On August 8, 2011 due to a sudden increase in pressure followed by the rupture in the roof to shell joints and spread of ammonia gas into the atmosphere of the Pars Energy special economic zone in the Assaluyeh Port, Bushehr, Iran. Next, decommissioning of this tank (TK-4501A) was ordered even though due to the unexpectedness of the incident, executive action or prior planning for decommissioning and internal inspection of the tank was not foreseen. Due to safety considerations stemming from the dangerous nature of the ammonia and the special design of this tank, the operation of complete drainage of the remaining ammonia in the bottom of the tank and the necessary ventilation for the entry of personnel into it for inspection took approximately 297 days from the time of the incident. Yet, this operation along with the hardships and difficulties in the planning and operation was a successful experience and created a new view in the operation of safe decommissioning of liquid ammonia atmospheric storage tanks. This paper discusses the decommissioning procedure to carefully and safely empty and purging of this tank and the problems, which have been occurred. The decommissioning took place in August 2011 until May 2012 and all together it covered 297 days Net Time: Emptying 5 days, Purging 60 days. 232 other days: Preparing new procedures and equipments. Because of the existence of another two tanks, there was not any problem in ammonia production and storage of the plant.

This paper has been presented during the Nitrogen & Syngas 2015 in Istanbul, in 2015.