Two people almost died and three others were injured after being exposed to toxic gas from decomposing fish waste on a fishing boat docked in Canterbury.
Four workers were taken to hospital after rotten fish and water was accidentally pumped into a machinery space on the vessel in the dry dock at Lyttelton Port in February last year.
Two contractors performing routine maintenance on Antarctic Discovery were able to escape through the rotting fish waste but two crew who went to investigate were knocked unconscious by hydrogen sulphide released from the decaying fish.
The Transport Accident Investigation Commission has released its findings into the accident.
Acting chief investigator of accidents Tahlia Fisher said while the unintentional starting of an offal pump led to the accident, the investigation found four broader safety issues that also affected other industries.
"In this case, the bow thruster machinery space had the hazards and characteristics of an enclosed or confined space but hadn't been recognised and managed as one," she said.
"Where multiple organisations are operating in the same workplace there will be overlapping responsibilities and safety depends on active coordination between everyone working on site."
A near-fatal gas poisoning
Two apprentice fitters were working on a pipe tucked behind a tank that held a mixture of decaying fish waste and seawater.
The offal pump control panel had been painted over so the labels and indicator light that showed when it was running were not visible.
Investigators found it was "as likely as not" one of the fitters accidentally pressed the offal pump's start button causing the contaminated water from the holding tank to rain down on them.
The two workers had no option but to climb up a ladder through the falling fish waste to escape to open air.
They were able to raise the alarm and the vessel superintendent entered the bow thruster room to investigate and was briefly overcome by hydrogen sulphide gas, a known by-product of decaying fish.
The chief engineer and second engineer came from another direction and collapsed. Crew used breathing apparatus to rescue the chief engineer, while the second engineer regained sufficient consciousness to crawl to safety.
Hydrogen sulphide is a colourless, flammable and highly-toxic gas known for its characteristic rotten egg smell at lower concentrations.
At high levels, people experience loss of smell, hindering detection, and exposure can be fatal in minutes due to respiratory failure.
The commission said multiple maritime safety agencies had issued warnings about decaying fish and seawater in refrigerated seawater tanks or fish holds could rapidly generate dangerous levels of hydrogen sulphide, especially at warmer temperatures, with fatalities often occurring during rescue attempts.
Failures that led to the fish waste overflow
A month before the accident, Antarctic Discovery was at sea when a valve for discharging fish waste from the tank at the front of the ship became blocked.
A temporary hose was used to pump waste to another tank. But it was mistakenly left connected to the offal pump with the open end tied to the ladder down into the bow thruster room.
The tank's outlet was left open and the offal pump was not isolated.
"In this case, the problem was not so much that one of the workers accidentally turned on the pump, it's the fact that the offal pumping system hadn't been deactivated correctly when it should have been," Fisher said.
The commission highlighted four safety issues:
- the identification of hazards associated with confined or enclosed workspaces;
- ensuring that machinery was safe prior to starting work;
- following the correct processes when safety-critical systems are modified;
- and when there were multiple parties on a shared worksite, ensuring each party was managing their risks appropriately.
Maritime NZ also investigated the accident and issued a warning, but wouldn't say to which company.
A spokesperson said it was a serious incident in which several workers were overcome by hydrogen sulphide, and it was relieved that all those affected had recovered.
"As the maritime regulator, we recommend ship operators, owners and maintenance workers understand the risks when working in confined spaces and have standard operating procedures to manage them.
"The incident had a range of parties involved from the owner of the vessel, the port, and contractors. All parties need to be aligned when it comes to understanding the risks and processes. If there are risks, such as with noxious gases, working in confined spaces can heighten these."
Changes made since the accident
The commission made recommendations to Australian Longline and Lyttelton Port Company to strengthen the management of its safety-critical systems and dry dock operations.
Australian Longline had since installed hydrogen sulphide detectors and cameras in the bow thruster room of Antarctic Discovery, along with sight glasses on the offal pump so the flow of waste could be observed when in use.
It had also bought hydrogen sulphide detectors for crew to wear and added the bow thruster room to the vessel's register of enclosed/hazardous spaces.
Australian Longline managing director Malcolm McNeill said the commission's inquiry was thorough and he appreciated the constructive nature of its findings and recommendations.
"Australian Longline remains committed to the ongoing review and continuous improvements of its safety management systems and operational procedures to ensure the safety of crew, contractors and all those who work alongside us," he said.
The commission found Lyttelton Port's safety standards and management of dry dock workers did not provide adequate protection from the accidental discharge of hazardous liquids and resulting gases.
No action had been taken to address the issue and it recommended the port company took steps to verify on-board systems with the potential to compromise safety were isolated and made safe prior to entering the dry dock and that awareness of the status of those systems was maintained during the vessel's time in the dry dock, the commission said.
It also recommended the company modify its processes to address how the overlapping responsibilities of parties conducting business in its dry dock were managed.
Lyttelton Port told the commission it was considering the recommendations.
Chief executive Graeme Sumner said it acknowledged the findings and recommendations in the report.
"Safety remains our highest priority and we are committed to continuous improvement across our operations."
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