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

Fire due to welding operation

A fire started at the manhole of an inspection pit for underground pipes of a petroleum storage depot during a welding operation as part of maintenance work on the piping supplying a tank. The underground pipes were feeding eleven tanks in different conditions. At 11:15 a.m., a leak of premium-grade gasoline occurred, followed by a sudden flash. Site technicians attempted to extinguish the ensuing pool fire. The operator activated the internal emergency plan, issued the order to close all motorised valves and called for assistance from petroleum industry partners. At 14.00, emergency responders were still unsuccessful in suffocating the fire with sand. At 15:20 an explosion occurred which was caused by two acetylene cylinders used in the welding operation. Fed by an unknown source, the fire continued to rage for several hours despite firefighting interventions. Eventually, the foot valve on the adjacent gasoline tank was found open by the firefighters. After its closure, the fire receded Intervention efforts were substantial and the toll quite heavy; 15 firemen were burned during the accident: 2 of them were badly hurt, 5 seriously and 8 slightly. Apparently, the firemen suffered burn injuries due to a gust of wind and for the cylinders' explosion. The entry valve of the adjacent tank was left open for an unknown reason.

Important findings
• According to the site director, the piping should have been submerged in water during the onsite works and therefore was omitted from the valve closure checklist and control diagram.

Firefighters encountered myriad difficulties, in particular:
• The fire route to the tank was submerged under a layer of burning hydrocarbons;
• Fire water pipes burst under the weight of vehicles evacuating the zone;
• Lack of information about the source of the fire.

Lessons Learned
• The accident scenario was not included in the site’s risk assessment study. Fires initiated from welding operations are abundant in the literature.  A hazard assessment of tank maintenance operations should examine all possible ignition scenarios (what if?) associated with hot work.
• In order to prevent subsequent fires or explosions to occur, ignition sources, such as the acetylene cylinders should be removed from the area of emergency operation.
• Operators should provide accurate information on location of safety instrumentation to the emergency responders as soon as possible, especially if such devices can contribute to the fire or explosion.

Source: European commission

HCL leak incident

In a sulphur dichloride (SCl2) distillation facility in a chemical plant, a spillage of SCl2 occurred in the retention area for a distillation column in the final stages of distillation, after a leak from a recirculating pump. The SCl2 hydrolysed upon contact with ambient humidity, causing an intensive emission of hydrogen chloride (HCl), which was not detected by the HCl gas detector of the column. But a safety detector installed in the unit gives the alarm at 13:12. The controller placed the unit in safety shut down and then triggered locally the audible and visual alarm while alarm messages appear on the control screens in the control room. The internal emergency plan was activated and the 35 employees were evacuated. The internal fire team, supported by 40 external firefighters, equipped themselves with breathing apparatus and plugged the leak. The cloud of HCl was overcome using 4 lateral fire hose lines. The 120 m³ of water used is collected in a retention pond for reuse in production. The internal emergency plan is terminated at 16:15 pm. The next day a specialized company pumped 800 liters (1,200 kg) of sulfur dichloride from the retention basin into a storage tank. The HCl release remained confined inside the building. 

Source:European commission

Lightning strike in an ethanol tank in distillery

In a distillery, a 5,000-m³ tank containing 1,000 m³ of ethanol at 96% concentration exploded when lightning struck and then ignited. The raised roof fell into the reservoir, which remained intact. However, the tank foot valve cracked upon impact. An emulsifier delivered 2 hours later enabled preventing the fire from spreading to the 1,000-m² retention basin. The blaze was extinguished in 3 hours and the fire-fighters for over 5 hours cooled 3 adjacent 2,500 m³-tanks exposed to the intense heat. During the emergency response, 23,000 litres of emulsifiers stored onsite and a total of 7,000 m³ of water (including cooling water) were used. The loss was valued at 30 million francs (including 2.5 million of alcohol destroyed and 3 million of emulsifier). The extinction water (1,500 m³) collected in the retention basins would be diluted in a lagoon. An outside organization was called to verify the electrical installations of the storage zone. 

An internal response plan drill conducted 2 months earlier, based on a comparable scenario involving one of the tanks involved in the accident, served to facilitate the actual intervention. It had been recommended to install flame arrestors on the vents and the breathing valves on the tanks following a lightning risk evaluation study conducted 18 months prior to the event.

Source: European commission

Hydrogen release incident

 While deplugging a cooling circuit, a block-age suddenly set loose, causing an un-controlled movement of a flexible hose connected to the system. The flexible hose hit several small pipes nearby. Due to the broken pipe work there was a release of hydrogen and butene that lasted about five minutes. Sprinkler systems were activated; no ignition occurred. One employee standing nearby was hit by the flexible hose, causing a severe cut on the upper leg. The estimated production loss was 7 days.

Source: European Commission 

Sulphuric acid tank leak due to foundation collapse

On 4th February 2005 a storage tank containing 16,300 t of 96 % sulphuric acid ruptured. The entire contents of the tank were spilled out into the bund and then overflowed out into the nearby dock. The environmental consequences of the accident were quite significant, the sulphuric acid emission had a serious effect on local flora in the inner and deepest parts of the harbor and harbor entrance area. When the sulphuric acid came into contact with the salt water an exothermic reaction occurred, producing a vapour cloud consisting of hydrogen chloride that drifted northwards along the coastline in the direction of the wind. Fortunately, the wind was blowing towards the sea and away from populated land areas and the cloud diluted very quickly. After the spill approximately 2,000 t of contaminated sulphuric acid remained in the bund. The acid also soaked into about 100,000 square metres of the ground surrounding the spill. 

The cause of this incident was a leak in an underground coolant supply pipe of reinforced concrete installed over fourty years before that resulted in a weakening of the ground under the tank farm. Apparently, water forced its way out of the pipe, eroding the ground near and around the sulphuric acid tank. This erosion damaged the ground under the tank which ultimately failed due to the lack of sup-port of the tank floor. A study of the appearance of the involved part of the coolant supply pipe suggests that the corrosion was a result of an acidic attack on the concrete.

Source: European commission

Pump cavitation causes flange leak

A leakage of a hexane solution from a pump discharge flange during use occurred. The hexane vapor was ignited by a static electricity spark and a fire occurred. Apparently, the flange was loosened by vibrations from the pump, due to cavitation, which was ignored. Routine operations were being carried out on site at the time of the accident. The operation involved the transfer of a hexane solution from an unreacted raw material recovery tank to the washing process through the outlet of the first flange of the pump. The hexane solution leaked, ignited, and burned. The financial costs of recovery and lost production were significant.

Source: European Commission