A Typical Scenario: The First Morning the Lifts Worked Again

Nok manages the juristic person office of an eight-storey condominium in Rangsit, Pathum Thani. Her team sandbagged the basement ramp until 2 a.m., but water pushed up through the car park drains and filled the basement within hours. The pump room, the residents' storage lockers and the central bin room were all submerged. Upstairs, the ground-floor lobby stood in knee-deep water for almost a week.

When the flood finally receded, the housekeeping team spent three full days pushing out mud, hosing down floors and scrubbing tiles. A technician got the second lift running again. Everyone assumed the worst was over. Then Monday morning arrived, and the residents' LINE group filled up with complaints. One person said that opening the lift doors was like opening a bag of wet laundry forgotten for days. Another posted photos of black spots creeping along the bottom of the mailroom walls. The mother of a fifth-floor resident, who has asthma, started coughing every time she came down to collect a parcel. A young mum asked the question directly: has the office actually disinfected anything, and is it safe for my baby to crawl in the lobby?

Nok admits she had no clear answer. What the team had done was cleaning, not disinfection, and the smell had settled into ceiling boards, partition walls, service shafts and basement air that barely moves. This scene repeats in condos in Nonthaburi, Pak Kret, Ayutthaya and Hat Yai every time a major flood comes through.

Why Condo Common Areas Become Reservoirs of Germs After a Flood

A detached house has an owner who looks after it and windows on several sides that can be thrown open. A condominium's shared spaces are completely different. Basements and covered car parks have few or no windows and rely on mechanical exhaust fans, which are often damaged by the same flood. Lobbies are usually decorated with materials that soak up moisture: carpet, fabric wall panels, upholstered sofas, plywood and gypsum ceilings. Plant rooms, pump rooms, bin rooms and lift pits are closed spaces that few people enter, so dampness can linger for weeks without anyone noticing.

Floodwater is never clean water

Water entering a condominium mixes rain, canal water, sewer overflow and backflow from the building's own tanks. It can carry faecal bacteria such as E. coli and Salmonella, gut viruses, and Leptospira, the bacterium behind leptospirosis, which is shed in the urine of rats living in drains and bin rooms. When the water drains away, these organisms do not simply leave with it. They remain in mud residue, tile joints, lift door tracks, door frames and every porous surface the water touched.

Mold grows faster than most people expect

The World Health Organization and the US Centers for Disease Control and Prevention both advise that wet materials should be cleaned and dried within 24 to 48 hours to limit mold growth. In reality, condo common areas rarely get that chance. The building has to wait for the water to recede, for power to be restored, for the insurer to inspect, and often for a committee resolution before work can begin. During that wait, molds such as Aspergillus, Penicillium and various black molds settle onto gypsum ceilings, wallpaper, wooden door frames and lobby carpets. Their microscopic spores are easily carried by fans and air-conditioning into other parts of the building.

Risk points unique to condominium buildings

• Basements and covered car parks: still, dark, humid air, often with engine oil mixed into the mud, which makes odours heavy and persistent.
• Lobbies and reception lounges: carpets, curtains, sofas and ceilings that absorb moisture, and the first impression every resident and visitor gets.
• Mailrooms and parcel rooms: wet cardboard is a perfect food source for mold, and every resident touches this room.
• Lift halls and lift pits: air from a pit that held water is pushed up the shaft every time the car moves, spreading the smell to every floor.
• Central bin rooms and recycling rooms: already high in bacteria, they become breeding grounds after flooding and attract rats and cockroaches.
• Ground-floor gyms, meeting rooms and kids' rooms: mats, rubber flooring and equipment that people touch with bare skin.
• Residents' storage rooms: boxes, clothes and old furniture that owners may not have come down to deal with yet.

Symptoms residents may notice, and who is most at risk

Prolonged exposure to mold spores and damp, stale air can cause a blocked nose, sneezing, coughing, itchy eyes and throat, skin rashes and headaches. In people who already have asthma or allergies, symptoms can flare up badly. Touching mud or surfaces contaminated by sewage and then touching the mouth can lead to diarrhoea, stomach cramps, nausea and vomiting. The groups who need extra care are older adults, small children who crawl and put everything in their mouths, pregnant women, and people with chronic illnesses such as diabetes, kidney disease, lung disease, or weakened immunity from cancer treatment. A single condominium may be home to dozens of people in these groups.

Important: Any resident or staff member who waded through floodwater and then develops a high fever, muscle pain (especially in the calves), red eyes or severe diarrhoea should see a doctor immediately and mention the flood exposure. These can be signs of leptospirosis or a gastrointestinal infection. Ozone treatment manages the building environment. It is not medical treatment.

What Juristic Persons and Residents Stand to Lose if Common Areas Are Not Properly Disinfected

Health

Common areas are shared by everyone, so germs left in the lobby or mailroom do not affect just one household. They can reach hundreds of residents a day through lift buttons, handrails, door handles, parcel lockers and the air itself. When musty odours and mold spores travel up lift shafts and service risers, people on upper floors who never saw a drop of floodwater can be affected too.

Money

Once mold works its way into ceilings, partition walls and lobby joinery, repair costs multiply compared with dealing with it early. Materials that might have been saved by fast drying and disinfection may have to be ripped out entirely once the growth runs deep. Unit values also drop in the eyes of buyers and tenants the moment they smell damp at the front door. Monthly rentals may stay vacant longer than usual, and co-owners may become reluctant to pay common fees when they feel the building is poorly managed.

Time and management workload

The manager answers dozens of messages a day, coordinates contractors, reports to the committee and negotiates with insurers. If cleaning has to be repeated two or three times, housekeeping hours are burned and urgent electrical or pump repairs get pushed back.

Reputation and community trust

One photo of black mold in the lobby can go viral in the residents' chat group within hours, shaking years of trust in the management team and hurting sales of any unsold units.

Why the Methods Most Buildings Use Are Not Enough on Their Own

Management teams mean well, but their tools were designed for routine cleaning, not flood recovery.

1. Pouring bleach and scrubbing floors. Chlorine-based products work well on hard surfaces you can reach, such as floor tiles and plastered walls. They cannot reach the air in the room, the void above the ceiling, the back of the mailbox units, or the inside of carpets and sofas. Using large amounts of chlorine in an enclosed basement also creates harsh fumes that irritate the airways of staff working there, and it must never be mixed with ammonia-based cleaners.

2. Running industrial fans day and night. Fans genuinely help surfaces dry faster, and drying is a step that must happen. But fans do not disinfect. Blowing air at a wall that already has mold can actually spread spores to other areas.

3. Air freshener sprays and charcoal bags. Fresheners only mask odours temporarily. When the fragrance fades, the musty smell returns, along with the impression that management is trying to cover up the problem. Charcoal has very limited effect in a space the size of a car park.

4. Painting over black mold. This gives the fastest visible result and carries the biggest long-term risk. If the wall is still damp and the mold underneath is still alive, the stains come back within weeks, and now the new paint has to be scraped off too.

5. Running the air-conditioning at full blast straight away. If ducts or air-handling units were flooded or exposed to high humidity, switching them on before inspection and cleaning can distribute mold across an entire floor. Always have an air-conditioning technician check the system first.

What all of these methods lack is the ability to reach every corner of an enclosed space, including the air itself. That is exactly where ozone gas performs well, because as a gas it spreads throughout the whole volume of a room.

How WHD's Ozone Disinfection Service Works for Condominium Buildings

World Health Disinfection (WHD) provides residential and building ozone disinfection for homes, condos, hotels, offices, factories, schools and hospitals. The principle is simple: an ozone generator releases ozone gas (O3) into a closed space. Ozone is a powerful oxidiser that breaks down the cell structures of viruses, bacteria and mold, and breaks apart the molecules that cause odours. Afterwards the ozone reverts to ordinary oxygen (O2), so no chemical residue is left on surfaces.

According to the test results certified for the company by Thailand's Department of Medical Sciences and Intertek (UK), ozone treatment eliminates viruses, bacteria and mold by 99.99%. You can review the details on the certification documents page.

The key to condo work: zoning

A condo's common areas are far larger and more complex than a single home, so ozone treatment is never a case of switching on a machine and leaving the whole building to it. The work is planned as a series of controllable, enclosed zones: the lobby, the mailroom, the bin room, storage rooms, basement lift halls, the gym and meeting rooms. Each zone must be closable, completely empty of people, and guarded at every entrance for as long as the machine is running. Open or semi-open car parks that cannot be sealed will not hold enough ozone concentration to be effective, so the team will assess them honestly and recommend a more suitable approach instead. That honesty matters, because nobody wants a building to spend money on work that will not deliver.

Step by step

1. Site survey and assessment. The team walks the building with the manager, checks the flood line, remaining moisture and damaged materials, and divides the area into zones.
2. Scheduling and resident notices. Each zone is booked for low-traffic hours, such as late night or mid-morning, and the team helps prepare notices for residents in advance.
3. Preparation. Confirm that mud removal, washing and drying are finished. Remove plants, pets and anything that should not be exposed to ozone. Close openings, post no-entry signs and confirm that no one is left inside.
4. Ozone release. The generator fills the zone so the gas reaches the entire space.
5. Contact time. The ozone reacts with microorganisms and odour molecules. A typical cycle takes about 30 minutes per zone, depending on size and severity.
6. Rest and ventilation. The machine is switched off, the ozone is allowed to revert to oxygen, and the zone is ventilated before anyone is allowed back in.
7. Handover and advice. The team checks the result, reports back, and advises on follow-up care such as humidity control.

Safety first: Ozone treatment is carried out only in an empty, closed space. All people, pets and plants must leave the zone and may only return after the rest and ventilation period is complete. High ozone concentrations irritate the respiratory tract, which is why condo work requires strict zoning and guarded entrances.

It also needs saying clearly: ozone treatment is a step that comes after mud removal, washing and drying. It does not replace them. If thick mud is still on the floor or walls are still saturated, ozone cannot work to its full potential, and mold will return because its root cause, moisture, is still there. If the building also wants surface spray disinfection, see WHD's disinfection service.

10 Reasons Condo Juristic Persons Choose Ozone After a Flood

1. It reaches the air and corners a mop never will. Ozone gas spreads through the whole zone, including above ceilings, behind mailboxes, under the reception counter and inside service ducts.
2. No chemical residue. Ozone reverts to oxygen, so a toddler crawling in the lobby or an older resident resting on the sofa is not exposed to leftover chemicals once the job is done.
3. It destroys odours at the source. Instead of masking smells, ozone breaks down odour molecules directly, and residents notice the difference as soon as they walk in.
4. Verifiable test results. According to test results certified for the company by the Department of Medical Sciences and Intertek, the treatment eliminates viruses, bacteria and mold by 99.99%, which the office can cite in its committee report.
5. Zoned work, no full building shutdown. Each zone takes about 30 minutes plus a rest period, so residents can carry on almost as normal. See the building ozone service for details.
6. Less chance of mold spreading upstairs. Treating spores in lift halls and the basement reduces what gets pushed up the lift shaft.
7. Suitable for items that cannot be washed. Lobby sofas, curtains and notice boards that have been dried but still smell can be included in a zone.
8. Cheaper than cleaning again and again. Following the right order, wash, dry, then ozone, means housekeeping does not have to return to scrub the same area because the smell never left.
9. A team experienced with many building types. Hotels, offices, factories and hospitals have taught the team how to zone safely around building users. Read more about the ozone cleaning service.
10. A free medical-grade disinfectant spray is included with ozone jobs of 15,000 baht or more, useful for ongoing care of high-touch points like lift buttons and door handles.

Before and After: How Common Areas Change

Example Case: A Riverside Condominium in Nonthaburi

The following example case is an illustrative scenario based on common situations, intended to show how the process works. It is not a review from any specific customer.

Ton sits on the juristic person committee of a twelve-storey condominium beside the Chao Phraya in Nonthaburi. The building has one basement level used as a covered car park and plant area. Floodwater stood about a metre deep there for nearly ten days. Afterwards, the building hired contractors to pump out the water and push out the mud, pressure-washed the floors and ran fans for a week. Yet the basement lift hall and bin room still smelled, and residents who parked downstairs said the odour followed them into their cars every day.

When the team surveyed the site, they found that most of the basement was an open car park connected to an open ramp, which is not suitable for ozone. The recommendation for the car park was ventilation and humidity control. Ozone work focused on the enclosed zones that were the real sources of the smell: the basement lift hall, which has fire doors that close, the central bin room, residents' storage rooms, the mailroom and the ground-floor lobby. The work was scheduled after 10 p.m. The office posted notices three days in advance, temporarily closed the basement lift stop and directed residents to a side entrance.

After each zone, the team waited for the rest period and ventilated before reopening it. The next morning, Ton was the first person to walk down to the basement lift hall. He said the musty wave that used to hit him when the doors opened had largely gone. What he valued most was having a process he could explain to residents, along with practical advice on running the exhaust fans on a schedule to stop moisture building up again.

Common Area Recovery Checklist for Building Managers

Phase 1: As soon as the water recedes

• Cut power to flooded zones and have an electrician inspect before re-energising, especially electrical and pump rooms.
• Photograph and video damage in every zone for the insurer.
• Give staff rubber boots, gloves and masks for mud removal, and make sure they wash their hands before eating.
• Remove mud, debris and waterlogged materials such as ruined carpet and collapsed gypsum boards as quickly as possible.
• Notify residents to clear their storage lockers by a set date.

Phase 2: Wash and dry

• Wash floors and walls with clean water and detergent, working from high to low.
• Open any windows and doors that can be opened, and use fans and dehumidifiers until materials are fully dry.
• Have a technician inspect air-conditioning and ductwork before use.
• Check the lift pit, pump room and sewage sumps for standing water.

Phase 3: Before ozone day

• Notify residents of dates, times, closed zones and alternative routes in advance.
• Remove potted plants, fish tanks and any pets from each zone.
• Assign someone to guard each zone's entrances and confirm nobody is inside.
• Brief the security team on the full schedule.

Phase 4: After ozone

• Reopen each zone only after the rest and ventilation period the team specifies.
• Wipe high-touch points such as lift buttons, handrails and parcel lockers regularly.
• Keep controlling humidity, run exhaust fans on a schedule and check walls weekly for the first month.
• If new mold appears, look for the leak or seepage first, then plan the next treatment.
• Encourage any resident who feels unwell after wading through floodwater to see a doctor.

Frequently Asked Questions

Can the whole building be treated with ozone at once?
We do not recommend it. Condo work should be divided into controllable, enclosed zones, each completely empty during treatment. This is safer and lets residents use the rest of the building normally.

Can an underground car park be treated?
It depends on whether the space can be sealed. An open car park connected to a ramp with permanent vents will not hold enough ozone. The team assesses on site and tells you honestly which zones are suitable and which need a different approach.

How long will the lobby be closed?
A typical cycle is about 30 minutes per zone, plus a rest and ventilation period before re-entry. After the survey, the team gives an overall timeline so management can announce accurate times. Night work is common.

If we use ozone, do we still need to clean?
Yes. Ozone comes after mud removal, washing and drying. If moisture or mud remains, mold can come back.

Can ground-floor residents book their own units?
Yes. WHD treats both common areas and private units. Management may want to collect requests from ground-floor owners so the team can schedule them on the same day.

Are there documents we can show our committee?
Yes. The certification documents and test results certified for the company by the Department of Medical Sciences and Intertek are available on the website's certification page, and the team can answer further questions directly.

Let Residents Walk Through the Lobby With Confidence Again

Talk to the WHD team about a common-area survey and a zone-by-zone ozone plan for your building.

Get a Condo Ozone Quote

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

Promotion: free medical-grade disinfectant spray with ozone jobs of 15,000 baht or more.

Related Services and Reading

• Residential and Building Ozone Disinfection
• Ozone Cleaning Service
• Disinfection Service
• Certifications and Test Results
• Contact Us

References

• CDC: Floods, cleanup and safety guidance
• World Health Organization fact sheets

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