In many Indian fabrication and machining shops, the answer to dust and fume sits on the roof. A row of turbo ventilators, a few wall exhaust fans, and often a pedestal fan pointed at the welder. Together they move a lot of air. They take very little dust out of it.
Ventilation and extraction both move air, but they do different jobs. Knowing which job you need done is the first step to cleaner air on the floor.
Ventilation dilutes. It does not remove.
A ventilation system replaces hall air with outside air. That lowers the average concentration across the building. It does nothing at the point where the dust is made.
A grinder releases dust less than a metre from the operator’s face. By the time a roof fan has exchanged that air, the operator has already breathed it. On its way to the roof, the same air crosses the bay, so the fitter at the next station breathes it too. A pedestal fan does the same thing faster. It pushes fumes away from the welder and into everyone else’s breathing zone.
The particles that matter most are the ones that stay up longest. Dust below 2.5 micron can stay in the air for hours, and it is also the fraction that travels deepest into the lungs. Coarse dust falls to the floor on its own. Fine dust follows the airflow, wherever the fans send it.
How extraction works
Extraction takes the opposite approach. It captures the contaminant where it is generated, before it reaches anyone, and filters it out of the air. ULMATEC, NAF’s German technology partner, describes it in four stages.
- Capture. A hood, extraction arm, downdraft table or direct machine connection draws in air at the source. Its shape and position decide how much is caught. A badly placed hood can miss most of the emission even at high airflow.
- Transport. Ducting carries the air to the filter. The air speed has to be high enough to keep dust from settling in the duct, and no higher, or energy is wasted.
- Filtration. The filter is matched to the contaminant. Cartridge filters handle dry dust. Mist collectors handle coolant and oil aerosol. Wet separators handle sticky or reactive dust. Activated carbon handles vapours and odour.
- Return or discharge. The cleaned air is either returned to the hall or sent outside. Returning it keeps cooled or conditioned air inside the building.
Filtration is where the difference becomes measurable. Cartridge filters built to HEPA class H13 or H14 remove more than 99.9% of particles from 0.3 micron upward, according to ULMATEC. A roof ventilator has no filter at all.
This is not an argument against ventilation. Hall ventilation removes heat, brings in fresh air and clears the low-level background that extraction does not catch. In a hot Indian summer, it matters.
But ventilation is built to change air, not to separate particles. Wherever a process has a defined source of dust, fume or mist, such as a welding bay, a grinding booth or a CNC machine, that source needs extraction. The two systems work together. One cannot stand in for the other.
Signs your ventilation is doing extraction’s job
If any of these sound familiar, the fans are being asked to do something they were never designed for.
- A haze under the roof sheets builds up by mid-shift and clears only when production stops.
- A film of dust returns on machine tops, electrical panels and lights within days of cleaning.
- Welders angle fans to push smoke away from their own faces.
- Complaints come from people who work nowhere near the process that makes the dust.
- Sensors, optics and guides on machines need cleaning more often than the maintenance plan allows for.
Where to start
Walk the floor and list every process that makes dust, fume or mist. Note what the material is, how many hours a day each process runs, and which ones run at the same time. That list is what an extraction design is built on. It also shows you which sources matter most, so you can start there rather than trying to fix the whole hall at once.
If you measure air quality, measure it at the workstation, in the operator’s breathing zone. A reading taken in the middle of the hall shows the diluted average. It tells you very little about what the person at the grinder is breathing.
Not sure which type of collector each source needs? Our guide to choosing the right collector for your factory works through it by contaminant. Or ask NAF for a site visit. Our engineers will see the problem on your floor before anything is designed.
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