The main objective of the CADDY project is to replace a human buddy diver with an autonomous underwater vehicle and add a new autonomous surface vehicle to improve monitoring, assistance, and safety of the diver's mission. However, the use of robots underwater may also bring additional safety requirements. Within the scope of this research, the existing vehicles that will be adapted for the purposes of the CADDY project were evaluated regarding safety issues. This will mainly focus on the vehicles' maneuvering capabilities as an indicator of whether the vehicles are safe to be used for interaction with divers. The hazards of ancillary equipment such as scaling lasers and acoustic modems were addressed as well. The design requirements, as well as the formal hazard identification and risk assessments guideline (HIRA) is developed in the beginning of the project to provide operational safety for each manned diving operation. All the CADDY vehicles are modified in order to comply with the design rules for safety. In fact, by the end of February 2015, 44 dives were conducted with a cumulative dive time of 1545 minutes without any accident. The HIRA and the diving methodology are proven to be effective means of safety.