UK: A ship’s second engineer working in the salt water tank of a trawler was asphyxiated by R22 leaking from the ship’s refrigeration system, investigators have reported.
The incident in August 2018 on board the UK-registered fishing trawler Sunbeam resulted in the death of 52-year-old William Ironside and the hospitalisation of four others.
According to the Marine Accident Investigation Branch (MAIB) report, published today, Ironside was found collapsed inside a refrigerated salt water (RSW) tank. Three of his crew mates went into the tank to help. All suffered breathing difficulties and one also collapsed. Two other crew members then donned breathing apparatus and rescued their struggling crew mates. Despite being rescued from the tank, Ironside could not be resuscitated.
MAIB reports that the tank was an enclosed space, without any of the normal safety precautions. There was no ventilation, the atmosphere was not monitored and Ironside was working alone without communications.
It was found on this occasion that R22 refrigerant had leaked into the tank through corroded tubes in the evaporator of the vessel’s starboard refrigeration plant.
The Sunbeam was a 56.17m steel-hulled trawler built in Spain in 1999; it had been lengthened from its original 48.75m in 2004 to increase its number of RSW tanks from six to nine.
The trawler was fitted with two refrigeration plants which could be operated individually or in parallel to chill seawater. The refrigeration systems were designed and manufactured by Technotherm A/S of Halden, Norway, and had been installed at build.
The evaporators comprised two shell and tube heat exchangers mounted horizontally, and each heat exchanger contained 142 corrosion resistant aluminium-brass alloy tubes.
While the continued use of R22 was permitted in existing systems, its removal for maintenance or the topping up of systems operating with it, was banned under the ozone depleting substances regulations since January 2015. According to the MAIB report, up until the end of 2017 the R22 refrigerant was decanted out of the system by the crew and stored on board in cylinders when the refrigeration plants were not in use. The decanting procedure was discontinued in January 2018, after advice from a refrigeration engineer.
Each of Sunbeam’s refrigeration plants was designed to operate with 486kg of R22. After the incident, Star Technical Solutions (STS), who had been commissioned to carry out an investigation of the refrigeration systems, removed 312kg of R22 from the port plant and 178kg from the starboard plant.
Since January 2018, Sunbeam’s crew had only operated the refrigeration plants in manual control, due to a failure of the port compressor’s automatic capacity control switch. This, combined with the crew’s assessment that automatic control could put an unnecessary high load on the system, resulted in both plants being operated only in manual control. This situation increased the risk of water freezing inside the evaporator tubes, and consequent risk of damage to the tubes.
Routine maintenance and defect rectification of the refrigeration plants was carried by the crew utilising contractor support where necessary. There was no formal plan or onboard record of refrigeration plant maintenance although the chief engineer’s diary contained some records of completed tasks.
In January 2018, evaporator tube failures had been detected and repaired in the starboard evaporator. Leaking tubes had been isolated with brass plugs.
It was also found that 17 tubes in the port upper heat exchanger had been blocked at each end with brass plugs. The starboard upper heat exchanger had 27 tubes plugged. Of these 27 plugged tubes, 23 had a plug in each end, while four of the tubes had a plug fitted at only one end. Pressure testing identified leaks on four of the tubes in the starboard evaporator, one of which, had only been plugged at one end.
STS reported that a pressure test prior to recharging the system with R22, would have clearly shown there were still leaks.
Metallurgical examination of the failed tubes on the starboard evaporator identified the presence of pinholes and cracks in the tubes.
Visual inspection of the pump discharge isolating valve for the aft centre RSW tank, where the fatal incident occurred, identifed that its disc was damaged by significant notches around the edge. Visual inspection of the pump suction valve for the aft centre RSW also showed a significant notch on the disc edge.
While not designed to be gas tight, tests on the Sunbeam’s seawater isolating valves demonstrated that R22 gas would leak past both valves when in the shut position by gravity from the evaporators located above.
STS assessed that the concentration of R22 in the bottom of the RSW tank at the time of the incident was no less than 200,000 to 300,000 ppm and was probably significantly higher.
It was decided by STS that the damaged top (pump discharge) isolating valve on the aft centre RSW tank provided the path of least resistance to the R22.
The MAIB found that while the Sunbeam had been subject to regular surveys, a lack of clarity regarding responsibility for assessing refrigeration equipment resulted “in an inconsistent level of oversight of this machinery”.
In addition, it recognised that fishing vessels were excluded from UK regulations for personnel entry into dangerous spaces, and guidance on enclosed space working was not included in the Maritime and Coastguard Agency’s Code of Practice for Fishing Vessels of 24m in length and over.