A story from the field: the lab door the teacher was not ready to open

Orawan teaches science at a secondary school in Mueang Nakhon Sawan district, not far from the Chao Phraya River near Pak Nam Pho. She is responsible for the chemistry and biology laboratories. During the 2026 floods, run-off from the north pushed the river higher and higher until it overflowed into the ground floor of the school's science building. Two laboratories and the chemical storeroom behind them stood in knee-deep water for several days.

When the water went down, teachers and caretakers began opening classrooms to start cleaning. Orawan stood outside the chemical storeroom for a long time without opening the door. She knew the lower cabinets held bottles of many different chemicals. Some labels had probably peeled off in the water. Some bottles might have tipped over or cracked. The water that had sat in the room could be contaminated. The smell drifting out through the gap under the door was not just mud. There was something sharp mixed in with it.

In the lab next door, the lower parts of the wooden lab benches had swollen with water. Equipment cabinets were coated with mud. Several microscopes that had been stored in a low cupboard had been underwater, and a line of black mold spots had started to appear along the walls at the height the water had reached. The school director wanted to reopen as soon as possible. Parents were messaging every day: when can our children come back, and is the school safe?

For a school in this situation, the key question is not only "How do we clean?" but "What do we do first, and who should do it?" This article sets out a safe order of work for school science laboratories and chemical storerooms after a flood, and explains where professional disinfection and ozone treatment fit in. It is written for teachers, school directors and the many volunteers and local officials who support them after a flood.

The core principle: chemicals are always handled first, by qualified people

A flooded chemical storeroom carries risks that are completely different from an ordinary classroom. Some chemicals may react with water. Some may leak from damaged containers. Different substances that have washed together in standing water may react in ways nobody can predict without proper assessment.

• Students, parents, volunteers and caretakers should not enter or clean the chemical storeroom themselves.
• The teacher in charge of the laboratory, together with people trained in chemical safety, should assess the situation, using the safety data sheet (SDS) for each substance and the school's chemical inventory.
• Appropriate personal protective equipment should be used, and the room should be ventilated before anyone goes in.
• Chemicals with damaged containers, missing labels or signs of floodwater contamination should be separated and sent for disposal through a licensed hazardous waste service, following the guidance of the school's governing agency and local authorities.
• If there is any doubt, the school should seek advice from provincial environmental or public health agencies before acting.

World Health Disinfection (WHD) does not move, sort or dispose of laboratory chemicals. Our work begins only after the school has dealt with the chemicals and confirmed that the area is safe. At that point we disinfect and ozone-treat the space to deal with floodwater germs, mold and musty odors.

There is a second reason for this order. Ozone is an oxidizer, so it should never be used in a room where chemicals are still stored. We only ozone-treat rooms from which chemicals have been removed, or where they have been sealed away separately according to the decision of the responsible staff.

Typical problems in a school science lab after a flood

• Swollen lab benches and wooden cabinets. Plywood and particleboard under the benches absorb water, grow mold and hold musty odors.
• Sinks and drain lines. Laboratory drains can push mud and sewage back into the room, creating a source of odor and germs.
• Teaching equipment. Microscopes, balances and electrical equipment that were submerged need to be assessed by a technician or the supplier before use. Glassware that survived intact can be cleaned using the lab's normal procedures.
• Electrical systems and extraction fans. These must be checked by an electrician before they are switched on, especially low-level sockets and fume cupboards.
• Mold on walls and ceilings. Rooms that stayed sealed throughout the flood become very humid. Mold can appear along the water line and on ceiling boards.
• Textbooks, worksheets and teaching materials. Wet paper tends to grow mold very quickly and is often a major source of smell.

The risks of reopening too early

Health. Floodwater that has flowed through a community is usually contaminated with wastewater and sewage. It may carry bacteria such as E. coli, which can cause diarrheal illness, and the bacteria that cause leptospirosis, which can enter through cuts and scratches. Mold in damp rooms can trigger allergies, coughing, sneezing and asthma in some students.

Safety. If chemicals have not been dealt with properly, students entering the room could come into contact with residues without realizing it.

Trust. Parents want to see that the school is handling things systematically. A clear, explainable sequence of work makes it much easier for the school to communicate with families.

Teaching time. If the lab has to be closed again because mold returns or the smell will not go away, practical science lessons are delayed even further, often at an important point in the school year.

Why a normal classroom clean is not enough for a lab

• Splashing bleach everywhere. In a lab where chemical residues may remain, mixing cleaning products without knowing what is already present can release dangerous gases. The person responsible for chemicals must confirm the area is clear first.
• High-pressure water jets. These can drive water into sockets, cabinets and wall cavities, and can scatter mold spores through the room.
• Painting over mold. If the wall is still damp, mold will bleed back through the new paint within weeks.
• Running fans and waiting for the smell to fade. Odors soaked into timber and ceiling boards rarely disappear with ventilation alone.

School staff work very hard after a flood, often with limited budgets and very little time. The aim is not to criticize those efforts but to make sure the effort goes into the right steps in the right order.

The recommended sequence for schools

1. Close off the chemical storeroom with a clear "no entry" sign until the responsible staff have finished their assessment.
2. An electrician checks the electrical system on the ground floor, in the labs and in the fume cupboards.
3. The responsible teacher and chemical safety specialists inspect, sort and deal with chemicals according to the inventory and SDS, sending damaged substances for disposal through proper channels.
4. Remove mud and damaged materials, such as swollen wooden cabinets, wet paper and moldy teaching aids.
5. Carry out basic surface cleaning according to the school's own procedures.
6. WHD disinfects and ozone-treats the laboratories, classrooms and connected corridors.
7. Ventilate and re-check before students are allowed back in.

Writing this sequence down and assigning a named person to each step is one of the simplest ways to avoid confusion when many people are helping at once.

How WHD works in school laboratories and teaching buildings

1. Site survey. The team walks through the building with the responsible teacher, checks how high the water rose, where mold and odors are worst, and confirms that the chemical storeroom has been dealt with and separated from the work area.
2. Preparation advice. We advise on mud removal, which damaged materials to discard, and moving or covering electronics such as computers, projectors and microscopes.
3. ULV disinfection fogging. Our disinfection service applies CHEMGENE HLD4H as a fine mist covering floors, lower walls, bench legs, the space under sinks and room corners.
4. Ozone treatment. Only in rooms where no chemicals are stored. The room is closed and an ozone generator runs at a controlled dose to reduce mold spores and break down musty odors. During treatment there must be no people, animals or plants in the room, including animals and plants kept for teaching.
5. Ventilation. Doors, windows and extraction fans (once approved by the electrician) are opened until the ozone has broken down and there is no sharp smell.
6. Re-check and handover. We check odor and condition together with the responsible teacher and give advice on managing humidity during the first weeks after reopening.

Schools can schedule this work on weekends or before term restarts, leaving enough time for ventilation before students return.

Why fogging and ozone complement each other in a school

Fogging addresses surfaces. Floodwater leaves a film of silt, organic matter and bacteria on floors, the lower part of walls, bench legs, sink cabinets and door bottoms. After mud is cleared and surfaces cleaned, a fine disinfectant mist settles on these areas, including the awkward spots under benches and behind cabinets that are difficult to wipe in a busy clean-up.

Ozone addresses air and porous materials. Musty odors and mold spores soak into ceiling boards, notice boards, curtains and timber. Ozone, being a gas, reaches into those materials and reacts with odor molecules and microorganisms. This is why a classroom can still smell after a thorough scrub, and why staff and students notice the difference after ozone treatment and ventilation.

Neither replaces drying and repair. If walls are soaked or a pipe keeps leaking, the moisture source must be fixed first. Our team will tell the school honestly if materials need replacing before treatment can be effective.

A practical checklist for the teacher in charge of the lab

The teacher responsible for the laboratory often becomes the coordinator for everything that happens in the science building after a flood. A short checklist helps keep the work organized and makes it easier to hand tasks to colleagues.

• Locate the most recent chemical inventory and the SDS folder, or the digital copies, before anyone opens the storeroom.
• Photograph each room from the doorway before cleaning starts, to record the damage for the school's reports and any insurance or budget requests.
• Mark the water line on a wall in each room with tape so that everyone can see which materials were submerged.
• List equipment that was underwater and needs technician or supplier assessment, such as microscopes, balances, hot plates and water baths.
• Agree with the school director who will contact the electrician, who will arrange chemical disposal and who will book disinfection and ozone treatment.
• Note which rooms will be ozone-treated and confirm that no chemicals, animals or plants remain in them on the day.
• Prepare a short message for parents once each stage is complete.

Teaching materials, records and specimens

Science departments often store more than chemicals and glassware. Preserved specimens, rock and mineral collections, student project boards, lab notebooks and printed teaching materials may all have been affected.

Paper materials. Wet worksheets and textbooks that have started to grow mold are usually not worth saving, because they keep releasing spores and odor. Important records, such as assessment files, should be photographed or scanned as soon as possible before decisions are made about recovery.

Specimens and collections. Preserved specimens in sealed jars are part of the chemical question, because they are kept in preserving fluids. They belong in the hands of the responsible teacher and chemical safety specialists, not general cleaners. Rock and mineral collections can usually be washed and dried.

Student projects and boards. Foam board and cardboard displays that were soaked should generally be discarded. Taking photos first allows students to keep a record of their work.

Removing these sources of mold and odor before disinfection and ozone treatment helps the results last much longer.

The first month after reopening

School buildings are large, and concrete walls and floors that sat in water keep releasing moisture for weeks. A few habits help prevent mold and odors from returning.

Open the rooms every morning. Ask the caretaker or the first teacher to arrive to open windows and doors in the labs for a while before lessons start.

Leave cabinets slightly open at first. Cupboards under benches stay damp for longer. Leaving doors ajar during the first weeks, where it is safe to do so, helps them dry.

Watch the water line. New dark spots along the old water line, a returning musty smell or peeling paint are early warning signs. Report them quickly so they can be dealt with while the problem is still small.

Plan for the next rainy season. Moving chemical storage and sensitive equipment to higher shelves or upper floors, where possible, reduces the risk if the river rises again next year.

Do not forget the rest of the ground floor

The science labs often get the most attention because of the chemicals, but other ground-floor spaces in the same building can be just as important for students' health.

• Toilets and washrooms. Drains may have backed up during the flood. These rooms need thorough cleaning and disinfection before students use them again.
• Canteens and drinking water points. Food preparation areas and water dispensers need special care. Water filters and dispensers that were flooded should be checked by the supplier, and the school should follow local health guidance on drinking water.
• Libraries and computer rooms. Books and electronics are sensitive to both moisture and ozone, so these rooms need a controlled ozone dose with equipment covered or moved out.
• Staff rooms and storage. Teachers' desks, cupboards of exam papers and sports equipment stores are easy to overlook but often hold strong odors after a flood.
• Corridors and stairwells. Mud tracked through corridors spreads contamination between rooms, so these shared areas should be included in the plan.

During the site survey, our team can look at the whole ground floor and suggest a zone-by-zone schedule, so the school can open the most important rooms first and finish the rest without interrupting lessons.

Communicating with parents

Many schools find that parents worry far less once they receive clear information. A simple message in the parents' LINE group might explain that the chemical storeroom has been inspected and dealt with by the responsible teacher, that the electrical system has been checked by an electrician, that the laboratories have been disinfected and ozone-treated, and that rooms have been ventilated before use. Sharing these steps with a few photos shows families that the school has taken care of their children thoughtfully, and it reduces the number of anxious calls to the school office.

It also helps to tell parents what students should do in the first weeks back: wash hands before eating, report any strange smells to a teacher, and avoid areas that are still taped off. Clear instructions give children a sense of safety and give teachers fewer things to manage.

10 reasons Nakhon Sawan schools choose WHD

1. We respect safety sequencing: the people responsible for chemicals act first, and we never skip that step.
2. ULV disinfection fogging reaches under lab benches and sinks that are hard to wipe.
3. Ozone treatment breaks down musty odors in classrooms that were sealed during the flood.
4. We use CHEMGENE HLD4H for surface disinfection.
5. No ozone in rooms where chemicals are still stored, for safety.
6. Controlled ozone doses, with advice on covering or moving electronics and teaching equipment.
7. Scheduling on weekends or before term so lessons are not disrupted.
8. We can cover the whole building: labs, classrooms, libraries and corridors.
9. An optional mosquito spraying service around school buildings while water is still standing.
10. Easy to reach by phone and LINE, covering Mueang Nakhon Sawan and nearby districts.

Before and after lab recovery

Customer voice (example scenario)

"What impressed me was that the first thing the team asked about was the chemical storeroom, and they told us clearly they would only start after we had finished dealing with the chemicals. On the day, they disinfected and ozone-treated the labs and the ground-floor classrooms on Saturday. On Monday the students were back and there was no musty smell."

— Orawan, science teacher at a secondary school in Mueang Nakhon Sawan (example scenario)

Frequently asked questions

Q: Can WHD move or dispose of chemicals from the lab?
A: No. Chemical work is for the responsible teacher, chemical safety specialists and licensed hazardous waste services. WHD starts only after the area has been made safe.

Q: Why not use ozone in the chemical storeroom?
A: Ozone is an oxidizer and may react with some chemicals. We only treat rooms from which chemicals have been removed or where they are sealed away separately.

Q: Is the disinfectant safe for students?
A: We fog when no students are in the area and tell the school when rooms can be used again.

Q: Can flooded microscopes and electrical equipment be used again?
A: They must be assessed by a technician or the supplier. WHD does not repair or certify this equipment.

Q: How long does the work take?
A: It depends on the number of rooms and the extent of damage. We will estimate and plan after the site survey.

Q: Do you serve schools in other districts of Nakhon Sawan?
A: Yes. Contact us on LINE @whd268 to arrange a survey.

Make the science room safe for students again

Book a survey of your school buildings and laboratories in Mueang Nakhon Sawan and nearby areas.

See Disinfection Service - Click Here

Book Ozone Treatment - Click Here

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

Related links

• CHEMGENE HLD4H spray, 750 ml
• Ozone odor and chemical residue removal
• Master Ozone Generator
• All articles

Health reference: World Health Organization (WHO): Floods · Department of Disease Control, Thailand