THE transparent liquid which left a nurse with burns when she sat on it was likely sodium hydroxide, a cleaning agent, the police said yesterday.

Nurse Wan Zahfirah Arshad, 24, was taking the MRT home on Thursday last week when she sat on a priority seat without noticing the liquid on it. Her left buttock was burnt and she needed hospital treatment.

It had been suspected that the liquid was sulphuric acid. But the police, who arrested a 52-year- old man on Sunday in connection with the incident, believe otherwise now.

Sodium hydroxide is a strong alkali used to make soaps and detergents, and dissolves easily in water. Given its corrosive nature, it can cause chemical burns when it comes into contact with skin.

The arrested man, believed to be a director in the food and beverage industry, is being investigated for allegedly committing a negligent act causing hurt.

A conviction carries with it imprisonment for a term of up to six months, or a fine, or both.

The police said: "As investigations are still ongoing, it is not appropriate to provide further details."

The Straits Times understands that the man was not involved in two other similar incidents.

Student Aung Phone Naing, 14, suffered second-degree burns on his right thigh after sitting on a "transparent liquid" at a bus stop in Bukit Batok East three weeks ago.

In March last year, a 27-year- old hairdresser was burnt by an unknown liquid after sitting in an MRT train.

The police had previously suggested that the three cases could be linked.

JALELAH ABU BAKER