Jakarta, Indonesia - As Ridwan Nur stepped through the side-door of the crowded state bus, Tyo al-Farabi knew there would be trouble.

Tyo had never met Ridwan, known locally as Tompel. But stuck in east Jakarta's crawling Friday morning traffic he had seen him by the roadside gathering with students from a rival high school - a sign, in his experience, that an attack was imminent.

Tompel carried with him nothing more offensive than a clear liquid in an open drink bottle. As he boarded the bus he launched the solution at Tyo's face.

Fortunately, Tyo's instinct was to turn away. "Suddenly I felt a burning on my neck and shoulders, extremely hot. And then there was just screaming," the 15-year-old said.

The solution that had been emptied onto him and 13 other passengers was a powerful hydrochloric acid. "Me and a woman standing next to me got it worst, we were just a metre away from the door. I'm lucky I turned around, but she got it in her face and in her eyes," Tyo said, now recovering at his home in Tebet, south Jakarta. "I've not seen her since the hospital, but I've heard she may have been blinded."

Joko Widodo, Jakarta's charismatic, Metallica-loving governor, has pledged to pay for the treatment of all those involved in the bus incident. But Tyo has received no money to pay for his dressings or medication and has not yet been contacted by City Hall.

Tompel is now awaiting trial and if found guilty, will face a jail sentence of up to five years.

Brawling tradition

Tawuran, the culture of student brawling, is nothing new to Indonesia. High school students have gathered before and after class to hack and beat each other, often fatally, since the early 1990s. Public buses containing students from rival schools are often attacked, with innocent bystanders regularly becoming entangled in the violence.

Spiked bats and machetes are common weapons of choice, but the use of acidic solution - in three reported high school incidents since the start of October - is a disturbing development.

Four students from Muhammidiyah Technical College (SMK), central Jakarta, sustained neck burns after being attacked by 10 students on motorcycles with an acid solution on October 11.

I never used acid when I was fighting. But people are using it because of the police sweeps. - Jambrong, 19-year-old high school graduate

Four junior high school students waiting outside an elementary school were injured, two seriously, after reportedly having Molotov cocktails mixed with an acid solution thrown at them by assailants on motorbikes in Ciamis, West Java, on October 13.

Responding to the string of incidents, Jakarta Deputy Governor Basuki Tjahaja Purnama announced recenlty the introduction of a compulsory "home study" period between 7pm and 9pm - effectively a curfew. Critics say the measures - to be trialed in Jakarta this month - are unlikely to affect student brawls that usually occur in the daytime.

"I never used acid when I was fighting. But people are using it because of the police sweeps," Jambrong, a 19-year-old alumnus of Muhammidiyah High School (SMA), central Jakarta, said.

"With a samurai sword or a machete - you need a big bag and the police will find it. But you can get acid easily. You can buy it in building supply stores or technical stores. No one will ask you what it's for. You can even get it from the school lab.

"It's hard to look for acid. You can just keep it in a plastic bottle - it's small and it looks anonymous."

But Jambrong said the most popular weapon in student brawls is a motor gear tied to the end of a karate belt. "You get someone in the head with that and it'll rip it up pretty bad. There are no rules to tawuran, there's no code. You just have to have the guts. If you dare to kill, then kill, if not you will be scarred. I got hurt a couple of times."

'Sense of hatred'

The startling ferocity of violence between students has taken a heavy human toll. In 2011 there were 339 student brawls nationwide resulting in 82 deaths, up from 37 deaths in 1999, according to media reports. Obtaining authoritative statistics for 2013 is difficult, but both police sources and students claim both the violence and death-rate is now declining in Jakarta.

"I don't personally know anyone who has died so far this year. When you fight the most important thing is to not go down. If you get knocked down and there are a lot of other guys, that's when you can die," Jambrong said.

Despite his claim to no longer be involved in the clashes, Jambrong, who graduated in 2012, still hangs out by Muhammidiyah SMA to "look out" for younger students after class finishes at midday.

Jambrong's alpha presence attracted the palpable admiration of a retinue of younger teenagers, and the nervous glances of passing bus passengers as he sat on his motorbike next to his former school.

Whether by direct order or indirectly - through bragging about former fighting glories - it is the alumni that dictate the passing down of the tradition to junior students.

Police want to impose a curfew in a bid to tackle youth gang violence [GALLO/GETTY]

"The sense of hatred between the schools is actually inherited from the alumni. Those values are transmitted to the juniors during their first two weeks of school," said national police commissioner Adrianus Meliala.

Spikes in violence are anticipated at the beginning of the Indonesian school year, in June and July, to coincide with the initiation of new students.

"There is a conformity in Indonesia, and Indonesian high school students are arguably more susceptible to the demands of conformity than other countries. Because this is the East, it's part of eastern culture," Meliala said.

"The student who committed the acid attacks, Tompel, had been involved in tawuran since he was 16-years-old, when he was asked by the seniors to fight. It's a kind of commitment test."

Unusual timing

Meliala said the timing of the sudden spate of acid attacks has been unusual as they have coincided with the preparation for mid-semester exams, when students are typically busy. Meliala, who is also a professor of criminology at the University of Indonesia, said the use of acid has less to do with a specific psychological motivation, and more to do with students having easy access to chemical substances.

"Tompel said he didn't know why he used acid. I'm afraid of the copycat problem though," Adrianus said. "The more these stories are published the more there is a desire to replicate that kind of behavior."

In recent years schools have been instructed to tighten their regulations and expel students who are found to be involved in tawuran. Adrianus claims improved policing and the introduction of school police representatives - students appointed to discourage and report those involved - has also helped to curb the violence.

Despite these measures it seems unlikely that Indonesia's historically lax policing will disrupt the tawuran tradition.

"In areas where there is a lot of student violence, the public actually retaliates by chasing students who are involved in the fighting and then grabbing them and taking them to the police.

"It's good to create that kind of vigilante situation, because if we depend upon the police, then the police are usually quite late arriving on the crime scene," Adrianus said.

His words will provide little reassurance for Tyo whose back will be permanently scarred from his injuries. He has written off the incident as a misfortune which he must accept, but as the tradition of tawuran spirals on, his anxiety about a future attack remains.

"Every time I get on that bus route now I feel tense. You never know if something like that could happen again," he said.