A story from the field: the Monday morning the big meeting room was not ready

Thanapol is the building manager for a mid-sized company whose offices occupy a four-storey building on Phahonyothin Road, a short walk from the Ha Yaek Lat Phrao junction in Chatuchak district. On the ground floor is the company's main meeting room, which seats around forty people. It is used for management meetings, staff training and, most importantly, for receiving clients. The room is cooled by two large floor-standing air conditioners in opposite corners. The floor is laid with carpet tiles, the chairs are upholstered in fabric, and the ceiling is made of acoustic panels.

During the 2026 floods, water entered the ground floor to a depth of about thirty centimetres and stayed for a week. Once it had drained away, the housekeeping team pulled up some of the soaked carpet tiles, washed the floor and wiped down the chairs. The building's electrician inspected the ground-floor electrical system and signed it off. Satisfied that the worst was over, Thanapol booked the room for a sales team meeting the following Monday morning.

That Monday, as soon as both floor-standing units were switched on, a damp, musty smell mixed with the odor of river mud rolled across the room. Several people began sneezing one after another. Others complained of headaches and stinging noses within the first half hour. Less than an hour in, the meeting had to move to a small room upstairs. Worse still, the company had an important presentation booked with a major client in that same room the following week.

Thanapol called the World Health Disinfection (WHD) team and asked for the room to be ozone-treated. The first advice he received was not what he expected: "Get an AC technician to inspect and clean the units first, because part of that smell is coming from inside them. The room, the carpet, the chairs and the air are what our team will take care of." From there, the two sides planned the work together in the right order.

Why a musty smell bursts out when the AC is turned on after a flood

A floor-standing air conditioner sits directly on the floor, so the lower part of the unit is right at flood level. That makes it very different from a wall-mounted split unit high up near the ceiling. The musty smell that pours out when it starts can come from several sources at once.

• The condensate drain pan and drain line. These can hold mud and leftover floodwater. When the unit runs and fresh condensation drips in, the mixture quickly turns into foul, stagnant water that smells.
• The evaporator coil and the blower wheel. Days of trapped humidity in a closed room allow mold and slimy microbial growth to settle on the coil fins and the blades of the squirrel-cage fan. When the unit starts, the airflow carries both odor and spores straight into the room.
• The air filters. They soak up moisture and muddy dust. If they are not removed and washed or replaced, they become a continuous source of smell.
• Carpet tiles and their adhesive. Even after some tiles have been removed, the remaining tiles and the glue beneath them may still be damp. That becomes a source of odor that the AC then spreads around the room.
• Fabric chairs and acoustic ceiling panels. These porous materials absorb humid air throughout the flood period, even if they were never directly underwater.

So the air conditioner is not the only culprit. It is the fan that takes the smell from every source in the room and delivers it to everyone's nose. Fixing one source while ignoring the others is why so many offices find the smell coming back after they thought they had dealt with it.

What it costs: staff health, company image and lost time

Staff health

Mold spores blown out of an air conditioner and stirred up from carpet can cause allergic symptoms: sneezing, a blocked nose, irritated eyes and throat. People with asthma may find their symptoms flare. A meeting room is a closed space where a large number of people sit for hours at a time, so each person breathes in far more of that air than they would in a corridor or an open-plan area. A floor that was covered in mud may also hold residual bacteria from sewage, such as E. coli. Housekeeping staff who clean up without boots and gloves should also be aware of the risk of leptospirosis, which can enter through small cuts on the hands or feet. Anyone who develops a fever or persistent symptoms after flood clean-up should see a doctor.

Company image

The meeting room is the face of the organisation. A client who walks in and notices a musty smell will quietly wonder how much attention to detail the company really has, however strong the presentation on the screen. In competitive industries, first impressions in that room carry real commercial weight.

Work and time

When the main meeting room is out of action, training sessions are postponed, meetings are split across several smaller rooms, or the company ends up renting a venue elsewhere. These are hidden costs that never appear as a single line item, yet they add up every single day the room stays unusable.

Who does what: the AC technician's job and the WHD job

The job of a qualified AC technician and electrician

• Inspect the electrical system, control board, motors and compressor of any floor-standing unit that was submerged, before it is used again.
• Strip down and clean the evaporator coil, blower wheel, drain pan and drain line, and wash or replace the air filters.
• Assess whether each unit should be repaired, have parts replaced or be replaced entirely, and check any ductwork if the system has it.

The WHD job

• Disinfection fogging of the floor, walls, tables, chairs and other surfaces in the meeting room.
• Ozone treatment to break down musty odors and reduce mold spores in the air, carpet, fabric chairs and ceiling panels, with the air conditioners and other electrical equipment switched off during treatment.
• Coordinating the order of work with the AC technician so that odors do not cycle back.

WHD does not repair air conditioners, does not clean their internal systems, and does not certify the electrical safety of any AC unit. The safety of the equipment is the responsibility of a qualified AC technician or electrician. Keeping that division clear protects everyone involved and makes sure no part of the job falls between the cracks.

Why the usual office fixes do not get rid of the smell

Spraying air freshener into the AC vents. The perfume blows out alongside the mustiness, leaving the room with an irritating mixed smell. Some products can also leave a sticky film on the coil that attracts more dust.

Running the AC all night to dry the room. If the coil and drain pan are still dirty, running the unit for hours simply spreads mold through the room and drives the smell deeper into chairs and ceiling panels. It can make the problem worse rather than better.

Cleaning the AC and nothing else. This removes the source inside the machine, which is essential. But the odor already absorbed by carpet, chairs and ceiling panels remains. When the AC is switched on again, the airflow carries that smell straight back out of the materials.

Charcoal bags or a small air purifier. These are fine for a small room with a mild smell. A forty-seat meeting room full of porous materials needs a much more thorough approach.

The WHD solution: fog and ozone-treat the whole room once the AC has been cleaned

Disinfection fogging with CHEMGENE HLD4H, delivered through ULV foggers, covers the floor, walls, meeting table, chairs, handrails, door handles and room corners. The team avoids spraying directly into electrical equipment and the air conditioners themselves. Chemgene HLD4H is a high-level surface disinfectant without the harsh smell of chlorine, which suits enclosed office spaces.

Ozone treatment follows the fogging. The room is closed, the air conditioning is switched off, and ozone is released at a dose calculated for the room's volume. Ozone diffuses into carpet fibres, chair upholstery, acoustic ceiling panels and every corner. It breaks down the molecules that cause musty odors and reduces airborne mold spores. When the treatment time is over, it reverts to oxygen, leaving no chemical perfume behind.

Because the AC technician has already cleaned the units before the room is treated, the first time the air conditioning is switched back on, it blows clean air across materials that are no longer holding odor. That is the moment the room finally smells right again.

Ozone safety in an office

• No people, animals or plants in the room during treatment. We recommend scheduling it outside office hours or at the weekend.
• Switch off the AC and any ventilation shared with other rooms, so that ozone does not leak into areas where people are working.
• The dose is controlled. Screens, projectors, microphones and other sensitive electronics should be removed or covered.
• After treatment, doors are opened for the ventilation period the team specifies before the room is used again.

Step by step: restoring a flooded meeting room with floor-standing AC

1. Stop using the AC for now until the technician has inspected and cleaned the units.
2. The AC technician checks the electrics and cleans the units: coil, blower, drain pan, drain line and filters.
3. Remove badly damaged materials. Carpet tiles that were underwater for a long time or have deep-set mold, and ceiling panels that are swollen or stained, should be replaced on the contractor's advice.
4. WHD site survey. The team locates the strongest odor points, measures the room and plans the treatment time.
5. Fogging with Chemgene HLD4H across all surfaces in the room.
6. Controlled-dose ozone treatment with the AC off, the room closed and nobody inside.
7. Ventilate, then test the AC. Once the ventilation period is complete, the cleaned AC units are switched on and the room is checked to confirm the smell does not return.
8. Plan ongoing care, such as washing the filters on a regular schedule and keeping an eye on any doubtful spots.

What the building team can prepare before the work day

• Book the AC technician to finish at least one day before the fogging and ozone visit, so the units are dry and ready to test afterwards.
• Clear out documents, portable whiteboards, sign stands and staff belongings, leaving only tables, chairs and fixed fittings.
• Tell staff and housekeeping in advance when the room will be closed, and put a sign on the door so nobody walks in during treatment.
• Check that vents or doors connecting to neighbouring rooms can be closed properly, especially if people will be working next door.
• Appoint one coordinator who can make decisions about timing and access on the day, so that the job is finished in a single visit.

Keeping the meeting room fresh in the months after the flood

Getting the smell out once is only half the job. The other half is making sure it does not slowly creep back as the rainy season continues and the building settles. Ground-floor rooms in Bangkok that have been flooded tend to stay a little more humid than the floors above for some time, because the concrete slab and the lower part of the walls release moisture gradually. A few practical habits make a big difference.

First, keep the air conditioning on a regular schedule rather than switching it off completely for days at a time. A room that is closed, warm and unused for a long weekend is exactly the environment in which mold restarts. Second, ask the AC technician to agree a filter-cleaning interval for the next few months that is shorter than usual, since the filters will catch more dust and spores while the building recovers. Third, avoid stacking cardboard boxes, spare chairs or rolled-up banners against the walls, where air does not circulate and damp patches go unnoticed. Fourth, walk into the room first thing on a Monday morning, before anyone switches anything on, and simply smell the air. If the mustiness starts to return, it is far easier and cheaper to deal with early than after it has soaked back into the carpet and chairs.

Finally, keep a simple log: the date the AC was cleaned, the date of fogging and ozone treatment, and any spots where the smell or dark marks reappear. That record helps the AC technician, the cleaning contractor and the WHD team see a pattern quickly if a follow-up visit is ever needed.

A note on shared air and neighbouring rooms

Many office buildings have more than one room on the ground floor: a reception area, a small pantry, a storeroom, perhaps a training room next door. If any of these were also flooded, or if they share corridors and doors with the meeting room, odor and spores move freely between them. Treating only the meeting room can leave a reservoir of smell next door that drifts back in every time the door is opened. During the survey, the WHD team will walk the whole ground floor with the building manager and point out where treating an adjoining space in the same visit would make the result more reliable. Where a building has a central ducted system rather than standalone units, the AC contractor should also advise on whether any ductwork needs cleaning, because that is outside the scope of a room treatment.

10 reasons to restore the meeting room properly, not piecemeal

1. Odor in carpet and fabric chairs needs a gas that penetrates materials, such as ozone treatment.
2. Clean AC, no recycled smell, because the room's materials are treated at the same time.
3. Fewer mold spores to trigger allergies in staff who sit through long meetings.
4. High-touch surfaces disinfected through our disinfection fogging service.
5. No harsh chemical smell. CHEMGENE HLD4H suits enclosed rooms.
6. Out-of-hours scheduling, so the business keeps running.
7. Clear responsibilities. The AC technician looks after the machines; WHD looks after the room and the air.
8. Your client-facing room restored, ready for the next presentation.
9. Lower hidden costs. No external venue hire, no postponed training.
10. Easy to extend to other areas, for example ozone treatment for odors and chemical residue after repainting or fitting new carpet.

Before and after

In the building manager's words

"I assumed a round of ozone would sort it out. The team explained that the AC had to be cleaned first or the smell would just come back. Once we did things in that order, the meeting room was ready in time for the client, and nobody has complained about the smell since."

— Thanapol, office building manager on Phahonyothin Road, Chatuchak (a story from the field)

Frequently asked questions about AC and meeting rooms after a flood

Q: Our floor-standing AC was submerged. Can we let it dry and switch it on?
A: No. A qualified AC technician or electrician must inspect the electrics, motor and control board first, and the coil, drain pan and blower should be cleaned to remove the source of the smell.

Q: Does WHD clean air conditioners as well?
A: No. Cleaning and repairing AC units is the AC technician's job. WHD handles disinfection fogging and ozone treatment of the room and helps coordinate the sequence of work.

Q: Can ozone treatment be done with the AC running?
A: The team recommends switching off the AC and any ventilation shared with other rooms during treatment, so the ozone stays within the unoccupied room at a controlled level.

Q: Can flooded carpet tiles be kept after ozone treatment?
A: It depends on their condition. Tiles that were underwater for a long time or have deep mold usually need replacing. Tiles that were only exposed to humidity can often be cleaned, treated and kept.

Q: How long does the work take?
A: It depends on the room size and the strength of the odor. The team will give clear times for fogging, ozone treatment and ventilation. Most jobs can be scheduled at a weekend or outside office hours.

Q: Is ozone safe for the projector, screens and microphones in the room?
A: The ozone dose is controlled, but sensitive electronics should still be removed or covered before treatment as a precaution. The team will go through the room with you beforehand and point out anything that should be taken out.

Q: Staff are still sneezing a week after the clean-up. Is that normal?
A: Lingering mold spores in carpet, chairs or the AC are a common reason. If symptoms continue after the room has been treated, staff should see a doctor, and the building team should ask the AC technician and WHD to re-check the room.

Q: Do other rooms in the building that stayed dry need treating?
A: If they share air conditioning or corridors with the flooded area, odor and humidity can spread. The team will survey the building and advise based on what they find.

Meeting room still musty when the AC is on? Let WHD restore it.

Ozone treatment and disinfection fogging for meeting rooms, training rooms and offices in Chatuchak and nearby districts, with out-of-hours scheduling available.

Book Ozone Treatment — Click Here

See the Disinfection Service — Click Here

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

Related links

• Ozone treatment for odors and chemical residue
• Master Ozone Generator
• Dust-mite removal for fabric chairs and reception sofas
• All articles
• External source: World Health Organization — Floods and health · Department of Disease Control, Thailand