TUALATIN — Ten children were taken to local hospitals with breathing problems after toxic chemical fumes were released in the air near the outdoor swimming pool at ClubSport Oregon.

The children, who range in age from 4 to 8, were playing in an outdoor swimming pool at about 5:30 p.m. on Saturday, when they began coughing.

The children complained of a burning feeling in their lungs and it being hard to breathe.

An employee at the fitness center on Lower Boones Ferry Road noticed the children reacting to a potential excess of chlorine vapors and called 911.

Meanwhile, ClubSport staff began evacuating the pool.

The children were all wading in the same part of the swimming pool when they began to experience the symptoms, according to Brian Barker, a Tualatin Valley Fire & Rescue spokesman.

That part of the pool is near a pipe that vents chlorine vapors, however it is not clear that the pipe was responsible for the leak.

“ClubSport had advised us that there was a portion of the pool system that periodically vents chlorine, but that no one had ever had any symptoms that were problematic,” said Cassandra Ulven, public affairs officer for the fire district.

The 10 children were taken immediately by Metro West Ambulance to area hospitals for evaluation as a precautionary measure.

Three children were taken to Legacy Emanuel Medical Center, three to Oregon Health & Science University, two were taken to Providence St. Vincent Medical Center in Cedar Mill and two others were taken to Legacy Meridian Park Medical Center in Tualatin.

No word was available on their condition.

In total, four TVF&R engines responded, bringing 16 firefighters, paramedics and emergency technicians to the scene. The district’s Hazardous Materials Team conducted air monitoring and declared the area safe by the end of the day.

When reached for comment, ClubSport general manager Jarod Cogswell said the incident had occurred during a backwashing operation, and that the club had since brought in a third-party pool specialist to investigate.

“We added an additional equipment safeguard to ensure that chemicals are released appropriately,” Cogswell said. “We’re changing some operating procedures so we don’t do backwashing during operational hours.”

The assumption, he said, is that the glitch was mechanical.

This is not the first time TVF&R crews have responded to a call at ClubSport concerning chlorine fumes. Only one of the 526 HazMat-related calls the district received last year involved chlorine, but it concerned ClubSport’s swimming facilities.

According to TVF&R records, in early 2011, an adult male claimed he smelled a “strong, irritating odor” near ClubSport’s outdoor pool. A responding firefighter was shown to the pool’s chemical room and was satisfied that all systems were running smoothly. No one was transported for medical attention at that time.

Cogswell said he couldn’t comment on the 2011 incident.