Staying indoors to avoid the haze? Then keep the doors and windows shut, and switch on a fan or the air-conditioner, advise doctors. Using an air purifier is also good.
"If you stay indoors but the windows are open, it doesn't help," said Dr Yap Wee See, a respiratory medicine specialist at Mount Elizabeth Novena Hospital.
"As long as there are any gaps, the small haze particles will be able to get through."
Last Saturday night, the 24-hour Pollutant Standards Index (PSI) rose into the unhealthy range, easing into moderate levels only at 10am yesterday.
Among the pollutants in haze, the ones that are particularly harmful are collectively known as PM2.5 - as they measure at most 2.5 microns, or about a thirtieth the diameter of human hair.
These particles are tiny enough to go deep into a person's lungs and enter the bloodstream, making them difficult for the body to get rid of.
Experts suggest keeping doors and windows shut when air quality hits unhealthy levels - when the 24-hour PSI level goes above 100.
An air purifier can also filter the air further even with the air-conditioner on, especially since closing doors and windows might inadvertently trap haze particles inside.
Said Dr Liew Woei Kang of the SBCC Baby and Child Clinic: "The lack of ventilation traps indoor air pollutants and can worsen the air quality. In such situations, it may be advisable to use an air purifier... to filter the air." When the haze clears, he said, windows and doors can be left open to remove remaining pollutants.
Those who have no choice but to be outdoors when the haze is in the higher levels of the unhealthy range - that is, above 150 - should cut down on physical exertions, even if they are perfectly healthy. This month, the 24-hour PSI peaked in the early hours on the morning of Polling Day, registering 182 in the southern part of Singapore.
"When we are jogging, for instance, we tend to breathe faster and a higher volume," said Dr Yap. "But if we walk, breathing is not so fast and hard, so exposure is less."
One person who has been keeping a close eye on the haze is Madam Leck Teng Ngin, who has six school-going grandchildren. "We have our windows and doors closed," said the 63-year-old, who added that they also turned on the air-con when the haze was worse. "Everyone is worried about the kids getting sick."
Doctors say people should refer to the PSI and PM2.5 levels posted by the National Environment Agency as a guide to air conditions.
"Not being able to smell the haze does not mean that there is no pollution," said respiratory specialist Steve Yang of the Raffles Internal Medicine Centre.
This article was first published on September 18, 2015.
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