Some mornings the skyline simply is not there. The tower cranes across the road fade to grey outlines, the air has that faint burnt smell, and the crew arriving at seven can already feel it at the back of the throat. Work is scheduled, the programme is tight, and somebody has to decide what happens next.

That decision gets made badly when it is made on the spot. Haze arrives with enough warning to plan for, the guidance in Singapore is unusually clear about what to do at each level, and the difference between a site that copes and one that improvises is almost always preparation done weeks earlier.

Two haze numbers, and which one to plan with

Singapore publishes two figures during a haze episode, and mixing them up leads teams to the wrong conclusion. The 24-hour Pollutant Standards Index (PSI) is the forward-planning number. It is smoother, less volatile, and the National Environment Agency (NEA) recommends it for individuals, institutions and companies making decisions ahead of time.

The second figure is the 1-hour PM2.5 reading, which tracks fine particulate matter and moves much faster. Its value is immediacy, telling you what the air is doing right now, which helps when deciding whether to pause a specific activity this afternoon.

The 24-hour PSI bands NEA publishes run from Good at 0 to 50, through Moderate at 51 to 100, Unhealthy at 101 to 200, Very Unhealthy at 201 to 300, and Hazardous above 300. Those band names carry specific advice, and the NEA guidance on air pollution is where the current position should always be checked, since advisories are updated as conditions change.

What the advisory asks of outdoor work at each band

The public health advisory is keyed to the 24-hour PSI and uses three deliberately different verbs. Read them precisely, because "reduce", "minimise" and "avoid" carry different instructions and are not interchangeable.

The employer's side of the same table

Employers work to a parallel set of expectations that starts earlier than the public advisory does. This is the same duty of care that runs through the Workplace Safety and Health Act and that our construction safety courses build on, since the obligation to take reasonably practicable measures does not pause because the hazard arrived on the wind. The Ministry of Manpower (MOM) guidelines on protecting employees from haze put a proper risk assessment at the centre, weighing the severity of the haze against the PSI reading, the health conditions of the employee, and their level of activity. Below a PSI of 100 the expectation is preparatory measures, and above it the restrictions tighten band by band.

Vulnerable workers get separate treatment throughout. Elderly and pregnant employees, and those with chronic lung or heart conditions, face more restrictive limits at every band, and MOM suggests flexible arrangements such as telecommuting or staggered hours where the role allows it.

Masks are a control, not the control

Mask guidance is where employers and the general public diverge, and following the wrong one leaves a site exposed. Public advice concerns N95 use mainly at hazardous levels. MOM's employer guidance sets a lower trigger, strongly urging masks where prolonged or strenuous outdoor work cannot be avoided in the 201 to 300 band.

There are limits to what the mask does. MOM notes that an N95 carries a protection factor of 10 and may not give sufficient respiratory protection at very high readings, and points to respirators with a higher protection factor for prolonged outdoor work in the most severe conditions. A mask handed out at the gate is not a completed control.

Fit and training are explicit employer duties. Employees who need masks or respirators must be fit-tested, sufficient stock must be available, training must be conducted and supervision provided so they are worn correctly. Workers with chronic heart or lung conditions, and elderly or pregnant workers, should speak to a doctor before using one. The Workplace Safety and Health Council's guidelines on preparing for adverse weather go further and suggest holding at least a week's supply of N95 masks as part of a haze business continuity plan.

The controls that work before a mask does

Reaching for respiratory protection first is the common mistake, because the measures that reduce exposure in the first place do more and cost less.

• Mechanical aids substituted for manual work wherever the task allows
• Job rotation, so no individual carries a long continuous stretch outdoors
• Rest breaks taken indoors or in enclosed, filtered spaces
• Hydration made easy and constant, with water stationed close to the work
• Health monitoring, with workers actively encouraged to report symptoms early

Haze rarely arrives alone

Haze season overlaps with the conditions that already make outdoor work in Singapore demanding, and the two hazards compound. A worker in a mask, in humid heat, doing physical work will fatigue faster than either factor alone would suggest, and the early symptoms of heat illness overlap uncomfortably with the throat and chest irritation haze produces.

MOM's heat stress measures for outdoor work run in parallel, built around Wet Bulb Globe Temperature bands with their own requirements for acclimatisation, hourly monitoring, rehydration and rest breaks. Supervisors who can recognise the signs of heat injury on a construction site will spot the compounded version faster, which is exactly the version that appears during a haze episode.

Talking to the crew

None of this lands unless the crew understands it. Many workers on Singapore sites are reading and listening in a second language, and a printed advisory pinned to a noticeboard does very little.

Short toolbox briefings work better. Say what today's reading is, what it means for the tasks on the programme, who has been moved and why, and what a worker should do if they start feeling breathless or their chest tightens. Repeat it daily while the episode lasts, because the numbers change.

The other half is permission. Workers need to hear clearly that reporting symptoms will be met with a sensible response and not an argument, and that stopping a task because the air has worsened is a decision the site backs. A crew that believes that will tell you early, which is the whole point.

Conclusion

Haze episodes are one of the few workplace hazards that announce themselves in advance. The sites that handle them calmly have already decided who watches the readings, what happens at each band, where the masks are and who has been fit-tested, and which activities get moved first. Everything after that is just following the plan.

If your supervisors would benefit from working through that thinking properly, we can help. Wong Fong Academy has trained Singapore's construction and industrial workforce since 2011, and our courses are delivered by people who have spent time on sites in exactly these conditions. Browse the programmes and sign up today so your team is ready before the next episode.

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