A fire which sparked the evacuation of a major underground US nuclear waste plant last month was preventable, according to a report out Friday highlighting safety lapses at the site.

Poor training, badly maintained equipment and unclear procedures were criticized in the report into the subterranean blaze at the Waste Isolation Pilot Plant (WIPP) near Carlsbad, New Mexico.

Eighty-six workers were underground when the fire broke out on a salt-hauling truck on February 5, in a rare accident at the site used to dispose of material including plutonium-contaminated waste.

Six workers were taken to hospital for smoke inhalation. Less than two weeks later a low-level radiation leak was detected, although it was not clear whether it was linked to the fire.

The report into the fire detailed a list of problems, including that the "fire protection program was less than adequate," and that both the maintenance and emergency management response programs were "ineffective."

There was also "ineffective training and drilling" and "inadequate Headquarters oversight," it added.

"The Board concluded that this accident was preventable," said the 187-page report by an Accident Investigation Board appointed by the US Department of Energy (DoE).

The DoE describes the New Mexico site as "the nation's first repository for the permanent disposal of defense-generated transuranic radioactive waste left from research and production of nuclear weapons."

The plant, some 270 miles (434 kilometers) southeast of Albuquerque, is used to dispose of material that includes plutonium-tainted waste from the Los Alamos National Laboratory, about 300 miles (483 kilometers) away, also in New Mexico.

The waste is dumped 2,150 feet (655 meters) underground in large rooms excavated in an ancient, stable salt formation.

Carlsbad is about 70 miles (115 kilometers) from Roswell, the infamous site of a mysterious 1947 crash which spawned conspiracy theories that the military had covered up a UFO landing, and captured aliens inside an alleged spacecraft.

Experts are hoping to re-enter the effected underground area in the next two or three weeks, the report noted.

"The re-entry team and support personnel continue to perform simulated re-entry scenarios .... The personnel re-entry is planned for later this month," it said.