What Happens to Fire Alarms in a Power Outage?

Fire safety is serious business. We’ve covered how alarm panels, their sensors, and the entire sprinkler system are designed to survive the end of the world. This extends beyond the panel itself and straight on to the infrastructure that runs it. Even during a power outage, most alarm systems will continue to function perfectly.


The Battery Backup

Most alarm systems have an integrated back up for when the power grid, or even building power supply fails. On the whole, an alarm system is a really low-power set up, making it ideal for battery operation. The fire panel itself is mostly a massive input/output complex, with just a handful of memory chips and processors doing the heavy lifting. In an extremely simplified sense, you could imagine the fire panel as a cell phone mother board, wired up to a massive sensor system.

The battery powering your cell phone is pretty tiny, but yet it keeps your phone chugging along for 12-48 hours, depending on the model and how exactly you use it. Now just imagine a bigger, simpler lead-acid battery, and it’s also powering a couple hundred smaller sensor devices, with cell-phone like processors in them. That is the situation inside most fire panels and other similar safety systems.

In most cases, local fire codes requires these alarms to function for about 24 hours on batteries alone. Given we’ve seen countries like Puerto Rico go dark for months from natural disasters, a good twenty four hours seems like the very least our alarms need to keep us safe.


The Diesel Backup

Larger facilities will go a step beyond batteries and have a full blown diesel generator under the fire panel’s control. This is where safety starts to get pretty serious. When the power fails, the alarm panel switches to internal power, and after perhaps five minutes decides its time to bring the big guns online. When the generator fires up, it triggers a supervisory alert to dispatch, because it’s now on very borrowed time.

The generator will supply power for the panel, the sensors, interior lighting, and the sprinkler pumps. As long as all is well, these generators are probably good for a couple of days. They’ll idle there and put out enough power to introduce any fool to zeus if they touch some exposed copper. At least, until the fuel runs out.

Once the generator goes dead, we’re back to stored energy. Wherever possible, building designers will try to create a gravity-powered reservoir for the sprinklers. This is in part why water towers are so common top of buildings and in rural areas: it’s stored energy. During a power outage, systems running on batteries alone will have to rely on only the water remaining in the sprinkler system and whatever pressure that comes with. The multi-million dollar alarm and sprinkler system will have just one job left: hold off the fire long enough to evacuate the building. The batteries will power the alarms, and the fire doors will close automatically because they rely on power to stay open in the first place. Most card-access systems will default to open or have crash-bars, should a fire occur.

Our modern designs are incredible in that, even during a catastrophic failure, with just a battery to run on, most people will get out unscathed. The insurance though, is going to be scathed by quite a large bill.


The Solar Backup?

On the horizon however, we might be able to completely solve the power failure problem. As Puerto Rico rebuilds, they’re turning to massive battery banks and solar arrays to build a decentralized grid. In the future, we may see industrial complexes with solar-backed batteries. They could run by day on solar, by night on batteries, and in a catastrophic failure, turn to diesel as the last resort instead of the main solution to prolonged outages.


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