Quick summary: Industrial boiler explosions typically stem from 5 main causes: overpressure (the safety valve not functioning correctly), low water level (the water level dropping too low, overheating the tubes), furnace fuel explosion (unburned fuel accumulating and igniting suddenly), corrosion and scale from poor water treatment, and improper operation or exceeding the design capacity.
Most of these causes give early warning signs and can be prevented through periodic inspection, proper maintenance, and thorough operator training.
1. Boiler explosions are a real risk, not a rare occurrence
An industrial boiler is pressure equipment operating at high temperature, and boiler-explosion incidents do still occur in practice in Vietnam. One example reported in the press is a boiler explosion in Vinh Cuu district, Dong Nai province, in May 2024, which injured a number of workers and remains under investigation by the relevant authorities.
The articles “What Regulations Must Industrial Boilers in Vietnam Comply With?” and “How Often Must an Industrial Boiler Be Inspected in Vietnam?” covered the legal framework and inspection schedule that help prevent this risk. This article looks deeper into the technical mechanisms behind boiler explosions, to help operating staff and factory managers recognize danger signs early.
2. Cause 1: Overpressure
Overpressure is regarded by many experts (including Thermodyne) as the most common cause of boiler explosions. When the internal pressure of a boiler exceeds the design limit, the pressure-bearing metal structure can fail suddenly.
Mechanism: The safety valve’s job is to automatically release pressure once it exceeds the allowable threshold — typically, a safety valve’s set pressure does not exceed 1.1 times the boiler’s maximum allowable working pressure. If the safety valve becomes stuck, is miscalibrated, or the pressure gauge is inaccurate, the boiler’s pressure can keep rising without being flagged or released in time.
Warning signs: The pressure gauge consistently exceeds the normal operating range; the safety valve does not vent even though the set pressure has been reached; unusual noises around the safety valve.
Prevention: Check, calibrate, and seal the safety valve periodically as part of the technical safety inspection process; do not attempt to remove or adjust the safety valve unless you are an authorized inspector or technician.
3. Cause 2: Low-water condition
A low-water condition is one of the leading causes of boiler failure, and many technical references rank it alongside overpressure in terms of danger.
Mechanism: When the water level in the steam drum drops too low, the steam-generating tubes, no longer cooled by water, overheat. If water is then suddenly fed in while the tubes are overheated or dry, the hot metal meeting the cold water undergoes thermal shock, creating major stress that can lead to cracking or an explosion.
Warning signs: The water level shown in the gauge glass is below the safe level; a low-water alarm is triggered; unusual noises from the tube bank during operation.
Prevention: Ensure the automatic feedwater system and water-level sensors work accurately; periodically check the gauge glass and water-level indicating devices; never feed water suddenly into a boiler that has just experienced a low-water condition without first letting it cool according to the proper procedure.
4. Cause 3: Furnace fuel explosion
This cause is particularly dangerous for fuel-burning boilers (oil, coal, rice husk, wood, etc.), often referred to as a “fuel-rich” condition.
Mechanism: When fuel does not burn completely, the unburned portion gradually accumulates in the furnace. If the oxygen supply then increases suddenly — for example, when the draft fan is switched back on, or the burner is restarted after flame-out without first purging leftover fuel — the entire accumulated fuel load can ignite all at once, causing furnace pressure to spike suddenly and destroy the furnace structure.
Warning signs: An unstable flame, with repeated flame-outs and re-ignitions; an unusual fuel smell around the furnace area; abnormal fluctuations in furnace pressure.
Prevention: Follow the correct start-up procedure and purge the furnace before re-ignition; do not allow fuel to accumulate in the furnace after burner shutdown; train operators to recognize signs of unstable combustion.
5. Cause 4: Corrosion and scale from poor water treatment
Feedwater for a boiler needs to be treated to meet the required quality standard (for example, TCVN 12728:2019). In practice, many facilities still draw water from sources that have not been fully treated — industrial-zone tap water, river or stream water, well water — leading to two parallel problems:
- Corrosion: Corrosion caused by steam and impurities in the water gradually weakens the boiler’s metal structure over time, particularly in an industrial environment with high impurity levels.
- Scale buildup: A layer of scale on the tube wall obstructs heat transfer, raising the wall temperature at the scaled location above normal; over time this can lead to localized overheating and tube failure.
Warning signs: Steam-generating efficiency gradually declines even though fuel consumption stays the same; an inspection detects scale or metal corrosion inside the boiler; blowdown water appears cloudy or carries a lot of sediment.
Prevention: Treat feedwater to meet the required standard before it enters the boiler; perform periodic blowdown correctly to remove settled sediment; include a check for scale and corrosion as part of every periodic inspection (internal examination).
6. Cause 5: Improper operation or exceeding the design capacity
Even when equipment meets technical standards, day-to-day operating mistakes can still lead to a serious incident.
Mechanism: An incorrect start-up sequence (raising the water temperature too quickly), continuously operating beyond the design capacity so that the feedwater pump, piping, and water-treatment system cannot keep up, or an incorrect standby procedure, can all create abnormal conditions that build up gradually and increase the risk of an incident.
Warning signs: The boiler is frequently operated at or beyond maximum load for extended periods; operating staff have not received thorough training on start-up/shutdown procedures; the operation log is incomplete.
Prevention: Follow the manufacturer’s start-up, operating, and shutdown procedures correctly; avoid operating a boiler beyond its design capacity for extended periods; ensure operators hold the appropriate safety-training certification (see the article “What Legal Documentation Does an Industrial Boiler System Need in Vietnam?”, operator-training section).
7. Summary table: early warning signs
| Cause | Warning signs to watch for |
|---|---|
| Overpressure | Pressure exceeding the normal range, safety valve not venting when it should |
| Low-water condition | Low water level in the gauge glass, low-water alarm triggered |
| Furnace fuel explosion | Unstable flame, unusual fuel smell |
| Corrosion/scale | Declining steam-generating efficiency, cloudy or sediment-heavy blowdown water |
| Improper operation/overloading | Continuous operation at maximum load, incomplete operation log |
8. The role of inspection and maintenance in prevention
Most of the 5 causes above can be detected early through periodic technical safety inspection and proper maintenance:
- The internal examination during inspection helps detect corrosion and scale before they cause localized overheating.
- Checking and calibrating the safety valve is a mandatory part of the inspection process, helping to prevent overpressure.
- The operation and maintenance log — one of the required documents — helps detect abnormal trends early, before they turn into a serious incident.
See the applicable inspection interval in the article “How Often Must an Industrial Boiler Be Inspected in Vietnam?”, and the list of documentation to prepare in the article “What Legal Documentation Does an Industrial Boiler System Need in Vietnam?”.
Frequently asked questions
Do electric boilers carry the same explosion risk as fuel-burning boilers?Electric boilers do not carry the risk of a furnace fuel explosion, since they do not burn fuel, but they still carry the risk of overpressure, low water, and corrosion/scale, since they remain pressure equipment operating at high temperature.
Is a newly installed boiler completely safe from these causes?No. Even if the equipment has just passed its initial inspection, causes such as improper operation or poor water treatment can still occur from the very start of use if the operating procedures and feedwater quality are not properly maintained.
How can you tell if a boiler’s safety valve is working correctly?The safety valve must be checked, calibrated, and sealed by an inspector during each periodic inspection. Companies should not attempt to test it by directly manipulating the valve without the appropriate expertise.
Conclusion
Most industrial boiler explosions can be traced back to 5 groups of causes: overpressure, a low-water condition, a furnace fuel explosion, corrosion/scale from poor water treatment, and improper operation. Recognizing warning signs early, combined with periodic inspection and thorough operator training, is the most effective way to prevent these unfortunate incidents.
(This article is a general technical summary and does not replace an in-depth technical assessment by a qualified inspector or safety engineer. If a company’s boiler shows any abnormal signs, it should contact a qualified inspecting body or technician immediately before continuing operation.)