Ten of them were hospitalized themselves, and 90 hospital personnel had to be called in to help with the emergency Wednesday night, said Tomoko Nagao, spokeswoman for the Red Cross Kumamoto Hospital in southern Japan.
The most severely injured was a 72-year-old pneumonia patient, whose condition worsened after exposure to the fumes, Nagao said. The hospital's emergency ward was closed and firefighters called in to decontaminate it.
The doctors were not wearing protective gear and were unprepared because the paramedics who brought the farmer to the hospital had not identified the pesticide, said a local police official, speaking on condition of anonymity because of protocol.
The incident came amid a string of suicides in Japan by people mixing household chemicals to create lethal fumes. Many bystanders in recent months have been sickened by fumes that escaped into adjoining rooms, apartments or homes.
Seishi Takamura, a doctor who treated the farmer, said he could not stop coughing after inhaling the fumes, which smelled like chlorine, Kyodo News agency reported.
Chloropicrin is a highly volatile pesticide with a pungent odor that can cause breathing difficulties and sometimes death when inhaled in large amounts.