Why it matters

Dengue is spread by the Aedes mosquito. A building site is full of places where rainwater sits. One forgotten canvas sheet can breed hundreds of mosquitoes. They bite your workers and the people living around the site.

Dengue can put a worker out for one to two weeks. A severe case can kill. NEA inspects construction sites often and can stop work when it finds repeated breeding.

How Aedes breeds

NEA says an Aedes egg can hatch in less than a day once it meets water. The larva becomes a pupa in about four days. An adult flies out about two days later. So a puddle left for a week can already have produced mosquitoes. This is why checks are weekly.

A female lays about 100 eggs at a time. NEA says the eggs can survive dry conditions for up to about nine months. When rain comes, they hatch. So tipping out the water is not enough. NEA advises wiping the rims of pails as well. Scrub or dry containers and store them upside down.

Aedes bite in the daytime. NEA says biting peaks at dawn and dusk.

Where to look

NEA lists these as places to check every week at construction sites. Use it as your round.

  • Unused containers and building waste around the site, worker quarters and site offices.
  • Building materials, canvas sheets, equipment and machinery.
  • Puddles on the ground and on concrete floors of every upper level and basement.
  • Water drums, tanks and storage containers, and bulk waste bins.
  • Trenches, lift wells and sump pits.
  • Safety barriers, rooftops, roof water tanks and treatment plants.
  • Air-con units and drip trays, inspection chamber covers, steel struts and walers, concrete test cube tanks.

Order of controls

Design the water out first. Treat only what is left.

  • Remove: clear debris and unused containers. Seal unused sinks, toilet bowls and gullies. Deploy stored barriers or keep them dry.
  • Drain: level uneven ground and give it a slope to the drains. Put a sump with an automatic pump at the low point of excavations. Fit gratings so drains do not choke with leaves.
  • Cover and store: keep materials and equipment under shelter. Store steel casings and coring buckets so they cannot fill with rain.
  • Modify: seal exposed brick holes with cement. Drill drain holes in struts and walers, or fill them with sand. Pipe air-con condensate straight to a drain.
  • Treat: apply anti-mosquito oil or an NEA-registered larvicide to water you cannot remove, at least weekly. Rain washes it away, so treat again after wet weather. Use sand granular insecticide in perforated bricks and sump pits.
  • Protect people: workers in mosquito areas wear long sleeves and long trousers. NEA says repellents with DEET, picaridin or IR3535 work best.
Fogging is not prevention

NEA's code says thermal fogging is only for high adult mosquito numbers or disease near the site, and only by a licensed operator. Routine fogging does nothing about the larvae in your puddles.

Run a weekly programme

NEA's code of practice for site Environmental Control Officers suggests splitting the site into zones, one for each working day. On a six-day week you have six zones. An in-house team covers one zone a day, so the whole site is checked every week.

Check upper floors as they are built. New slabs hold water before anyone thinks to look. Put upper-floor checks in the vector control contract.

Report every find to the site supervisor so the cause is fixed, not just the water. Keep records of each round and each service report from the vector control operator. If the operator's work is poor, replace them.

Dengue in your workers

The WHO says symptoms usually start 4 to 10 days after a bite. Watch for sudden high fever, a bad headache, pain behind the eyes, muscle and joint pain, nausea and rash.

Tell workers with these signs to see a doctor early and to report it. Do not let them take aspirin or ibuprofen on their own; the WHO says these raise the risk of bleeding. A sick worker should use repellent so mosquitoes do not pick up the virus from them.

Danger signs often come as the fever drops. They include severe stomach pain, constant vomiting, fast breathing, bleeding gums or nose, and blood in vomit or stools. Get that worker to hospital at once.

What the rules require

In Singapore, the Control of Vectors and Pesticides Act makes it an offence to allow conditions that let mosquitoes breed. NEA's code of practice for ECOs lists the penalty under section 15 as a fine of up to $5,000, jail of up to 3 months, or both, for a first offence. Repeat offences carry up to $10,000 and 6 months.

  • Environmental Control Officer: NEA requires a part-time ECO on sites with a contract sum above $10 million up to $50 million, for at least 15 hours a week. Above $50 million, a full-time ECO is needed for at least 40 hours a week. Source: NEA.
  • Vector control operator: the ECO code says the occupier must engage an NEA-registered vector control operator. The service must start at the beginning of the project and run at least once a week.
  • Programme: the ECO and the occupier must draw up and carry out a vector control programme that covers each stage of the project.
  • Enforcement: NEA can issue Stop Work Orders. From July 2020, NEA set composition sums for construction sites at $3,000 for a first breeding offence and $5,000 for a second. From the third, the case goes to court. Source: NEA.
Small sites are not exempt

A site under $10 million needs no ECO. The duty not to let mosquitoes breed still applies to every premises under the Control of Vectors and Pesticides Act.

Common mistakes

NEA keeps finding the same things on sites.

  • Checking the ground floor but not the upper slabs and basements.
  • Canvas sheets left folded with water in the creases.
  • Oiling puddles once and not again after rain.
  • Relying on fogging instead of removing water.
  • Leaving air-con units and drip trays outdoors with water inside.
  • Forgetting the worker quarters, site offices and canteen.

Use it on site: the dengue and vector control on worksites checklist and the toolbox talk to brief your crew.

Sources

  1. Mosquito control in construction sites, National Environment Agency.
  2. Code of Practice for Environmental Control Officers for Specified Construction Sites (5th edition), National Environment Agency.
  3. Environmental Control Officers for Specified Construction Sites, National Environment Agency.
  4. NEA to impose heavier penalties from 15 July 2020 for repeated mosquito breeding offences, National Environment Agency.
  5. Aedes mosquito, National Environment Agency.
  6. Dengue cases, National Environment Agency.
  7. Dengue and severe dengue, World Health Organization.

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.