PROCESS SAFETY MANAGEMENT BLOG WITH RISK BASED PSM INSIGHTS : November 2017

November 28, 2017

HYDROGEN SULPHIDE POISONING DURING PLANT SHUTDOWN

One worker died due to inhalation of H2S while trying to take out a safety valve for maintenance. It was later determined that he removed the flange bolts of the wrong relief valve and he was working without a permit. His supervisor had pointed to the safety valves (there were two of them at a height) and told him to remove one. He assumed the worker knew which valve to open.

November 24, 2017

Tank collapse incident

A fixed atmospheric storage tank was taken out of service for repairs. During re commissioning, the tank was filled up with water to check for leaks. After the leak check, the contractor handling the testing process was instructed to drain the tank of water using the 4” drain valve located at the bottom of the tank. As the contractor was pressed for time, he decided to open the 24” tank bottom manway also, to speed up the process of draining. After some time, a loud bang was heard and the tank collapsed due to vacuum. The venting arrangement in the tank was not sufficient to prevent vacuum in the tank when the manway was opened.

November 22, 2017

Ammonia storage and business continuity risk

I recently attended an international conference in the Middle East, about issues with large scale storage of ammonia and new developments in ammonia production. There was an interesting case where an operator of a large atmospheric ammonia storage tank located in a port city for many years was forced by the authorities to decommission the tank as there was a threat by an adversary to hit the tank with missiles. The case study pointed out that the company had taken measures to protect the tank. Though dispersion models predicted a much smaller exclusion zone in the event of a tank rupture, the public relations measures and risk communication by the company could not prevent the court judgement and finally the tank was decommissioned. A group of scientists had published a report that in the event of an attack on the ammonia tank, the effect would be similar to the dropping of 5 atomic bombs. But the results of QRA studies did not match with the prediction.

The case study has lessons for us in India. The FACT ammonia tank supreme court judgement many years ago took a pragmatic view of the matter. But today, public's perception of risk is only about consequences and does not consider probability of occurrence! There are a large number of atmospheric ammonia storages in India where construction of houses by public, near the tanks, have been permitted by authorities, with the net result that the buffer zone that was originally present has disappeared. It's a point to ponder! Industries with large quantities of toxic materials may be the ones that may be asked to move...