Working in a shipyard can expose workers to a variety of hazards. One hazard is poor air quality while working in confined or enclosed spaces. Poor air quality can occur as a result of several factors, such as stagnant air where there is insufficient air flow, or the accumulation of air contaminants resulting from a source pollutant (e.g., residual sewage or residual hazardous materials). When such conditions exist, the use of ventilation is necessary to remove contaminants (e.g., fumes, dust or vapors) and provide a healthful and safe working environment. This document provides employers with the basic principles of ventilation for use in shipbuilding, ship repair and shipbreaking activities. The document includes methods for the selection, installation and use of ventilation equipment to ensure proper air quality in confined and enclosed spaces.