Buildings and Structures 2 Natural and Mechanical Ventilation

Aim To provide students with information to allow them to deal with incidents involving buildings and structures safely and effectively.

Learning Outcomes At the end of the session students will be able to: State the characteristics of natural and mechanical ventilation Understand the function of a range of mechanical ventilation systems and their effects on firefighting operations.

Natural ventilation Combination of wind entering from outside and air currents created inside Many types of air inlet and outlets are fitted The most common is known as an ‘Air Brick’ Older commercial buildings may be fitted with lantern lights or louvers Modern buildings may be fitted with automatic ventilators, some rain sensitive.

Natural ventilation.

Mechanical ventilation Mechanical ventilation assists in or fully ventilates a building Found in buildings where large numbers of people congregate in a relatively small area Also found in commercial premises where occupants require protection from harmful fumes or dust created by the production process.

Mechanical ventilation. Conditioning plant Motor & fan unit Ducts at ceiling level Roof Second floor First floor Ground floor

Mechanical ventilation Mechanical ventilation can be divided into three principal groups; Vitiated air is extracted by fans, fresh air naturally entering through doors and windows Fresh air forced in by fans, vitiated air naturally exiting through doors and windows Fans both force fresh air in and vitiated air out.

Mechanical ventilation Methods 2 and 3 maintain the air pressure inside the building slightly higher than outside in order to prevent incoming draughts Referred to as ‘balanced systems’ All mechanical systems consist of ducting, used to channel the flow of air Firefighters should be aware of possible smoke and fire spread through these systems.

Air conditioning systems Basic air conditioning system consists of; Fans for moving air Filters for air cleansing A means of warming the air A means of humidifying the air A refrigeration plant Heat exchange surface e.g. finned coils or chilled water sprays.

Dust extraction systems Usually required by legislation in commercial premises where occupants require protection from excessive dust or a need exists to remove or dilute a potentially explosive hazard.

Dust extraction systems Dust collected by extractor fans and sent through ducting to a collection area Fine dust of any sort poses a hazard of fire or explosion Any fire in ducting is extremely dangerous, attempts should be made to cut off the forced air supply and introduce either fixed sprinklers or spray jets into the duct.

Fume extraction systems Usually found where chemicals are used, especially liquids Need for fumes to be extracted to ensure safety Automatic fire protection is usually required and safety regulations are strict Ducting often fitted with light panels to either vent an explosion or to provide access.

Confirmation Assessments will be based on this lesson and the corresponding study note Learning Outcomes State the characteristics of natural and mechanical ventilation Understand the function of a range of mechanical ventilation systems and their effects on firefighting operations.

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