When the air outside turns unhealthy, staying indoors seems like the obvious solution. But how much does being indoors actually help you escape the haze? You wake up, check your phone and see that the PSI has crept into the unhealthy range. Your first thought: Fine. I’ll just stay indoors today.
Except… where exactly is “indoors”?
Your bedroom? The MRT? Campus? A shopping mall? The café downstairs? The gym? And if you’re spending the whole day in air-conditioned spaces, does that automatically mean you’re breathing clean air?
Not necessarily.
First stop: getting to campus
If you’re only walking from your home to the bus stop, or from the MRT station to campus, you probably don’t need to panic. Singapore’s Ministry of Health says healthy people generally don’t need an N95 mask for short-term exposure, such as commuting to school or work.
What matters more is how long and how intensely you’re exposed.
When the 24-hour PSI reaches the unhealthy range of 101–200, healthy people are advised to reduce prolonged or strenuous outdoor physical activity. The 1-hour PM2.5 reading can also be useful for deciding what to do right now, such as whether it is a good idea to go for a run.
So that 15-minute walk to class? Different proposition from an hour-long run outdoors.
Next stop: the air-conditioned classroom
Here’s where things get interesting. You made it inside. Air-con on. Windows closed. Haze escaped.
Except that air-conditioning doesn’t necessarily mean your room is sealed off from the outside world. According to the National Environment Agency, PM2.5 particles can enter air-conditioned buildings through fresh-air intakes, as well as through openings and gaps. During a haze episode, particulate levels indoors can build up too.
In other words, your air-con isn’t necessarily a magic haze force field.
How protected you are depends partly on how the building’s ventilation and filtration systems work. NEA’s updated 2026 guidance recommends efficient filtration for air-conditioning systems and notes that filters can help reduce indoor air pollution from microscopic particles.
Which means that the giant air-conditioned shopping mall might be doing a better job of keeping particles out than your bedroom with a split-unit air-con.
What about the mall?
This is where things get counterintuitive. A shopping mall, cinema or office building may have sophisticated mechanical ventilation and filtration systems. But every building is different. And the same applies to cafés.
That cosy café with its doors permanently propped open? It may be indoors, but if you’re sitting right next to the entrance, you’re still pretty connected to the outside air.
So “indoors” isn’t really a binary thing. There are degrees of indoor.
The gym is probably not your haze escape plan
If your normal response to bad air is to move your workout indoors, check the air quality advice before going hard. The issue isn’t just the air you’re breathing — it’s how much air you’re breathing.
Running or doing a high-intensity workout means breathing faster and deeper than sitting at a desk. That’s why MOH’s advice focuses specifically on reducing prolonged or strenuous outdoor physical exertion when the PSI is unhealthy.
So a haze day might be the day to swap the 10km run for something less strenuous — or simply take a rest day.
Finally: home
This is probably where you have the most control.
When outdoor air quality is worsening, HealthHub recommends closing doors and windows to reduce the amount of haze entering your home. Portable air purifiers can further reduce indoor particle levels, while air-conditioners can be used for cooling and circulation, depending on how they draw and filter air.
If you’re considering an air purifier, NEA says one of the useful numbers to look at is CADR (Clean Air Delivery Rate). A higher CADR generally means the device can deliver more clean air, but it needs to be considered alongside the size of the room.
And you don’t necessarily need to turn your home into a laboratory. The basic strategy is pretty simple: reduce outdoor air entering when the air outside is poor, avoid creating additional indoor pollution, and improve filtration if you need it.
So, can you actually escape the haze?
Sort of. There isn’t a magical building in Singapore where haze particles cannot reach you. But your exposure isn’t simply a matter of outside = bad, inside = good. Besides, it’s not our first hazy situation – we’ve been facing this issue on and off for decades.
It’s about the combination of where you are, how the building is ventilated and filtered, how long you’re there, and what you’re doing. And that’s probably the most useful thing to remember the next time the PSI starts climbing.
You don’t have to become a haze hermit. But maybe that outdoor run can wait.
