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

Monday morning: the machines are ready, the workers are not

Wit owns a small plastic packaging factory down a side street in Lat Krabang, on the eastern edge of Bangkok. About forty people work there across two shifts. The production hall is a single high-roofed building; at the front is a two-storey office, and along one side runs a locker room, staff toilets and a small canteen where a cook sells lunch every day. At the back is a raw-material store with sacks of plastic pellets on wooden pallets and stacks of corrugated cartons for packing, piled almost to the roof beams.

Between 24 and 27 September 2026, continuous heavy rain flooded large parts of Bangkok. According to news reports, around 300 mm fell in roughly 48 hours, and the eastern side of the city was hit hardest. Wit stopped the lines on the first night, when water began to cover the car park. His team lifted moulds and document boxes onto higher ground, but murky water from the street and the drains still seeped under the roller shutters into the back store, and sat on the floor of the locker room and canteen for several days.

When the water finally drained away, the electricians checked the control panels and motors, and the machines started again. Everyone was relieved. But the next problem had nothing to do with the machines. A shift leader told Wit that the locker room smelled so musty that many workers were changing in the toilets instead. The lower part of the gypsum walls in the staff room was showing black specks creeping up above the waterline. The bottom row of cartons had gone soft and grown a white fuzz. And when the office air conditioner was switched on for the first time, it blew out a sour smell, like wet laundry left in a bag for a week.

The most worrying call came from his biggest customer, a food manufacturer, asking about the next delivery and for written confirmation that the production area and stores had been cleaned and disinfected after the flood, because Wit's packaging would end up touching food. Wit was not only worried about orders. He was worried about the workers who had waded through floodwater to reach the factory while the streets were still under water, and about how to bring people back into a building that had just been flooded without them feeling unsafe.

Many SME factories in eastern Bangkok now face the same question: the machines are back, but is the building ready for people? This guide covers where germs and mold hide, why quick fixes fall short, and where ozone disinfection fits.

The late-September 2026 floods, and why eastern Bangkok factories need extra care

According to news reports, the heavy rain of 24 to 27 September 2026 left water standing across Bangkok, and on 26 September the Bangkok Metropolitan Administration declared all 50 districts a disaster zone. Eastern Bangkok was among the worst affected, with areas such as Khlong Chan and Bueng Kum mentioned in coverage. Governor Chadchart Sittipunt 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 Si Burapha and Lat Phrao, still had 20 to 40 cm of water.

Thai media compared the event with the great flood of 2011, and one Thai business report cited a Thai Chamber of Commerce estimate of about 12,300 million baht in damage. That figure is a reminder that the floods hit businesses directly: shops, warehouses and factories that had to stop work. Lives were also lost, according to reports; people's safety around electricity and floodwater comes first.

For SME factories in Lat Krabang and nearby areas, the risk after a flood is higher than in a typical home for several reasons. First, factories tend to have large ground floors full of absorbent materials: cartons, wooden pallets, wiping rags, pipe insulation, gypsum partitions and office ceilings. Second, many people work closely together in enclosed spaces and share toilets, locker rooms and a canteen, so any germs left behind have plenty of chances to spread. Third, many factories sit inside someone else's supply chain, especially in food, beverages, pharmaceuticals and cosmetics, and those customers expect hygiene standards they can verify.

Where germs and mold come from in a flooded factory, and where they hide

Urban floodwater is not clean rainwater. It mixes with drain water, septic overflow, mud, rubbish, oil from the roads and animal waste. When that water enters a factory and stays for days, it carries bacteria, viruses and mold spores into every surface it touches. Once it drains away, the moisture left in materials, combined with Bangkok's hot and humid air, creates ideal conditions for mold. The World Health Organization and the US Centers for Disease Control and Prevention both advise that wet materials which are not cleaned and dried within 24 to 48 hours are likely to start growing mold.

Hotspots that SME factories often overlook

• Locker rooms and changing areas. Steel lockers rusting at the base, safety boots left inside, and damp towels and uniforms all harbour bacteria and mold that can keep a room smelling musty for weeks.
• Staff toilets and showers. Floodwater can push sewage back up through drains, contaminating floors, tiled walls and grout lines with faecal bacteria.
• Canteens and rest rooms. Tables, chairs, fridges, dish racks and lower walls are high-touch surfaces directly linked to food.
• Raw-material and packaging stores. Corrugated cartons, slip sheets and wooden pallets soak up water. When stacked against walls or directly on the floor, mold appears first on the hidden side.
• Ground-floor offices. Gypsum walls, ceiling boards, carpet, upholstered chairs and paper files are favourite food for mold, usually in tightly closed air-conditioned rooms.
• Air conditioners and ducts. Filters, drain pans and cooling coils that stay damp can spread spores and musty air around the room every time the unit runs.

The main germs to know about

Bacteria from sewage and faeces. These include organisms that cause diarrhoea and food poisoning. They spread when hands touch contaminated surfaces and then the mouth, especially in canteens and rest rooms. Common symptoms are loose stools, stomach cramps, nausea and fever.

Leptospirosis. This bacterium comes from the urine of rats and other animals in floodwater, and enters the body through cuts or skin softened by long exposure to water. Workers who waded to work or moved stock while the water was high are directly at risk. Key symptoms are sudden high fever, headache and muscle pain, especially in the calves. Anyone with these symptoms after wading must see a doctor immediately and mention the floodwater exposure. Ozone treatment is not a treatment for this disease.

Mold. Black spots on walls and ceilings, or white and green fuzz on cartons and wood. Mold spores become airborne easily and can cause sneezing, a blocked nose, itchy eyes and coughing, and can trigger attacks in people who already have asthma.

Who in the factory is most at risk?

Workers with chronic conditions such as diabetes, kidney disease, lung disease or asthma, pregnant workers, older staff and anyone with wounds on the feet or legs deserve extra care. Canteen staff, cleaners and store workers who handle wet cartons are also more exposed than others. Provide full protective equipment and keep vulnerable staff out of uncleaned areas.

What it costs a factory owner to leave germs and mold behind

Worker health

When staff return to a building that is still damp, the first signs are usually a blocked nose, coughing, a scratchy throat, headaches and skin rashes. If sewage has contaminated the toilets or canteen, a cluster of diarrhoea cases is possible. When several people fall ill at once, production stalls.

Money and time

A factory that has already lost days of output naturally wants to restart as fast as possible. But restarting in a building that still has problems can cost more than doing it properly: sick leave, rework, and extra raw material lost as mold spreads. Moldy packaging gets scrapped by the lot, and musty goods reaching customers cost even more.

Customer trust

Many SME factories survive on the trust of a handful of customers. If a customer visits after the flood and finds musty air, black stains on the walls or fuzzy cartons, years of trust can be dented in a single day. A clear recovery record is very valuable right now.

Morale and workers' families

Many workers have been flooded at home too. They come back tired and anxious. If the workplace smells musty and looks unsafe, the feeling that "the company doesn't care" spreads quickly. On the other hand, when an owner invests in making the rest rooms, toilets and canteen clean and safe before calling everyone back, staff notice immediately.

Why the usual quick fixes are not enough

Most factories act fast once the water drops, which is right. But common methods have limits.

Pressure-washing and stopping there. Hosing removes mud well, but without proper drying, water forced into wall cavities, under lockers and into porous materials actually adds moisture that helps mold grow.

Wiping bleach only on visible surfaces. Bleach can disinfect smooth hard surfaces, but it penetrates porous materials such as gypsum, wood and paper poorly, and it does not reach the air in the room, the gaps behind lockers or the space above the ceiling. It also has a strong smell and is dangerous when mixed with other cleaning products.

Running industrial fans all day. Fans dry the surface faster, but they also blow mold spores around the whole building if moldy materials have not been removed first.

Air fresheners and fragrance. These only mask smells. They do nothing to the germs causing them, and the musty smell returns as soon as the fragrance fades.

Painting over mold. Some sites do this to look ready for a customer visit. But the mold under the paint is still alive and often pushes the paint into bubbles or reappears as new spots within weeks.

What these methods share is that they only deal with what can be seen and reached. A factory has many cavities and gaps that no cloth can reach, and a large volume of air in which germs and spores float. That is where ozone treatment comes in, as an additional step after washing and drying.

How the WHD ozone disinfection service helps a factory

Ozone (O3) is a strongly oxidising gas. According to World Health Disinfection (WHD), ozone breaks down the cell structures of viruses, bacteria and mold, as well as odour molecules, and then reverts to oxygen (O2) without leaving chemical residue. The big advantage of a gas is that it spreads through the whole volume of a room and reaches corners, gaps behind cabinets and places that are hard to wipe.

According to test results certified for the company, the service has been tested by Thailand's Department of Medical Sciences and by Intertek (UK), eliminating viruses, bacteria and mold by 99.99%. Details are available on the company's certification page, which is useful for factories that need to show evidence to customers or auditors.

How the work is done in a factory

1. Survey and zoning. The team walks the site with the owner or plant manager and splits it into zones such as offices, locker rooms, toilets, canteen, QC room and stores, so the work can be sequenced and sized.
2. Readiness check. The team confirms that mud has been removed, the area washed and dried, heavily moldy materials taken out, no standing water remains and no open food is left inside.
3. Clear and seal. The zone being treated must be empty: no workers, no animals and no plants. Doors and windows are closed and "no entry" signs are posted.
4. Ozone fill and contact time. A typical cycle takes about 30 minutes per zone, covering filling the space with ozone and the contact period.
5. Rest and ventilation. The ozone is left to break down into oxygen, then the zone is ventilated before anyone is allowed back in.
6. Handover and aftercare advice. The team advises on humidity control, stock placement and daily cleaning to reduce the chance of mold returning.

For a factory, the practical benefit is that treatment can be planned zone by zone on a day off or between shifts, without shutting the whole site at once. After rest and ventilation, the zone is usable again with no chemical film left behind.

If your factory also has chemical odours from repainting or new epoxy floors after the flood, WHD offers a separate ozone chemical-residue and odour removal service. For high-touch surfaces, ozone can be combined with Chemgene HLD4H disinfectant used according to the label.

10 reasons Lat Krabang SME factories should ozone-treat before bringing staff back in full

1. It reaches where hands cannot. Ozone gas spreads behind lockers, under racking and into high ceiling corners that mops and cloths never touch.
2. It treats the air, not just surfaces. Mold spores and germs floating in a closed room come into direct contact with ozone, unlike wiping, which only works on surfaces.
3. No residue. Ozone reverts to oxygen, which suits canteens, rest rooms and areas linked to food packaging. See the ozone disinfection service for details.
4. Zone by zone, no full shutdown. About 30 minutes per zone means treatment can be scheduled on a day off or during a shift change.
5. Backed by test results. According to test results certified for the company, tested by the Department of Medical Sciences and Intertek (UK), eliminating viruses, bacteria and mold by 99.99%.
6. It tackles musty smells at the source. Ozone breaks down odour molecules rather than covering them, so locker rooms and offices do not depend on fragrance.
7. It gives you a story your customers can check. The factory can record the date, zones and steps in its post-flood recovery report for customers or auditors.
8. It protects vulnerable staff. Workers with allergies, asthma or pregnancy return to better air once washing, drying and ozone treatment are complete.
9. It lowers the chance of mold spreading to new stock. When stores have been cleaned, dried and treated, the next batch of cartons is less likely to be contaminated.
10. Professional team and aftercare. You get a humidity and cleaning plan, plus a free medical-grade disinfectant spray with ozone jobs of 15,000 baht or more. Ask on the service page.

Before and after: a factory restored step by step

Note: results depend on the condition of the space and on cleaning before treatment. This comparison is illustrative.

Example case: a three-day recovery plan for a packaging factory

Example case (a simulated situation based on typical jobs, not a real customer review)

Back to Wit. After talking with his customer and shift leaders, he decided not to call every worker back on Monday. Instead, a small team would clean first, following a three-day plan.

Day one. Wearing boots, rubber gloves and masks, the team shovelled mud out of the store and locker room, threw away every wet carton, set aside pellet sacks that had split for inspection, removed every air-conditioner filter, and cut away about half a metre of water-stained gypsum from the bottom of the walls so the frames inside could dry.

Day two. Floors were washed with detergent; lockers, canteen tables and toilet surfaces were wiped down. The roller shutters were opened and dehumidifiers and fans were used to dry the building, but only after moldy items had been removed. An air-conditioning technician cleaned the coils and drain pans.

Day three was a Sunday with no shifts. The WHD team ozone-treated the site zone by zone, starting with the office, locker room, toilets and canteen, then the back store. Every zone was closed, signed "no entry" and empty during treatment. After the rest and ventilation period, the shift leader walked through with Wit and recorded the date and zones in the recovery report.

The following Monday, workers changed in the locker room as usual. Wit sent the recovery report, with before-and-after photos, to his customer. A worker who mentioned fever and calf pain after wading the previous week was told to see a doctor first, without worrying about lost pay. What Wit told his team that day was simple: "We can fix machines, but if people are sick or don't want to work here, we can't carry on."

Factory flood-recovery checklist: before and after ozone

Safety first

• Keep flooded circuits off until an electrician has checked panels, sockets and motors. Never switch anything on while standing on a wet floor.
• Check canteen gas cylinders, chemicals, oils and solvents for leaks or displacement.
• Everyone cleaning should wear boots, rubber gloves, a mask and eye protection, with wounds fully covered.

Before ozone

• Remove all mud and debris; wash floors and walls with detergent.
• Discard cartons, slip sheets and porous materials that were submerged or moldy.
• Remove wet or moldy gypsum, insulation and ceiling boards.
• Clean air conditioners and drain pans; replace filters.
• Dry the space with ventilation, dehumidifiers and fans, after moldy materials are out.
• Remove food, medicines and staff belongings; tell the team about any sensitive materials or equipment.
• Plan zones and times with nobody working; inform staff in advance.

During treatment

• No people, animals or plants inside. Post "no entry" signs and lock doors.
• Assign one factory coordinator to make sure nobody walks in by mistake.

After treatment

• Re-enter only after the rest and ventilation period the team specifies.
• Keep controlling humidity; keep cartons and pallets off the floor and away from walls.
• Wipe high-touch surfaces regularly: handles, canteen tables, taps and handrails.
• Record dates, zones and steps in a recovery report for customers and auditors.
• Watch staff health. Anyone with fever, muscle pain (especially in the calves), diarrhoea or infected wounds should see a doctor immediately.

FAQ: ozone disinfection for factories after a flood

1. Can ozone replace washing and cleaning?

No. Ozone treatment comes only after mud removal, washing and drying. Thick mud and dirt shield germs, and materials that are still wet will let mold return.

2. Can staff work in other zones during treatment?

The zone being treated must be empty and sealed. Other zones that are clearly separated may be able to operate, depending on the layout and the team's assessment, but the best option is a day off or a period with no shift.

3. How long does it take?

A typical cycle is about 30 minutes per zone, not counting preparation and the rest and ventilation period. The number of zones depends on the size and layout of the factory.

4. Do undamaged raw materials and products need to be moved out?

Food, medicines and anything staff will consume should be removed. Sensitive materials should be discussed with the team first. Cartons or materials that were submerged should be discarded before treatment, not kept in the hope that ozone will save them.

5. Is there documentation for customers or auditors?

The company has a certification page showing test results, and the factory can record dates, zones and steps for its recovery report. Ask the team directly about any specific documents you need.

6. If a worker falls ill after wading, will ozone help?

Ozone treats the space, not people. Anyone with fever, muscle pain, diarrhoea or infected wounds must see a doctor and mention their floodwater exposure.

Get both your machines and your people ready

Talk to the WHD team about a site survey and a zone-by-zone ozone plan on days that do not disrupt production.

Book a factory survey and ozone treatment

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

Related services

• Residential and building ozone disinfection
• Ozone chemical-residue and odour removal
• Disinfection services
• Chemgene HLD4H medical-grade disinfectant
• Contact us

References

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