Coal Zoom | Passive Dust Control At Conveyor Transfer Points

Passive Dust Control At Conveyor Transfer Points

July 25, 2026 - Most belt conveyors experience some spillage and dust at the transfer point, leading to safety and air quality concerns. Passive dust control is achieved by retrofitting the conveyor transfer point to seal the enclosure and control airflow within it, allowing dust to settle back onto the material stream, rather than using powered air cleaners or HVAC hoods to extract particulates. Although passive methods are not a silver bullet, this engineering control should be the first step toward transfer-point dust suppression, for the long-term ROI with low maintenance and a track record of compliance.

Nearly all global government air quality regulations for bulk handling address respirable crystalline silica (RCS) due to its association with silicosis, pneumoconiosis, and chronic obstructive pulmonary disease (COPD). Raw material handlers are acutely affected by RCS. However, general particle emissions are also harmful, so most bulk handlers, such as recyclers, agricultural operations, ports, and steel producers, greatly benefit from the workplace safety that passive dust control provides.

Have Dust, Will Travel

The skirtboard enclosure is essentially a settling chamber. The basic concept is that a dust particle will settle out of a laminar air stream based on the speed of the air flow, V_air, and the terminal velocity, V_t, of the dust particle. [Fig.1]

Figure 1 - Theoretical dust particle settling distance “L” in skirtboard enclosure

Current practice for conveyor enclosures is to design for V_air ≤1.0 m/s by increasing enclosure height. Two common rules of thumb for the enclosure length are 2 times the belt width or 0.6 m per 1.0 m/s of belt speed. It is interesting to note that if H is increased, the distance (L) that the average dust particle must travel also increases.

Controlling Airflow

The average air velocity through the skirtboards is directly proportional to the induced airflow and cross-sectional area. Average velocities in the skirtboards due to induced air can range from 0.8 to 2.8 m/s. Belt speed has a minor effect on the average velocities. The maximum air velocities are almost always found where the air flows under the skirtboard curtains.[Fig.2]

Figure 2 - Typical recirculation air flow results with 3 curtains

Particle Density - Particles of 40 and 100 microns (μm) in size -- roughly the size of a human hair -- settle quickly. A particle 10 μm or smaller is “respirable,” or able to penetrate the lungs’ natural defenses and cause serious lung diseases. As bulk density increases, respirable dust emissions decrease moderately and must be properly contained.

Curtains - The best results are obtained using three or more curtains. Martin^®A.I.R. Control™ Dust Curtains create controlled recirculation zones that allow dust particles to agglomerate and settle.[Fig.3]

Figure 3 - The Martin® A.I.R. Control™ Dust Curtain slows dust and turbulent air flow through the transfer point.

Loading Chute and Tailbox - The width of the loading chute should be narrower than the skirtboard width. This folds the airflow between the first curtain and the tailbox, encouraging it toward the top of the enclosure rather than along the material's surface.

Skirtboard Length - If airflow is under 0,5 cubic meters per second (1000 cubic feet per minute), the length of skirtboard is 0,6m (2 ft) for every 0,5 mp/s (100 fpm)of belt speed. If airflow is greater than 0,5 cmp/s (1000 cfpm), the length of skirtboard is 0,9 m (3 ft) for every 0,5 mp/s (100 fpm) of belt speed. This allows enough room to establish circulation zones and – if properly sealed with skirting like Martin^® ApronSeal™ Urethane Skirting – results in passive dust control.[Fig.4]

Figure 4 - The choice of one- or two-piece Martin® ApronSeal™ Urethane Skirting depends on the available space along the belt edge.

Skirtboard Height - An enclosure height beyond 600 mm (24 in.) for the standard conveyor with a single exit curtain can reduce nuisance emissions but, space allowing, a taller enclosure increases the average settling path for greater control.

Conclusion

Along with reducing emissions and spillage, passive dust control requires no power and only limited maintenance. By controlling airflow, dustbags can be added for an extra layer of passive particle suppression. Retrofitted equipment decreases cleaning labor, increases system life, improves compliance, and reduces downtime, making a quantifiable case for a short return on investment.

Martin Engineering is a global leader in bulk materials handling solutions. For over 80 years, Martin has designed, manufactured and installed innovative products that make the world’s foundation industries cleaner, safer, and more productive. Based in the USA, the privately owned company has drawn on its unrivalled experience and expertise to help operations improve safety, enhance material flow, reduce spillage and dust, and minimize downtime. With factory-owned facilities in 20 countries, on-the-ground presence in another 40, and a worldwide service partner network, Martin has built an enviable reputation for high performance products delivered with exceptional technical service and support. The company’s comprehensive Foundations™ textbooks, learning resources, and training programs are the global standard for the efficient and effective design, operation, and maintenance of bulk materials handling equipment. For more information visit martin-eng.com, email info@martin-eng.com, or call 800.544.2947.