Is It Safe to Swim Outdoors When the PSI Reaches 100, 150 or 200?
By Coach Tan Meng Chew (MC), SG Sink or Swim
Three numbers come up again and again when parents message me during haze season: 100, 150 and 200. "MC, the PSI is 100, is it okay?" "It's 150 now, should we still swim?" "It's almost 200, surely we cancel?"
These are sensible questions, because they are the natural landmarks on the PSI scale. But "is it safe?" is a harder question than it sounds, and I want to answer it honestly rather than with a neat slogan. There is no official number that says "below this, swimming is safe, above this, it is dangerous." What we do have is a set of official activity bands, a facility plan from Sport Singapore (SportSG), a growing body of general research on exercise and air pollution, and, this week, a very practical development: ActiveSG has closed a long list of its swimming complexes because of elevated PM2.5 readings.
I'm Coach Tan Meng Chew, known to most people as MC. I run SG Sink or Swim, a swimming school and coaching brand serving the west side of Singapore, teaching from Nursery and Level 1 (Baby & Toddler) through to SwimSafer Stages 1 to 6. I am a swim coach, not a doctor, so I will stick to what the published sources say, mark my own judgement clearly, and send you to a doctor for anything medical.
The short answer
At PSI 100, official guidance says normal activities for everyone, including children and people with chronic conditions. It is the edge of the Moderate band, and 101 is the first Unhealthy number, so I would watch the trend and be a little more careful with sensitive swimmers.
At PSI 150, you are in the middle of the Unhealthy band. Official guidance asks healthy people to reduce prolonged or strenuous outdoor exertion, children to minimise it, and people with chronic lung or heart conditions to avoid it. For outdoor swimming, and especially for children, I lean towards not swimming, or keeping it very light.
At PSI 200, you are at the top of the Unhealthy band, one point from Very unhealthy. Under SportSG's plan, outdoor and non-air-conditioned facilities close at 201 to 300. I would skip outdoor swimming.
None of these numbers is a cliff. The 1-hour PM2.5, the venue's decision, the type of pool and your child's health all matter as much as the PSI.
In practice, the question may already be decided for you. As of the ActiveSG closure page I read, timestamped 14 October 2026, 5.03 pm, many swimming complexes across the East, Central and West regions were listed as closed due to elevated PM2.5, effective 14 October 2026 until further notice.
Let me walk through each of the three numbers, and then through the things that matter beyond the number.
First, what the official guidance actually says
The activity bands
The National Environment Agency (NEA) groups people into three categories: healthy persons; elderly, pregnant women and children; and people with chronic lung or heart disease. The advice for the 24-hour PSI, as set out in the NEA advisory and the Ministry of Health (MOH) FAQ, is as follows. (The text of the NEA PDF came out jumbled when I read it, so I mapped its table by order. MOH's FAQ states the same bands in prose. Please confirm on haze.gov.sg.)
24-hour PSI | Healthy persons | Elderly, pregnant women, children | Chronic lung or heart disease |
100 or below | Normal activities | Normal activities | Normal activities |
101 to 200 (Unhealthy) | Reduce prolonged or strenuous outdoor exertion | Minimise prolonged or strenuous outdoor exertion | Avoid prolonged or strenuous outdoor exertion |
201 to 300 (Very unhealthy) | Avoid prolonged or strenuous outdoor exertion | Minimise outdoor activity | Avoid outdoor activity |
Above 300 (Hazardous) | Minimise outdoor activity | Avoid outdoor activity | Avoid outdoor activity |
Sport Singapore's poster explains the three action words: Reduce means do less, Minimise means do as little as possible, and Avoid means do not do. Notice also the words prolonged and strenuous. The advice is about how hard and how long you breathe in the air, which is why a swimmer working hard is the kind of person it is aimed at.
The facility phases
SportSG's Haze Management Plan (April 2026) sets out phases by 24-hour PSI:
24-hour PSI | Outdoor or non-air-conditioned facilities | Air-conditioned facilities |
0 to 50 | Open | Open |
51 to 100 | Open, with advisories displayed, at-risk staff monitored, N95 masks stocked and ventilation maintained | Open |
101 to 200 | Operate with conditions; organisers must carry out a risk assessment, and anyone feeling unwell must stop and seek medical attention | Open |
201 to 300 | Close | Operate with conditions |
Above 300 | Close | Close |
The PM2.5 overlay
The 24-hour PSI is the planning number. The 1-hour PM2.5 is used for immediate decisions, and SportSG's plan says it cannot override facility advisories based on the 24-hour PSI. The bands are Normal (55 and below), Elevated (56 to 150), High (151 to 250) and Very high (above 250), in micrograms per cubic metre. Reports of NEA's advice describe, at the Elevated level, healthy people reducing strenuous outdoor activity for the next hour and vulnerable groups avoiding it, and at the High level (151 to 250), avoiding strenuous outdoor activity, with vulnerable people avoiding all outdoor activity. The wording differs slightly between reports, and I have only seen it second-hand, so please check NEA's own channels.
PSI 100: the edge
What the guidance says
At 100 or below, official guidance is normal activities for everyone. The Unhealthy band starts at 101, and MOH describes a PSI of 101 and above as unhealthy. SportSG's facilities are open, with advisories displayed and at-risk staff monitored.
Why I treat 100 as a "watch" number, not a green light and not a red one
It is a boundary, not a cliff. A reading of 100 and a reading of 102 are not meaningfully different for your lungs. What matters is the trend. If the PSI has been climbing all day and is about to cross into Unhealthy, I look at the 1-hour PM2.5 and the forecast. If it is falling, the picture is better.
The 24-hour PSI smooths over the hour-to-hour picture. It tells you about the day, while the 1-hour PM2.5 can move up or down within hours. A news report of the morning of 9 October, for example, showed the western region's 24-hour PSI at 166 alongside a 1-hour PM2.5 of 114, in the Elevated band, and on other mornings the two have pointed in different directions. So even near the 100 mark, I check the PM2.5 before deciding.
Sensitive swimmers are a separate question. HealthXchange advises that children with asthma should follow their asthma action plan if the PSI is above 100 and they have a cough, wheezing or shortness of breath. If your child has asthma, the doctor's advice is the thing to follow, not the headline band.
My take at PSI 100
For a healthy child or adult, an outdoor swim is consistent with official guidance, and I would go ahead if the PM2.5 is Normal and the venue is open. I would keep an eye on the trend and on anyone who is coughing or irritated, and I would be more careful with children who have breathing conditions.
PSI 150: the middle of Unhealthy
What the guidance says
At 150, you are in the Unhealthy band. The official advice is to:
Reduce prolonged or strenuous outdoor exertion if you are a healthy person.
Minimise it if you are elderly, pregnant or a child.
Avoid it if you have a chronic lung or heart condition.
SportSG's plan says outdoor and non-air-conditioned facilities operate with conditions, with a risk assessment required before continuing activities, while air-conditioned facilities stay open.
What actually happened this week
Here is where theory meets practice. On 13 October, a news report of the 9 am readings put the 24-hour PSI at 172 in the west, 169 in the central region, 154 in the east, 134 in the south and 127 in the north, all in the Unhealthy range, with 1-hour PM2.5 in the Elevated band in the west, central and east. Then ActiveSG moved beyond "operate with conditions."
As of 14 October, 5.03 pm, the ActiveSG facilities closure page carried a haze banner saying that, due to elevated PM2.5 readings, SportSG was taking "additional precautionary measures" to temporarily close outdoor and non-air-conditioned facilities at affected sport centres across the East, Central and West regions. It listed, among the closures, effective 14 October 2026 until further notice, the following swimming facilities: Bishan, Bukit Batok, Choa Chu Kang, Clementi, Delta, Geylang East, Heartbeat @ Bedok, Hougang, Jalan Besar, Jurong East, Jurong West, Katong, Pasir Ris, Queenstown, Senja-Cashew, Serangoon and Tampines swimming complexes, plus Jurong Lake Gardens Pool, the MOE (Evans) Swimming Complex and the ActiveSG Sport Park @ Teck Ghee Swimming Complex.
This matters for two reasons.
First, it answers a question my earlier articles had to leave open. The SportSG plan and the first closure notice did not say how swimming pools are classified. This list shows ActiveSG treating its swimming complexes as part of the closure. The page does not specify which pools or areas within each complex are affected, so each entry appears to cover the whole listed facility, and I cannot tell you how any individual enclosed pool hall is treated. Not every ActiveSG pool is on the list, and I cannot tell from the page whether an unlisted pool is operating normally. Please check.
Second, it shows that a PSI in the 150 to 170s, with elevated PM2.5, was enough for ActiveSG to close its outdoor facilities, including pools, across several regions. That is a stricter step than the plan's baseline for the 101 to 200 band, and the banner itself calls it an "additional" measure. It tells me the operator is responding to real-time air quality, and it tells me that for outdoor swimming, PSI 150 with elevated PM2.5 is already a level at which closures are happening.
I do not know the status of these closures as I write, because they can change at any time. Please check go.gov.sg/activesgfacilitiesclosure and the Sport Centre's Facebook page.
My take at PSI 150
Children: official guidance says minimise prolonged or strenuous outdoor exertion. For an outdoor pool, I would skip. If an enclosed pool is open and your child is healthy, a short, gentle session may be reasonable, but I would not push it.
Healthy adults: official guidance says reduce. A short, easy swim is consistent with that, if the venue is open and the PM2.5 is not High. A hard training set is what the advice is trying to discourage.
Anyone with asthma or a chronic lung or heart condition: official guidance says avoid prolonged or strenuous outdoor exertion. Follow your doctor's advice, and I would not swim outdoors.
PSI 200: the top of Unhealthy
What the guidance says
At 200 you are at the very top of the Unhealthy band. The advice is the same as at 150 on paper, but the practical consequences are different, because 201 is the next step.
At 201 to 300 (Very unhealthy):
Healthy people are advised to avoid prolonged or strenuous outdoor exertion.
Children are advised to minimise outdoor activity.
People with chronic lung or heart disease are advised to avoid outdoor activity.
SportSG's plan closes outdoor and non-air-conditioned facilities and suspends outdoor activities, with air-conditioned facilities operating with conditions.
Beyond facilities, a news report on the Haze Task Force said it was ready to activate the next tier of its action plans if air quality reached the Very unhealthy range, including N95 mask distribution for more vulnerable Singaporeans, opening haze shelters if the PSI exceeds 201, and advisories for preschools, schools and workplaces. HealthHub says N95 masks are recommended for healthy people when the PSI is above 300 and they must be outdoors for several hours, and for people with chronic lung or heart disease when the PSI is above 200.
My take at PSI 200
I would skip outdoor swimming. At this level, you are one reading away from the point at which SportSG's plan closes outdoor facilities, official advice for children is moving to minimise outdoor activity, and the readings can change within hours. If you are considering an enclosed, air-conditioned pool because it happens to be open, please be cautious: the plan has such facilities "operating with conditions" from 201, and the official guidance asks for strenuous indoor activity to be minimised for young children when the air is Unhealthy. In a recent NEA announcement on measures, for example, preschools were said to limit long outdoor play and minimise strenuous indoor physical activities for children in that range.
A side-by-side summary
This table is my own coaching summary of the official guidance for generally healthy people, and it is not an official protocol. For people with asthma or other chronic conditions, the doctor's advice comes first, and the official guidance is more cautious for them at every level.
PSI 100 | PSI 150 | PSI 200 | |
Official band | Moderate (edge of Unhealthy) | Unhealthy | Unhealthy (top of band) |
Official advice, healthy adults | Normal activities | Reduce prolonged or strenuous outdoor exertion | Reduce prolonged or strenuous outdoor exertion |
Official advice, children | Normal activities | Minimise prolonged or strenuous outdoor exertion | Minimise prolonged or strenuous outdoor exertion |
SportSG plan, outdoor facilities | Open with advisories | Operate with conditions | Operate with conditions (closes at 201) |
Outdoor pool, healthy adult | Generally fine; watch trend | Short and easy at most, if open | I would skip |
Outdoor pool, healthy child | Generally fine; watch trend | I lean towards skipping | I would skip |
Enclosed pool, healthy child | Generally fine | Short, gentle session may be reasonable if open | Be cautious; consider skipping |
Child or adult with asthma or chronic condition | Follow your doctor's plan | Official advice: avoid prolonged or strenuous outdoor exertion | Skip |
Why the PSI alone is not enough
If you take only one thing from this article, let it be this: the PSI number is where you start, not where you finish.
1. The 1-hour PM2.5. The PSI is a 24-hour measure and the PM2.5 is a one-hour reading. A day with a PSI of 120 can contain an hour at PM2.5 of 40 and an hour at 160. NEA's advice is to use the PM2.5 for immediate activities and the PSI to plan ahead. Reports of NEA's advice say that at the High level (151 to 250), people should avoid strenuous outdoor activity for the next hour. If the PM2.5 is High, I would not start an outdoor lesson, whatever the PSI.
2. Your region. Regions differ, sometimes a lot. On 13 October, for example, the western 24-hour PSI was 172 while the north's was 127. Read your own region's numbers.
3. The venue. If a venue closes or suspends activities, the numbers no longer matter for that lesson. The ActiveSG list shows how quickly that can happen.
4. The pool type. An open outdoor pool exposes swimmers to outdoor air throughout. An enclosed pool hall may offer less exposure depending on ventilation and filtration, though I cannot confirm that for any specific venue, and "indoor" does not mean "haze-proof."
5. The intensity and duration. The official advice is about prolonged or strenuous exertion. A short, easy session breathes in much less than a long, hard one. A California Air Resources Board page says exercisers can exchange "up to 10 or 20 times more air" than at rest, and the US Environmental Protection Agency says where particles deposit in the lungs depends on physical activity and whether you breathe through your nose or mouth. Swimming is largely mouth-breathing exercise.
6. The swimmer. Children, the elderly, pregnant women and people with chronic lung or heart conditions are more sensitive, according to MOH. HealthXchange explains that children's lung defences are still developing.
7. The days after. MOH and HealthHub say effects can appear one to three days after exposure. A swim that seems fine can show up as a cough the next day.
So, is it safe? The honest answer
"Safe" is not a yes-or-no label here, and I would be misleading you if I gave you one. Here is what I can say.
Short-term effects for healthy people are usually mild. MOH says short-term haze exposure over a few days mainly causes irritation of the eyes, nose and throat that usually resolves on its own, and HealthXchange says mild symptoms in children should ease on their own if exposure is limited.
Sensitive people can be affected more seriously. MOH cites a local study that found a 3.1% increase in asthma hospital admissions for each 10-unit rise in the 24-hour PSI.
I could not find research that measures the risk of swimming in haze specifically, so I cannot tell you how much risk a given swim adds.
The long-term effects of short, episodic haze are unknown. The MOH FAQ says there is no local or international data on the long-term health impact of short-term, episodic haze exposure, while overseas studies link continuous, multi-year exposure to fine particles with problems such as reduced lung development. (The MOH FAQ is dated 21 November 2016, so please check for an update.)
So my framing is not "safe" versus "unsafe." It is "how much risk am I willing to take on, for whom, for what benefit." For a healthy adult doing an easy swim at PSI 100, the added risk is small. For a child doing a hard outdoor set at PSI 190 with elevated PM2.5, it is a risk I would not ask anyone to take, especially since a missed lesson is easy to recover from.
Warning signs: stop and seek help
At any PSI, stop the activity and have the swimmer rest if you see:
A cough that persists or worsens.
Wheezing, a whistling sound when breathing.
Difficulty speaking in full sentences because of breathlessness.
Chest tightness or chest pain.
Unusual paleness, bluish lips, dizziness or faintness.
A swimmer who looks distressed or cannot catch their breath.
MOH advises anyone not feeling well to seek medical attention, and people with chronic heart or lung conditions to keep their medications readily available. In an emergency, such as severe difficulty breathing, call 995. If your child has asthma, follow their asthma action plan.
What about masks, filters and "just a quick swim"?
Masks. Nobody can swim in a mask. HealthHub says N95 masks are not needed for brief trips between buildings or for indoor use, and HealthXchange notes they may not fit children well and that surgical masks do not filter fine particles well.
"Just a quick swim." A short, easy swim exposes you to less than a long, hard one, which is consistent with the official focus on prolonged or strenuous exertion. But "quick" is not a guarantee, particularly for sensitive swimmers or at high PM2.5.
"The water will protect me." Water does not clean the air above it. A swimmer breathes the air at the pool.
How SG Sink or Swim decides
Here is how I approach the three numbers at SG Sink or Swim. We serve the west side of Singapore and teach many young children. These are my working principles, and they are a coaching approach, not an official rule. Details depend on the venue and the day.
The venue decides first
If a venue closes or suspends activities, our lessons there are off. The ActiveSG closures this week are a clear example.
I read the west, and I check close to lesson time
I look at the western 24-hour PSI to understand the day, and the western 1-hour PM2.5 shortly before the lesson.
My rough thresholds for outdoor lessons with healthy children
PSI 100 or below, PM2.5 Normal: go as normal.
PSI around 101 to 150, or PM2.5 Elevated: I lean towards adjusting or skipping outdoor lessons. If the venue is open and the child is healthy, I keep it short and gentle. For young or sensitive children, I skip.
PSI above roughly 150, or PM2.5 High: I skip outdoor lessons.
PSI 200 or above: skip.
I am more cautious with sensitive swimmers
Babies, toddlers, young children and anyone with a known breathing sensitivity get a more conservative approach, whatever the numbers say.
I want to know about your child's health
Please tell me about asthma, allergies or any breathing concern, and where prescribed medication is kept.
I do not give medical advice
I follow the plan your child's doctor has given you, but I do not diagnose or decide on medication.
I keep progress visible through a pause
Our programmes run from Nursery and Level 1, through Level 2 (Beginner) and Level 3 (Intermediate), and on to SwimSafer Stages 1 to 6. Because progress is tied to that pathway, a haze pause does not leave families guessing where their child stands, and we can restart from the right point.
If you would like to talk about how we handle haze, or how lessons would work for your child, you are welcome to get in touch through sgsinkorswim.com.
Frequently asked questions
Is it safe to swim outdoors at PSI 100?
Official guidance for 100 or below is normal activities for everyone. It is the edge of the Unhealthy band, so I would watch the trend and the 1-hour PM2.5, and be more careful with sensitive swimmers.
Is it safe to swim outdoors at PSI 150?
You are in the Unhealthy band, where official guidance asks healthy people to reduce, children to minimise and people with chronic conditions to avoid prolonged or strenuous outdoor exertion. ActiveSG has closed many swimming complexes at recent PSI levels in this range with elevated PM2.5. I lean towards skipping outdoors, especially for children.
Is it safe to swim outdoors at PSI 200?
I would skip. It is the top of the Unhealthy band, one point from Very unhealthy, where SportSG's plan closes outdoor and non-air-conditioned facilities.
Is there an official PSI limit for swimming?
Not that I could find. There are official activity bands and SportSG facility phases, but no swimming-specific threshold.
Are indoor pools safe at these levels?
They may offer less exposure, but ventilation varies, and official guidance asks for strenuous indoor activity to be minimised for young children when the air is Unhealthy. Ask the venue.
My pool is not on the ActiveSG closure list. Is it open?
I cannot tell from the page. Check the venue's own notices and your provider.
What matters more, PSI or PM2.5?
They do different jobs. Plan with the PSI, and use the PM2.5 for immediate decisions.
My child swam yesterday and is coughing today. Is that the haze?
It might be: effects can appear one to three days after exposure. Other causes are common too, such as swallowing water or a cold. If it persists or comes with wheezing or breathlessness, see a doctor.
Should I take my child with asthma to swim at any of these levels?
Please ask your child's doctor and follow their asthma action plan. Official guidance is more cautious for people with chronic lung conditions at every level.
Where do I check the numbers?
NEA's haze website, haze.gov.sg, publishes the 24-hour PSI and the 1-hour PM2.5 by region. For pool status, check ActiveSG's facility closure page and the Sport Centre's Facebook page.
The bottom line
PSI 100: official guidance is normal activities. It is a boundary, so watch the trend and the PM2.5, and take extra care with sensitive swimmers.
PSI 150: officially in the Unhealthy band. I lean towards skipping outdoor swimming, especially for children. ActiveSG has been closing swimming complexes at recent PSI levels like this when PM2.5 was elevated.
PSI 200: I would skip outdoor swimming. One point higher, SportSG's plan closes outdoor facilities.
No number is a guarantee of safety or danger. The 1-hour PM2.5, your region, the venue, the pool type, the intensity and your child's health all matter.
When in doubt, skip. A rescheduled lesson is easy to recover from, and your doctor's advice comes first for any breathing condition.
Haze seasons pass, and a swimmer's journey is long. The people who do best are the ones who read the numbers calmly, check with their venue and coach, and get back into a regular rhythm as soon as the air clears.
At SG Sink or Swim, we teach from a first splash through to SwimSafer Stage 6, and keeping swimmers safe is always part of the job. If you have questions about lessons during haze, reach out at sgsinkorswim.com.
Stay safe, breathe easy, and see you at the pool when the air is clear.
Coach Tan Meng Chew (MC) SG Sink or Swim | sgsinkorswim.com
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