SMOKE damage has forced Penarth Leisure Centre to remain closed for the remainder of this week after a fire broke out over the weekend.
A South Wales Fire Service spokesman, speaking after an investigation was carried out on Monday, said it was believed that the fire was started accidentally in the sauna.
Six fire crews from across Wales attended the scene on Sunday evening after the fire broke out around 5.15pm.
Jacuzzi users reportedly attempted to extinguish the fire themselves with buckets of water as it threatened to spread throughout the building.
Around 25 members of the public and staff were evacuated from the building before fire crews attended the scene.
Nobody was hurt or suffered smoke inhalation from the fire as staff evacuated the building as quickly as possible.
One gym user said they saw smoke 'billowing' out of reception and that people from the gym, swimming pool and a circuits class were all huddled outside in foil blankets.
Staff have been praised for evacuating everyone safely and offering people the warmth of their cars to those that were been forced to jump out of the swimming pool in just their bathers.
Crews from Penarth, two from Cardiff Central, a water bowser from Barry, Roath, a command unit from Cwmbran and a hydraulic platform from Ely all attended the scene.
A South Wales Fire Service spokeswoman added that three hose reel jets and six breathing apparatus were used to tackle the blaze that started in the back of the building.
Ian Buckley, station manager of Bridgend Fire Station, said at the scene:
"It burnt through the roof of the sauna at the rear of the premises.
"The fire broke through the roof but we can't make any estimate about the damage.
"We don't know how it started and an investigation is ongoing.
"Nobody was hurt and everybody was evacuated safety."
Parkwood Community Leisure, which operates Penarth Leisure Centre on behalf of the Vale of Glamorgan Council, said the building was evacuated as soon as possible and thanked staff and fire crews for their quick response.
A meeting is due to be held today, February 27, to discuss the future planned reopening of the leisure centre.
The leisure centre will be open for public enquiries only today, February 27.
Penarth and Cardiff South MP Stephen Doughty also attended the scene and said that the key thing was that nobody was hurt and that the fire service had the situation under control.
He added that he was “shocked and concerned” when he first heard about the fire, and praised the work of staff for working “calmly and professionally” in evacuating the building.
Gym user Katie Mitchell said she saw smoke “billowing” out of reception and that it was all “very dramatic”.
She added that some people continued their personal training sessions outdoors after they had been evacuated.