When a fire alarm system goes into alarm, it does more than sound signals. It shuts down or switches fans, releases fire doors, unlocks doors on exit routes and sends elevators to a safe floor. These interfaces are where the fire alarm meets other trades, and they are among the most common places for a system to fail its verification or annual inspection.
What the interfaces do
Each interface exists to stop a fire from spreading smoke through the building or to keep exits and firefighting routes usable. The fire alarm control unit operates them through relay or control modules, according to a written sequence of operation. The building code, CAN/ULC-S524 and the standards for each piece of equipment set what is required, and the designer turns that into a specific list of inputs and outputs for your building.
HVAC: fans, dampers and smoke control
An air handler that keeps running during a fire can carry smoke from one floor to every other floor it serves. In most buildings, the fire alarm shuts down air handlers above a certain size when their duct smoke detectors, or the building's general alarm, operate. Smoke dampers in ducts and shafts close to keep smoke out of other zones.
Larger buildings, atriums and high buildings may instead have a smoke control system, which uses fans and dampers to exhaust smoke or pressurize stairs and other areas. Here the fire alarm does not just stop fans; it puts them into specific modes, and firefighters may have a control panel to override them. Smoke control sequences are complex and need careful coordination between the fire alarm designer, the mechanical designer and the controls contractor.
A common failure point is the building automation system. The fire alarm must be able to stop or command fans regardless of what the automation system wants, through hard-wired connections arranged so the fire alarm wins. See our guide to building automation systems for how those controls are organised.
Doors: hold-opens and locked doors
Fire doors held open
Fire doors in corridors and stair lobbies are often held open for convenience by electromagnetic hold-open devices. The magnet only holds while it is powered. On alarm the fire alarm cuts power to the holders, and each door's closer shuts it. If power fails, the doors close as well. This fail-safe arrangement is the principle behind most door interfaces.
Locked doors on exit routes
Access control and exit doors are where security and life safety meet. Building and fire codes limit how doors on exit routes can be locked. Electromagnetic locks and some delayed-egress hardware are typically allowed only with conditions, such as releasing on fire alarm activation, on loss of power and from a manual release near the door. Stair doors may also need to unlock on alarm so that people can re-enter floors from the stair. The rules vary with the code in force and the occupancy, so check the code that applies to your building. Our guide to access control, door hardware and safe egress covers this in detail.
Elevators: firefighters' recall
Elevators are not used for evacuation in most buildings, because a car could open onto a smoke-filled floor. Instead, detectors in elevator lobbies, machine rooms and hoistways signal the elevator controller to recall the cars to a designated floor, where they park with doors open for firefighters. CSA B44 governs the elevator side of this, and the fire alarm provides the signals the elevator controller needs.
Recall testing involves the elevator contractor, the fire alarm technician and often the elevator regulator in your province. Plan for it early on any project, because the elevator's own mandated inspection and the fire alarm verification both depend on it. See our guide to elevator maintenance and inspections.
Signals coming in from other systems
Interfaces run both ways. The fire alarm also receives signals from other fire protection systems and acts on them:
- Sprinkler systems report water flow as an alarm and closed valves, low air pressure or fire pump trouble as supervisory signals.
- Kitchen hood suppression systems report when they discharge, so the building goes into alarm and the hood's fuel or power is shut off as designed.
- Special suppression systems, such as clean agent systems in server rooms, report their status and may have their own release panels that the fire alarm monitors.
- Generators and fire pumps may report running, failure or low fuel conditions as supervisory or trouble signals.
Each of these needs to be in the matrix too, with a clear statement of whether the input causes an alarm, a supervisory signal or a trouble signal.
Making interfaces work on test day
Most interface failures are coordination failures. Each trade tests its own equipment, but nobody tests the whole chain from detector to closed damper until the verification technician does it, and by then the schedule is tight. A few practices prevent most of that:
- Write an input and output matrix. A table listing every input down the side and every output across the top, with a mark where an input should operate an output. It becomes the test script.
- Name the responsible party for each end. The fire alarm contractor provides the relay; the mechanical, door hardware or elevator contractor connects to it and makes their equipment respond.
- Test end to end before verification. Operate a real device and walk to the fan, door or elevator to confirm it responded, not just that the relay changed state.
- Retest after changes. An automation system upgrade, a door hardware replacement or elevator modernization can quietly break an interface. Include fire alarm interface testing in the scope of those projects.
- Record the results. Keep the matrix and the test record with the fire alarm documents for the annual inspection under CAN/ULC-S536.
Do not bypass interfaces to stop nuisance problems. Disabling an interface because fans shut down during a false alarm, or because doors keep closing, removes a life safety function. Fix the cause of the false alarm instead, and if an interface must be out of service for work, follow your fire safety plan and notify the monitoring company and, where required, the fire department.
How ehZee can help
We write sequences of operation and input and output matrices, coordinate the mechanical, door and elevator trades, and design the fire alarm side of every interface as part of our fire alarm system design service. Drawings are sealed by a licensed professional engineer where required, and the finished interfaces are tested during verification to CAN/ULC-S537.
Common questions
Why did our air handlers shut down during a false alarm?
Because the sequence of operation shuts them down on alarm, which is usually what the code requires. Investigate the cause of the false alarm, and ask whether fans restart automatically after reset or need a manual restart so you know what to expect.
Who is responsible if a damper does not close during testing?
It depends on where the chain broke: the fire alarm relay, the wiring to the actuator or the damper itself. An end-to-end test with both contractors present finds the break quickly. The input and output matrix should say who owns each piece.
Do magnetic locks have to release on fire alarm?
In most situations where codes permit them on exit routes, yes, along with other conditions. Requirements depend on the code in force and the occupancy, so confirm them for your building before installing or changing locks.