SINGAPORE - The liquid on an MRT train seat which burnt a nurse last Thursday is likely to be sodium hydroxide, police said on Tuesday.
It was previously believed to be sulphuric acid.
It is also likely the 52-year-old man arrested on Sunday in relation to the incident had no hand in two previous similar incidents, The New Paper understands.
Three weeks ago, student Aung Phone Naing, 14, suffered second-degree burns on his right thigh after sitting on a "transparent liquid" at a Bukit Batok East bus stop.
A 27-year-old hairdresser was also burnt by an unknown liquid after taking a seat on an MRT train in March last year.
Commonly known as caustic soda or lye, sodium hydroxide is a strong alkali mainly used in the industry to make soaps, detergents and cleaners, said Dr Ng Sek Yeo, a senior lecturer at Singapore Polytechnic's School of Chemical and Life Sciences.
It is also the common alkali that students use in acid-base titrations and quantitative analysis in schools, he added.
"Concentrated solutions are corrosive; also quite viscous," he said, adding its household uses included unblocking drains and cleaning ovens.
Used by professional cleaners and plumbers rather than small households, the chemical wouldn't be carried by grocery stores but more likely by DIY shops, said Dr Perry Chan, a senior lecturer at Nanyang Polytechnic's School of Chemical and Life Sciences.
The suspect, a director in the food and beverage industry, was arrested near Toa Payoh MRT station for a case of negligent act causing hurt.
This means his act wasn't accompanied by mens rea, or guilty intention, said Mr Paul from East Asia Law Corporation. "There was no sinister motive."
Police said investigations are ongoing.
Get The New Paper for more stories.