WBGT monitoring on site: who needs a meter and how to measure it right
Some sites must measure WBGT with their own calibrated meter; others can use NEA's readings. Here is how to tell, and how to measure properly.
Every heat-stress measure from MOM starts with one reading: the Wet Bulb Globe Temperature (WBGT). It decides how long the rest breaks are, how much water workers need and when vulnerable workers come off outdoor work. If the reading is wrong or missing, everything that depends on it is guesswork.
This guide covers who needs their own meter, what that meter must be able to do, and how to take a reading you can rely on.
WBGT is not the temperature on your phone
Air temperature only tells you how warm the air is. WBGT also takes in humidity, wind and direct sunlight, which is why it is used for heat stress. On a humid, still afternoon in Singapore, the WBGT can sit in a high band even when the air temperature does not look extreme.
Who needs a WBGT meter on site?
MOM requires on-site measurement with a portable WBGT meter for:
- construction sites with a contract value of S$5 million or more
- shipyards
- the process industry
Other workplaces can use the WBGT readings from the National Environment Agency, available in NEA's myENV app. The rule for everyone is the same: check the WBGT every hour during work, especially in the hotter parts of the day.
What the meter has to meet
For sites that must measure on site, MOM's FAQ sets out the minimum specification:
| Item | Requirement |
|---|---|
| Measuring range | 10°C to 50°C WBGT |
| Resolution | 0.1°C |
| Accuracy | ±2°C |
| Calibration | Every year, or as the manufacturer specifies |
| Who calibrates | The manufacturer's authorised supplier, or a SAC-accredited laboratory |
Keep the calibration certificate with your site records. An expired calibration is one of the easiest gaps for an inspector to spot.
How to take a reading that holds up
Where and how you place the meter matters as much as the meter itself.
- Put it where people work, in direct sun, not in the site office or under a shelter.
- Mount it about 1 metre above the ground.
- Let it settle for at least 10 minutes before you note the reading.
- Record the time, the reading and who took it, every hour.
- Act on the band straight away: tell supervisors when the reading moves up, so rest breaks and water rounds change with it.
Make the hourly WBGT check one named person's job on each shift. When "everyone" is responsible, the 2 pm reading is the one that gets missed.
What to do with the reading
The reading only helps if it changes what happens on site. As a quick reminder:
| WBGT | What changes |
|---|---|
| Below 31°C | Baseline measures: water, shade, acclimatisation, monitoring |
| From 31°C | At least 300 ml of water an hour, buddy system, move heavy work to cooler hours |
| From 32°C | At least 10 minutes' continuous rest every hour for heavy physical work |
| From 33°C | At least 15 minutes' rest every hour for heavy work, emergency cooling ready, vulnerable workers off outdoor work |
For the full detail, read what to do at each WBGT level.
How HeatAware helps
For sites that need one, the HeatAware kit includes a calibrated WBGT meter, and yearly renewal covers recalibration by an accredited lab. For other sites, the app shows NEA's WBGT readings. Either way, readings and alerts are recorded, so you have the hourly log ready if anyone asks.
Size your kit to see whether your site needs a meter.
Frequently asked questions
Can we use the myENV app instead of a meter?
Yes, unless your site is a construction project of S$5 million or more, a shipyard or in the process industry. Those must measure on site.
How often does the meter need calibrating?
Every year, or as often as the manufacturer specifies, whichever applies.
Is one reading for the whole site enough?
If work areas are far apart or very different (open deck versus shaded ground floor), take readings where the most exposed work is happening.
General guidance based on MOM's FAQs on Heat Stress Measures for Outdoor Work. Always check the latest official guidance.