A story from the field: the night the doors had to close

Ploy coordinates a small temporary shelter tucked into an old lane in Phra Nakhon, the historic heart of Bangkok. The shelter is run by a group of volunteers and supported almost entirely by donations. It occupies three connected shophouses. On the ground floor there is a kitchen, a shared washroom and a storeroom stacked with donated blankets, clothes and spare mattresses. Upstairs is a single long dormitory with about thirty steel bunk beds. Most residents are older people with no home to return to, day laborers who have lost their work, and a few people recently discharged from hospital who simply have nowhere else to go.

When the 2026 floods reached the old town, water rushed in from the street and the storm drains and rose to almost half a meter on the ground floor. It stayed for several days. The volunteers had to walk residents, some of them slowly and with canes, to an emergency shelter run by local authorities. Ploy says that the night she locked the front door was the hardest night of the whole year. For many of the people she serves, this building is the only place in the city where a bed is waiting for them.

When the water finally drained away, she went back inside. The first thing that hit her was the smell: river mud mixed with the sour, heavy odor of sewage. A straight brown waterline ran along every wall downstairs, and beneath it small black and green spots of mold had already appeared. The spare mattresses in the storeroom had swollen with water. A whole pile of donated blankets that had not yet been handed out was soaked through. Upstairs, the water had never reached the dormitory, yet the damp had climbed the stairwell, and the room where thirty people sleep smelled so musty that she could hardly stay inside.

Her first question to our team was simple and honest: "Many of our residents are not strong. Some cough all the time, some have wounds on their feet. If we reopen too soon, are we going to make them sick? And how do we do this properly with the little money we have?" This article brings together the practical answers we gave her, and they apply to any homeless shelter, transitional house, night shelter or shared temporary housing that has been through a flood.

Why shared housing is riskier than an ordinary home after a flood

Many people share a small space. A dormitory where bunks stand close together, a washroom used by dozens of people, and a kitchen that cooks several times a day all create easy routes for germs to pass from one person to the next. In an ordinary family home, a contaminated door handle might be touched by four people. In a shelter, it might be touched by forty. If surfaces still carry residue from floodwater, the risk multiplies accordingly.

Many residents are vulnerable. Older adults, people living with chronic illness, people with weakened immune systems and people with open wounds or skin problems are generally more affected by bacteria and mold than healthy adults. Life on the street can also leave people with untreated conditions. Anyone with a cough, breathing difficulty, fever, diarrhea or an inflamed wound should be checked by a health professional. This article is general guidance about cleaning and disinfecting buildings, not medical advice.

Urban floodwater is rarely clean. Water that has flowed across roads, through drains and past markets usually carries bacteria from sewage, such as E. coli, and may carry Leptospira, the bacteria that cause leptospirosis, which is common where rats live. These germs settle on floors, bed legs, the lower part of walls and anything that sat in the water. They do not leave just because the water level has dropped.

Mold grows fast in old buildings. The old shophouses of Phra Nakhon often have thick masonry walls that release moisture slowly, few ventilation openings and shared walls with neighboring buildings. After a flood these walls can stay wet for weeks, and mold starts to appear within a few days. Airborne mold spores are a well-known trigger for allergies and asthma symptoms, and they travel easily from a damp ground floor up a stairwell into a sleeping area.

Most belongings are donated and limited. Mattresses, pillows, blankets and spare clothing usually come from donors, and there is never quite enough. Throwing everything away may leave the shelter without enough bedding to reopen. Managers therefore have to decide carefully what must be discarded and what can be washed, disinfected and used again.

What is at stake: health, time, money and trust

Health. If residents return while rooms are still damp and moldy, people with breathing problems may cough more, people with wounds may pick up infections from floors and bedding, and a washroom that has not been disinfected can become the starting point of a diarrhea outbreak. In shared housing, such an outbreak spreads quickly and is hard to stop once it begins. Volunteers and staff are exposed too, and a shelter without healthy volunteers cannot operate.

Time. Every day the shelter stays closed is a day residents must stay somewhere else or go back to sleeping on the pavement. Shelters need a way to recover quickly but not carelessly. Reopening in a rush and then having to close again because people fall ill is the worst outcome for everyone.

Money. Most shelters depend on donations. Buying all new furniture and bedding or repainting the whole building is often beyond what they can afford. A clear plan that separates the jobs that need professional help from the jobs volunteers can do themselves makes every donated baht go further.

Trust. Some residents have had bad experiences in dirty or crowded places. If they come back and find a musty smell or black spots on the walls, they may decide not to stay. Donors and volunteers also want to see that hygiene is taken seriously. A systematic, visible recovery protects the confidence of everyone who keeps the shelter running.

Why the usual quick fixes fall short in shared housing

Pouring bleach everywhere. Bleach can disinfect smooth surfaces, but used too strong in a closed room it releases fumes that irritate the airways, which is a poor choice when some residents already have weak lungs. It does not reach mold that has grown into porous plaster, and it does nothing for the musty smell hanging in the air. Most importantly, bleach must never be mixed with toilet cleaners or ammonia, because the combination produces dangerous gases.

Running fans for days. Fans help surfaces dry, but in a building with few openings they may simply stir mold spores into the air and push them around the room, including from the damp ground floor up into the dormitory where people sleep.

Air fresheners and incense. A pleasant scent covers a bad smell for a few hours, but the source remains. In a crowded dormitory, strong perfumes or smoke can make some people feel tight in the chest.

Painting over the stains. If walls have not dried and the mold has not been dealt with first, fresh paint will blister and the mold will push through again within weeks. That is money and volunteer time lost.

Rinsing blankets in plain water and drying them indoors. Fabric that sat in floodwater needs washing with detergent and drying in strong sunlight until it is completely dry. Dried in a damp, shaded room, it will keep its smell and may grow mold again.

The solution: Chemgene HLD4H disinfection fogging combined with ozone treatment

World Health Disinfection (WHD) provides disinfection fogging and ozone treatment for buildings recovering from floods, from family homes to shophouses and shared spaces. Using the two methods together tackles both germs on surfaces and the musty odor in the air.

ULV disinfection fogging. Our team applies Chemgene HLD4H as a fine mist. Because the droplets are very small, they drift into corners, under bunk beds, behind lockers, across washroom walls and over kitchen floors, the places a mop never quite reaches. This makes fogging especially suitable for spaces that many people share.

Ozone treatment. Ozone is a gas that spreads through an entire room. It helps deal with mold spores and breaks down odor molecules, including the smell of mud, sewage and damp that soaks into mattresses, curtains and walls. We use the Master Ozone Generator and adjust the dose and duration to the size and condition of each room.

Ozone safety always comes first. During treatment there must be no people, pets or plants in the area. Our team seals off the space and posts clear no-entry signs. After treatment, the area is ventilated until it is safe before anyone goes back in. In a shelter, where residents may turn up unannounced, we recommend that a volunteer stays at the entrance for the whole treatment period. Electronics, rubber kitchen equipment and other ozone-sensitive items are covered or moved out, and the dose is controlled carefully.

Step by step: restoring a shelter zone by zone

1. Walk-through survey with the coordinator. We inspect every floor, note the flood line, mark mold spots and strong-smelling areas, and identify which zones residents use most. The building is then divided into zones, such as dormitory, washroom, kitchen, storeroom and stairwell, so the work can be done in a sensible order.

2. Advice on mud removal and sorting belongings. Mud should be shoveled out and floors washed with clean water and detergent. Mattresses and pillows that sat in floodwater should be taken out of the building. A mattress that has absorbed floodwater rarely recovers and is usually best discarded. Blankets, sheets and clothes should be washed with detergent and dried in full sun. Volunteers helping with this work should wear rubber boots, rubber gloves and a mask.

3. Electrical check by an electrician. Before switching on lights downstairs or running a water pump, have a qualified electrician inspect sockets, wiring and breakers that were under water.

4. Disinfection fogging in every zone. We start with the dirtiest zones, usually the washroom and storeroom, then move to the kitchen, corridors and finally the dormitory. Floors, lower walls, bed frames, stair rails, door handles and lockers are all covered, since these are the surfaces hands touch most often.

5. Ozone treatment with the area closed. Doors and windows are shut and each floor or zone is treated while the building is empty. A dormitory full of mattresses and curtains usually needs a longer treatment than other rooms.

6. Thorough ventilation. All doors and windows are opened and exhaust fans run until the ozone smell has faded and our team confirms it is safe to enter.

7. Re-check before residents return. We come back to check moisture, odor and the mold spots found earlier. If walls are still very damp, we advise waiting before painting or pushing beds against them, and we schedule a spot re-treatment if needed.

A reopening checklist for shelter managers

• Dormitory: flood-soaked mattresses removed; remaining mattresses dry and odor-free; beds placed at least a hand's width away from walls.
• Shared washroom: toilets, sinks, floors and drains cleaned and disinfected; soap available at every basin.
• Kitchen: dry food and condiments that touched floodwater thrown away; cookware washed with clean water and detergent; water storage tanks inspected.
• Donation storeroom: goods lifted onto shelves; no cardboard boxes left on damp floors.
• Entrance: hand gel available, plus a simple way for residents to tell a volunteer when they feel unwell so the shelter can connect them with local health services.
• Notices: clear, simple signs on washroom use, waste disposal and opening windows for ventilation.

10 reasons shelters choose professional post-flood restoration

1. Disinfection fogging reaches every corner of a crowded dormitory, including the hard-to-clean space under bunk beds.
2. Ozone treatment tackles mold spores and musty odors trapped in mattresses, curtains and walls.
3. We use Chemgene HLD4H, a disinfectant designed for surface disinfection work.
4. It reduces the need for harsh chemicals in closed rooms, which matters when residents have sensitive airways.
5. Zone-by-zone planning lets parts of the shelter reopen sooner, for example the kitchen for food distribution before the dormitory.
6. Our team advises on what to discard and what can be saved, protecting scarce donated goods.
7. Clear ozone safety procedures: area closed, ventilated and confirmed safe before anyone returns.
8. Volunteers spend less time scrubbing the same surfaces again and again, and more time caring for residents.
9. Residents, donors and neighbors can see the shelter takes hygiene seriously.
10. It can be extended with our dust mite removal service for mattresses and pillows, and mosquito spraying around the building while water still stands in the lane.

Before and after restoration

In the coordinator's words

"At first I thought we would just scrub everything ourselves. Then I realized the dormitory upstairs smelled too, so the whole building needed treating. The team helped us split the work into zones. We reopened the kitchen first so we could hand out meals, and the beds came later. When the first uncle came back and said the room did not smell anymore, I felt a huge weight come off my shoulders."

— Ploy, coordinator of a temporary shelter in Phra Nakhon (an illustrative scenario from the field)

Keeping the shelter healthy after residents return

Open the windows every morning. Let air flow through the dormitory for at least one or two hours a day, especially while the walls are still drying out.

Rotate mattresses and pillows into the sun. A weekly schedule where residents help carry mattresses outside to air in the sun keeps bedding fresh and gives everyone a role in caring for their home.

Wipe shared touch points daily. Door handles, stair rails, taps and light switches should be wiped every day using Chemgene HLD4H spray or another suitable disinfectant.

Watch for new mold. If new spots appear on a wall or in a corner, photograph them and note the date. If they spread quickly, ask our team to re-check.

Manage rubbish and standing water outside. Piles of flood debris in front of the building attract rats and cockroaches. Coordinate collection with the district office and empty any container holding water to reduce mosquitoes.

Link residents with health services. If a resident develops a high fever, severe muscle pain especially in the calves, or an inflamed wound after wading through floodwater, help them see a doctor promptly and mention their flood exposure. Further guidance is available from Thailand's Department of Disease Control.

Treating people with dignity during the recovery

Restoring a shelter is not only a cleaning project. Residents often have very few possessions, and the bag under a bunk may hold everything a person owns. Before any work starts, give each resident the chance to collect, check or move their belongings, and ask before discarding anything that is not clearly ruined. Explain in plain words why some mattresses and blankets must go. When people understand that the aim is to protect their health, they are far more willing to help.

It also helps to tell residents when they can come back, even if the date is only an estimate. Uncertainty is stressful for anyone, and especially for someone who has already lost a home. A notice board at the entrance, or a message passed through the outreach volunteers who know residents by name, can make a big difference. Our team can work around these needs, scheduling ozone treatment for quiet hours and finishing ventilation before residents are due back.

Finally, include residents in the new routine. Many are happy to take turns opening windows, airing mattresses or wiping handles if they are asked respectfully. Shared care keeps the building healthier and builds a sense of ownership that lasts long after the floodwater has gone.

Frequently asked questions

Do all residents need to leave the building during the work?
No one may be in an area while it is being treated with ozone. In a larger building it may be possible to treat one floor at a time, provided connecting doors and stairwells are closed off properly. We plan this with you during the survey.

A mattress was only wet at the bottom. Can we keep it?
Mattresses that absorbed floodwater usually hold moisture and contamination deep inside and are very difficult to make safe again, so we generally recommend discarding them. Mattresses that stayed dry but smell musty can be sun-dried and included in the ozone treatment.

How long before people can go back in after ozone treatment?
It depends on room size and treatment time. Our team ventilates the space and confirms with the coordinator before anyone returns.

Is one treatment enough?
Many buildings show a clear improvement after a single round. If walls are still very wet or flooded items remain inside, a spot re-treatment may be needed. We assess this during the re-check.

Our budget is tight. Where should we start?
Start with the shared washroom, the kitchen and the dormitory, which affect residents' health most directly. Storerooms can often be cleaned by volunteers first. Contact us on LINE @whd268 and we will help you prioritize.

Which areas do you serve?
We serve Phra Nakhon, Pom Prap Sattru Phai, Samphanthawong, Dusit, Bangkok Noi and other districts across Bangkok and the surrounding provinces.

Make your shelter a safe place to sleep again

Book a survey for a flooded shelter or shared housing in Phra Nakhon and nearby districts.

View Disinfection Service – Click Here

Book Ozone Treatment – Click Here

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

Related links

• Residential ozone disinfection
• Ozone deodorizing and chemical residue removal
• Dust mite removal service
• All articles
• External sources: WHO: Floods and health and Department of Health, Thailand