MOM heat stress measures for outdoor work: what to do at each WBGT level
MOM ties its heat-stress measures to the WBGT reading. Here is what applies below 31°C, from 31°C, and from 33°C, in plain language.
If your workers spend most of the day outdoors without permanent shade, the Ministry of Manpower (MOM) expects you to manage heat stress under the Workplace Safety and Health (WSH) Act. The responsibility sits with the employer and the occupier of the worksite.
MOM's heat stress measures are built around one number: the Wet Bulb Globe Temperature (WBGT). As the WBGT goes up, more measures apply. This guide walks through each band so your site team knows what to do when the reading changes.
What WBGT is, and why it matters
WBGT is a heat-stress index. Unlike the air temperature on a weather app, it also accounts for humidity, wind and direct sun. That makes it a far better guide to how hard the body is working to stay cool on an open worksite.
You need to check the WBGT every hour during outdoor work. Some sites must measure it on site with their own meter:
- construction projects worth S$5 million or more
- shipyards
- the process industry
Other sites can use the WBGT readings published by NEA.
Measures that apply at every WBGT level
These are the baseline. They apply even on a mild day, below 31°C WBGT.
| Measure | What it means on site |
|---|---|
| Acclimatisation | New or returning workers build up their heat exposure over at least 7 days |
| WBGT monitoring | Check the reading every hour |
| Hydration | Cool drinking water close to where people work, and regular water breaks |
| Rest and shade | Shaded areas to recover in, set up near the work where possible |
| Emergency response | A heat-illness emergency plan and a way to report incidents |
| Vulnerable workers | Know who is at higher risk, and have a plan to redeploy them |
When WBGT reaches 31°C
Everything above still applies, plus:
- Drink at least 300 ml of water every hour, and more for heavier work.
- Move strenuous work to cooler hours where you can, such as early morning.
- Watch workers closely, and pair them up in a buddy system so someone notices the early signs of heat illness.
- Improve airflow with fans or air coolers, and encourage loose, light-coloured clothing.
From 32°C WBGT, workers doing heavy physical work need a rest of at least 10 minutes every hour, in the shade.
When WBGT reaches 33°C
This is the highest band. On top of all the measures above:
- Rest breaks go up to at least 15 minutes every hour for heavy physical work, and longer as the WBGT keeps rising.
- Emergency cooling must be ready on site: cold water, ice packs or water spray, kept in cooler boxes where needed.
- Vulnerable workers should be moved off outdoor work.
- The buddy system is essential, so heat illness is spotted early.
A simple rule for supervisors: every time the hourly WBGT reading moves into a new band, check that the rest schedule, water and cooling supplies match it.
Who counts as a vulnerable worker?
MOM lists several groups at higher risk from heat. These include workers who:
- are 65 or older
- are pregnant
- are overweight
- are new to outdoor work, or have not finished acclimatising
- are returning after more than a week of leave
- are unwell, or have a chronic condition, take certain medication, or have had heat illness before
MOM notes that this list is not complete. When in doubt, ask a doctor whether the worker is fit for hot outdoor work.
Putting it into practice
The measures are clear on paper. The hard part is having everything ready on the day: water stations within easy reach of each work area, a shaded rest spot, a working WBGT reading every hour, and cooling supplies that are actually cold when someone needs them.
A practical starting point:
- Check your site against all the measures, not just the obvious ones. Training records and emergency plans are easy to miss.
- Size water and rest areas by work area, not by site entrance. Workers should not have to walk far to drink or cool down.
- Make the hourly WBGT check someone's named job, with a record of each reading.
- Brief supervisors on the bands, so they know when to lengthen breaks or stop heavy work.
HeatAware can help with this. Size your kit in three steps and take the 17-point readiness check to see which measures your site already covers.
Frequently asked questions
Do the measures apply to every outdoor job?
They apply to outdoor work done mainly in the open without permanent shade, which covers most construction, shipyard and many maintenance sites.
Is the weather app temperature enough?
No. MOM's measures use WBGT, which also reflects humidity, sun and wind. A day that feels moderate can still reach a high WBGT band.
Do I need my own WBGT meter?
Only if your site is a construction project of S$5 million or more, a shipyard or in the process industry. Other sites can use NEA's WBGT readings.
This article is general guidance based on MOM's Heat Stress Measures for Outdoor Work. Always check the latest official guidance and your own risk assessment.