The world’s largest oil rig sank off the coast of Brazil today, and workers for the state oil company Petrobras are racing to prevent oil from spilling into the sea. Some 400,000 gallons of crude oil and diesel were stored on the rig or in nearby pipelines, and a company spokesperson said ships were standing by to contain any oil slick that emerges. In the past three years, Petrobras has suffered two major oil spills and other incidents that led to the deaths of 81 workers; some employees claim the company puts workers and the environment at risk by hiring inexperienced labor to cut costs.