The accident took place in one of the small pharmaceutical manufacturing units of the Pune facility of HAL, currently on manufacturing lease agreement to RPG Life Sciences Ltd (RPGLS), affecting the technicians operating the equipment.
The deceased has been identified as Sadavarte (30), police said.
The victims admitted to Nirmaya hospital in Pimpri were suffering from acute respiratory distress syndrome, according to a senior doctor.
A company spokesman said all operations at the facility were suspended and a high powered team comprising senior management and technical experts from RPGLS had rushed to the spot to analyse the cause of the accident and provide support and relief.
The company has clarified that there was no further danger from the gas and currently no traces were present in the area.
The company spokesman said they were investigating the incident and its cause. Being a leased facility from HAL and the fact that in the same area other companies were also operating their pharmaceutical manufacturing lines, it will take some more time before the actual cause of the accident can be ascertained, he added.
A company source said the accident occurred when the chemical engineers were testing a new drug which can be used for treating renal failure.
As the testing was going on, a sudden chemical reaction occurred generating considerable heat causing an explosive reaction, followed by emmission of gas and fumes.
Meanwhile, Dr Dilip Kamath of Nirmaya hospital said the seriously injured was bleeding from trachea as the gas fumes, suspected to be hydrogen sulphide, were highly corossive.