A typical scenario (an illustrative situation based on common cases, not a review from a specific customer)

One sheet of paper that kept Nid awake at night

Nid's two-storey detached house sits in a narrow soi in Bueng Kum, on Bangkok's eastern side. Between 24 and 27 September 2026, news reports described roughly 300 mm of rain falling in about 48 hours. The canals filled, street water poured in, and the ground floor sat under shin-deep water for days. The particleboard cabinets, the fabric sofa and the laminate floor swelled beyond saving.

Once the water drained, Nid and her husband hired workers to scrape out the mud, wash everything down and repair the house as fast as possible. Their five-year-old son needed to get back to school, and Nid's mother, in her seventies, wanted her old ground-floor bedroom back. The painters rolled a damp-proof primer over every wall, added two coats of colour, lacquered the timber staircase and installed a brand-new flat-pack kitchen. Within a week the house looked new. It did not smell like home.

A heavy paint-and-thinner smell hung over the whole floor. Opening the windows all day barely helped. Grandma complained of headaches and the boy kept rubbing his eyes. Nid booked an ozone chemical-residue service. The team measured the air before starting, measured it again afterwards, and handed her a one-page report: two sets of numbers, an unfamiliar unit and several measuring points. The numbers had gone down. But Nid still wondered: "Is this drop enough?" "Why is the kitchen still higher than the bedroom?" "If I keep the house shut tomorrow, will it go back up?"

The late-September 2026 Bangkok floods, and why indoor air becomes the next problem

According to news reports, continuous heavy rain from 24 to 27 September 2026 flooded large parts of Bangkok, and on 26 September the Bangkok Metropolitan Administration declared all 50 districts a disaster zone. The eastern side of the city was hit hardest, with areas such as Khlong Chan and Bueng Kum frequently mentioned. Governor Chadchart said the canals were full and that drainage would take two to three days after the rain stopped. As of 30 September, some roads, including Sri Burapha and Lat Phrao, still had around 20 to 40 cm of water. Thai media compared the event with the 2011 floods, and one Thai business report cited a Chamber of Commerce estimate of about 12,300 million baht in damage. Lives were also lost, and we extend our condolences to every family affected.

When the water recedes, the problem is no longer just mud and debris. The recovery period is when people inhale the widest mix of chemicals at once: the cleaning agents used for scrubbing, fuel and engine oil carried in by floodwater, damp-proof primers, wall paints, thinners, lacquers, epoxies, flooring adhesives and the engineered wood in new furniture. Many of these release volatile organic compounds, or VOCs. Because contractors are racing the clock, painting and furniture installation often happen in the same week, so VOCs from several sources build up together.

What makes post-flood repairs different from an ordinary renovation is the moisture still trapped in walls and floors. Damp substrates slow paint curing, so solvents keep evaporating for longer, while musty odours from mud and wastewater are still in the mix. Families often cannot tell what they are smelling or how strong it really is. That is exactly why a TVOC measurement matters: it turns "it still smells" into data that can be compared.

What TVOC is and why it is used to track chemical odours at home

VOCs (volatile organic compounds) are carbon-based chemicals that evaporate at room temperature. In a freshly repaired home, common sources include the solvents in paint and thinner, lacquer and varnish, flooring glue, and formaldehyde that may be released by some types of plywood and particleboard.

TVOC stands for total volatile organic compounds: the combined amount of these chemicals in the air at the point where you measure. The key word is "total". A field TVOC meter does not separate out which chemicals are present; it reports one number that reflects the overall load. Think of weighing a whole bag of fruit: you learn how heavy it is, but not how many oranges or mangoes are inside.

That is why TVOC is best used for comparison rather than as an absolute verdict: before versus after ozone, a freshly painted room versus an untouched one, this week versus next week. When readings come from the same instrument, the same method and similar conditions, the change in the number tells you clearly whether things are improving.

How VOCs can affect health, and who should be most careful

High VOC exposure in a closed space may cause eye, nose and throat irritation, headaches, dizziness, nausea or unusual tiredness. Symptoms often ease when the person steps outside into fresh air, which is one sign that indoor air may be the cause.

Those who need extra care include young children, who breathe faster relative to body weight and play close to the floor; older adults; pregnant women; and anyone with allergies, asthma, chronic lung disease or other long-term conditions. If someone has difficulty breathing, chest tightness, or symptoms that do not improve after leaving the house, they should see a doctor promptly. Anyone who waded through floodwater and then develops fever, muscle pain (especially in the calves) or diarrhoea should also see a doctor, because these may signal water-borne illness such as leptospirosis, which has nothing to do with odour and needs medical treatment.

Reading the units: ppm, ppb and µg/m³

The first source of confusion on any TVOC report is the unit. Different instruments display different units, and two numbers that look wildly different may describe the same amount.

• ppm (parts per million) is a volume ratio: parts of a substance per million parts of air. It is common on portable meters.
• ppb (parts per billion) is a thousand times finer. 1 ppm equals 1,000 ppb. If one report says ppb and another says ppm, convert before you panic about the difference.
• µg/m³ or mg/m³ is mass per cubic metre of air. Converting from ppm requires the molecular weight of the substance; because TVOC is a mixture, meters usually assume a reference compound, so the result is an approximation.

The simplest rule: only compare numbers that share the same unit and come from the same instrument. Do not set a reading from an inexpensive online-bought gadget directly against a professional report. Different sensor types respond differently to different chemicals, and their calibration differs.

Is there a standard? How low should it be?

Several countries and organisations publish indoor TVOC guideline values or reference levels, but they do not all agree, and many are designed for office buildings or green-building certification rather than as a hard line between safe and dangerous. For a homeowner, a good result is one that is clearly lower than before treatment and closer to the level of an unrenovated room or the outdoor air, which the team can measure as a reference. If you want to know which benchmark your report uses, ask the team directly whose guideline they reference and under what conditions they measured.

Why numbers move: eight factors to understand before reading a report

TVOC is not a fixed property of a room. It shifts with conditions, and if you ignore them you can easily misread a report.

1. Temperature. Heat drives more evaporation from walls and furniture, so a closed room on a Bangkok afternoon often reads higher than the same room in the morning.
2. Humidity. Flood-damaged homes are humid, which slows paint drying and prolongs emissions. Some sensors also respond to humidity itself.
3. Ventilation at the time of measurement. Measure straight after opening windows and the number will be temporarily low; measure after a night shut up and it will be higher.
4. Time since painting. Emissions are strongest soon after application and decline over time.
5. Position. Readings next to a freshly painted wall, a new cabinet or inside a closed wardrobe are higher than mid-room.
6. Height. An adult's breathing zone differs from a child's on the floor. A good report notes the approximate height.
7. Temporary interference. Air freshener, sprays, alcohol, glass cleaner, cooking, even someone's perfume near the meter can spike the reading briefly.
8. Instrument condition. Sensors need calibration and warm-up time. An uncalibrated meter can be far off.

What it costs you not to know your indoor air

Health. Many families bring grandparents and children home the moment the contractor packs up because the house looks clean. But eyes cannot see vapours, and noses adapt quickly. People who spend all day indoors may feel the smell has faded while concentrations remain high; visitors walking in from outside often notice it far more.

Money. Without data, households try one fix after another: several air purifiers, charcoal bags, perfumes, even repainting because they assume the first paint was faulty. Repainting simply adds another emission source, so the money never reaches the root cause.

Time. Families staying with relatives or in temporary rentals need to know when they can return. Without comparable numbers the decision rests on feelings alone; some wait far longer than needed, others return too soon.

The usual fixes, and why they fall short

Trusting your nose. The nose is an excellent alarm but a poor instrument. It adapts within minutes, sensitivity varies from person to person, and some irritating chemicals have little smell.

Air freshener and fragrance sprays. These only mask odours, and fragrances themselves contain VOCs. Measure TVOC after spraying and the number may actually rise.

Opening windows alone. Ventilation is essential and should always be part of the plan. But in rainy, humid weather, leaving the house open brings moisture in and can slow drying further, and on streets that still have standing water, outside odours drift in too.

WHD's ozone chemical-residue service: measure, treat, measure again

World Health Disinfection (WHD) provides an ozone service for removing chemical residue and odours in homes, condos, offices, factories, construction sites, hotels, storage facilities and automotive settings. According to the service information, ozone (O₃) breaks down odour molecules at the source instead of masking them. It targets paint, thinner, epoxy and lacquer odours, VOCs and musty smells, as well as bacteria, viruses and mold, then reverts to oxygen with no residue. The space is ready to use about two hours after treatment.

Most relevant to this article: according to the service information, WHD measures TVOC with calibrated instruments both before and after treatment and uses a Master Ozone Generator. You see the result as comparable numbers, not just a promise.

The process in brief

1. Survey and questions. How deep was the flood, what was repaired, when was painting done, which materials were used, and is anyone in the household especially sensitive?
2. Choose points and take baseline readings. Define measuring points in each room, note position, height and window status, and record the starting TVOC.
3. Prepare the space. All people, pets and plants leave. Doors and windows are closed to create a sealed space, and oxidation-sensitive items are stored as the team advises.
4. Ozone treatment. The Master Ozone Generator runs according to area and severity inside an empty, closed space with no people, pets or plants.
5. Rest and ventilation. The machine stops and ozone reverts to oxygen, followed by ventilation. Nobody enters until the rest and ventilation period has ended.
6. After readings. TVOC is measured at the same points, heights and similar conditions, and the team walks you through the results and aftercare.

Safety reminder: ozone treatment is carried out only in an empty, closed space. People, pets and plants must be out, and may return only after the rest and ventilation period ends. Ozone is a step after mud removal, washing and drying. It does not replace cleaning, repairs or medical care.

How to read a before-and-after TVOC report, line by line

1. Check the unit first. Before and after must use the same unit; convert if not.
2. Check the point labels. Each room should have a clear point, such as "living room centre", "bedside" or "kitchen next to new cabinets", so you know where each number came from.
3. Check time and conditions. When was it measured, were windows closed, was air-conditioning on, what were temperature and humidity? If the report records these, the method was systematic.
4. Work out the percentage change. (Before minus after) divided by before, times 100. A percentage is easier to grasp than raw numbers.
5. Compare with a reference point. If the team measured an untouched room or the outdoor air, see how close the after reading comes.
6. Find the stubborn spots. A room clearly higher than the rest usually still has an active source: new particleboard, a freshly lacquered floor or a wall that is still damp.
7. Read the recommendations. How to keep ventilating, when to re-measure, and where to look for remaining sources.

Odd-looking numbers and likely explanations

The kitchen is still higher than the bedroom after treatment. New flat-pack cabinets can keep releasing compounds from the material itself. Ozone reduces airborne chemicals and odour, but some new materials also need steady ventilation over the following period.

After a day with the house shut, a faint smell returns. Paint on a still-damp wall may continue to off-gas, and on a hot day with the house closed, compounds accumulate again. Ventilate regularly at first, and if the odour clearly returns, ask the team to reassess.

The baseline was already low but it still smells musty. Mustiness from mold or mud trapped inside wall cavities does not always show up as high TVOC. In that case the moisture and mold source has to be addressed as well.

What a TVOC number cannot tell you

• It does not identify which chemicals are present. That requires air sampling and laboratory analysis.
• It does not measure germs and cannot say a home is free of bacteria or mold. Surface disinfection after a flood requires washing and a suitable disinfectant.
• It does not measure moisture in walls or under floors, a major cause of post-flood mustiness and mold.
• It is a snapshot. New sources such as extra painting or more new furniture will change it.
• It is not a medical diagnosis. Anyone with symptoms should see a doctor.

10 reasons to choose an ozone service that measures TVOC before and after

1. Results you can see as numbers, not just the opinion of a nose that has already adapted.
2. Treating the source, not masking it. According to the service information, ozone breaks down odour molecules instead of covering them with fragrances that add more VOCs.
3. No chemical residue. Ozone reverts to oxygen, so it adds no further chemical load to a home already scrubbed with cleaning agents.
4. Many odours in one visit: paint, thinner, lacquer, epoxy and the mustiness that so often mixes with them after a flood.
5. Help against airborne germs and hidden corners. Per the service information, ozone also targets bacteria, viruses and mold, complementing surface cleaning and disinfection.
6. Quick return. The space is ready about two hours after treatment, so displaced families can plan their move home.
7. Professional equipment: a Master Ozone Generator and calibrated TVOC instruments.
8. Data to share with family members or tenants, ending arguments and supporting landlords and shops reopening after the flood.
9. Pinpointing remaining problems. If one room stays high, the team helps work out the likely source.
10. Suitable for many spaces, from homes and condos to offices, factories and warehouses. See the chemical-odour removal service page for details.

Before and after: the picture in a flood-repaired home

Note: results vary with materials, time since painting, humidity and ventilation. Actual figures appear in each job's measurement report.

Example case (a hypothetical scenario reflecting common problems, not a real customer review)

Nid in Bueng Kum: from worry to a data-based decision

Back at Nid's house, the team went through the report room by room. The living room and Grandma's bedroom had dropped clearly compared with the baseline. The kitchen, with its new cabinets, had also dropped but remained higher than the other rooms. The team explained that new particleboard may keep releasing compounds for a while, and suggested leaving cabinet doors open, ventilating the kitchen regularly at first and avoiding sealing it up on hot afternoons.

Nid calculated the percentage reduction herself using the formula the team showed her and immediately understood why the kitchen differed. That night Grandma slept in her own room again and the boy went back to playing in the living room. Nobody argued about the smell anymore, because everyone was looking at the same numbers.

What Nid told her neighbours was simple: she did not just want a house without a smell, she wanted confidence that she had made the right call. The before-and-after numbers gave her that.

Recovery checklist: before and after TVOC measurement and ozone

Before your appointment

• Remove mud, wash and dry the house as thoroughly as possible. Public-health guidance generally advises cleaning and drying quickly, ideally within 24 to 48 hours, to limit mold.
• Disinfect flood-contaminated surfaces after the mud is gone with a suitable product such as Chemgene HLD4H, following the label dilution and contact time.
• Tell the team when you painted, lacquered or installed new furniture.
• Avoid air fresheners, sprays and scented candles before measurement so the baseline is not distorted.
• Arrange a place for older relatives, children and pets, and move plants out during treatment.
• Secure documents, medicines, food and valuables.

After treatment

• Re-enter only after the rest and ventilation period the team specifies.
• Keep the TVOC report. If you re-measure later, use the same points and conditions.
• Ventilate regularly at first, especially rooms with new furniture.
• Avoid adding new VOC sources straight away, such as more painting or heavy fragrance use.
• Watch for symptoms in the household and see a doctor if anything is unusual.
• If the odour clearly returns, ask the team to look for the cause, such as walls that are still wet.

Frequently asked questions

1. Should TVOC be zero after treatment?

No, and it rarely is. Normal air contains some VOCs from many sources. Look for a clear drop compared with the baseline and a result close to the reference point.

2. Why must everyone leave during treatment?

Ozone treatment is done only in an empty, closed space. People, pets and plants stay out until the rest and ventilation period ends. This safety rule has no exceptions.

3. How soon can we go back in?

According to the service information, the space is ready about two hours after treatment. Follow the time the team gives on site, based on area and actual conditions.

4. Does ozone mean I can skip washing and disinfecting surfaces?

No. Ozone comes after mud removal, washing, drying and surface disinfection. It does not replace them.

5. One room is still higher than the others. Do I need another treatment?

It depends on the cause. New materials that are still off-gassing may be better handled with continued ventilation; damp or moldy walls need the moisture fixed first. The team will help you assess it.

Want to know what is really in the air of your repaired home? Let the numbers answer.

Talk to WHD about before-and-after TVOC measurement and ozone removal of paint, thinner and chemical residue odours.

Get advice on ozone chemical-odour removal

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

Related links

• Ozone chemical-residue and odour removal service
• Residential and building ozone disinfection
• Chemgene HLD4H medical-grade disinfectant

References

• 2026 Bangkok floods (Wikipedia)
• Al Jazeera: Disaster zone declared across Bangkok
• CDC: Floods
• WHO fact sheets