Ventilation & Local Exhaust

Ventilation is an engineering control that removes or dilutes airborne contaminants before workers breathe them. Used well, it can make respirators unnecessary. Used badly, it blows dust into someone else’s face or does nothing at all.

• Construction
• General Industry

Two main types

Making local exhaust work

• Get close: a capture hood loses most of its pull a short distance from its opening. Keep it within about one hood-diameter of the source and move it as the work moves.
• Position the hood so contaminants are pulled away from your breathing zone, not past it.
• Use tool-mounted shrouds with HEPA vacuums for silica-producing tools. See Dust Extractors.
• Check airflow before work: flow indicators, gauges, or a smoke tube.
• Keep ducts free of dents and blockages; change filters on schedule.
• Provide make-up air so exhaust systems can actually pull air.

Portable fans and blowers

• In tanks, vaults and confined spaces, blow fresh air in from a clean source, away from engine exhaust. See Confined Spaces.
• Use fans rated for flammable atmospheres where vapors or dust may be present.
• Test the air before and during work; ventilation doesn’t replace monitoring. See Gas Detectors.

Common mistakes

• Blowing contaminated air toward other workers or into building air intakes.
• Pointing a fan at a welder so it blows fume around instead of away.
• Using pure oxygen to “freshen” air. It creates a severe fire hazard.
• Recirculating air from dust collectors indoors without proper filtration.
• Assuming an open window or door is enough.

Before you start

• Source of the contaminant identified
• Hood or shroud positioned close to the source
• Airflow checked and working
• Exhaust discharged away from people and air intakes
• Air monitoring in place where needed

Last updated: October 2, 2026