06:40, the car park behind the public health division

Thursday 12 June 2025. The sky over Kamphaeng Phet province was still heavy from the rain that had fallen all night. Wichan Sriboonruang, 44, a senior public health officer with the provincial administrative organisation, crossed the car park around the puddles, a folder of the week's field schedule under one arm and an unopened tin of coffee in the other hand.

His team was due in Khlong Nam Lai sub-district, Khlong Lan, to fog for Aedes mosquitoes around a school and a temple after three new dengue cases had been reported in a fortnight. The schedule was tight. The council owned six thermal foggers and had to rotate them across eleven districts, so no machine ever really rested.

He reached the pickup parked under the flame tree, and stopped.

The truck bed was wet. Not rainwater wet. The film on the steel was thicker than that, and it caught the light like oil. In the left corner near the wheel arch, the pearl white paint had turned a mottled yellow brown, and the edge of the stain had lifted into small blisters, as though the paint were peeling away from the metal beneath it.

"Khun Wichan, come and look at this," called Anucha Panthong, the team's driver and spray assistant, from the far side of the bed.

Anucha tilted the AIROFOG AT35 fogger, asset number 054-63-0004, onto its side and pointed at the chemical tank. A chalky white line ran down the moulding seam, from just below the neck almost to the base, roughly nine centimetres long. It was not new. Dried chemical had crusted brown along both sides of it. And wrapped around it, three turns of brown masking tape had gone soft and stringy, peeling off in threads.

"How long has that been there?"

"Two months, I think," Anucha said, quieter now. "The Lan Krabue team taped it when they took the machine out. They said it was only weeping a little and it still sprayed fine. And the cap leaks too. However hard you tighten it, chemical still creeps out along the thread."

Wichan crouched beside the machine and unscrewed the cap. The ring gasket that should have been soft and springy was hard, its surface crazed with fine cracks like dried mud, with a permanent flat dent where it had been compressed for months. He squeezed it. It did not spring back.

Three questions lined up in his head. Where had the missing chemical been going for two months? What had the men lifting this machine on and off the truck every day been touching? And if the internal auditor saw this, what would go into the report?

He got the answer to the third question six days later.

One machine, eleven districts, and how tape became a spare part

The problem in many provincial and municipal health divisions is not a shortage of machines. It is that the machines never stop. Field schedules are set a month ahead, and any district reporting new dengue cases gets squeezed in. A single fogger can travel from district to district for three weeks without ever coming back to the depot.

The consequence is that nobody truly owns the machine. Team A receives it from Team B with whatever faults it already has, finishes the job, and hands it to Team C. Small faults that should have been reported on day one get passed along instead, together with the improvised fixes: masking tape, electrical tape, and sometimes a strip of bicycle inner tube cut to sit under the cap.

Wichan pulled the machine's usage log. Asset 054-63-0004 had been signed out continuously for 47 working days, through the hands of four district teams, without a single repair request being raised. In the remarks column there were three short entries in three different handwritings: "usable", "works normally", "normal".

He then tried to put a number on the loss. Comparing chemical drawn from stores against the area actually treated, the gap came to roughly 1.2 to 1.8 litres of mixed solution per spray run. Over eighteen runs in a month, that is around 25 litres of prepared insecticide that never landed on a single breeding site. It went onto the truck bed, onto the road, and onto the boots of the crew.

Worse, the areas that were treated received less active ingredient than the protocol called for. Thailand's Department of Disease Control is explicit that under-dosing is one of the classic reasons vector control fails, and that it also accelerates the development of insecticide resistance in mosquito populations.

One page from the internal auditor changed everything

On 18 June 2025 the council's internal audit unit carried out a scheduled spot check on the public health division's fixed assets. The auditor walked the line of six foggers in the store, and spent longest at machine 054-63-0004.

Three findings went into the working papers that day.

• Finding one: a damaged asset was still being issued for operational use, with no repair request recorded in the asset register and no evidence of any pre-use safety assessment.
• Finding two: the asset had been temporarily repaired with unsuitable materials, namely masking tape and electrical tape, neither of which is resistant to solvents or heat, and neither of which can be shown to make the equipment safe to operate.
• Finding three: there was evidence of chemical leakage onto a government vehicle, with visible paint damage, which constitutes damage to public property and must be reported.

The closing instruction was short and heavy: repair the asset so that it is safe to operate, assemble complete supporting documentation, and report back within 30 days.

This is the point at which many public bodies start to feel uncomfortable, because "repaired with documentation" does not mean taking the machine to a workshop and attaching the receipt. It means producing an auditable trail: what the fault was, what was actually done, which parts were replaced, whether those parts were genuine and model-specific, whether the repair was tested, and what warranty applies.

Thailand's public procurement and supplies administration regulations require government bodies to keep their assets maintained in good working order, and to carry out an annual asset verification before the end of September each year. A damaged asset is therefore never something that can simply be left alone. There has to be an answer: repair it, dispose of it, or explain what is being done.

The safety side is no different. Whatever the exact legal framework that applies to a local authority, the principle is the same everywhere: the organisation is expected to provide occupational safety standards for the people doing the work. Asking staff to carry a machine that leaks concentrated insecticide onto their hands every day is not defensible in any forum, whether that is an internal audit meeting, a council session, or a conversation with residents.

Five hidden costs inside a nine centimetre crack

Most people treat a cracked chemical tank as a minor issue, because the machine still fogs. Put numbers and risks against it and a very different picture appears.

1. The health cost to your crew

Fogging solutions are typically synthetic pyrethroids carried in a solvent or diesel base. Repeated daily skin contact commonly produces irritation, itching, burning, and tingling in the fingertips, and in sensitive individuals eye and respiratory irritation as well. The real danger is that crews rarely wear gloves for lifting the machine on and off the truck, because they think of that as handling, not spraying.

2. The budget leaking out every single day

Losing 1.2 to 1.8 litres of mixed solution per run sounds trivial. Multiply it by the number of runs per month and the unit price of the concentrate your organisation procures, and the annual loss from one machine usually exceeds the cost of a new tank and seal kit several times over. That is before you add spot respraying of the truck bed, which a bodyshop will not do cheaply.

3. The reputational cost

Every phone is a camera. A council truck trailing chemical along a road outside a school, or a fogger wrapped in tape, reaches the village group chat within the hour. The question that follows is never technical. It is "where did our tax money go?"

4. The cost in time and scheduling

The moment one machine is withdrawn from service, an eleven district rotation collapses. Teams wait, affected areas wait, and if the delay runs past the mosquito's breeding cycle, the next treatment is close to meaningless because a new generation has already emerged.

5. The audit and accountability cost

For a public body this is the heaviest of the five. Once a finding is raised, failing to act on it, or acting without documentation, does not end at the health division. It reappears in the annual audit report and becomes something that has to be explained to management and to external reviewers later on.

Why the usual fixes never actually work

Fix 1: wrap it in tape

The most common answer and the shortest lived. Almost no general purpose adhesive is designed to survive solvents and diesel. Within hours the adhesive softens, the backing swells, and the wrap peels away. Worse, the tape hides the crack, so nobody can see how far it has travelled. We regularly open machines where a three centimetre crack under the tape has quietly become twelve, leaving a tank that could split in two at any moment.

Fix 2: let a general workshop weld the plastic

It sounds sensible, but most fogger chemical tanks are HDPE or PE, which is difficult to weld and requires filler rod of the same polymer. Get the heat wrong and the plastic scorches and turns brittle, so the weld bead becomes a new weak point that fails faster than the original crack. Remember too that this is not a simple storage container: on many machines the tank is pressurised by the pump throughout operation, so an amateur weld can burst while the machine is running.

Fix 3: fit a generic or improvised tank

The problem with a substitute tank is not capacity, it is the detail you cannot see. The neck thread has to match a cap that carries the air line and the pickup fitting. The pickup port has to sit at the correct point in the base. The wall thickness has to hold the manufacturer's rated pressure. The polymer has to resist the solvent. A cheap substitute usually fails at least one of those, and the result is either a fresh leak somewhere new or a pressure drop that leaves you fogging thin, patchy smoke.

Fix 4: leave it until the end of the budget year

Quietly the most expensive option, because leakage does not stay at the tank. Chemical runs down onto wiring looms, the coil lead, the switch assembly and the carburettor body. Once solvent has embrittled the wiring insulation, the next symptom is a machine that will not start or that cuts out mid-run, and you now have two repair jobs instead of one.

Fix 5: budget for a whole new machine

This looks decisive and is usually the slowest route in practice. You have to raise the budget, run the procurement process, and wait for delivery, and the damaged asset still needs a formal answer about repair or disposal. Meanwhile the engine, ignition system, barrel and nozzle on the existing machine are typically close to perfect. Replacing the tank and seal kit is a far better use of public money.

Why tanks split along the seam, and why cap seals die early

Tanks do not crack through bad luck. They crack because several loads act on them at once, and an experienced technician can read the cause from the shape of the crack.

Cause 1: environmental stress cracking

Polyethylene left in prolonged contact with a solvent or diesel carrier swells at the molecular level and loses toughness. Combined with residual moulding stress in the wall, fine crazing appears and slowly extends into a line. It starts wherever stress is highest, which is the moulding seam, a corner radius, or the area around the neck. That is why the crack looks like a chalky white line rather than the star pattern you get from an impact.

Cause 2: accumulated heat from the machine

A thermal fogger works by injecting solution into a very hot barrel. Some of that heat radiates back into the body and the tank. If the heat shielding has degraded, or the machine is repeatedly laid on its side, the tank sees temperatures above its design range. Hot polyethylene softens briefly and deforms permanently by a fraction each time, thinning the wall in specific spots.

Cause 3: tank pressure above specification

Many machines feed solution by pressurising the tank with air from the pump. If the pressure relief valve is blocked or degraded, or a check valve sticks, pressure builds beyond what the wall was designed for. The tank swells slightly on every run and relaxes when the machine is shut down. A few thousand cycles of that swelling and relaxing is the perfect recipe for a split along the seam.

Cause 4: transport and vibration

A machine laid loose in a truck bed with no cradle and no strap jumps with every bump on a laterite road. Each impact between the tank and the bed rail, or between the tank and the machine body, adds stress at the same point. Machines that rotate between districts take far more of this punishment than machines that stay at one depot.

Cause 5: a dead cap seal and overtightening

The cap gasket is the most forgotten consumable on the machine. It degrades from three things at once: chemical attack, heat and sunlight. Once it goes hard and takes a permanent set, operators compensate by tightening the cap harder and harder, which feeds torque straight into the tank neck. A surprising number of cracked tanks start at the neck for that reason alone.

The answer: fogging machine repair by World Health Disinfection

After the audit finding, Wichan did not take the machine to a general small engine shop, because what he needed was not simply "make it stop leaking". He needed evidence that explained the whole process. He contacted the fogging machine repair service from World Health Disinfection, which services thermal foggers and ULV cold foggers of every brand, including the models most commonly held by public bodies such as the AIROFOG AT35, U260, UM2 and UM4.

How a leak is diagnosed systematically

A tank leak repair done properly does not begin by fitting a new tank. It begins by establishing every point that leaks, and why. These are the steps a technician actually follows.

1. Photograph the machine as received. The crack, the cap seal, the chemical staining, the asset number and the serial plate, so the condition before work started is on record.
2. Drain and wash the tank before inspection. Dried chemical residue reliably hides hairline cracks from the naked eye.
3. Soap and air leak test. Pressurise the tank to the manufacturer's low test pressure and brush soap solution over the body, neck, cap thread, air line fitting and pickup port. Wherever bubbles form is a genuine leak. This is how the hairline paths that nobody can see get found.
4. Pressure hold test. Close the valve and time the pressure drop over ten minutes. If pressure falls fast with no visible bubbles, the loss is in the air line or a check valve, not only in the tank body.
5. Inspect the pressure relief valve and check valves. This is the step that finds the root cause of the crack. Skip it and the new tank will crack again within months.
6. Inspect solution hoses, fittings and the metering valve. Any hose that is swollen or hardened by chemical attack is replaced at the same time, because it is always the next leak.
7. Check for consequential damage. Wiring, connectors, the ignition coil and the carburettor body all get inspected for solvent embrittlement.
8. Issue an inspection report before quoting. The customer sees exactly what will be replaced, what it costs, and why it is necessary.

What was actually done to machine 054-63-0004

The inspection found three leak points, not the single one visible to the eye: the long crack down the side seam, a cap gasket that had gone hard and taken a permanent set, and the air line fitting at the tank, where a perished O-ring produced a slow stream of bubbles under test. In addition, the pressure relief valve was partially blocked with residue, allowing pressure to build above normal. That was the true root cause of the crack.

The work therefore comprised: fitting a genuine model-specific chemical tank from the manufacturer, replacing the complete cap seal and O-ring set, replacing the swollen solution hose, cleaning and replacing the pressure relief valve, removing chemical residue from the machine body and wiring loom, checking the nozzle and metering valve, then repeating the pressure hold test and running a live spray test before handover.

10 reasons organisations choose WHD for fogging machine repair

1. Detailed, targeted fault diagnosis. No guessing and no replacing parts just in case. Every symptom is traced to a cause with test evidence behind it, so you know exactly what you are paying for.
2. Technicians with over 10 years in this specific field. Working only on thermal foggers and ULV sprayers means knowing which cracks come from heat, which come from pressure, and which come from impact.
3. 100% genuine, model-specific parts from the manufacturer. Tanks, cap seals, O-rings and solution hoses are all specified to resist the chemicals and hold the pressure the machine was designed for, rather than being something that merely fits.
4. Every machine is started and spray tested before handover. Not just reassembled and returned, but run, and observed producing an even, leak-free fog.
5. Root cause fixed, not just the symptom. If the tank cracked because pressure was too high, the pressure system is corrected too, so the repair does not reappear as a duplicate line in next year's budget.
6. Complete documentation for public sector work. Quotation, pre-repair inspection report, parts list, handover note and warranty terms, so every question an internal auditor asks has an answer on paper.
7. All brands serviced. AIROFOG AT35, U260, UM2, UM4 and machines bought in different years from different suppliers can all be handled in one place instead of being scattered across several workshops.
8. Fleet inspection available. Organisations rotating several machines usually find the same fault developing in every unit that travelled the same route. Inspecting the fleet together prevents repeats and lets you plan the repair budget ahead.
9. Practical guidance for the people who use the machine. How to tighten the cap correctly, how to flush the tank after use, how to strap the machine in a truck bed, and when to change the seal. This is what genuinely extends asset life.
10. Significantly cheaper than buying a replacement machine. When the engine, ignition system and barrel are still sound, replacing only the damaged components is the best value for public money, and it happens far faster than a new procurement cycle.

Before and after, side by side

What customers say

The documents you should get from every equipment repair

If your organisation is about to send a fogger for repair, use this as a checklist. This document set is what makes a single repair genuinely closed in the eyes of an auditor.

• A pre-repair inspection report stating the symptoms found, every leak point, the pressure test results and the assessed cause, with supporting photographs.
• An itemised quotation that separates each part from labour, so the reasonableness of the price can be verified.
• A parts list stating that the parts are genuine and model specific. This is the single most common auditor question.
• A record of post-repair testing, covering both the leak test and the live start and spray test.
• A handover note and written warranty terms, with the scope and period stated clearly.
• Before and after photographs to attach to the report and to the asset register entry.

Once you have the pack, record the repair history in the asset register. What an internal auditor is really looking for is not a receipt but evidence that the organisation maintains its equipment continuously, rather than repairing things only when it is told to.

How to stop the same failure coming back

For organisations rotating machines between districts or communities, a common standard for handing machines between teams matters just as much as the machine itself.

Before every use

• Take a torch around the whole tank, especially the moulding seam and the neck, looking for chalky white lines that signal the start of a crack.
• Open the cap and inspect the gasket. If it is hard, crazed or permanently dented, replace it now rather than waiting for a leak.
• Confirm the pressure relief valve moves freely and is not clogged with residue.
• Check the solution hose is neither swollen nor brittle and that the clamps are still tight.

During use

• Tighten the cap by hand only. Never use pliers or a rag for extra grip, because excess torque is one of the leading causes of neck cracks.
• Do not lay the machine on its side or upside down while it is still hot.
• Stop immediately if you see chemical seeping. Do not tape it and keep spraying.

After use and in transport

• Drain any remaining solution. Never leave chemical standing in the tank overnight, because prolonged soaking is what accelerates degradation of both the tank and the seal.
• Flush with clean water or the fluid the manufacturer specifies, then invert and let it dry.
• Store the machine in shade. Sunlight ages the rubber seal remarkably fast.
• Transport it on a cradle with straps, never loose in an empty truck bed.

For machines shared between areas

• Use a handover sheet signed by both the outgoing and incoming team, recording the machine's condition on the day.
• Define which faults mean "do not pass this on", for example a cracked or weeping tank or perished wiring. Those go to repair, not to the next district.
• Set a mid-year condition check rather than relying only on the annual asset verification.

This mirrors what the World Health Organization emphasises about vector management: the effectiveness of control does not rest on the choice of insecticide alone, but on equipment quality and application standards as well. If you would like a team to carry out treatment on site, you can also review the mosquito fogging service in more detail.

Is your tank leaking right now? Do not wait for the auditor

Treat any of these as a signal to send the machine in immediately: chemical weeping from the tank or damp patches around the body, a chalky white line running along the moulding seam, solution creeping out of the cap thread even when tightened, having to use abnormal force to close the cap, staining or lifted paint wherever the machine sits, or chemical consumption that no longer matches the area actually treated.

World Health Disinfection repairs thermal foggers and ULV cold foggers of all brands. Detailed and targeted fault diagnosis, technicians with over 10 years of experience, 100% genuine model-specific parts from the manufacturer, and a live start and spray test on every machine before handover, with full supporting documentation for public sector work.

For service details and pricing, click here

Frequently asked questions about fogger tank leaks

Can a cracked chemical tank be repaired, or must it be replaced?

In practice, a tank with a long crack along the seam should be replaced rather than repaired. The tank is pressurised during operation, so welding or filling creates an unpredictable weak point that can burst while the machine is running, which is a direct hazard to the operator. If the damage is only a surface scuff or a very early mark, a technician can assess whether it is safe to monitor or should be replaced straight away.

How often should the cap seal be replaced?

There is no fixed figure, because it depends on the chemical used, how often the machine runs, and how it is stored. The workable rule is to inspect the seal before every deployment and replace it as soon as it is hard, crazed or permanently flattened. Many organisations running heavily used, shared machines simply replace the seal annually as a matter of routine, because a seal costs far less than the damage a leak causes.

How do we stop leaking chemical from ruining the truck paint?

First, fix the cause and stop the leak. Then use a chemical-resistant tray or cradle under the machine and strap it down properly, and wash the truck bed immediately whenever you see a spill rather than letting it dry in place, since the longer the solvent sits the more time it has to attack the paint system. Paint that has already blistered needs a spot respray, which is money wasted if the leak has not been stopped first.

Can we tape or epoxy the crack just to finish the current job?

Strongly not advised. General adhesives and tapes do not withstand solvents and heat, so they fail during operation with no warning. More dangerous still, they conceal how far the crack has spread. From an audit perspective, repairing an asset with unsuitable materials is itself a reportable finding. The safer route is to withdraw that machine, rotate in a spare, and send it for repair.

What documentation does a public body need for an equipment repair?

Generally: a pre-repair inspection report, an itemised quotation separating parts from labour, a parts list confirming that genuine model-specific components were used, a record of post-repair testing, a handover note, written warranty terms, and before and after photographs. The repair history should then be entered in the asset register. Exact requirements vary between organisations, so confirm the details with your own procurement officer.

We rotate several machines across districts. Send them one by one, or as a fleet?

If those machines are used the same way and travel the same routes, wear tends to appear at much the same time. A fleet inspection is usually better value, because you see the overall condition of the asset group, can plan the repair budget in advance, and avoid the situation where several machines fail together in the middle of an outbreak. Stagger the actual repairs so you always keep machines in service.

Do you service brands other than AIROFOG?

Yes. WHD services thermal foggers and ULV cold foggers of every brand, including the models public bodies most commonly hold, such as the AIROFOG AT35, U260, UM2 and UM4. If you are unsure whether parts are available for your model, send photographs of the machine and its model plate via LINE and we will check first.

Related services and reading

• Fogging machine repair service, all brands, technicians with over 10 years of experience
• AIROFOG AT35 thermal fogger, specifications and product details
• ULV cold fogging machines for vector control work
• Mosquito fogging service for organisations and communities
• Disinfection service for buildings and public spaces

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fogger tank crack and seal repair | thermal fogger chemical tank leak | fogging machine cap gasket replacement | fogger tank pressure test | genuine fogger spare parts | council and municipality equipment repair with documentation | AIROFOG AT35 U260 UM2 UM4 | Call 065-556-6294 | LINE @whd268