Haze and PSI thresholds for cancelling lessons

By Coach Tan Meng Chew (MC), Founder and Head Coach, SG Sink Or Swim

Lightning gets most of the attention when people ask about weather-related cancellations at Singapore's outdoor pools, and understandably so, it's the far more frequent disruptor. But during the drier months, typically the Southwest Monsoon season from June to September, when regional haze can blanket Singapore within 24 to 48 hours, a different set of thresholds comes into play, and I think it's worth explaining clearly, since it's less commonly understood than the rain-and-thunder situation.

I'm Coach Tan Meng Chew, or MC, and I run SG Sink Or Swim. This article walks through exactly how Singapore measures haze severity, what the official activity guidance says at each level, and how that translates into decisions about swim lessons specifically.

The PSI: Singapore's Core Haze Measurement

The Pollutant Standards Index, or PSI, is the National Environment Agency's headline measure of air quality and haze severity. NEA publishes readings in two forms: a 24-hour PSI, which is a rolling average over the preceding day and serves as the main reference for planning activities and major decisions, and a 1-hour PM2.5 reading, used for more immediate, short-term decisions about outdoor activity right now.

The general PSI bands, and their standard activity guidance, run roughly as follows:

• 0 to 50 (Good): No health concern. Outdoor activities as normal.

• 51 to 100 (Moderate): Generally safe to maintain normal activities, though the general public advice at PSI 100 and below is to carry on as usual.

• 101 to 200 (Unhealthy): A PSI reading of 101 and above is officially deemed unhealthy by the Ministry of Health. At this level, healthy individuals are advised to reduce prolonged or strenuous outdoor physical exertion.

• 201 to 300 (Very Unhealthy): Guidance shifts from "reduce" to "avoid" outdoor activity.

• Above 300 (Hazardous): Avoid all outdoor activity. This is also the point at which the Ministry of Health specifically notes that healthy individuals needing to be outdoors for extended periods may wear a well-fitted N95 mask to reduce exposure.

It's worth noting that these bands describe general public health guidance, and different organisations, schools, the SAF, sports bodies, translate them into their own specific operational thresholds, which is where things get more concrete for a swim lesson specifically.

How Sport Singapore Approaches Haze

This is the part most directly relevant to lessons at ActiveSG pools. Sport Singapore maintains its own Haze Management Plan, which uses the 24-hour PSI as a rolling average of air pollutant concentrations to determine graduated activity guidance across escalating bands, generally moving from "minimise outdoor activity" at lower elevated readings toward "avoid outdoor activity" at higher ones. The plan also includes practical measures for sport facilities at these escalated levels, such as ensuring air ventilation devices and systems, air purifiers, fans, are available, and providing N95 masks to staff.

What this means practically: unlike lightning, where a single detected strike risk triggers an immediate, clear-cut pool closure, haze-related decisions tend to be more graduated and forecast-based, weighing the 24-hour PSI trend, how prolonged and strenuous the activity is, and the specific guidance band, rather than a single hard cutoff that closes every pool the moment a number is crossed.

Why Swimming Specifically Is a Judgement Call During Haze

Swimming sits in an interesting position during haze events, because the activity itself happens largely at or below water level, with breathing patterns quite different from, say, a 2.4km run. That said, swim lessons still involve real physical exertion, deeper, more frequent breathing during strokes, treading water, and time spent standing at poolside between drills, all of which count as outdoor exposure during a lesson's duration.

Reduced, not eliminated, exertion at moderate-to-unhealthy readings. At the unhealthy band (roughly PSI 101 to 200), the standard guidance to reduce prolonged or strenuous outdoor exertion applies to swim lessons the same way it would to running or team sports. A lesson at this level might reasonably continue but with shorter duration, less high-intensity drilling, and more frequent rest breaks, rather than being cancelled outright.

Very unhealthy and above generally means lessons pause. Once readings move into the very unhealthy band and beyond, the standard "avoid outdoor activity" guidance becomes harder to responsibly work around for something as exertion-heavy as a swim lesson, and pausing outdoor lessons at this point is the sensible, safety-first call.

The rolling 24-hour average matters more than a single alarming hourly spike. Since NEA's headline PSI figure is a 24-hour rolling average, a brief spike in the 1-hour PM2.5 reading doesn't necessarily mean the 24-hour PSI has crossed into a more severe band. It's worth checking both figures rather than reacting to either one in isolation, since the hourly reading matters more for an immediate decision right now, while the 24-hour figure better reflects the sustained conditions relevant to planning a lesson.

A Genuinely Vulnerable Group: Children

This deserves specific mention, since most of our students are children. Haze affects everyone, but children, particularly younger ones, are generally considered more vulnerable to air quality issues than healthy adults, due to smaller airways, higher breathing rates relative to body size, and still-developing respiratory systems. A child with pre-existing asthma or other respiratory conditions, conditions that affect a meaningful proportion of children in Singapore, warrants extra caution even at readings where a healthy adult might be relatively unaffected.

If your child has asthma or any other respiratory condition, I'd encourage you to apply a more conservative personal threshold than the general public guidance, and to tell your coach about it directly, so we can factor that into decisions about whether a specific lesson should proceed, be shortened, or be rescheduled, even on a day where the official band alone might not automatically call for a pause.

How This Differs From Lightning Closures

It's worth being clear about a structural difference here, since it affects what you can expect from us.

Lightning closures are immediate, binary, and made by the venue, not us. The moment lightning risk is detected, the pool closes, full stop, and neither we nor any other coach or school teaching there has any discretion in the matter.

Haze decisions are more judgement-based, and shared between the venue's own policies and our own responsible discretion as your coach. ActiveSG facilities themselves may implement their own closures at sufficiently severe haze levels, but at moderately elevated readings, the call about whether to proceed, shorten, or modify a lesson often sits more with the coach on the ground, exercising sensible judgement based on the current guidance band, the specific child's health, and how strenuous that day's planned lesson actually is.

This means communication matters more during a haze episode than during a lightning event. Since the decision isn't always a simple closed-or-open binary, I'd encourage you to check in with your coach directly on days with elevated PSI readings, rather than assuming either that the lesson will automatically proceed as normal, or that it will automatically be cancelled.

How to Check Current Conditions Yourself

NEA's 24-hour PSI and 1-hour PM2.5 readings are published and updated regularly, and are the primary reference for both immediate and next-day planning.

The haze.gov.sg portal provides the official government guidance poster explaining how the 24-hour PSI forecast is used to guide both individual risk assessment and major decisions like school closures or training suspensions.

Singapore is divided into several regions for PSI reporting purposes, so it's worth checking the reading specific to your area, or the area your pool is in, rather than only the nationwide figure, since haze severity can vary meaningfully across the island on a given day.

Practical Guidance for Families During Haze Season

Check the 24-hour PSI reading before heading to a lesson, particularly during the Southwest Monsoon months when haze risk is elevated.

Tell your coach about any respiratory conditions your child has, ideally well before haze season begins, so that a more conservative approach can be applied for your child specifically when conditions are borderline.

Don't assume a lesson will proceed just because it isn't officially "hazardous." A responsible coach may shorten a session, reduce intensity, or suggest rescheduling at the unhealthy band, even without an official pool closure in place.

Bring an N95 mask for the journey to and from the pool during severe haze, even if the lesson itself proceeds, since the commute itself is outdoor exposure too.

Be understanding if a lesson is paused on your coach's judgement, even at a reading that might seem borderline on paper, since erring toward caution with children's respiratory health is the right instinct, not an overreaction.

What Happens to Your Lesson If Haze Affects It

Consistent with how we handle lightning and rain-related disruptions, if a lesson is cancelled or meaningfully shortened due to haze, whether because the venue itself closes, or because your coach makes the judgement call that conditions aren't suitable for continuing safely, we arrange a free makeup lesson, with no forms and no penalty fees. Haze-related pauses are treated the same as any other weather-related interruption outside your control, not something you should be charged for.

How SG Sink Or Swim Approaches Haze Days

We monitor conditions and use sensible judgement, not just a single fixed number. Rather than applying one rigid cutoff regardless of context, our coaches weigh the current 24-hour PSI band, how strenuous the planned lesson is, and any specific health considerations for the individual swimmer.

We take children's specific vulnerability seriously. If your child has asthma or another respiratory condition, tell us, and we'll factor that in more conservatively than the general public guidance alone might suggest.

Free makeup lessons for haze-related disruptions, on the same terms as any other weather-related cancellation.

Certified, qualified coaches making these calls. Our coaches hold NROC-recognised swimming qualifications and are certified SwimSafer Instructors with current first aid and CPR/AED certification. Ask us for the details and verify them yourself on CoachSG's National Register of Coaches.

Open communication on uncertain days. If you're unsure whether a lesson will proceed given current haze conditions, message your coach directly rather than guessing.

To ask about how we're handling a specific haze episode, or to check on a scheduled lesson, call (65) 9113 1462 or visit sgsinkorswim.com.

Frequently Asked Questions

What PSI reading typically causes a swim lesson to be cancelled?

There's no single universal cutoff for swim lessons specifically. Standard public health guidance calls for reducing strenuous outdoor exertion at PSI 101 to 200, and avoiding outdoor activity above that, and this generally shapes the judgement a coach applies, alongside the specific pool's own operating decisions.

Is haze as common a disruption as lightning in Singapore?

No, considerably less frequent. Haze is largely seasonal, most associated with the Southwest Monsoon period from June to September, while lightning-related closures can happen year-round given Singapore's frequent afternoon thunderstorms.

Should my child avoid swim lessons entirely if they have asthma and haze is present?

This is worth discussing directly with your coach and, where relevant, your child's doctor. Applying a more conservative personal threshold than the general public guidance is a sensible approach for any child with a respiratory condition.

Does a high PSI reading automatically close ActiveSG pools?

Not necessarily in the same binary way lightning does. Sport Singapore's Haze Management Plan applies graduated guidance across escalating PSI bands, and specific facility decisions can vary. Check the specific pool's current status if conditions are elevated.

What's the difference between the 24-hour PSI and the 1-hour PM2.5 reading?

The 24-hour PSI is a rolling average and the main reference for planning ahead, while the 1-hour PM2.5 reading is used for more immediate, right-now decisions and can spike or fall faster than the 24-hour figure reflects.

Will I get a makeup lesson if haze affects my session?Y

es, on the same terms as any other weather-related disruption, a free makeup lesson with no forms and no penalty fees.

How do I get started?

Book a trial lesson, and tell us about any respiratory health considerations for your child so we can apply the right level of caution during any future haze episodes.

Final Thoughts

Haze is a less frequent but genuinely important factor in outdoor swim lessons in Singapore, particularly during the drier months. Unlike lightning's clear, binary closure trigger, haze decisions involve more judgement, weighing the 24-hour PSI band, the specific intensity of the planned activity, and the individual swimmer's health, particularly for children, who are more vulnerable to air quality issues than healthy adults.

Checking current PSI readings, communicating any health considerations to your coach, and trusting a responsible coach's judgement on borderline days are the best ways to navigate haze season safely without unnecessary anxiety.

If you have questions about how we handle a specific haze episode, or want to flag a health consideration for your child, SG Sink Or Swim is happy to talk it through. You can reach us at (65) 9113 1462 or through sgsinkorswim.com.