Exhaust Fan

The Job an Exhaust Fan Does

An exhaust fan removes air from a compartment and discharges it to open deck, pulling the space slightly negative relative to the spaces around it. That negative pressure is deliberate: a galley extract keeps cooking fumes and grease-laden air from drifting into the accommodation, a paint locker extract keeps solvent vapour from building up, and a battery room extract removes hydrogen given off during charging before it reaches an ignition source. Engine room extraction works differently, removing heat and combustion by-products roughly in balance with the supply fans rather than running deliberately negative. The direction of airflow, not the fan itself, is what separates this equipment from a supply fan doing the opposite job in the same ventilation system.

Main Components

• Impeller – axial for high-volume, low-resistance duties like engine room extraction, centrifugal where duct runs and resistance are higher.
• Motor – standard enclosure for general spaces, explosion-protected (Ex d or Ex e) where the fan serves a hazardous area such as a battery room or a gas-dangerous space.
• Flexible duct connection – isolates fan vibration from the ductwork and structure.
• Fire damper – fitted where the duct passes a fire boundary, normally open and closed remotely or by fusible link.
• Spark-proof grille or non-ferrous impeller – required where the fan handles air that could contain flammable vapour.
• Weather terminal – goose-neck or cowl on open deck with a non-return flap to stop green water or backflow entering the duct.

Selection and Sizing

Air change targets vary sharply by space: a paint locker typically needs mechanical extraction sized for a set minimum number of air changes per hour under class rules, a galley needs enough capacity to clear heat and grease-laden air at the cooking line, and an engine room extract is sized to match its supply fans rather than to a fixed ACH figure. Static pressure has to cover duct losses, grille resistance and any silencer, and hazardous-area duties fix the motor's explosion-protection class before capacity is even considered.

Regulations and Class

SOLAS Chapter II-2 requires fire dampers at fire boundaries and remote stopping of ventilation fans serving machinery spaces and galleys from outside the space, coordinated with the release of any fixed fire-extinguishing system so the fire is starved of ventilation rather than fed by it. Paint locker mechanical extraction is a SOLAS requirement in its own right. Hazardous-area fans, such as those serving battery rooms or gas-dangerous spaces, must meet the applicable IACS unified requirements for spark-proof or explosion-protected construction.

Typical Faults

What to Look for in a Supplier

• Ex motor certificates matched to the specific zone classification of the space, not a generic explosion-proof label.
• Damper actuators compatible with the ship's existing fire detection and release panel.
• Spare impellers and bearings held for the exact model fitted.
• Noise and vibration figures where the fan sits near accommodation.

Test the fire damper and emergency stop for every extract fan at each fire drill, not just the ones an inspector is likely to check; a damper that has silently seized shut is invisible until the fan can no longer clear the space.