INCIDENT DUE TO BLOCKING OF ISOLATION VALVE

 In 2008, facility workers in the US closed an isolation valve between the heat exchanger shell and a relief valve to replace a burst rupture disk. Maintenance workers replaced the rupture disk on the day, however, they forgot to reopen the isolation valve. The next day, other facility workers closed a block valve to isolate the pressure control valve from the heat exchange so that they could connect a steam line to the process line to clean the piping. The steam flowed through the heat exchanger tubes, heated the liquid in the exchanger shell, and increased the pressure in the shell. The closed isolation and block valves prevented the increasing pressure from safely venting through either the pressure control valve or the rupture disk and relief valve. The pressure in the heat exchanger shell increased until it violently ruptured.

CONFINED SPACE FATALITY

https://www.gov.uk/maib-reports/entry-to-enclosed-space-on-fishing-vessel-sunbeam-with-loss-of-1-life

Do not depend on remotely operated valves for isolation for maintenance work

The two incidents below highlight the fact that you should not depend on rmotely operated valves for isolation during maintenance activities. ROV's are meant for use only during emergencies to prevent a major loss of primary containment:

1. A bolted joint was opened for maintenance on a pump but reliance for isolation was placed on a remotely actuated valve. The valve was inadvertently opened either from the control room or from the motor control centre resulting in a major release of flammable gas, with subsequent explosion.
   
2. A fire occurred during the removal of a blind. The blind was located downstream of an air actuated valve which was inadvertently opened during blind removal. This released flammable liquid, resulting in a large fire and multiple fatalities.
   

On the 36th anniversary of the Bhopal Gas Disaster

Are we better off in Process Safety Management than what we were when the Bhopal disaster occurred in 1984? I would answer this by saying that those who wanted to improve have certainly done so, with the help of various process safety initiatives by industry. But we continue to hear about many incidents every year that mar the image of the chemical industry. Based on my 41 years of experience (out of which the first 20 years were in operating plants and the next 21 years were in process safety consulting), I think the answer boils down to this basic fact. Some one said " The whole World moves on Vitamin M (Money)". After an incident, there is always a big reaction, but after some time, it becomes business as usual in some companies, and that's when another incident occurs. Can technology prevent incidents? The answer is yes, to a certain degree. But ultimately, it is decisions taken by the humans (and I am not talking about the human sitting in the control room) that cause an incident to occur. In Bhopal gas disaster too, decisions taken far away from the plant had an impact on the plant. 

Mahatma Gandhi had once said "The Earth has enough for everyone's need, but not for everyone's greed". Your views, please....

Nitrogen hose burst due to overpressure

A release of ammonia occurred from a chemical plant when a hose burst following maintenance to an ammonia filter. The release of ammonia was detected by operators due to ammonia alarms and a high flow of ammonia to the plant. The site emergency siren was activated to alert people of the incident and operators isolated the supply of ammonia to the plant. Operators donned personal protective equipment and doused the leak with water in order to gain access to the area to isolate the leak.

Cause

Ammonia filters were used to remove contaminants from the liquid ammonia, prior to it being processed in the plant. An essential step in the maintenance of filters is a nitrogen purge of the system. After purging occurs, the filter is changed, resealed and the nitrogen hose disconnected. The relevant valves are then opened to recommission the system with ammonia. In this instance, the nitrogen hose remained connected to the filter and drain valves were left open allowing the hose to become pressurised with liquid ammonia. While the hose was suitable for the pressures normally experienced under service with nitrogen, the hose was not suitable for the much higher pressures of liquid ammonia and as a result the hose burst in two places.

Source: http://www.dmp.wa.gov.au