We have built a worker-safety monitoring system (WSMS) for use in the shipbuilding and offshore industry (S&OI). The WSMS combines metal-conductor communication wireless networks with location-estimation technology that uses ultrasound signals in the frequency band 18 to 22 kHz, which is above the normal range of hearing (<15 kHz) in human adults. This system can be used in environments that include many metal barriers. The developmental process included deriving stakeholder requirements, transforming system requirements, designing system architecture, and developing a prototype. The prototype WSMS was tested by applying it to H Company, a Korean S&OI. Use of the WSMS increased the productivity of workers and managers by reducing the cost of on-site patrols and handwritten input. As a result, the number of worker location information updates increased from 2/day to 20/min, and productivity increased by 30 min/day compared to the previous method. Therefore, shipyards that introduce worker-safety management systems may consider applying this method.