INCIDENT DUE TO VALVE BUSH LEAK

 https://www.ppsa.org/assets/SaftyAlerts/hazard_alert___valve_failure.pdf

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.

How To avoid PRV performance problems

 https://www.valvemagazine.com/magazine/sections/features/4427-how-to-avoid-prv-performance-problems.html

MY ARTICLE IN CEP ISSUE JANUARY 2021

My fourth article "Understand Process Hazards to Safely manage Change" has been published in the January 2021 issue of the CEP magazine of the American Institute of Chemical Engineers. Read it after logging in in this link https://www.aiche.org/publications/cep

You have to be a member of AIChE to read it.

WHEN ISOLATIONS GO WRONG

 https://www.hse.gov.uk/chemicals/workshop/safe-isolation-10/go-wrong.pdf

Tank explosion due to a chemical reaction

The accident occurred when nitric acid delivered to a factory by a tank truck was unloaded into the wrong tank. The tank exploded due to a chemical reaction within the tank.Around 5:30 in the afternoon on the day of the accident, the driver of the tank truck carrying nitric acid arrived at the factory, handed over a delivery slip to the employee inc harge of accepting deliveries, and connected the hose of the tank truck to the flange(for unloading).As this was the first time for the driver to make deliveries to this factory, his co-worker who has delivered to this factory before told him that the flange for nitric acid was the second from the left. However, as the second flange from the left was made of vinyl chloride and the driver did not think that this could be the pipe for nitric acid, the driver connected the hose to the second flange from the right, which was made of stainless steel.After the connection of the hose, the employee in charge of accepting deliveries opened the electromagnetic valve, and the driver started the discharge. As the liquid surface of the nitric acid tank did not rise, however, the driver checked the label of the tank and found that he was unloading nitric acid into the tank for triethanolamine.The driver informed the employee in charge of accepting deliveries of the mistake,connected the hose to the correct flange for the nitric acid tank, and completed the unloading in about 20 minutes. When the driver was going out from the front gate, he noticed white smoke being emitted from the tank. Around 6:25 in the afternoon, the sub-tank and main tank for triethanolamine that were wrongly charged exploded,releasing a chemical spill in the area.No injuries or fatalities were caused by this accident.

Causes

The following can be considered as the causes of this accident.The hose of the truck delivering nitric acid was mistakenly connected to the pipe for the wrong chemical. The contact and coordination procedures for chemical delivery work were insufficient.Safety and health education for workers was insufficient.

Source: tamu.edu

HAPPY NEW YEAR!

 A VERY HAPPY AND SAFE NEW YEAR TO ALL MY SUBSCRIBERS! KEEP SAFE!

STARTING MY 11TH YEAR OF BLOGGING!

Dear Readers,

Thank you for being with me for the past 10 years since I started my blog. 

1800 posts, 325000 views, about 800 incidents and many of my readers spreading the information from the posts through process safety one point lessons within their own organizations...I am still far from satisfied. My mission in life has been "Preventing another Bhopal" and let us not rest till we have achieved it. How can you help? By the following steps:

1. Never be silent when you see something going wrong - it could be a decision that is not in the interest of process safety - speak up!
2. Share past incidents (internal incidents and external incidents) and their root causes, with all your colleagues - we see the same old incidents repeating
3.  As an engineer, be ethical when taking decisions and do not take decisions because they please the boss
4. Update your technical knowledge continuously
5. Do not be carried away by all the technologies that vendors try to sell you. Thoroughly study them and employ only those technologies that are useful to you. Don't get carried away by Jargon.
6. Wear your engineering hat always, even when you go up the management ladder.
7. Be aware of normalization of deviations around you. Report them and determine the root causes. You work in a chemical plant. You and your colleagues should not have the misfortune of seeing people die before your eyes because of an incident....

I end by quoting Robert Frost, "The woods are lovely, dark and deep, but I have miles to go before I sleep"

The working of a flame arrester

 

Process safety beacon on flame arrestor

 https://www.aiche.org/sites/default/files/cep/20160420.pdf

Can a flame arrester element be made of a non metallic element?

Flame arresters are often provided on vent lines in atmospheric storage tanks storing flammable materials. The principle of operation is by cooling the flame and extinguishing it before it reached the inside of the tank. As the flame travels through the element, it is exposed to a large area of the element, which can be folded meshes etc. But do you know that the element inside does not necessarily have to be metal? The flame arrester element itself experiences very little warming, because it is subjected to a high temperature for a very short time. Heat transfer is initially due to convection/diffusion and then later due to conduction after flame has been extinguished. Hence non metallic elements like PTFE can be used to avoid plugging. See one vendors catalogue here https://www.protego.com/products/detail/FA-I-PTFE.html

Note: This is for information only.

CSB releases airgas safety spotlight

 https://www.csb.gov/csb-releases-airgas-safety-spotlight-/

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

Heat exchanger tube leak causes ammonia gasket failure

A mixture of process gases was released to the atmosphere through a failed gasket during the start-up of a chemical plant. Operators had just completed the start-up when they heard a large sound and received alarms from ammonia detectors.The plant was shutdown, however the plume released travelled off-site necessitating the evacuation into refuges of a small number of workers on a neighbouring site. No-one was injured as a result of the release.

An investigation showed that the gasket failed as a result of a hole in a boiler tube which had allowed water to pass from the boiler side into the process side. The temperature generated during start-up caused the pooled water to rapidly boil leading to a surge in pressure which resulted in the failure of the gasket. Non-destructive testing of the boiler tubes showed gouge-type corrosion believed to have been caused by flow distribution problems in the boiler. This resulted in excessive metal temperature, which led to corrosion of the tube.

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

Accident due to a temporary connection

The alkylation unit was going into shut down. Two contractors were fixing a copper tube to a T-piece of a drain. During the work they turned the T-piece over 90°. Due to this fact a valve on the T-piece was accidentally opened and an amount of hydrogen fluoride (HF) was released. One of the contractors was very seri-ously injured. His eyes, nose and mouth were burned and he inhaled HF fumes, which caused internal injuries to them. The second person only had small injuries around his mouth.CausesBecause the alkylation unit was shut down, the biggest equip-ment was already emptied and the installation was cleaned with nitrogen. Then it was decided to drain the unit to remove all flu-ids left. The drain consisted of two valves and a blind flange. The blind flange was removed and replaced by a T-piece consisting of a manometer and a small valve. The T-piece was mounted in a horizontal way. A permit was written for two contractors to add a copper tube to the small valve on the T-piece. Because it was not easy to work with the T-piece mounted horizontally they decided to rotate the T-piece. While rotating the piece, the handle of the small valve touched a pipeline which opened the valve and 360ml HF was released. 

Important findings

The T-piece on the drain was a temporary piece only installed for the shutdown. There was no standard in the company to which temporary pieces had to comply. The T-piece used screw thread which made it possible to turn the T-piece. The accident showed that a standard for temporary pieces must be drawn up.In the company it was seen as normal that the manual valves in the line on which the T-piece was fitted had a small internal leak. So in the work permit protective clothing should have been specified for working on this line since they should have antici-pated that HF would build up between the fixed (leaking) valves and the quarter turn valve on the temporary T-piece. A quarter turn valve is easily manipulated accidentally, certainly while doing mechanical work in the immediate vicinity.

Source: European commission

What will go wrong will go wrong!

 On July 14, maintenance works were completed in a soy beans extraction plant. Following the inspection by the plant operator, the start-up of the facility was initiated at 21:30. Steam was admitted to the toaster and to the jackets of hexane inlet pipes to heat-up the toasters and the extractor to the proper operating temperatures.
At about 21:45 the toasters reached their operating temperature and admittance of flakes commenced through the inlet screw conveyor. After that the night shift took over. They had some difficulties controlling the process temperature (dropped), and therefore increased heat supply to the toaster. About the same time, the sound of the safety flap valve lifting was heard, and it released hexane and steam into the extractor building, where the smell of hexane was detected by the operators. The hexane concentration in the extraction building finally reached a level which forced the staff out of the extractor building. A bus driver passing the plant detected the vapours and informed the Traffic Control Centre that “airplane fuel was spilled on the road”. With this information, at their arrival, firefighters took a precautionary approach and parked the fire engine at a safe distance, walking the last hundreds of meters. The plant manager arrived at the scene and discussed with the incident commander how to stop the outflow of hexane vapour, and deciding ultimately to cutoff the power supply to the extraction plant. The manager there after asked the power control unit to turn off two transformers under the load. (There was also one unloaded). Due to inherent risk of possible sparks he rejected stopping the electrically loaded transformers and instead, disconnected the third, unloaded transformer. Approximately 30 seconds later, a sudden fire was observed outside the plant which was followed by a violent explosion. The explosion injured 27 persons, among 7 emergency responders and 20 staff members of the plant. The extraction plant was destroyed by the explosion and was notre-established. The explosion was probably initiated by the attempt to disconnect one of the three supply lines to the extraction plant.

Important findings
• Apparently, the smell of hexane which was detected by the operators was not an abnormal occurrence during the start-up.
• The site also stored large amounts of chlorine and hydrogen in the facility. Therefore, it was urgent that the incident commander and the plant manager work quickly together to prevent the explosion.
• The investigation revealed that no emergency shut-down procedure existed for the extraction plant.

Lessons learned
• Due to the conflict of following orders, the question arises who is in charge to give orders relating to operation of the plant, is it the incident commander or the operator? Who makes final decisions to shut down the electricity? Roles should be identified during normal operation when the operator drafts the internal emergency plan. The fire brigade should have visits to the plant to become familiar with the operation and discuss the emergency procedures with the plant manager and the control room operators.
• Emergency shut-down operations are crucial when operating a plant with the hazards of release of toxic materials or fire/explosion and that these protocols are followed.
• No alarm was activated to inform the public about the hexane release. Information to the public and activating the alarm is one of the most important emergency protocol in case the consequences might affect the nearby population.

Source: European commission