The ammonia escaped when a valve on the container malfunctioned at about 8 a.m., said Lt. Eugene Germain Jr., a Miami-Dade Fire Rescue spokesman. The port reopened after the leak was stopped and a vapor cloud that had formed over the area dissipated.
Ammonia _ used as a cleaner and in fertilizers and manufacturing, as well as refrigeration _ is corrosive and can cause burns when touched or when vapors are inhaled. It is generally not considered to be a danger to explode or ignite unless the gas is highly concentrated.
Tim Gallagher, a spokesman for Carnival Cruise Lines, said that about 2,000 passengers aboard one returning ship were kept on board because of the leak but that it posed no danger to them.
The Port of Miami, in addition to being a stopping point for more than 3 million cruise ship passengers annually, is a major cargo port, with more than 8 million tons passing through each year.
The shutdown snarled rush-hour traffic near downtown while roads into and around the port were closed.