It’s not the smoke, it’s the humidity: Fire crews dealing with false alarms

Fire trucks heading out. (Photo by Michael Gabelmann/Flickr, CC BY-NC 2.0)

HALIFAX — Fire officials are shedding light on a little-known phenomenon that can cause the number of false alarms to soar in the muggy summer months: Some smoke detectors can be accidentally set off by high humidity.

It’s a problem smoke detectors with ionization sensors appear particularly susceptible to, as hot, humid air can be mistaken for smoke.

Halifax Fire and Emergency Services said Tuesday crews have responded to a spike in false alarms as a blanket of extreme humidity settles over the region.

“We’ve had days where it’s three times the regular false alarm calls,” said Matt Covey, division chief for fire prevention.

“Our field people are telling us it’s humidity that is setting off these alarms … it’s definitely a contributing factor.”

Fire officials in Toronto and Victoria said they haven’t experienced a similar uptick in false alarms during humid weather.

However, they said ionization detectors are more sensitive to steam, and photoelectric smoke alarms are generally preferred close to bathrooms or kitchens.

“What we see here when humidity sets off an alarm is, it’s placed too close to the kitchen area or too close to the bathroom door,” said Capt. Adrian Ratushniak with Toronto Fire Services.

“That’s the circumstances we’ve seen, not a general ‘We’re having a humid day here in the city and it’s setting off smoke alarms.”’

Brad Sifert, assistant chief of fire prevention with the Victoria Fire Department, said he hasn’t seen weather trigger smoke alarms but it sounds “reasonable” that it could occur in cases of intense humidity.

The Maritime provinces have been under a heat warning this week, as temperatures reached 36 degrees with the humidex.

Ian Hubbard, a meteorologist with Environment Canada, said humidity in the region has been higher than normal over the last few days.

Although showers are expected to cool temperatures later this week, he said the humidity will stick around.

“We’ve got a lot of moist air, a lot of southwesterly flow, and we’re not seeing dry air push in from the west or the north at any point in the next several days,” Hubbard said.

“It’s going to stay humid and sticky for most of the week — maybe not as hot but certainly as humid.”

A spokeswoman with the Office of the Fire Marshal in New Brunswick said she was not aware of any specific cases involving smoke alarms being set off accidentally due to humidity so far this year.

Alexandra Davis said in an email that photoelectric alarms are generally superior to ionizing alarms, which can be set off by humidity and cooking.

Meanwhile, Halifax Fire’s Covey said regular maintenance and cleaning of smoke alarms could help prevent false alarms.

When an ionization detector is dusty, he said it makes the humidity more likely to contribute to setting off the alarm.

Covey recommended following the manufacturer’s instructions, but said that generally a soft bristle brush head on a vacuum or a damp cloth would effectively remove the dust.