simply, a caisson. Ventilation filtration systems: The word caisson is also used as a name for an airtight housing for ventilation filters in facilities that handle hazardous materials. The housing usually has an upstream compartment for a pre-filter element and a downstream compartment for a high-efficiency filter element. It may have multiple sets of compartments. The housing has gasketed access doors to allow for the change out of the filter elements. The housing is usually equipped with connection points used to test the efficiency of the filters and monitor changes in the differential pressure across the filter media. See also , a mobile barge-mounted engineering caisson used in the Port of Gibraltar , a temporary water-excluding structure built in place, sometimes surrounding a working area as does an open caisson. , for information on geotechnical considerations. Patents – Improvement in construction of sub-aqueous foundations References External links