinery or work equipment, a strobe can be added so we can get a sound or strobe base. If people can’t hear the sound, at least they can see the strobes flashing, which will allow people to realize that there’s an alarm activation.
We also fit MCP, which means manual call point. They’re the red brick glass units. The call points today have a plastic resettable imitation glass. The idea is that it removes the user of the fire alarm system from having to have spare glasses. All they need now is a key to reset the brick glass unit. We also have double knock covers. They’re transparent covers that fit over the brick glass, and this prevents accidental activation of the call point units.
In Deansrath school, we have completed the wiring phase and are nearing completion. On the second fix of the addressable devices, the next phase of our project will be commissioning, and commissioning is a long enough process.
It takes quite a while because this is one of the most important parts of the job. Once all devices are fitted on the loop, we have to address them. Each device will be given a number; call points, smoke detectors and Sounders or even IO units will be given an address. An IO unit is a switch that’s connected to the fire alarm system.
As the fire alarm system activates, the switch will activate. We can use that switch then to give a signal to bring a lift to the ground. We can use the IO to unlock electronic doors, such as access control doors that would normally be locked. If the fire alarm goes off, the doors will automatically open via the IO unit (IO meaning interface unit). We also use the IO a lot for turning off any gas. If there’s gas supplied to the building and the fire alarm activates, it’s usually requested that the gas be cut off to the building so the IO can switch off the gas if the fire alarm activates.
The IO would be used for opening AOVs or automatic opening vents. They would normally be at the top of the stairwell, so less if there was smoke in that area to let the smoke out through the vent in the event of a fire alarm.
When we’re commissioning the fire alarm system, once all devices have been addressed, we then turn on the fire alarm system. We would wire, for example, loop one in. We already know how many devices are around that loop so we would go to the comms menu on the fire panel and press auto-learn. The panel then scans the loop, sees all the addresses that we have input onto the loop, and then we would be expecting an exact tally to what we had on our drawings. Once that is completed, we would go to our drawings and find the numbers of the devices on the loop. For example, in Classroom one, address one on the loop, and we write down in the software and label each device so when the fire alarm activates, it will tell us the location of the activation. That’s very good for finding faults. If there’s a faulty device on the loop, it can bring us straight to it.
Once all the devices are addressed, we then carry out a test of all devices. This involves two engineers, one engineer that will go out into the school and use an item called a smoke pole. A smoke pole is in a telescopic pole with a device that sends smoke into the detector. And when that happens, the smoke detector will activate and the fire alarm will activate.
We’ll then be able to say hypothetically, I’m in Classroom one, address one, and then the person at the panel will be able to check the panel and see that what I’ve said is the same information that’s been displayed on the panel. Once that’s done, we can move on to the next one, and so on until we’ve double-checked and tested everything on the loop.
At that stage, then we have finished one of the most important parts of commissioning, which is labelling, confirmation and testing. We will carry out a decibel level test to ensure that we achieve 65 dBs throughout the property. No matter where we are, we have to get 65 dBs and the only exception we would look for above 65 dB would be in an area that maybe has a higher dB level or in sleeping accommodation such as apartments or hotels. Tests have been carried out in the past, and it’s suggested that a person won’t wake up with decibels lower than 75 dB, i.e. most people need more than 75 decibels to wake up.
The fire alarm system is usually monitored, so a relay, which is an automatic switch similar to an IO but onboard the fire panel itself, is used to connect to a dialler, a GSM dialler normally, which connects to a monitoring station.
In the event of a fire alarm activation, the monitoring station will receive a signal saying, for example, “this school Deansrath Community College’s fire alarm”. They can then call the fire brigade or the management of the school.
Once all tests are completed, Sounders tested, all devices are known to be working, we then do a handover, and that’s where we show the users the layout of the fire alarm system, the drawings, give them all the instructions, and then give them training. Normally, if it’s in the school, we would ask for maybe about 10 to 15 teachers to stand around, and I would demonstrate the use of the fire alarm system. I’d go through the codes what to do when the fire alarm goes off, how to read the panel, how to know where to find a device. And I would activate the fire alarm system, then silence and reset the system. I then get some of the teachers to carry out what I have just shown them. I find that’s the best way to get them to remember how to use the fire alarm system.
In addition to this, we handover a operation and maintenance folder. This will have full instruction of use as well as drawings. There would also be a full list of all materials used.