Updated

Five people were hospitalized in intensive care Tuesday as federal investigators sought the cause of an ammonia leak a day earlier in a plant that freezes chickens.

An attorney for Millard Refrigerated Services, which operates the coastal Alabama plant, said there had been no similar problems at the site before.

About 130 people sought help after a vapor cloud on Monday caused respiratory problems for those in the immediate area, authorities said. The plant is located near an industrial canal alongside Mobile Bay.

Four of those in intensive care were at the University of South Alabama Medical Center and one was at another facility, Infirmary West. Officials said none appeared to have life-threatening injuries but details of their conditions weren't released.

Theodore is a major staging area for Gulf oil spill recovery workers south of Mobile and many of those taken to hospitals were working on disaster response, authorities said.

Ammonia is a suffocating gas that can be fatal in high concentrations and is particularly dangerous because its vapors are heavier than air and hug the ground, according to the Centers for Disease Control and Prevention. Along with breathing difficulties, symptoms can include throat irritation, burns and blisters.

Doug Anderson, an attorney for Millard, said the facility hadn't had problems with handling ammonia before.

"This is the first time," he said.

In 2007, the Omaha, Neb.-based company paid a $5,100 fine after a worker was hurt in a machinery accident at the Theodore plant, according to Occupational Safety and Health Administration records. Records indicate that's the only time OSHA has fined the company for violations at that plant.

(This version CORRECTS Corrects that 2007 fine appears to be the only fine for the Theodore plant from OSHA.)