The Singapore students went for an outdoor camp in Malaysia which was supposed to include some fun at a campfire.
But they got a first-hand lesson on dealing with fire instead when 14 of them got burned.
The boys were among 60 Secondary 3 students from Ahmad Ibrahim Secondary School who went for a four-day three-night Outdoor Learning Experience camp on Monday.
They were accompanied by six teachers to the Xcape Resorts in Taman Negara, a national park in Pahang, for a camping and survival training programme.
Some of the boys said the flash fire caught everyone by surprise while they were preparing for a campfire on Wednesday evening, their last night.
The New Paper (TNP) spoke to three of the injured boys, who were sitting on a log when the accident happened.
In the scramble to get out of the way, the log was pushed and Devandran Balasubramaniam, 15, said he fell towards the flame.
Devandran told TNP: "The fire happened in a flash.
"I fell face forward and felt the heat on my chin and nose.
"My first thought was to find water for my burns but there was no source of water around."
He had second-degree burns around his facial area, and on his right thigh and shin.
Kobbikaanth Krisnan, 15, who fell backwards from the log, had second degree burns on his right leg.
The third boy, Ivan Nedunjaziyan, 15, suffered minor burns to the leg.
Since it happened so quickly, it was difficult to confirm what sparked the flash fire.
Kobbikaanth said: "It was drizzling that night, and the fuel must have spread out from the pile of wood meant for the fire."
The three boys said they thought that someone may have dropped a candle accidentally and sparked off the fire.
Earlier that evening, the students had gone on a night trek around the resort and were told not to bring their mobile phones and bags.
They were divided into groups of five and each group was given one candle.
Their walk was supposed to end with a campfire to celebrate the end of the training.
The campfire was to be held on a slope, and students and teachers were seated around the area.
It was to be lit by one of the teachers with a torch pole. Three resort instructors were there to supervise.
Since it was drizzling, the fuel that had been poured on the wood appeared to have been carried by the rainwater down the slope and near the feet of the students there.
That was when the flash fire erupted.
The resort instructors then told the injured students to spread butter on their burns.
But their science teacher warned them not to do so and to clean their burns immediately.
Students with more serious injuries were then rushed to a nearby clinic, which was a 30-minute drive away.
The rest were taken to a local government hospital, about 1½ away.