ULV Cold Fogger Droplets of 15–30 Microns: Why This Number Decides Indoor Mosquito Control, Explained for Public Health Officers and Mayors Alike

This article is written so that two very different readers end up understanding the same thing. One is the public health technical officer who wants evidence-based reasons. The other is the mayor, subdistrict chief or municipal clerk who must approve the budget for a mosquito sprayer used inside schools, child development centers, offices and health facilities. Our example is the AIROFOG U260, a German-made electric ULV cold fogger.

Executive summary (1-minute read)

• The problem: Buildings get sprayed, yet mosquitoes remain, floors are wet, desks are sticky and teachers complain. A commonly overlooked cause is the wrong droplet size.
• The simple rule: Large droplets fall to the floor fast and miss the mosquitoes. Right-sized small droplets hang in the air, meet flying mosquitoes more often and use less chemical.
• The solution: Use a ULV sprayer that produces droplets of about 15–30 microns for indoor work.
• Why the AIROFOG U260: Made in Germany, 800 W electric motor, adjustable nozzle, 15–30 micron droplets, designed for hospitals, laboratories and high-safety sites.
• Next step: Call 065-556-6294 or LINE @whd268 for specifications and a quotation, request an indoor demonstration, then budget by the rules.

We Sprayed the Whole Building. Why Are the Children Still Being Bitten? (illustrative scenario)

Napaporn is a public health technical officer at a subdistrict municipality in northern Thailand. Early in the school term, two pupils at a municipal school fall ill with dengue. The mayor orders every classroom sprayed before Monday, so on Saturday the team takes its existing sprayer through all three floors.

On Monday morning, class teachers post photos to the executives' LINE group. There are rings of solution on the floors, desks are sticky, and notebooks left on desks are stained. Some parents worry their children will touch the chemical. Worse, by the afternoon teachers can still see mosquitoes under desks and behind storage cabinets.

The mayor calls a meeting and asks directly: "We sprayed, so why are the mosquitoes still here, and why is the room such a mess?" Napaporn inspects the machine and finds a worn nozzle. The droplets coming out look more like a shower head than a fine mist. Most of the solution lands on floors and desks within seconds instead of hanging in the air to meet mosquitoes flying or resting in dark corners.

The team did not skip any rooms. The problem was droplet size, a small number many agencies never write into their equipment specifications. This article explains why 15–30 microns matters and why leaders should ask about it every time they approve an indoor sprayer.

Understanding "Microns" in 3 Minutes, for Leaders

Picture it this way. A human hair is roughly 50–100 microns thick, depending on the person. A droplet of 15–30 microns is therefore several times thinner than a hair. When sprayed, it looks like a light mist, not drops of water.

An everyday comparison. Turn on a shower and the water falls as big drops that hit the floor immediately. Press a facial mist spray and the droplets hang in the air for a moment before fading. Indoor mosquito spraying needs the second kind: solution that stays airborne long enough to meet flying mosquitoes.

The takeaway for leaders: when your team proposes an indoor mosquito fogger, ask one question: "What droplet size does it produce, in microns, and can it be adjusted?" If nobody can answer, that is a warning sign.

What Wrong-Sized Droplets Cost an Agency

1. The health of children, patients and staff

Aedes mosquitoes carry dengue, chikungunya and Zika, and they like to rest indoors in dark corners, under desks, behind curtains and inside wardrobes. Dengue brings high fever, headache and muscle pain, and some patients go into shock as the fever falls. Those most at risk, including children, older adults, people with chronic illness and pregnant women, are often found in buildings local governments manage: schools, child development centers and health facilities. If droplets never reach the mosquitoes hiding indoors, the risk to these groups stays the same.

2. Insecticide budget lost to the floor

Solution that lands on floors and desks does nothing to flying mosquitoes. Part of the chemical budget is spent without effect, and staff time is then spent cleaning up. A machine with the right droplet size makes every drop work harder.

3. Image and trust among parents and residents

Photos of wet classrooms and sticky desks make an agency look unprofessional, however good its intentions. By contrast, a light mist that leaves no residue, combined with clearly communicated safety steps, builds real confidence.

4. Complaints and social media

One photo of residue on a school desk in a parents' group can keep a leader explaining for a week. Choosing equipment suited to indoor work from the start prevents the problem at its source.

5. Staff workload

When spraying fails, the team must return to re-spray, clean rooms and answer questions from teachers and parents. A one-day job stretches into several. The right machine removes that duplicated work.

Why 15–30 Micron Droplets Suit Indoor Spraying, Explained Simply

Point 1: small droplets stay airborne longer. Basic physics tells us that larger droplets fall much faster than smaller ones. Visible drops reach the floor within moments, while droplets of a few tens of microns stay suspended far longer, giving them time to meet mosquitoes flying in the room.

Point 2: mosquitoes are small, so droplets must be small enough to meet them. Space spraying is not meant to coat surfaces. It aims for droplets to contact the body and wings of mosquitoes flying through the mist. Many small droplets spread throughout a room have a far better chance of meeting a mosquito than a few large ones.

Point 3: the same amount of solution makes many more droplets. Break a given volume into small droplets and you get many times more droplets than if you break it into large ones. That is why a ULV system uses little solution yet covers a whole room.

Point 4: no wet residue on surfaces. Small airborne droplets do not pool into wet spots on desks or floors the way large droplets do, so rooms stay cleaner and occupants worry less.

Point 5: not so small that the effect is lost. Droplets that are far too small may drift out of the target area or evaporate before reaching a mosquito. The 15–30 micron range balances long hang time with enough active ingredient per droplet for indoor work.

General vector control literature agrees that space spraying against adult mosquitoes should use small droplets in the range of a few tens of microns. Readers who want detail can consult materials from the Department of Disease Control and the World Health Organization.

Why the Usual Indoor Approach Falls Short

Old machines with worn nozzles. A worn or partly blocked nozzle quietly produces larger droplets. The machine seems to work, but performance drops sharply.

No droplet adjustment. A small room, a hall and a corridor need different settings. A fixed machine performs well in only some of them.

Thermal foggers in closed rooms. A thermal fogging machine is excellent outdoors and in drains, but thick smoke in a closed room can alarm occupants and demands more care with heat and safety. For indoor work, electric ULV sprayers are the usual choice.

Wrong timing and procedure. Leaving doors and windows open, not waiting the label time before ventilating, or spraying while people are inside all reduce effectiveness and raise risk.

Cheap machines with no stated droplet size. Some models never state droplet size in their documents, so buyers do not know what they are getting and have no basis for acceptance testing.

No training or after-sales service. Operators do not know how to adjust the nozzle or clean the machine, and when it breaks there is no technician.

The Solution: AIROFOG U260 ULV Cold Fogger With 15–30 Micron Droplets

The AIROFOG U260 is an electric ULV sprayer made in Germany, designed for places that demand precision and high safety, such as hospitals and laboratories. Its key facts:

• Made in Germany, a country known for machine engineering.
• 800 W electric motor, plugs into a standard indoor outlet with no engine exhaust.
• Adjustable nozzle to suit room size and the task.
• 15–30 micron droplets, a range that stays airborne well and suits indoor spraying.
• Built for high-safety sites, including hospitals, laboratories and buildings with vulnerable occupants.

For local governments responsible for schools, child development centers, offices and health facilities, the U260 is government mosquito control equipment that answers every concern a leader has: effective against mosquitoes indoors, no wet residue, and tidy electric operation. Supplied by World Health Disinfection, which holds ISO and GMP standards, every unit passes 100% quality control before delivery, with technicians, spare parts and full after-sales service, meeting Thai government equipment standards.

Where the U260 Fits in a Local Government Toolkit

No single machine does every job. A well-equipped local government usually combines a vehicle-mounted unit or thermal fogging machine for streets, drains and open community spaces, a backpack sprayer for lanes and backyards, and an electric ULV unit such as the U260 for the inside of public buildings. Each tool covers a gap the others leave. When outdoor fogging and indoor spraying are scheduled together around a case, mosquitoes have far fewer places to escape to, and residents see a coordinated response rather than a one-off visit. Planning the toolkit this way also makes budget requests easier to justify, because each purchase is tied to a clearly defined task.

What the Leader Gains

For the Public Health Team: The Technical View

• Purpose of indoor spraying: rapidly reduce adult mosquitoes resting inside buildings, especially after cases at a school or facility. Always combine it with larval surveys, breeding-site removal and the Department of Disease Control's "3 Keeps to prevent 3 diseases" campaign.
• Droplet size: 15–30 microns helps droplets hang in the room and reduces surface deposit. Check nozzles regularly, because wear makes droplets larger.
• Indoor procedure: remove people and pets, cover food and sensitive equipment, close doors and windows, spray from the far end of the room back toward the door, keep the room closed for the time on the product label, then ventilate before re-entry.
• Priority spots: under desks, behind cabinets, curtains, dark corners, storerooms and bathrooms, all favored resting places of Aedes mosquitoes.
• Chemicals: use registered products labeled for indoor use, mix according to the label and record type and quantity.
• Operator safety: wear a mask, goggles, gloves and long sleeves; check the cable and plug before every use.

10 Reasons to Choose the AIROFOG U260 for Indoor Work

1. 15–30 micron droplets hang in the air and meet flying mosquitoes more often.
2. No wet residue on desks, beds or documents, so fewer complaints from occupants.
3. Less solution thanks to ULV, which turns a small volume into countless droplets.
4. An 800 W electric motor that runs from an indoor outlet with no engine exhaust.
5. An adjustable nozzle for classrooms, meeting rooms, corridors or wards.
6. German manufacture with engineering suited to long service.
7. Designed for high-safety sites. Trusted in hospitals and laboratories, so you can be confident using it in schools and child centers.
8. Multiple missions, from vector control to indoor insect control with suitable products.
9. Clear figures for specifications, making it easy to write requirements and run acceptance tests.
10. Technicians, parts and after-sales service from ISO and GMP certified WHD. For buildings without outlets, also see the cordless AIROFOG AIROSTAR, and find full details on the AIROFOG U260 product page.

Before and After Paying Attention to Droplet Size

5 Questions a Mayor Should Ask Before Signing

1. "What droplet size does it produce, and can it be adjusted?" Expect a clear figure from product information, not just "very fine."
2. "Electric or engine, and is it suited to closed rooms?" Indoor work calls for a machine suited to enclosed spaces and vulnerable occupants.
3. "If it breaks, who fixes it and how long does it take?" The supplier should have local technicians and parts.
4. "How will our staff be trained?" Training in indoor procedure, nozzle adjustment and safety should be part of the purchase.
5. "Which buildings will we use it in over the year?" Sharing one machine across schools, child centers, offices and health facilities multiplies its value.

Procurement Tips for an Indoor Sprayer

Leaders can forward this table to their public health, education and procurement units. It is general guidance; adapt it to the rules your agency follows.

Thinking about value: consider the number of buildings and rooms served each year, solution saved when less falls to the floor, reduced cleaning labor, fewer repeat visits and working life with after-sales support, rather than purchase price alone.

One-Page Checklist to Forward Before Any Indoor Spraying

• ☐ Notify teachers, parents or occupants of the date and time in advance
• ☐ Remove people, children and pets before spraying
• ☐ Store or cover food, drinking water containers and toddlers' toys
• ☐ Check the nozzle and cable; adjust for a fine mist
• ☐ Close doors and windows; spray from the far end back to the door
• ☐ Keep the room closed for the label time, then ventilate
• ☐ Photograph before and after; record product type and quantity
• ☐ Clean the machine after use and store it dry and secure
• ☐ Survey larvae around the building and deal with water containers

Next Steps in 3 Moves

1. Call or LINE for a quotation and specifications. Phone 065-556-6294 or LINE @whd268 and say which kinds of buildings you need to treat.
2. Request a demonstration and training. Ask for a demo in one of your own rooms so leaders can see the mist with their own eyes.
3. Budget and procure by the rules. Use the droplet size and motor figures in your specification and acceptance criteria.

Example Field Perspective

"We never used to think about droplet size. We assumed that if something came out of the machine, that was enough. Once we saw a demonstration in a real classroom, everyone understood immediately. Our old machine sprayed drops that landed on the desks. The fine-droplet machine made a light mist that floated across the room and slowly faded. When we reopened the room after the waiting time, the desks were not sticky and teachers did not have to wipe everything down. The mayor, who came to watch, said an hour of explanation would not have been as clear as seeing it."

Note: a composite perspective based on typical field work, not a quote from any specific person or agency.

Frequently Asked Questions

Q: What is a micron, and how small is 15–30 microns?
A: A micron is one thousandth of a millimeter. A human hair is roughly 50–100 microns thick, so 15–30 micron droplets are several times thinner and look like a light mist.

Q: Why are small droplets better than large ones indoors?
A: Small droplets stay airborne longer and so meet flying mosquitoes more often. Large droplets fall fast, waste solution and leave residue.

Q: Is smaller always better?
A: No. Droplets that are far too small may drift away or evaporate before reaching a mosquito. The 15–30 micron range is a sensible balance for indoor work.

Q: What power does the U260 need?
A: It is electric, with an 800 W motor, and runs from an indoor outlet. Check cables and connections before each use.

Q: Can it be used outdoors?
A: It is intended mainly for indoor work. For wide outdoor areas, consider a thermal fogger such as the AIROFOG AT35 or a vehicle-mounted unit.

Q: How long before people can re-enter?
A: It depends on the product used. Follow the label strictly and ventilate before re-entry.

Q: How can we tell the machine is still producing the right droplet size?
A: Watch the mist: it should stay fine and should not leave drops on surfaces. Clean and inspect the nozzle as the manual describes, and have a technician check the machine on a regular schedule, especially before the rainy season.

Make Indoor Spraying Work With the Right Droplet Size

Request specifications, a quotation and an AIROFOG U260 demonstration in your own building.

See U260 Product and Price, Click Here

Phone 065-556-6294 · LINE @whd268 · worldhealthdisinfection@gmail.com

Browse the Government Mosquito and Insect Control Equipment Hub

World Health Disinfection Co., Ltd., 88 268 Kanlapaphruek Road, Bang Khae, Bangkok 10160

Related Links

• Government mosquito and insect control equipment hub
• AIROFOG U240 ULV cold fogger
• MASTER ELECTRIC ULV fogger
• Department of Disease Control, Ministry of Public Health
• WHO fact sheet: Dengue and severe dengue