Despite abundant evidence for the adverse health effects associated with welding fume, shipyard welders continue to have exposures that routinely exceed safe limits. Welding in shipyards can be particularly hazardous due dynamic conditions and work in enclosed and confined spaces. Currently, there are no specific ventilation guidelines available to shipyard welders, beyond general regulatory requirements for local exhaust and general dilution air flow rates. In this study, general ventilation guidelines were developed for inclusion in a training intervention. Using an observational tool based on those guidelines, a baseline characterization of the work practices and use of ventilation in enclosed and confined space welding tasks was performed at a Seattle shipyard. To assess ventilation effectiveness, a scoring system was developed to compare actual and recommended ventilation practices. Comparing ventilation techniques and estimated exposure suggests that adoption of the intervention guidelines reduces the potential for welding fume exposure. Additionally, an inter-observer assessment based on side-by-side field measurements shows good agreement for the observational behavior tool, establishing the method as a reliable way to detect a change in ventilation-related behavior post-intervention.