Since 1959 IMO has introduced many measures in conventions, recommendations, and other instruments. Most important:
International Convention for the Safety of Life at Sea, 1974 (SOLAS)
Convention on the International Regulations for Preventing Collisions at Sea, 1972 (COLREG)
International Convention on Standards of Training, Certification, and Watchkeeping for Seafarers, 1978 (STCW)
SOLAS covers various aspects of ship safety:
construction
fire protection
life-saving appliances
radio communications
safety of navigation
carriage of cargoes
safety measures for high-speed craft