Some Canada Post workers on rural routes near Ottawa have become so concerned about exhaust spewing into the cabs of their aging delivery trucks that they've started carrying carbon monoxide detectors.

But Canada Post denies there's a widespread problem and says the vehicles are well maintained.

For Julie Stewart, a Canada Post delivery driver in Kemptville,Ont., the problems began back in the spring. One day in April, the 48-year-old parked her white Grumman LLV truck and walked into the local hospital, believing she was experiencing a heart attack.

I just don't want to drive these trucks that could possibly kill me or kill somebody else. - Julie Stewart, Canada Post employee

Stewart's heart was fine, but doctors asked whether she might have been exposed to carbon monoxide.

On May 31, she entered the words "exhaust smell strong" into her truck's logbook. On June 1 she wrote, "Exhaust smell extreme in cab." Five days later, she repeated the observation: "Exhaust extremely strong in cab."

Then on June 23, feeling drowsy and unable to understand her husband's simple questions, Stewart went to the hospital again. This time, she was given oxygen.

She took a week off work and said co-workers who drove her truck during her absence also complained about a strong smell of exhaust.

Stewart is convinced her truck, and others, are poorly maintained.

"I just don't want to drive these trucks that could possibly kill me or kill somebody else," she said.

Grumman manufactured the LLV, or Long Life Vehicle, from 1987 to 1994. (Stu Mills/CBC)

Complaints ignored, employees say

Stewart isn't the only Canada Post employee complaining about the trucks.

"We've gone to our supervisors, but they say they can't do anything, and it's not going anywhere," said Diana Bayer, a 20-year employee of Canada Post who works out of the Smiths Falls branch.

In June, doctors at Kemptville District Hospital treated Canada Post worker Julie Stewart with oxygen after she complained of dizziness, confusion and low energy at the end of her delivery shift. (Supplied)

Some of Bayer's colleagues have purchased their own carbon monoxide testers to use inside the trucks, she said.

On May 8, one of those employees, Carla Lavigne, took a reading of 49 parts per million in the cab of her truck in Brockville. The legal maximum for workplace exposure set by Ontario's Ministry of Labour is 25 parts per million over a 40-hour work week. Short-term exposure is considered dangerous at 100 parts per million.

Lavigne told CBC she refused to drive the truck after taking that reading, and demanded her bosses at Canada Post repair the vehicle. She said the truck's exhaust system was replaced, and she hasn't detected any carbon monoxide in the cab since.

A carbon monoxide reading of 49 parts per million, taken inside the delivery truck of Canada Post employee Carla Lavigne in Brockville, Ont., on May 8, 2017. (Carla Lavigne)

"If we see [high] numbers [on the detectors] we're just getting out. We're not going to drive it. Carbon monoxide is sneaky. It's [called] a silent killer for a reason," Bayer said.

One colleague who became tired and disoriented while behind the wheel of a truck also went to hospital and was diagnosed with carbon monoxide poisoning, she added. That employee has asked to remain anonymous over fears of retribution.

But others, including Bayer, are speaking out.

"I don't want to see them suffer. And I don't want to go to one of their funerals," she said.

Aging trucks slowly being replaced

The Grumman LLV ceased production in 1994. Originally built under contract for the U.S. Postal Service, the right-hand-drive trucks were supposed to be safer, healthier and more ergonomically suited to mail delivery.

In 2010 Canada Post signed a deal with Ford Canada to supply replacement vehicles that the Crown corporation promised would be "much more efficient and environmentally friendly" than the Grummans.

But the Grummans are still on the road, and the newest among them is 23 years old. Replacement parts are becoming difficult to find.

Julie Stewart noted the smell of exhaust in the cab of her delivery truck several times in May and June of this year. (Supplied)

Stewart's truck leaks water around the rusted windshield frame and the heater, which can no longer be regulated, blows hot air in summer and winter. A tangle of wires hangs from the spartan aluminum dash and, nearly two weeks into July, the truck still boasts winter tires.

"They're decrepit. They can't fix them, they can't get parts," said Bayer. "The garages are bandaging them together.

'Extensive testing'

Canada Post spokesperson Jon Hamilton denied there's a widespread problem with the trucks, saying the fleet is regularly maintained and tested, including exhaust systems.

"It's not the truck," said Hamilton. "We've done extensive testing. We take it incredibly seriously."

But some employees claim testing is only carried out after repairs are performed and say that explains why the trucks are coming up clean.

Julie Stewart said that's why she's speaking out.

"I don't know what else to do," she said.