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

The morning the water went down, the first smell was not mud. It was a petrol station.

Thana manages the juristic person office of a twenty-something-storey condominium in eastern Bangkok. At six in the morning he was standing at the top of the ramp to the basement car park. Almost two full days of rain had sent water pouring down the ramp faster than the building's sump pumps could cope. Dozens of residents' cars sat half submerged; a few were under water up to the roof. When the district pumps and the building's own pumps finally pulled the water out and left only wet mud on the floor, the relief lasted about a minute. What followed was a sharp, eye-watering smell, like standing next to a fuel nozzle, mixed with old engine oil and drain water.

Within hours the office phone would not stop ringing. Residents on the third to fifth floors reported a petrol smell drifting up through the lift lobby and the fire stairs. An elderly resident whose unit sits beside the lift shaft said she had felt dizzy since she woke up. A new mother asked whether she should take her baby somewhere else for a while. Thana switched on every exhaust fan, had the floor scrubbed with detergent and put out hundreds of charcoal bags. Three days later the smell was still circulating, worst in the evening when the air was still and humid.

This did not happen in only one building. According to news reports, from 24 to 27 September 2026 Bangkok received continuous heavy rain of around 300 mm in roughly 48 hours. On 26 September the Bangkok Metropolitan Administration declared all 50 districts a disaster zone. Eastern Bangkok was hit hardest, with areas such as Khlong Chan and Bueng Kum mentioned in coverage. Governor Chadchart said the canals were full and drainage would take two to three days after the rain stopped, and as of 30 September some roads, including Si Burapha and Lat Phrao, still had 20 to 40 cm of water. Buildings with basement or ground-level car parks became collection points for floodwater, and for the oil of every vehicle parked inside one enclosed space.

This article explains where the petrol and oil smell in a flooded car park comes from, why it climbs to upper floors, what it can do to health, why the usual fixes fall short, and how a correctly ordered recovery, finished with the ozone odour and chemical-residue removal service from World Health Disinfection (WHD), can be carried out safely for residents and staff.

Where does the fuel smell in a flooded car park come from?

When a car park floods, every submerged vehicle starts releasing small amounts of fluid into the water at the same time. The first source is fuel itself, both petrol and diesel, which can seep from loose filler caps, tank vent lines or ageing joints. The second is the collection of other fluids under the bonnet and the chassis: engine oil, gear oil, brake fluid and coolant. The third is old oil that has dripped onto the concrete over years. On a normal day it is dry and barely noticeable, but once it is soaked and stirred by moving water it lifts off as a rainbow film on the surface.

Oil is lighter than water, so it floats. As the water level drops, the film does not disappear; it is gradually deposited on every surface the water touched: concrete walls, columns, kerbs, cable conduits, drainage channels and any low ceiling panels or insulation. On the walls it leaves a dark tide line that feels slippery and sticky. Heavier fractions mix with mud and settle as black sludge in corners, inspection chambers, drainage grates and sump pits, places almost nobody goes down to clean.

What makes the smell so persistent is concrete itself. Concrete and plaster are full of tiny pores. After hours or days of soaking in oily water, hydrocarbons migrate into the material. When the floor begins to dry, they slowly evaporate back out as vapour. That is why many buildings scrub the floor until it looks clean, yet the smell returns every time the weather heats up or the ramp doors are closed at night.

What are fuel vapours, and why do they reach the upper floors?

The fuel smell is made of volatile organic compounds, or VOCs: chemicals that evaporate at room temperature. Petrol contains hundreds of hydrocarbons. The group most often discussed for health is known as BTEX: benzene, toluene, ethylbenzene and xylene. Health agencies worldwide pay close attention to them, and benzene in particular has long been classified as a human carcinogen. Risk depends on concentration and duration, so smelling fuel does not mean you will fall ill immediately. It does mean the air contains substances you should not keep breathing for long periods.

Tall buildings add a complication called the stack effect. Warmer indoor air rises through vertical openings such as lift shafts, stairwells, service risers and refuse chutes, and air from the lowest level is drawn in to replace it. When the lowest level is a car park full of fuel vapour, the whole building behaves like a chimney, pulling the odour up and releasing it into each floor's corridor. Units beside the lift shaft usually smell it most, especially at night.

Petrol vapour is also heavier than air, so it collects in low points such as sump pits, drainage trenches and dead corners, where staff need extra care about both oxygen deficiency and fire risk.

Symptoms that may appear after breathing fuel vapour in an enclosed space

• Headache, light-headedness and a foggy feeling, especially after more than ten or twenty minutes in the area
• Nausea, loss of appetite and an upset stomach
• Stinging eyes, watering eyes, a burning nose, throat irritation and a dry cough
• Drowsiness, poor concentration and unusual tiredness
• Flare-ups in people with asthma or allergies, including wheezing and chest tightness

If anyone has severe symptoms such as difficulty breathing, fainting, confusion, seizures or chest pain, move them to fresh air and call a doctor or the 1669 emergency line immediately. An odour-removal service is not medical treatment and never replaces seeing a doctor.

Who is most at risk in the same building?

Older people who stay in their units all day, young children who breathe faster than adults relative to body weight, pregnant women, and anyone with lung disease, heart disease or allergies should avoid fuel vapour the most. The group with the heaviest exposure, though, is the staff: security guards, housekeepers, building technicians and drivers who spend whole days in the car park during recovery. Juristic offices should provide respirators with organic-vapour cartridges, oil-resistant gloves and boots, and limit how long each person works in the strongest-smelling areas.

Safety comes before odour: electricity and flammable vapour

According to news reports, three people died in these floods, one of them from electrocution in a car park. Our sincere condolences go to every family affected. It is a sombre reminder that a car park still holding water is an electrical hazard. Before anyone goes down to clean, the building electrician must isolate power to flooded zones and check distribution boards, sockets, lighting and any electric-vehicle chargers.

Another point that is often overlooked is that petrol vapour ignites very easily. In the first days after the water recedes, if the smell is still intense, there must be no smoking, no open flames, no welding or cutting, and care with plugging in equipment that could spark where vapour collects. The correct starting point is continuous mechanical ventilation, removing and absorbing as much oil as possible, and having a specialist assess whether the space is ready for the next step.

That is why ozone is never the first step. It is the final step for odour still trapped in materials, after power is isolated, water and mud are removed, oil is absorbed, floors are washed and ventilation has brought fuel vapour down. Nobody should run an ozone machine where fuel is still pooled or the petrol smell is heavy.

The cost to residents and the juristic office when the fuel smell will not go

Health

Smelling fuel for hours every day for a week or more leaves many residents with headaches, poor sleep and irritated airways. People working from home and older residents who rarely go out are affected more than those who leave for work all day.

Money

According to news reports, one Thai business report cited a Chamber of Commerce estimate of about 12,300 million baht in damage from these floods. Part of that is property inside condominiums: cars, pumps, electrical systems and common areas. For a juristic office, a lingering smell means repeated cleaning, electricity for fans running around the clock and maintenance spending drawn from the common fund. For owners who rent out their units, a smelly building can lead tenants to cancel or ask for a rent reduction.

Why the usual fixes do not make the fuel smell go away

1. Scrubbing with detergent alone. It removes some surface film, but oil that has entered the pores of the concrete stays. Large volumes of rinse water can also carry oily water into inspection chambers and drains, creating a new hidden odour source under the grates.

2. Running exhaust fans alone. Ventilation is essential and should be done, but fans only deal with vapour in the air at that moment. They do not stop walls and floors from releasing more. When the fans stop or break down, the smell comes straight back, and in some buildings fans running the wrong way can even push vapour towards the lift lobby.

3. Painting over oil-stained walls. Many paints will not bond to oily surfaces and soon peel. Worse, new paint adds a layer of solvent smell while the old fuel odour keeps escaping from behind it.

4. Mixing strong chemicals. Some people combine bleach, toilet cleaner and degreaser hoping for faster results. Mixing certain products, such as chlorine bleach with acids or ammonia, can release dangerous gases, and in an enclosed basement that risk is greater. It also stacks a cleaning-chemical smell on top of the fuel smell.

None of these methods is entirely wrong; several are necessary steps. But none of them breaks down odour molecules trapped in materials and floating in the air of a large enclosed space. That is the gap ozone fills.

WHD ozone chemical-odour removal: breaking odour molecules at the source

According to WHD service information, ozone (O₃) treatment breaks down odour molecules at the source instead of masking them. Ozone is an unstable form of oxygen with three atoms. When it meets VOCs and odour molecules, the extra oxygen atom oxidises them, changing their structure so the smell is reduced. The service targets paint, thinner, epoxy and lacquer odours, VOCs and musty smells, and also helps reduce bacteria, viruses and mold. Afterwards ozone reverts to oxygen with no residue, and the space is ready to use about two hours after treatment.

What makes the service suitable for condominiums is measurement. WHD measures TVOC (total volatile organic compounds) with calibrated instruments before and after treatment, giving the juristic office numbers to report to the committee and residents rather than just a feeling that things smell better. The team uses a Master Ozone Generator and works across homes, condos, offices, factories, construction sites, hotels, storage facilities and automotive jobs.

How the work is done in a condo car park

1. Site survey and assessment: the team walks the site with the juristic office, identifies hot spots such as inspection chambers, sump pits, the generator room, lift lobbies and fire-stair entrances, and confirms that power isolation, pumping, mud removal and oil absorption are complete.
2. Baseline TVOC readings: measurements are recorded at several points for later comparison.
3. Zoning plan: car parks are large and open on several sides, so the area is divided into zones, with ramps, doorways and connections to lift lobbies and stairwells temporarily sealed. During treatment there must be no people, pets or plants in the zone, and cars should be moved out of the zone being treated.
4. Advance notice to residents: closure times and temporary routes are announced so nobody wanders in.
5. Ozone release and contact time: the Master Ozone Generator treats the sealed zone for a duration set by the team according to size and odour level.
6. Rest and ventilation: after the machine stops, ozone is allowed to revert to oxygen and the area is ventilated. Nobody enters until the team confirms it is safe; typically the space is ready about two hours after treatment.
7. Post-treatment TVOC readings and handover: readings are taken at the same points and compared, with advice on ongoing care.

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 set by the team has ended. Ozone comes after mud removal, washing and drying. It does not replace cleaning and it does not replace medical care.

10 reasons juristic offices choose ozone for fuel odour in flooded car parks

1. It works on the cause, not the cover-up: ozone chemical-odour removal oxidises odour molecules, unlike fragrance that simply adds another smell.
2. It reaches every corner: as a gas, ozone spreads under beams, behind pipes and into dead corners a mop never reaches.
3. No residue: ozone reverts to oxygen, so you do not add a new chemical to a space that already has too many.
4. Results you can show: calibrated TVOC readings before and after give the committee real numbers.
5. Fast handback: the space is ready about two hours after treatment, so zones can be closed one at a time with minimal disruption.
6. Germ reduction at the same time: ozone also helps reduce bacteria, viruses and mold brought in by floodwater and sewage.
7. Less odour drawn up the lift shafts: once the source in the basement falls, the stack effect carries less smell upstairs.
8. It fits around renovation: after repainting lane markings, walls or epoxy floors, you can treat paint and solvent odours with ozone again.
9. Experience across building types: from condos and offices to hotels, factories, warehouses and vehicles.
10. Confidence for residents: clear steps and measured results reduce anxiety and complaints. Ask WHD for a site assessment.

Before and after: what juristic offices typically see

Note: results vary with site conditions and cleaning quality.

Example case: a Lat Phrao condo where the fuel smell reached the fifth floor

Example case (a simulated situation to explain the process, not a verified customer review)

Sunee sits on the committee of a mid-sized condo in the Lat Phrao area. After three days of shovelling and scrubbing, a fuel smell still reached the fifth floor, especially units beside the lift shaft, and two elderly residents moved in with their children for a while. Some committee members wanted to repaint the whole level; others wanted to wait.

The committee chose to work in order: technicians checked the electrics and pumps, a crew removed sludge from the inspection chambers and sump pit (the main source everyone had overlooked), absorbent material lifted residual oil, the tide-lined walls were degreased, and ventilation ran until the floor was dry.

Once the space was ready, the ozone team surveyed it, took TVOC readings, split the car park into three zones and asked residents to move cars upstairs in rotation. Connections to the lift lobby were sealed and each zone was treated during the day, when most residents were at work. After the rest and ventilation period, readings were repeated at the same points. Sunee said what helped most was not only the reduced smell but having clear steps and numbers to share in the residents' LINE group, which visibly cut the complaints.

The lesson: ozone works best when the main odour sources, such as oily sludge in chambers, have been removed first. Skip that step and the smell creeps back from what is left.

Recovery checklist for a flooded condo car park, before and after ozone

Phase 1: Safety (first day after the water recedes)

• Isolate power to flooded zones; have an electrician check boards, sockets, lighting and EV chargers before re-energising
• No smoking or open flames in the car park; post clear warning signs
• Run mechanical ventilation continuously and open the ramps for airflow
• Give staff gloves, boots, eye protection and respirators suitable for organic vapour
• Tell residents not to start flooded cars themselves; contact the insurer or a garage first

Phase 2: Remove the odour sources

• Pump out all standing water, including chambers, sump pits and drainage channels
• Collect oily sludge in closed containers and arrange appropriate disposal; never dump it into public drains
• Use absorbent pads or granules to lift oil from floors and around columns
• Wash walls and floors with a degreaser per the label; never mix different products
• Remove materials soaked with oil, such as low insulation, ceiling panels or rubber mats

Phase 3: Dry and disinfect surfaces

• Ventilate until floors and walls are dry; international guidance is to dry within 24 to 48 hours to limit mold
• After cleaning, disinfect shared touch points such as lift buttons, handrails and door handles with a suitable product, for example Chemgene HLD4H at the label dilution

Phase 4: Ozone for residual odour

• Book a survey, take baseline TVOC readings and plan zones
• Announce closures, move cars, seal links to lobbies and stairs, and confirm no people, pets or plants remain
• Treat for the set time, then rest and ventilate; nobody enters until the team gives the all-clear
• Take post-treatment TVOC readings and file them in the juristic office's records

Phase 5: After treatment

• Run normal ventilation and check the smell morning and evening for one to two weeks
• If lane markings, walls or floor coatings are redone, consider a follow-up ozone treatment to cut solvent odour
• Advise anyone still feeling unwell to see a doctor, especially people who waded through floodwater and then developed fever or calf pain, possible signs of leptospirosis

Frequently asked questions

1. Can we use ozone right away while the fuel smell is still very strong?

No. Power must be isolated, water pumped out, sludge and oil removed and the space ventilated until fuel vapour falls. The team assesses whether the site is ready. Ozone is the final step for residual odour, not a way to deal with pooled fuel.

2. Do residents have to leave the building during treatment?

Not usually. Nobody may be in the zone being treated, and links between the car park and lift lobbies or stairs must be sealed. The team plans timing, temporary routes and announcements with the juristic office.

3. When can people go back in?

According to WHD service information, the space is ready about two hours after treatment, but only once the team confirms the rest and ventilation period is complete.

4. Will ozone remove all the oil that soaked into the concrete?

Ozone significantly reduces odour and vapour released from materials, but if large sources remain, such as sludge in chambers or oil-soaked materials, the smell can return. Remove the sources first; heavily contaminated areas may need a repeat treatment.

5. What about upper-floor units where the smell has got into curtains and sofas?

Once the source downstairs is under control, those units can book residential ozone disinfection. The unit must also be empty of people and pets during treatment.

Give every floor clean air to breathe again

Talk to WHD about a car park survey, TVOC measurement and a zoned ozone plan.

Get a quote for ozone chemical-odour removal

Tel 065-556-6294  |  LINE @whd268  |  worldhealthdisinfection@gmail.com

Related pages

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

References

• Wikipedia: 2026 Bangkok floods
• Al Jazeera: Disaster zone declared across Bangkok as heavy rain triggers flooding
• CDC: Floods, safety and cleanup guidance