Singapore is collecting data on the haze as it weighs possible action under its Transboundary Haze Pollution Act, the Straits Times reported on Wednesday, citing Minister for Sustainability and the Environment Grace Fu.

The law, enacted in 2014, targets those responsible for causing or condoning fires if the resulting haze causes the Pollutant Standards Index (PSI), a measure of air quality, to remain in the unhealthy range for 24 hours or more.

The gauge ranged between 125 and 206 across the island as of 6am local time, with the western region recording the highest reading. Air quality is considered “very unhealthy” when 24-hour PSI levels are 201 and above. A reading above 300 is considered “hazardous” and would trigger school closures.