90 Staff with Headaches and Blocked Noses Across a Whole Floor. HR Assumed It Was Stress Until They Checked the Air Conditioning
Last updated: 6 Sep 2026 | 9 Views |
Ozone disinfection service 2026 for offices and workplaces
90 Staff with Headaches and Blocked Noses Across a Whole Floor. HR Assumed It Was Stress — Until They Checked the Air Conditioning
Why symptoms that improve immediately at the weekend point at the building, not at the job.
When staff across a whole floor complain of headaches, blocked noses and unusual fatigue at the same time, most HR departments think first about workload and stress. It is a reasonable interpretation and it is usually wrong. This is the true story of a company that took eight months to look at the air conditioning.
Headaches, blocked noses, throat irritation, dry eyes and unusual fatigue affecting many people in the same building has a name in occupational health: sick building syndrome — symptoms that ease on leaving the building and return on going back in.
There are several possible causes: inadequate ventilation, volatile compounds from fit-out materials, and biological contamination in the air conditioning system. The last of these is the most common cause in office buildings in a hot, humid climate.
This article tells the true story of a company whose ninety staff lived with this for eight months, explains why the central air conditioning system is the most overlooked place of all, and what ozone treatment does about it.
The story
Symptoms that started with a few people and spread across the floor
Tanya's company is a ninety-person consultancy leasing the twelfth floor of an office building: six hundred square metres of open plan with four meeting rooms.
It began with three or four people in one zone complaining of afternoon headaches and a blocked nose all through the working day. Over the next three months the same complaints spread across the whole floor.
HR ran an internal survey and found that sixty-one of the ninety staff had at least one symptom on the list: headache, blocked nose, throat irritation, dry eyes or unusual fatigue.
What led HR to read it as stress was that the company had a major project running at the time and people genuinely were working hard — so they assumed the symptoms came from workload.
The data that contradicted the stress hypothesis
The company acted on that hypothesis. It hired consultants to redesign workflows, added annual leave, ran stress-reduction activities, and created more break space in the office.
Three months later workload had genuinely fallen, but the number of people with symptoms had barely changed — the first sign the hypothesis might be wrong.
What made it clear was the second survey, which added a question about how symptoms were at weekends. Eighty-four per cent of those with symptoms said they improved noticeably on Saturdays and Sundays, and many said symptoms cleared within two hours of leaving the office.
At the same time, company sick leave was up thirty-eight per cent on the previous year, and four employees had resigned citing in their exit questionnaires that the working environment made them feel unwell.
What they found when the ceiling came down
Tanya consulted the occupational health physician the company uses for annual check-ups, whose first recommendation was to inspect the air conditioning system before anything else.
When technicians opened the ceiling to inspect the ducts and supply diffusers, they found thick accumulated dust and black spotting on the inner duct surfaces in several sections, particularly near the system's cooling coil.
The insulation around some duct sections also showed signs of past moisture, which the technicians attributed to condensation during periods when the system ran irregularly.
The building is nineteen years old and, according to building management, its ductwork had never been cleaned. When Tanya plotted the worst-affected staff onto the floor plan, they clustered entirely beneath the supply diffusers.
What they could do immediately while waiting for building management
The problem was that the ductwork belongs to the building, not the tenant. Cleaning the entire duct system had to go through building management and would take months to schedule.
What Tanya could do immediately within her own leased area was ozone-treat the whole floor, with the air conditioning on recirculation during treatment so the ozone travelled into the ducts and diffusers within the leased space.
The team treated the whole six hundred square metres on a Friday night after everyone had left, including the four meeting rooms, the pantry and the file room, in cycles of about thirty minutes, then ventilated overnight.
On Monday morning several staff commented in the group chat that the office felt clearer. In the third survey, run three weeks later, the number reporting symptoms had fallen from sixty-one to nineteen.
What it actually costs
Symptoms improving at weekends is the clearest signal and the most overlooked
When eighty-four per cent say symptoms improve at weekends and clear within two hours of leaving, that pattern points directly at the building — not at workload, which does not disappear on a Saturday.
Sick leave rises and nobody connects it to the building
A thirty-eight per cent rise in sick leave is usually explained away by the season or a general outbreak — when read alongside individual symptom data, it points at the building environment.
Staff resign for a reason the company could have fixed
Four employees resigned citing the working environment — a reason that can be fixed at modest cost, if the company knows where the cause is.
Fixing the wrong thing costs both money and time
The company hired consultants, added leave and ran stress-reduction activities — good investments in themselves, but they did not address what people were actually experiencing, and eight months were lost.
Why the usual fixes fail
Redesigning workflows and reducing workload
Reducing workload is worth doing in its own right. But if the symptoms come from air quality in the building, it will not change the number of people affected at all — which is exactly what this company found after three months.
Adding annual leave and stress-reduction activities
These measures genuinely help staff wellbeing, but they do nothing about what people breathe for eight hours a day — and they can leave a company believing the problem has been addressed.
Installing floor-standing air purifiers
An air purifier filters particles that pass through it, but the central air conditioning blows air out far more strongly and continuously, and the purifier does nothing about the source inside the ductwork.
Changing the filters at the supply diffusers
New filters help somewhat and should be changed on schedule. But the filter is at the end of the path, while the accumulated dust and black deposits sit in the ducts before it. Changing the filter does not touch the cause.
Waiting for building management to clean the whole duct system
Cleaning the building's ductwork is worth doing and does work. But it is the building's job, has to go through an approval process, and often takes months to schedule — while staff have symptoms every day in the meantime.
What a tenant can do in their own space
Every office tenant faces the same constraint: the central air conditioning belongs to the building, so fixing the source requires building management and takes time.
But what can be done immediately within a leased area is managing the air inside the floor — including the sections of ductwork and diffusers within the leased ceiling, which ozone treatment with the air conditioning on recirculation reaches.
Ozone is a gas, so it travels the same path as the airflow and penetrates the ducts, the insulation, the carpet, the chair upholstery and gaps ordinary cleaning cannot reach. This service uses the Master Ozone Generator, the only brand in Thailand certified by the Department of Medical Sciences, Ministry of Public Health, at 99.99 per cent effectiveness against deep-seated mould in air conditioning and furniture.
10 reasons the AIROFOG U260 solves it
1. A tenant can do it without waiting for building management
Ozone treatment happens inside your own leased area and modifies no building system, so it can start immediately while the request to clean the whole duct system is still in the building's queue.
2. It reaches the ducts and diffusers within your leased ceiling
With the air conditioning on recirculation during treatment, ozone travels into the ductwork and diffusers in your ceiling — which changing a filter cannot reach.
3. It treats carpet, chair upholstery and insulation at the same time
Dust and spores blown down from the diffusers settle in carpet, in office chair upholstery and in curtains. Ozone gas penetrates those materials — which a vacuum cleaner and an air purifier cannot.
4. It runs on a Friday night with no effect on working hours
An office floor is empty from Friday evening until Monday morning. The treatment takes about thirty minutes per cycle, then ventilates overnight, and staff come in as normal on Monday.
5. No chemical residue on desks and equipment
Ozone reverts to oxygen after reacting, so there is no chemical residue on keyboards, desks or staff belongings — something HR has to be able to answer for.
6. It adds no humidity to a floor full of IT equipment
Unlike steam treatment or liquid spraying, ozone is a gas and does not dampen carpet, paperwork or IT equipment — every IT department's first concern.
7. It treats the meeting rooms and pantry, the densest points
Sealed meeting rooms used continuously all day, and a pantry where everyone eats at once at lunchtime, are the two worst air quality points in any office and should be treated every time.
8. Certification you can cite to staff and management
The Master Ozone Generator is tested by the Department of Medical Sciences, Ministry of Public Health, and by Intertek in the UK — something HR can communicate to staff credibly.
9. It can be run on a standing cycle to prevent recurrence
A company that has had this problem should treat quarterly alongside tracking staff symptoms — prevention rather than chasing, and something that can go into the company's occupational health plan.
10. It costs less than losing one employee
The company lost four people over the working environment. Recruiting and training one replacement costs many times more than treating the whole floor — and on bookings of 15,000 baht or more you also receive a free CHEMGENE HLD4H disinfection spray service.
Before and after
Before
- 61 of 90 staff reporting headaches, blocked noses, throat irritation, dry eyes or unusual fatigue
- HR hypothesising that it was stress from workload
- 3 months of reduced workload, added leave and stress-reduction activities with almost no change
- 84% of those affected saying symptoms improved at weekends and cleared within 2 hours of leaving
- Sick leave up 38%, and 4 staff resigning citing the working environment
- Thick dust and black deposits found in the ductwork of a 19-year-old building never cleaned
After
- The whole 600 sqm floor ozone-treated on a Friday night after everyone had left
- The air conditioning run on recirculation so ozone reached ducts within the leased space
- Four meeting rooms, the pantry and the file room included, about 30 minutes per cycle
- Ventilated overnight, with staff back in as normal on Monday morning
- Third survey three weeks later: those reporting symptoms down from 61 to 19
- A quarterly standing cycle set, alongside pushing building management on duct cleaning
How we get you started, in 3 steps
1. Survey the floor and review the symptom data alongside it
We look at the floor area, ceiling height, where the central system's diffusers sit, and how many meeting rooms and pantries there are — and if the company has staff symptom data, we review it too, because plotting affected staff on the floor plan usually pinpoints the problem.
2. Treat the whole floor outside working hours
The area is sealed, the air conditioning is set to recirculate so ozone reaches the ducts within the leased space, and the treatment runs for the set time — about 30 minutes per cycle on the timer, with nobody in the area.
3. Ventilate, measure with a survey, and set a standing cycle
Ventilate until the ozone smell has gone and the space returns to normal use. We recommend repeating the symptom survey two to three weeks later to measure the result concretely, then setting a quarterly standing cycle.
What a customer says
“We thought it was stress, because we genuinely did have a big project on. We hired consultants to redesign workflows, added leave, ran wellbeing activities. Three months later the workload was lighter and the number of people with symptoms was the same. It was only when we added a question about weekends and eighty-four per cent said they felt better immediately that we knew it was not about the work.”
Tanya — HR director, 90-person consultancy
How to tell whether symptoms come from the work or the building
The single question that separates the two best is how symptoms are at weekends and during holidays — because accumulated workload does not vanish on a Saturday, while exposure to something in the building stops the moment you leave it.
If symptoms ease within a few hours of leaving work and return on Monday morning, that pattern points clearly at the building environment. Symptoms from accumulated stress do not usually resolve that quickly.
The second useful question is to ask staff for their seat location and plot the affected people on the floor plan. If they cluster in a zone — particularly beneath supply diffusers or near a plant room — that is strong evidence.
A company can collect both of these itself with a short survey, and they are far more valuable than guessing from workload, which is a much harder hypothesis to test.
Why central air conditioning is an office building's blind spot
In an office building, the tenant looks after their own space — cleaning desks, vacuuming carpet, changing diffuser filters — while the building looks after the mechanical plant and the duct system.
The problem is the gap between those two responsibilities. The ducts running through the tenant's ceiling belong to the building, but the consequences fall on the tenant. And in practice, cleaning a whole building's ductwork is a large, expensive job that tends to be deferred.
In a fifteen to twenty year old building whose ducts have never been cleaned, dust and organic matter accumulate in a thick layer — and in a hot, humid climate with occasional condensation, that layer becomes a growth medium for micro-organisms.
This is why a tenant should handle what they can within their own space first, alongside pressing building management on duct cleaning, rather than only waiting.
Frequently asked questions
Can a tenant do this without building management's permission?
Ozone treatment inside your own leased area modifies no building system. We do recommend informing building management as a courtesy, and we provide the machine documentation for you to do so.
How long does a 600 square metre floor take?
Not long per cycle with a machine at this power, plus a closed-space period. In practice it is done on a Friday night and ventilated over the weekend, with staff back as normal on Monday.
Will computers, monitors and paperwork be damaged?
No, because ozone is a gas rather than a liquid, so it does not wet equipment or paperwork — and afterwards there is no chemical residue on surfaces.
Does the air conditioning need to be running during treatment?
It should be, on recirculation, because that is what carries ozone into the ducts and diffusers within your leased space — the part changing a filter cannot reach.
How do we know whether it worked?
The most concrete method is a staff symptom survey before and after, two to three weeks apart — data HR can report to management, and exactly what the company in this case study used.
How often should we treat?
Quarterly for an office that has had this problem, and twice a year for a typical office, alongside filter changes on schedule and pressing the building on duct cleaning.
Should meeting rooms and the pantry be treated too?
Strongly recommended, because they are the two densest and stillest air points in an office: sealed meeting rooms used all day, and a pantry where everyone unmasks to eat.
What does it cost?
It depends on the floor area and number of rooms. Send us the floor plan for an assessment — and on bookings of 15,000 baht or more you receive a free CHEMGENE HLD4H disinfection spray service.
If the symptoms clear at the weekend, the problem is not the work
Tanya's company spent eight months fixing the wrong thing, lost four employees and saw sick leave rise thirty-eight per cent, before finding the answer in the ductwork of a nineteen-year-old building that had never been cleaned.
Ozone treatment is something a tenant can do immediately in their own space without waiting for the building's queue. It runs on a Friday night with no effect on working hours and leaves no chemical residue on staff desks.
If your office has staff with these symptoms, run a short survey asking how they feel at weekends, then send us the floor plan and the results and we will help you work out where to start.
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