Effective dust filtration design follows a simple rule: capture the dust cloud before it spreads. A dust collector (including a baghouse filter) can only perform if the hood, ducting and airflow are designed correctly.
Design for legal duty and real exposure control
South Africa’s Occupational Health and Safety Act require employers to provide and maintain a working environment that is safe and without risk to employees’ health, and it highlights controlling hazards before relying on PPE.
The Hazardous Chemical Agents (HCA) Regulations list engineering controls such as enclosure and local extraction ventilation (LEV) on processes, equipment and tools as measures to control airborne emissions.
Make the hood do the hard work
Capturing hoods are widely used, but they often fail when the capture zone is too small or disrupted by draughts. A key rule is distance: capturing hoods are usually only effective when the source is within about two hood diameters of the hood face.
Use design targets
Typical capture velocity ranges are 0.5–1.0 m/s for welding/soldering-type clouds, 1.0–2.5 m/s for crushing/spraying, and 2.5 m/s to >10 m/s for cutting and grinding (which often needs partial enclosure or a receiving hood).
After capture, keep dust moving in ducts: recommended minimum duct velocities are about 15 m/s for fine dusts, around 20 m/s for process dusts (e.g. cement/brick/grinding), and around 25 m/s for large or damp dusts.
