Dozens of parents across the country are raising safety concerns about fraying straps on their Evenflo child car seats, prompting Transport Canada to investigate.

Katie Thomas of Cambridge, Ont., says she noticed in December the straps of her son's Evenflo Symphony car seat were tearing.

"The straps were twisted, so my husband pulled them all the way out from under the seat to untwist them," she told CBC News.

"That's when he noticed it was frayed on one side. He checked the other side and it was frayed there too."

The straps were part of the seat's five-point harness, which helps to keep the child secured and the seat mounted in the vehicle.

"What would have happened if we had been in an accident? With the kind of force that comes with a collision, it could cause the straps to snap," Thomas said.

She's not the only parent who has encountered the potential safety problem. Transport Canada says it has received 94 complaints about frayed harness straps in Evenflo car seats. The majority of the complaints are from this year.

The frayed straps were part of the seat's five-point harness, which helps to keep the child secured and the seat mounted in the vehicle. (Submitted by Katie Thomas)

There were enough to trigger an investigation. The federal safety watchdog is currently checking three models: the 2011-18 Evenflo Symphony, 2012-18 Evenflo Triumph and 2016-18 Evenflo SafeMax.

The investigation will determine whether the manufacturer should order a recall.

Not a new problem

CBC News first reported the problem in 2014 when an Ontario father discovered the harness of his daughter's Evenflo Symphony seat had been completely severed.

Evenflo told CBC News the breakage was "from small rodent damage." The U.S-based company said these types of problems were rare, though it would not say how many complaints it had received.

No recall was issued.

Thomas says she didn't notify Transport Canada when she first discovered the fraying, but did send photos of the damage to Evenflo.

The company's explanation? The same as five years ago.

"They said it was caused by small rodents." Thomas said.

"We were shocked to hear that, because we've never noticed rodents in our car."

Jia Maheshwari, a mother in Winnipeg, had the same reaction when she received that explanation from Evenflo in January 2018.

"It sounded ridiculous to me," she said.

Jia Maheshwari of Winnipeg was told the frayed straps on her son's Evenflo seat were because of rodents. (Submitted by Jia Maheshwari)

In an email to Maheshwari, an Evenflo representative said the fraying is "consistent with damage caused by an animal chewing and/or clawing on the strap."

The fraying could not have been caused by a defect, the company said, because "the plastic and metal components in contact with the strap have smooth and rounded edges."

But Maheshwari has her doubts.

"If it was a rodent, why would it chew only the straps on the car seat? I should see damage on the seat cover."

Maheshwari got a replacement seat, but says she won't use it after learning of Transport Canada's investigation. (Justin Fraser/ CBC)

Maheshwari and Thomas have since received replacement seats from the company, though both say they will no longer use them upon learning of Transport Canada's investigation. Thomas has also requested a refund.

"You think you're the only one it has happened to, and then you find out it's happened to so many people." Thomas said.

In a response to CBC News, Evenflo said "the root cause is still being assessed between Transport Canada and our engineering team" and in the meantime "no defects have been found."

'Prime place' for rodents

Pamela Fuselli, the interim president at Parachute, a Toronto-based organization that educates Canadians on preventable injuries, says rodent damage on child car seat straps "isn't common, but it certainly has happened."

"When you take a look at child car seats, it's a very attractive place for rodents and mice. It's full of crumbs and foam. If they do get into vehicles, and they have in the past, that's a prime place for them to go," Fuselli said.

Thomas, though, still finds it hard to believe rodents are to blame.

Safety expert Pamela Fuselli says child car seats are a 'prime place' for rodents, though such damage is not very common. (Kelda Yuen/ CBC)

"For everybody to have the same damage on the same part of the car seat, and no damage anywhere else in their car, or evidence of rodents, it's ridiculous," she said.

Regardless of what caused the fraying, Fuselli says there's no doubt it could put a child in danger.

CBC News showed Fuselli photos of Thomas's damaged straps. She said there's "definitely a tear in the webbing."

"As soon as you've compromised the strength of that webbing, then you are potentially in a dangerous situation."

Transport Canada is asking anyone who owns one of the three Evenflo seats under investigation to inspect the harness straps. (Transport Canada)

Transport Canada is asking anyone who owns an Evenflo model currently under investigation to inspect the harness straps under the seat cushion and, if they are frayed, to contact them.

Thomas says that's something she will be doing with every child car seat.

"I would encourage everybody, regardless of what kind of car seat they have, to every now and again pull the straps all the way out and do a full examination," she said.

"You never know."