Surge in arsons over school holidays
There have been more than 300 fires started deliberately since the school holidays began 10 days ago, figures show.
Two teenagers have been arrested in connection with a fire at a Cardiff primary school on Tuesday.
Elsewhere in south Wales, crews have tackled 208 fires, mostly on grassland. Crews in mid and west Wales have dealt with 103 with 22 in north Wales.
Of those started deliberately, 128 have been grass fires.
"It's an every day occurrence in the Blaenau Gwent valleys. Young teenagers hang round, light fires and then disappear without thinking of the consequences," said Dan Andrews from South Wales Fire and Rescue Service.
Last month, a grass and gorse fire broke out near the seafront in Porthcawl.
The blaze on Locks Common opposite the esplanade sent a large plume of thick smoke over the seaside town.
There have also been 39 hoax calls to the fire services in Wales since the schools broke up.
Firefighter Laura Thomas, who helps educate youngsters on the dangers of starting fires, said: "It's about helping them to think about the consequences about what could happen.
"If we want to prevent it from happening we need to engage positively with the young people and find a way of working with them rather than against them all the time."
On Wednesday, South Wales Police said a 16 and 17 year old have been arrested in connection with a fire at Birchgrove Primary School in Cardiff.