Why it matters

Singapore has lightning on about 176 days a year, roughly one day in two. NEA's Changi station records this. The WSH Council calls Singapore's lightning density among the highest in the world. A strike on an open site can kill.

Storms bring more than lightning. Strong wind lifts loose sheets and tips over barriers and bins. Heavy rain floods basements and collapses trench walls. Scaffolds, cranes and gondolas can fail. Weather turns fast here, so the plan must be ready before the sky darkens.

Know the season

The Meteorological Service Singapore describes four periods. Each brings a different risk to plan for.

  • Northeast Monsoon, December to early March: the early part brings monsoon surges with long spells of heavy rain. The later part is windy and drier.
  • Inter-monsoon, late March to May: light winds, hot afternoons and afternoon or early evening thunderstorms, sometimes severe.
  • Southwest Monsoon, June to September: Sumatra squalls can bring gusts of 40 to 80 km/h, usually from before dawn to midday.
  • Inter-monsoon, October to November: afternoon and evening thunderstorms again, and usually wetter than the first.

Watch the weather

Subscribe to NEA's myENV app alerts for your site. It sends lightning, rainfall, heat stress and air quality alerts. A lightning alert fires when cloud-to-ground lightning is detected within 6 km of your chosen location. It also fires when thundery showers are forecast there in the next two hours.

Name one person on each shift who watches the alerts. Set up a way to reach every worker fast: radio, siren or loudhailer. The WSH Council also suggests portable lightning detectors on site. No detector catches the first strike, so watch the sky as well.

Lightning: stop and shelter

The WSH Council rule is simple. Stop outdoor work once thunder is heard or lightning is seen. Thunder means lightning is close enough to strike you.

Send workers to the nearest building or lightning-protected shelter. Tell them where it is before the storm. Sheds, tents and open-sided rest areas do not protect against lightning. A hard-topped metal vehicle with windows up is the fallback if no building is near.

Keep away from isolated trees, lamp posts, cranes, scaffolds and rooftops. Stay off ladders and away from fencing and metal pipes.

US OSHA and NOAA advise staying in shelter for at least 30 minutes after the last thunder. Restart only when that time has passed.

Do not start what you cannot stop

If storms are building, do not begin a lift, a concrete pour or work at height that cannot be made safe in a few minutes.

Strong winds

The WSH Council adverse weather guidelines link wind speed to what happens on site. Around 39 to 49 km/h, workers can be thrown off balance and flat sheets act like sails. Above 60 km/h, unsecured materials fly and heavy objects tip.

  • Stop all outdoor work once wind passes 60 km/h.
  • Stop boom lifts and scissor lifts above 45 km/h, or the maker's limit if lower. Park them in a set safe spot before the limit is reached.
  • Stop non-guided gondolas above 50 km/h, or the maker's limit if lower. Ground and secure them first.
  • Follow the maker's limits for tower cranes. The guidelines say these are typically 72 km/h in service and 151 km/h out of service.
  • Take down banners and sheeting that catch the wind. Stow or tie down loose materials.
  • Give workers safety glasses against wind-blown dust and debris.

Heavy rain and flooding

Rain soaks into soil and weakens trench walls and slopes. Water runs downhill into basements, tunnels and pits.

The guidelines say to stop work and get everyone out of underground and low-lying areas unless they are protected against flooding. Shore excavations properly. Add tie-backs to temporary structures so water cannot carry them away. Teach workers about the hazards that remain after a flood, such as live cables in standing water.

Make a response plan

The guidelines ask each workplace to plan for its own risks. Deal with temporary structures and equipment in this order.

  • Dismantle and remove what you can before its limits are reached.
  • Lower and secure what you cannot remove, with extra tie-backs, props or storm anchors.
  • Communicate and clear the collapse zone around anything left standing. Keep people out of it.
  • Name who does what, including specialist contractors such as crane contractors.
  • Plan for workers who need help to evacuate.
  • Keep an adverse weather kit with first aid, an AED, torches and radios. Phone lines may fail.
  • Share the plan with contractors. Drill it.

What the rules require

MOM says the WSH Council's adverse weather guidelines are not mandatory. But the WSH Act still applies. Employers and occupiers must keep workers safe, including by planning for emergencies. MOM says it will check workplaces and take action against those who are culpable. Source: MOM.

The guidelines spell out the duties. Occupiers must keep the workplace, its access routes and its equipment free of risk. Employers and principals must have emergency procedures. Workers must follow the safety rules in place. Weather belongs in your risk assessment under the Risk Management Regulations.

Share the plan with contractors

The WSH Council says occupiers should share their adverse weather plan with contractors and involve them in writing it. Contractors and their workers should follow it when it is triggered.

After the storm, and common mistakes

Check before you restart. Do not use damaged machinery or equipment. Ask the supplier for a checklist if you are unsure. Drain waterlogged areas. Check the ground for movement. Inspect scaffolds and other temporary structures. If anything looks unstable, keep the area closed. Workers must report unsafe conditions to their supervisor straight away.

  • Sheltering in a tool shed, tent or open-sided rest area during lightning.
  • Going back out the moment the rain eases while thunder is still near.
  • Leaving a MEWP raised or a gondola hanging as the wind picks up.
  • Keeping workers in a trench during a downpour.
  • No one on the shift watching the alerts.
  • Restarting without inspecting scaffolds, cranes and excavations.

Use it on site: the lightning, monsoon and severe weather checklist and the toolbox talk to brief your crew.

Sources

  1. WSH Guidelines on Preparing for Adverse Weather, WSH Council.
  2. WSH Guidelines on Preparing for Adverse Weather (press release), Ministry of Manpower.
  3. Preparing for Adverse Weather Events, WSH Council.
  4. Written reply to PQ on lightning alert system, Ministry of Sustainability and the Environment.
  5. Climate of Singapore, Meteorological Service Singapore.
  6. Lightning Safety When Working Outdoors, US OSHA and NOAA.

This is practical guidance, not legal advice. Laws and codes of practice change; always check the current official text and your site's own procedures.