Police have charged the head of the Charoen Pokphand Foods wastewater treatment section with negligence over the deaths of five people at CPF's plant in Bang Na on Friday.
Preecha Tamporn was charged after being questioned for several hours by investigators at Bang Na district police station on Monday evening, Metropolitan Police Bureau commissioner Pol Lt Gen Sanit Mahathavorn said on Tuesday.
The charge is violating Section 291 of the Criminal Code, which deals with acts of negligence resulting in a death, he added.
If found guilty on this charge the maximum penalty is 10 years in jail and/or a fine of 200,000 baht.
The CPF section head was released on police bail because he had demonstrated his intention to cooperate by turning himself in, Pol Lt Gen Sanit said.
The five victims were a 5th year veterinary student at Chulalongkorn University who was visiting the plant with a friend, a company environmental officer and three other CPF employees.
The 23-year-old student reportedly fell into the pond first, prompting the environmental officer and three other staff members to rush in and try to rescue her.
They are thought to have died from inhaling toxic gases given off by the pond, which handles 5,500 cubic metres of wastewater per day.
The pond at the CPF poultry-processing plant on Soi Bang Na-Trat 20 is 3 metres wide, 4 metres long and 2.5 metres deep. The lid weighs about 30 kilogrammes and has two handles. The entrance hole was not closed.
The Industrial Works Department has ordered CPF to close the wastewater treatment area for 30 days and improve safety measures.
Police are also investigating why visitors were allowed near the open wastewater treatment pond in what should have been a highly restricted area.
Mongkol Pruekwatana, director-general of the Industrial Works Department, said on Monday the tragedy occurred when students were given an unofficial tour of the plant through a personal connection.
The environmental official who showed them around had only worked there for six months.
Police would have to investigate what happened, and why the lid was not in place, he said.