Good hood design is the difference between effective local exhaust ventilation and chasing dust all day. With most construction dusts, capture at source is the easiest win: get the hood shape and position right, and you will reduce airborne particulate, clean-up time, and exposure risk.

Pick the right hood for the process

Choose receiving hoods where dust has a clear trajectory (e.g. bench sawing or chop saws) so the hood sits in the natural throw. Use capture hoods for diffuse emissions (e.g. sanding, grinding) and get close to the point of release. Slot hoods with flanges are useful along edges and walls, while bellmouth inlets reduce entry losses and help flow evenly across the opening. Where possible, part-enclose the source on three sides; even simple skirts or flanges can dramatically improve capture.

Placement: closer, between source and worker

Place the hood as close as practicable without obstructing the task. Position it between the source and the worker so the airflow pulls dust away from breathing zones. Keep the hood facing the plume; small changes in angle can halve capture. Avoid gaps that let cross-draughts undercut performance; shielding the rear or sides with a flange stabilises the capture zone. For fine dusts such as respirable crystalline silica, small increases in distance cause large drops in capture, so prioritise proximity over hood size.

Control airflow under load

Size extraction for the hood you actually use, not a free-air rating. Hoses, filters and tool shrouds add resistance that reduce flow. Check under-load airflow and adjust: shorten flexible hose, use smooth-bore duct, and avoid tight bends. Keep filters clean and bags changed to avoid flow collapse from filter loading.

Verify and tune on site

Prove capture with simple checks: a smoke puff or tissue strip shows whether air is moving into the hood across the emission zone. A particulate monitor or PM meter helps confirm improvements after adjustments. If source capture cannot be fully achieved, add a layer of control with an air scrubber or negative air machine, and keep housekeeping tight with an industrial vacuum fitted with high-efficiency filtration. Avoid dry sweeping or compressed air, which re-suspend dust.

Practical takeaways

• Match hood type to the emission: receiving for throws, capture for diffuse plumes, flange where possible.
• Put the hood between source and worker; get it as close as the task allows.
• Stabilise capture: shield cross-draughts, add flanges, and face the plume.
• Measure under-load performance; shorten hose runs and maintain filters.
• Back up with air filtration and disciplined vacuum-based housekeeping.

LEV performance is ultimately judged by exposure. HSE’s WEL for respirable crystalline silica is 0.1 mg/m³; keep this in mind when validating capture. Prioritise prevention at source, then control in the air, then thorough surface capture.