SINGAPORE - The haze situation in Singapore improved slightly on Wednesday (Sept 30) but the 24-hour Pollutant Standards Index (PSI) remained in the unhealthy range.

For Thursday, the 24-hr PSI is expected to be in the high end of the unhealthy range and low end of the very unhealthy range, and may deteriorate to the mid-section of the very unhealthy range if denser haze is blown in, the National Environment Agency (NEA) said in an update on Wednesday evening.

The agency also said that it has sent notice to another Indonesian company, namely, PT Bumi Mekar Hijauis. " NEA has sent a Preventive Measures Notice pursuant to Section 9 of the Transboundary Haze Pollution Act to another Indonesian company, namely, PT Bumi Mekar Hijau.This is in addition to earlier Preventive Measures Notice sent to four Indonesian companies," it said.

Under the Notice, NEA has requested PT Bumi Mekar Hijau to carry out the following: Deploy fire-fighting personnel to extinguish or prevent the spread of any fire on land owned or occupied by them; Discontinue, or not commence, any burning activities on such land; Submit to NEA any plan of action to extinguish any fire on such land or to prevent its recurrence.

Last Friday, four Indonesian companies – Rimba Hutani Mas, Sebangun Bumi Andalas Wood Industries, Bumi Sriwijaya Sentosa and Wachyuni Mandira – were told to take measures to inguish fires on their land, not to start new ones, and submit action plans on how they will prevent future fires.

As of 5am, the 24-hour PSI was 146-186. The three-hour PSI, which is not tied to a health advisory, stood at 184.

The two photos below were taken at different times on Sept 30 from the 23rd floor of Block 214 at Marsiling Lane: at 7am (left), when the three-hour PSI reading was 125; and at 3.30pm when the reading was about 203.

The National Environment Agency (NEA) said in an advisory on Tuesday evening that the air quality is expected to remain between the unhealthy (101-200) and very unhealthy levels (201-300) on Wednesday.

The update sent at around 7.30pm on Tuesday said the 24-hour PSI for the next 24 hours is expected to be in the high-end of the unhealthy range and the low-end of the very unhealthy range.

Heavy rain over most parts of Singapore early Wednesday also brought some temporary respite.

Given the air quality forecast, healthy people should reduce prolonged or strenuous outdoor physical exertion. The elderly, pregnant women and children should minimise prolonged or strenuous outdoor physical exertion, while those with chronic lung or heart disease should avoid prolonged or strenuous outdoor physical exertion.

Ahead of the Primary School Leaving Examinations (PSLE) that start on Thursday, several schools said they have put in place precautionary measures such as shifting some classes to air-conditioned classrooms.

Those with chronic heart or lung conditions should seek medical attention if they are feeling unwell.

For updates, visit the NEA website and the haze microsite, and follow NEA's Facebook page or Twitter account, or download the myEnv app.