Police have warned of the danger of mixing sulphuric acid and caustic soda to clean a clogged pipe, after three people died in a small toilet at a family home in Chon Buri.  

Police issued the warning on Tuesday following the death of a policewoman and her two daughters at their house in Chon Buri province on Monday.

They said the family had used an unlicensed sulphuric acid product to clear a clogged pipe in their toilet. If mixed with caustic soda, the acid reaction could produce a mixture of deadly fumes known as sewer gas.

The toilet was small with only one hole for ventilation. As the door opened inwards, anyone trying to help a person inside the toilet must close the door, trapping the air inside.

On Monday police found the three women unconscious in the toilet. Their mouths were full of saliva and their fingertips and lips were dark green. One of them was already dead and the two others were later pronounced dead at Chon Buri Hospital.

Exposure to sewer gas can cause suffocation and death.