SODIUM CYANIDE LEAK

 Incident
A plant operator responded to a bund alarm and observed sodium cyanide solution overflowing from a storage tank. A pool of approximately 84 000 litres of solution had formed and was contained within the tank bund. The site emergency plan was enacted and an exclusion zone was established around the area whilst the product in the bund was transferred to another tank. The concrete bund contained the spill, and the recovered solution and all of the washings were kept for use in future blending operations.

Cause
The combination of a faulty valve and failure by an operator to follow standard operating procedure, led to the tank overfilling. The overflow spilt into the bunded area and activated the bund alarm.

Consequences
The defective valve was repaired and the tank high-level critical alarm system has been reviewed and improved. The tank overflow piping is also under review to identify options to prevent recurrence. The responsible operator has been counselled on appropriate self-check work systems. There were no injuries or damage to any property as a result of the incident and the emergency response plan functioned as intended.

Source: Department of Minerals and Energy, Australia

CHLORINE LEAK DUE TO STRESS CORROSION CRACKING OF SS BOLTS

 Incident
Approximately 150 kg of chlorine gas was released over a period of 140 minutes, due to failure of bolts on a vacuum gas regulator attached to an on-line liquefied chlorine gas drum, used for water treatment. The incident occurred outside work hours, however plant operators were not called out, as the plant alarm system was not correctly programmed. Impact from the release to the surrounding community was limited to chlorine odour being detected by a passing motorist who reported the odour to the operator of the
site. The leak was isolated by a plant operator who arrived at the scene after the release was reported.
Cause
Inspection of the vacuum gas regulator revealed that the release was due to the failure of four bolts on the regulator. Material test results show that the failure of the stainless steel bolts was due to chloride-induced-stress cracking from chlorine attack, which is assumed to have resulted from an extremely small leak over a short duration.
Consequences
As part of the investigation, a number of changes to prevent recurrence of the event have been identified and implemented. These include introduction of a weekly leak check, the company committing to inspection of all vacuum regulators, the replacement of any inappropriate bolts and reprogramming of the chlorine alarm. In addition, the company will investigate the use of different alloy bolts.

Source: Department of Minerals and Energy, Australia 

NITROGEN HOSE BURST AND RELEASED AMMONIA

Incident
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.
Consequences
The incident occurred as a result of the failure to follow the appropriate procedure and the company has taken the action of reviewing the competence of each operator to carry out the task. The company has also reviewed the operating procedures associated with the filter cleaning process to ensure they are appropriate. 

Source: Department of Minerals and Energy, Australia

RELEASE OF TOXIC LIQUID THROUGH STEAM COIL LINE GASKET LEAK

 Incident
A release of toxic liquid (containing arsenic trioxide) from a storage tank occurred following the shutdown of a chemical plant. The release occurred from a steam coil passing through a storage tank used to store the solution during the shutdown. The release flowed into a surface-drainage system,through a series of secondary catchment sumps and ponds, into Cockburn Sound.
Cause
An investigation into the incident has identified that the toxic liquid was released through a hole in a gasket of a flange. The flange was located on the steam coil pipework within the tank. It was found that the steam-line terminated outside the bunded area in a partially-covered surface-drainage system.
Consequences
To prevent a recurrence, all steam-lines within the plant were cut to ensure that they terminated within the bunded area. The company has also decommissioned the plant and will commission a new plant that does not utilise arsenic compounds.

Source: Department of Minerals and Energy, Australia 

FAILED GASKET DURING START UP

 Incident
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 steam release 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. None was injured as a result of the release.
 

Cause
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. 

Consequences
A complete boiler inspection has now been conducted and boiler tubes showing signs of corrosion have been plugged off. Actions to prevent a recurrence include the addition of insulation at the top of all boiler tubes and further investigation into the boiler water chemistry to minimise potential for corrosion. The company has also modified the boiler to incorporate a drain valve in order to provide early warning in the event of water leakage.

 Source: Department of Minerals and Energy, Australia

START UP INCIDENT IN AMMONIA PLANT

 Incident
A mixture of synthesis gas and ammonia was released from an ammonia plant during the start-up process following a shutdown for maintenance. The release occurred from a high vent after ammonia had been allowed to collect in the vent system through a valve left open as a result of failure to tag the valve as out of service.
During the start-up, operators failed to control levels in the process, resulting in a high level alarm in an ammonia catchpot which led to a release of synthesis gas (as designed) into the vent system. However, as the vent system already contained ammonia, the gas mixture was forced out of the high vent. The wind direction took the gas cloud over an adjacent construction area on the same site resulting in fourteen
contract employees experiencing irritation and discomfort and later seeking medical attention. Six of these contractors were physically affected as a result of the exposure but nobody suffered serious or long-term injuries. The ammonia release dispersed and was not detected at neighbouring premises.
Cause
The incident was caused by a combination of factors including a failure of the tagging system and the failure to adequately control the catchpot level during start-up.
Consequences
The tagging system for equipment which is out of service, has been reviewed to ensure during maintenance there is no unauthorised operation of equipment. Resource allocation has been reviewed to ensure that process control is secured and level indicators in the catchpot have been assessed to ensure accuracy for process control. Also, workers at the adjacent construction site will now carry gas respirators at all times and will be notified of any operating conditions, such as start-ups and shutdowns, with the potential to lead to releases of gas.

Source: Department of Minerals and Energy, Australia 

AMMONIA LEAK FROM REFRIGERATION SYSTEM

Incident
Approximately 56 kg of anhydrous ammonia was released to the atmosphere from
a 25-year-old refrigeration system. The emergency services stopped the leak by
closing an isolating valve. There was no injury. The site was not licensed for the
storage of anhydrous ammonia.
Causes
One valve failed to close and stop filling up the accumulator of the refrigerating
system. This resulted in flooding of the refrigeration compressor by liquefied
anhydrous ammonia, causing one of the compressor O-rings to fail, thereby causing
the release of anhydrous ammonia to the atmosphere. This points to an inadequate
maintenance program.
Consequences
The operator has been instructed to take appropriate measures so that the
refrigerating system complies with the relevant safety standard and the Dangerous
Goods Regulations. The operator was successfully prosecuted for failing to placard
the site and have a licence to store anhydrous ammonia.

Source: Department of Minerals and Energy, Australia

LOOSE BOLTS - CAUSES

 Www.smartbolts.com/insights/loose-bolts-causes-ways-prevent/

A pressurized bolted flange joint assembly begins to leak, creating a safety hazard. A rotor with its blades separates from the nacelle and spins off a wind turbine, crashing to the ground. Under constant vibration from the engine of an ocean freighter, loose bolts on a large piece of mining equipment work their way off the bolted joints and roll around the hull, inflicting further damage to the equipment.