Monsoon Season and Your Fire Alarm: Why Storms Cause Trouble Signals and False Alarms

If you manage a commercial building in Arizona, you probably see more fire alarm trouble signals and false alarms during monsoon season than any other time of year. Dust storms load up smoke and duct detectors, power outages drain panel batteries, and lightning can damage panels and communicators. The good news is that most of it is preventable with the right maintenance at the right time.

Monsoon season officially runs from June 15 through September 30, according to the National Weather Service in Phoenix. That is a long stretch of dust, wind, heat and electrical storms, and fire alarm systems feel all of it.

Why do dust storms set off smoke detectors?

Most commercial smoke detectors are photoelectric. They work by shining a light inside a small chamber and watching for particles that scatter it. Smoke scatters light. So does fine dust. When a haboob rolls through, dust gets pulled into buildings through doors, rooftop units and outside air intakes, and some of it settles inside detector chambers.

A little dust makes a detector more sensitive. A lot of dust can push it into alarm or into a trouble condition. Many modern addressable panels track how dirty each detector is getting and flag it before it causes a false alarm, but only if someone is looking at those reports.

What are duct smoke detectors, and why are they a monsoon problem?

Commercial buildings with larger HVAC systems are usually required to have duct mounted smoke detectors. Their job is to sense smoke moving through the air handling system and shut the unit down, so a fire in one part of the building does not get blown into every other part. That shutdown is supervised by the fire alarm system.

Duct detectors sit right in the airflow, which makes them especially vulnerable to dust. After a big storm, a rooftop unit can pull a heavy dose of dust straight across the detector. The result can be a supervisory signal, a false alarm, or HVAC units shutting down on the hottest afternoon of the year, which is the last thing a tenant wants to hear about.

Keeping duct detectors clean, making sure their sampling tubes are oriented correctly, and keeping HVAC filters changed on schedule all go a long way. Duct detectors also need to be tested annually along with the rest of the system to confirm they actually shut down the fans.

How do power outages affect a fire alarm system?

Every fire alarm panel has backup batteries sized to run the system through an outage and still sound the alarm. Monsoon storms bring frequent power hits, and each one draws down those batteries. Batteries that were already near the end of their life (Arizona heat shortens it) may not recover, and the panel will report a battery trouble.

Other common power related issues include:

• AC power failure troubles that linger after power returns because a breaker tripped.
• Communication failures when the device that sends signals to the monitoring company loses power or its phone or cellular path.
• Power supply troubles on remote power supplies that feed strobes and horns throughout the building.

Fire alarm batteries should be inspected every six months and load tested every year under NFPA 72. Doing the semiannual check right before monsoon season starts, in late spring, is an easy win.

Can lightning damage a fire alarm?

Yes. Nearby lightning strikes can send surges through power lines, phone lines and long wire runs between buildings. Damage often shows up as a dead communicator, failed modules or a panel that will not clear its troubles. Proper grounding and surge protection help, and any time a building takes a close strike, it is worth having the fire alarm checked rather than assuming it is fine because the lights came back on.

What about roof leaks?

Monsoon rain finds every weak spot in a roof. Water dripping into a ceiling can soak smoke detectors, junction boxes and wiring, which causes ground faults and trouble signals. If your fire alarm panel shows a ground fault after a storm, a roof leak is one of the first things to check.

What should property managers do before and after monsoon season?

Before the season (April to early June):

• Have the semiannual battery inspection done and replace weak batteries.
• Review detector sensitivity reports from the panel and clean or replace dirty detectors.
• Check duct detector housings, covers and sampling tubes.
• Confirm the monitoring company is receiving signals correctly.
• Change HVAC filters and check rooftop unit seals.

After a major storm:

• Look at the fire alarm panel. Any trouble, supervisory or ground fault light needs attention.
• Do not just keep silencing or resetting. Repeated troubles have a cause.
• Check for roof leaks above devices.
• Call for service if the panel will not clear or the monitoring company reports communication problems.

How do I tell a false alarm from a real one?

You do not, at least not at first. Every fire alarm should be treated as real until the building is checked. Once everyone is safe and the fire department has cleared the building, look at the panel history. It will show which device activated. A single smoke or duct detector going into alarm right after a dust storm, with no smoke anywhere, points to contamination. Several devices in the same area, a heat detector or a waterflow switch is a different story and needs a closer look right away.

Write down the time, the device and the weather. That log makes troubleshooting much faster when the technician arrives.

Does summer heat affect other fire protection equipment?

Yes. The same heat that is hard on fire alarm batteries also wears out emergency light and exit sign batteries, which is why the annual 90 minute test so often finds units that cannot last through an outage. Extinguishers stored in hot exterior cabinets or vehicles can lose pressure faster, and fire pump rooms without good ventilation can run hot enough to stress controllers and diesel batteries. A late spring checkup that covers alarms, lights and pump rooms sets your building up for the storm season.

Why not just reset the panel?

Resetting clears the symptom, not the cause. A detector that went into alarm from dust will do it again, and repeated false alarms frustrate tenants, waste fire department resources and can lead to false alarm fees in some Valley cities. Worse, people start ignoring the alarm. A system that cries wolf is a life safety problem.

A trouble signal that keeps coming back is the system telling you something is wrong. Tracking down the real cause (a dirty detector, a weak battery, a damaged module, a wet junction box) is what keeps the system reliable when it counts.

The bottom line

Monsoon season is hard on fire alarms, but you do not have to spend the summer chasing trouble signals. Schedule battery and detector maintenance before the storms, check the panel after them, and fix the causes instead of resetting. If your building is fighting monsoon related alarm problems, book a free consultation or call 480.910.1842. See our fire alarm inspection and repair and emergency lighting services for more.