HUNDREDS of people were evacuated from Tower Park in Poole this afternoon.
The emergency services were called to the leisure and retail venue at 2.20pm.
Police said that one person had been treated for minor injuries.
At 4.10pm, it was thought that the gas was not dangerous and the incident would be scaled down. At 5.15pm the building was still being checked.
At 6pm, a spokesman for Dorset Fire and Rescue Service said emergency services had now left the scene.
Dorset Police said that units were called at 2.21pm to a report of a chemical spill from Dorset Fire and Rescue Service.
A spokesman said that the injector had burst in a chlorine pump at Splashdown.
Those who were using the swimming pool at the time were given foil blankets to keep them warm and were being looked after at LA Fitness.
Emily Woodgate and Zoe Barnes had both travelled from Weymouth to visit Splashdown, and stood outside wearing sheets of foil - known as Space Blankets – over their bikinis.
Zoe said: “It was absolute chaos when the alarm went off.
“No one seemed to know what was going on, and we had to leave everything in the lockers, even though we’d opened the door.”
Emily added: “The teenagers were all laughing, but lots of the kids were in tears.”
They added that no food or water had been provided.
Bethany Etheridge and Gary Pickering took 10-year-old Bradley to the centre.
The family, who come from Salisbury, had been using the slides for around an hour when they were told to evacuate.
“I don’t really think anyone knew what was happening,” Bethany said.
“We were just told that it wasn’t a drill and we needed to get out right away.”
Dorset Fire and Rescue Service's East Dorset District Commander, Ray Jones, told the Daily Echo at the scene that crews were called to a chemical spillage and two appliances from Poole, one from Redhill Park and one from Westbourne were sent to the scene.
A specialist unit from Poole was also sent.
Mr Jones said that there was concern that the gas might be harmful and firefighters in breathing apparatus went inside the building to check that it was safe to return.
He added that, with the permission of the Environment Agency, the chemical was washed away down a drain.
The evacuation caused traffic problems around the park as people tried to leave.
This evening, Splashdown released a statement following the incident.
Following the discovery of a malfunction of the dosing injector in the upstairs plant room the decision was taken, as a precuation, in the interests of public safety, to evacuate the building and call the emergency sevices to ensure that there was no threat to the safety of our customers, staff and those using the other facilities at Tower Park.
Following thorough checks of the building by Dorset Fire Services, staff and then customers were allowed back in to the building.
Jackie Richmond, Splashdown’s co-owner said: "No one was affected apart from the disruption and inconvenience, for which we apologise.
"All pools have chemical dosing machinery and if there is any suggestion that there is a problem then we take it very seriously; an alarm triggered and in the circumstances it was better to be safe and get it checked out properly in connection with the emergency services.
"A small leak was detected and appropriate action taken to clear it up and repair the equipment. Following the repair and testing of the equipment I am pleased to be able to say that we will be open as normal again tomorrow.
"We would like to express our thanks to all our staff who acted promptly and efficiently to evacuate the buildings and to Tower Park management team and other on-site businesses and their staff for their help in looking after our customers."