The morning Teacher Nok was afraid to open the door

(A typical scenario based on situations we see often; names and details are illustrative.)

Teacher Nok looks after about forty children aged two to five in a subdistrict child development centre in Bang Ban, Phra Nakhon Si Ayutthaya. The centre is a single-storey building beside a canal road. Every rainy season, families in the area move their belongings up to higher shelves and wait for the Chao Phraya to settle. This year the water came faster than anyone expected. Tea-coloured floodwater rose almost to the classroom window sills and stayed there for nearly three weeks.

When the water finally drained away, Nok and a group of volunteer parents shovelled out the mud and scrubbed the floors until they were soaked in sweat. Plastic toys went into buckets of cleaning solution and then out into the sun. The soaked nap mats were piled behind the building. The rooms looked dramatically better. Yet four or five days later, Nok noticed things that made her stomach drop. Tiny black dots appeared on the lower wall behind the bag shelves. A yellow ring spread across the ceiling board in the corner of the nap room. The wooden bookcase full of picture books smelled so musty that she closed its doors to contain it. And every morning, the moment she unlocked the room, a wave of rotten-mud and damp odour greeted her before any child could.

Meanwhile, the parents' LINE group was filling up. "When will the centre reopen?" "Is the room safe yet? My son has allergies." "I heard kids at the next subdistrict's centre got diarrhoea after it reopened." Nok read every message and had no confident answer. Deep down, she was not sure that a room that looked clean was clean enough for toddlers who crawl on the floor, sleep on mats and put everything in their mouths.

This scene is not unique to Ayutthaya. It repeats itself in nurseries, kindergartens and primary schools across Pathum Thani, Nonthaburi, Sukhothai, Ubon Ratchathani, Chiang Mai and Hat Yai whenever a major flood hits. For school leaders, the real question is not simply "when can we reopen?" but "how do we reopen so that children are genuinely safe?" This guide walks through the hidden germs, the impacts that are easy to underestimate, the common fixes that fall short, and where professional ozone disinfection fits in as the final step before the children come back.

What is waiting for children in a classroom after the water recedes?

Floodwater that has passed through streets, drains, septic tanks, animal pens and rubbish heaps does not just leave mud behind. It leaves a mixed population of microorganisms clinging to every surface it touched. Once the water is gone, Thailand's warm temperatures and high humidity turn a damp building into an incubator. These are the main groups to understand.

1. Mold: the silent problem in walls, ceilings and mats

Common post-flood molds such as Aspergillus, Penicillium and various black molds can begin to grow on wet materials within one to two days. The WHO and US CDC therefore advise cleaning and drying flooded buildings within 24 to 48 hours wherever possible. In schools, mold favours the lower section of gypsum or plastered walls, ceiling boards that absorbed moisture, foam nap mats, carpets in reading corners, particle-board cupboards, bookshelves and fabric toy bins. Mold spores are small enough to stay airborne for a long time, and children napping on the floor breathe at exactly the height where concentrations tend to be highest.

For young children, spores are a powerful allergy trigger: sneezing, runny or blocked noses, itchy red eyes, skin rashes and, most worrying, asthma flare-ups. A child whose asthma was well controlled may suddenly start coughing at night and wheezing badly enough to need a hospital visit.

2. Gut viruses and bacteria from contaminated water

Floodwater is frequently contaminated with sewage from toilets and septic tanks. That means gut pathogens such as E. coli, Salmonella and Shigella bacteria, and viruses such as rotavirus and norovirus, which are leading causes of diarrhoea in young children. These germs settle on floors, table legs, door frames, taps and any toy that sat underwater. Preschoolers who are still learning to wash their hands properly, and who constantly put fingers in their mouths, pick them up easily. Symptoms include watery diarrhoea, vomiting, stomach pain and fever. The real danger is dehydration, which develops much faster in small children than in adults.

3. Infections that spread quickly among children

A childcare centre is a place where children stay close together all day. They eat at shared tables, nap side by side and pass the same toys around. Infections that spread through touched surfaces and droplets, such as hand, foot and mouth disease (caused by enteroviruses), colds and other respiratory infections, can move through a group rapidly. After a flood, many children are also run-down from staying in temporary shelters, sleeping irregularly and eating less balanced meals. A room that is still damp and stuffy only helps germs persist on surfaces for longer.

4. Leptospirosis: a risk for teachers and volunteer parents

During the clean-up, adults who wade through water or mud without rubber boots risk leptospirosis, often called "rat urine disease" in Thailand. The bacteria can enter through cuts or skin that has been soaked for a long time. Typical signs are a sudden high fever, headache and severe pain in the calf muscles. Any teacher or volunteer who develops these symptoms after helping with the clean-up should see a doctor immediately and mention that they waded through floodwater. Do not wait for it to pass.

Who in a school is most at risk?

• Children under five, whose immune systems are still developing, who breathe faster and who spend the most time close to the floor.
• Children with allergies, asthma or chronic conditions, such as congenital heart disease, or those on immune-suppressing medication.
• Pregnant teachers, who should avoid heavy mud removal and strong chemicals.
• Older teachers, caretakers and anyone with a chronic illness such as diabetes or lung disease, who catch infections more easily and recover more slowly.
• Kitchen staff, because a contaminated kitchen can expose every child through a single meal.

The impact goes far beyond a dirty classroom

It is tempting to treat post-flood problems as ordinary housekeeping. For a school, however, the ripple effects are wide.

Health

When one child develops diarrhoea, the infection can reach classmates within days. A cluster outbreak in a childcare centre can force a second closure. Some children may need hospital care for dehydration, while those with allergies may wheeze for weeks, which directly affects their sleep, appetite and development.

Budget

Most local child development centres run on limited municipal budgets. If the root cause is not addressed, mold spreads until walls must be cut out, ceilings replaced, cupboards discarded and a whole set of new mats purchased. Those costs are many times higher than doing it properly the first time.

Time and learning

Every day the centre stays closed is a day children lose learning, a nutritious lunch and the routine that helps them feel secure after a frightening event. Reopening and then closing again because a group falls ill wastes far more time than preparing properly from the start.

Trust and reputation

Parents hand schools the most precious thing in their lives. If rumours spread that classrooms smell musty or several children got sick, confidence evaporates quickly. For a small private kindergarten, that means lost income overnight; for a public centre, it means difficult questions from the community and supervising agencies.

Families

When a centre stays closed, parents who need to go back to work to rebuild their homes and income have nowhere to leave their children. And when a child brings an infection home from school, it can pass on to elderly relatives and infant siblings.

Why the usual fixes are not enough for young children

Teachers and communities always put in enormous effort. But several of the methods used in a hurry only deal with the surface, and some even introduce new risks for children.

1. Splashing bleach everywhere and calling it done. Bleach can disinfect smooth surfaces that have already been cleaned, but it does not reach behind cupboards, into ceiling joints, under wooden floors or deep inside mats. Strong chlorine fumes also irritate the airways of asthmatic children, and mixing bleach with some toilet cleaners can release dangerous gases.
2. Running fans and waiting for things to dry. Fans do speed up surface drying. In a room where mold has already started, though, they blow spores around the room and into neighbouring rooms.
3. Spraying air freshener to mask the smell. Fragrance only hides the odour for a while. The cause is microbes and organic residue that are still there, and some fragrance compounds can trigger allergies in children.
4. Painting over mold stains before the first day back. This is the most common shortcut because everyone wants the room to look new. Paint does not kill mold growing inside the wall. Within weeks, dark patches bleed through again, along with a stale smell that lingers.
5. Reusing soaked mats and toys after one day in the sun. Sunlight helps to a degree, but thick foam mats and fabric toys soaked in contaminated water often stay damp inside, becoming a source of germs right next to a child's nose.
6. Wiping only what you can see. Many germs are in the air, in air-conditioning ducts, in corners and on surfaces nobody thinks about: the underside of children's tables, stair rails, door handles and light switches.

What all of these methods miss is a step that treats germs in the air and in the corners hands cannot reach, without leaving chemical residue behind for children. That is the gap ozone disinfection fills.

WHD ozone disinfection: the final step before the laughter returns

World Health Disinfection (WHD) provides residential and building ozone disinfection for homes, condominiums, hotels, offices, factories, hospitals and schools. Ozone (O3) is a highly oxidising gas. When it disperses through a sealed room, it breaks down the cell structures of viruses, bacteria and mold, and it also breaks down the molecules that cause musty odours. Afterwards it reverts to ordinary oxygen (O2) on its own, so there is no chemical film left on tables, toys or mats that children touch.

The company states that its process has been tested by Thailand's Department of Medical Sciences and by Intertek (UK), eliminating 99.99% of viruses, bacteria and mold according to the test results the company has received. School administrators can request the certification documents to support reports to parents or supervising agencies.

Two points we always make clear: ozone treatment is carried out only in an empty, closed space. Children, staff, pets and plants must all be out of the area, and nobody re-enters until the rest and ventilation period set by the team has passed. Second, ozone comes after mud removal, washing and drying. It does not replace cleaning, repairing damaged materials, or medical care for anyone who is unwell.

How the process works in a school

1. Survey and zoning. The team walks the building with the head teacher or responsible staff and divides it into zones: classrooms, nap room, children's toilets, kitchen, sick bay and library, sequencing them around the school's own clean-up schedule.
2. Preparation. We confirm each zone has been washed and wiped dry, open cupboards, drawers and toy boxes so the gas can reach inside, close windows and vents, remove people and plants, and post "no entry" signs.
3. Ozone fill. The generator runs until the concentration suits the size of the space.
4. Contact time. The room stays closed while ozone works on the air, surfaces and hidden corners. A typical cycle is about 30 minutes per zone.
5. Rest and ventilation. Ozone is allowed to revert to oxygen, then the room is aired before anyone is allowed back in.
6. Handover and advice. We point out spots to monitor, such as walls that are still damp or materials that should be replaced, so the school can keep on top of them.

For schools with several buildings there is a practical bonus: when an ozone job is 15,000 baht or more, WHD includes a free medical-grade disinfectant spray, useful for teachers to treat high-touch points every day after reopening.

10 reasons schools and childcare centres should use ozone before reopening

1. It reaches where cloths cannot. As a gas, ozone travels behind cupboards, under shelves, into ceiling voids and inside toy crevices that no teacher can wipe completely.
2. It treats the air children breathe. Not just surfaces, but spores and germs suspended in the nap room.
3. No chemical residue. Ozone returns to oxygen, so there is no film on lunch tables or on toys that go into mouths. Read more about chemical residue.
4. It removes flood odour at the source rather than covering it with perfume, so the classroom air feels genuinely fresh again.
5. Backed by testing. Tested by the Department of Medical Sciences and Intertek (UK), according to the test results the company has received.
6. Fast turnaround. Around 30 minutes per zone makes it realistic to treat several rooms in a single day before term restarts. See the service details.
7. Lower chance of cluster outbreaks. When environmental sources of germs are reduced, there are fewer opportunities for infections to pass around a room.
8. Helps slow mold regrowth when combined with thorough drying and leak repairs, reducing the chance mold returns before materials are fully dry.
9. Something concrete to tell parents. Schools can explain with confidence that a professional disinfection step was completed before reopening. Request a quote for your school.
10. A team used to many building types, from homes and hotels to hospitals and schools, which means an understanding of tight timetables and child safety.

Before and after: the same classroom, two different atmospheres

Example case: a small Pathum Thani kindergarten and its two-week reopening plan

(An illustrative example to explain the process, not a verified customer review.)

Khun Prae runs a small private kindergarten in Lat Lum Kaeo district with six classrooms, a nap room, a kitchen and two children's toilets. Floodwater about half a metre deep sat in the building for ten days. Once it receded, she aimed to reopen within two weeks, but she was not willing to risk children falling ill.

Days 1 to 4: Teachers and caretakers, wearing rubber boots, gloves and masks, removed the mud and washed floors and walls with clean water and detergent. Windows were opened and fans used only in rooms without visible mold. All foam nap mats that had been submerged were thrown away, and roughly thirty centimetres of swollen gypsum wall were cut out on a builder's advice.

Days 5 to 8: The structure was left to dry. A roof leak over the nap room was repaired. Plastic toys were washed in soapy water, disinfected and dried. Fabric toys that had soaked for days were discarded.

Day 9: The WHD team surveyed the site and treated it zone by zone, starting with the nap room and the youngest children's classroom, then the kitchen, toilets and staff room. Nobody was in the building during treatment. Only after the rest and ventilation period did teachers go back in to set up the rooms.

Days 10 to 14: New mats were laid out, wall moisture was checked every morning, and a letter went to parents explaining each step taken, asking them to watch their children and tell the school about any fever or diarrhoea.

In this scenario, what changed most for Khun Prae was the conversation with parents. Instead of answering "is it safe?" with nothing to show, she could explain step by step what the school had done and what it was still monitoring. That transparency is what gives parents the confidence to send their children back.

School recovery checklist: before and after ozone

Before cleaning starts

• Switch off power and have an electrician inspect the building before use, especially low sockets in toddler rooms.
• Everyone cleaning wears boots, rubber gloves, a mask and eye protection, with any cuts fully covered.
• Photograph damage in every room for reporting or insurance claims.
• Assign pregnant staff and those with chronic illness to paperwork rather than mud removal.

During cleaning

• Remove all mud, then wash floors, walls and furniture with clean water and detergent.
• Aim to dry materials within 24 to 48 hours using ventilation and dehumidifiers if available.
• Discard foam mats, soft toys, carpets and books that soaked in contaminated water and are damaged.
• Cut out swollen gypsum board or insulation; mold inside materials will not wipe away.
• Wash plastic toys in soapy water, disinfect and dry them completely.
• Clean the kitchen thoroughly and throw away all food and ingredients touched by floodwater.

On ozone day

• Confirm no children, staff, pets or plants remain in the zone being treated.
• Open cupboards, drawers and storage boxes so the gas can circulate.
• Post no-entry signs on every door and brief the caretaker or security guard.
• Re-enter only after the team confirms the rest and ventilation period is complete.

After reopening

• Open windows each morning and watch for damp patches or dark spots returning.
• Teach handwashing with soap before meals and after the toilet, with teachers modelling it.
• Wipe high-touch points such as door handles, rails and taps every day.
• Screen children each morning; if a child has fever, diarrhoea or mouth sores, separate them and ask parents to see a doctor.
• Keep a simple illness log for the first two weeks so any outbreak is spotted early.

Frequently asked questions

Can children go back into the room straight after ozone?

No. Everyone must wait until the rest and ventilation period set by the team has passed, and nobody may be in the area during treatment. Once the team confirms it is complete, teachers can set up the room and welcome children as normal.

If we use ozone, can we skip washing the rooms?

No. Ozone is a step after mud removal, washing and drying. Thick mud and grime block the gas from reaching surfaces, and materials that remain soaked will grow mold again. All the steps work together.

Will ozone damage toys or teaching materials?

The team assesses each zone and sets concentration and time to suit the room size and contents. If you have valuable or special items, mention them during the survey so they can be stored separately or planned around.

Our centre has many rooms. How long will it take?

A typical cycle is about 30 minutes per zone, not counting preparation and ventilation. The team sequences zones so several can be completed in a single day to meet your reopening date.

Some children have diarrhoea after the flood. What should we do?

Ask parents to take them to a doctor, particularly if the child has frequent stools, vomiting, drowsiness, little urine or fever, and to give oral rehydration fluids as advised by health staff. Disinfecting the building reduces environmental sources of germs, but it is not treatment for a child who is already ill.

Can a local authority request a quotation and supporting documents?

Yes. Contact WHD for a site survey, quotation and the company's test certification to support your procurement process.

A teacher who helped clear mud now has a fever and calf pain. What now?

They should see a doctor promptly and mention wading through floodwater or mud. These can be signs of leptospirosis, which responds well to early treatment.

Make reopening day a day everyone feels confident

Talk to the WHD team about an ozone disinfection plan for your school, kindergarten or child development centre after the flood.

Book School Ozone Disinfection

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

Related services and reading

• Residential and building ozone disinfection
• Disinfection services for organisations and schools
• Reducing chemical residue with ozone
• Certification documents

References

• CDC: Floods and Your Health
• World Health Organization fact sheets