Site search 19 minutes ago Calum Watson BBC Scotland PA Media The 'significant incident' took place while Glen Sannox was sailing from Arran in June last year. A faulty valve on a CalMac ferry led to a sudden and uncontrolled release of highly flammable methane gas, venting 700kg—enough to fill a four-bedroomed house—over 12 minutes while carrying 82 passengers from Arran to the mainland. So much methane was released that some of it was sucked into a ventilation intake, setting off gas alarms in the ship's generator room. CalMac described it as a 'critical failure' in the gas fuel system and said lessons had been learned. The propulsion systems for Glen Sannox were designed, supplied, and commissioned by Finnish firm Wartsila, a world leader in liquefied natural gas (LNG) engines, who worked as subcontractors to the Ferguson Marine shipyard. Details of the incident have not previously been made public and have only emerged after a freedom of information request from BBC Scotland News. Since it happened, CalMac has not run the ship's main engines on LNG, and the methane tank was completely emptied last November.
On 3 June 2025, the 15:10 sailing of Glen Sannox, the first UK-built ship capable of directly powering its engines with LNG, left Troon in South Ayrshire, bound for Brodick on Arran. During the 80-minute crossing, while running on LNG, gas detector alarms sounded inside the ship, and crew in the gas tank room reported hearing a strange noise. The port main engine also 'tripped' out—an automatic shutdown when the safety systems detect an irregularity such as unusual gas pressure. The ferry continued its journey to Brodick running on diesel. An internal CalMac investigation later found the crew should have avoided using the gas systems until they had identified the cause of the alarms and unusual noise. Instead, testing was carried out while berthed in Brodick, which found the engines seemed to work satisfactorily on gas, albeit with some abnormal gas flow readings. The ferry set off at 17:20, bound for Troon, but during this journey a large and uncontrolled release of gas occurred from a small vent at the side of the ship.
Glen Sannox can run on LNG while out at sea, but the ship's masters switch the engines to diesel as it approaches harbour to avoid engine tripping. During this voyage, a valve used in the flushing process failed and defaulted to the open position, allowing high-pressure LNG fuel to escape through the vent pipe. The crew initially tried to restart the engine on gas before realizing methane was escaping from the side of the ship. Engineers had to physically shut the valve because it was not responding to electrical control. The unusually high quantity of vented methane meant some of it was sucked back into ventilation intakes, triggering gas detector alarms in the ship's generator room and other spaces. The failed valve was examined by Wartsila, which found that a metal casing was damaged, likely worn away by a loose component. Glen Sannox has a known vibration problem while moving backwards, linked to propellers also designed by Wartsila and due for replacement.
The methane used on the ships is stored under pressure and at minus 162°C as a liquid but, in its gaseous state, is similar to domestic boiler gas, with potential to form an explosive mixture with air. However, methane is lighter than air, and most of the released gas would have dispersed quickly outside the ship. Andy Alderson, a marine safety expert, said the gas sucked back inside was unlikely to reach explosion levels, and while some safety systems were absent, gas detectors functioned as expected, triggering automatic fuel shutoffs. The biggest issue was the missed opportunity to prevent the incident by not investigating the valve issue before restarting the engine.
Wartsila was previously aware of reliability issues with the valve but is unclear who was informed. The firm published service notices recommending valve upgrades or replacements, but Ferguson Marine and CalMac did not have access to this information. The valve that failed was replaced, and CalMac provided additional training. The ship is not currently operating on gas. CalMac stated that lessons were learned, and remedial actions were taken, ensuring the vessel is safe to operate on LNG. The Marine Accident Investigation Branch reviewed CalMac's report and indicated satisfaction with the firm's actions.
The incident reignited debate on whether LNG was the right choice for CalMac ferries. LNG burns cleaner than diesel but also releases unburnt methane, a potent greenhouse gas. CalMac initially chose LNG due to its cost-effectiveness and compliance with new regulations on NOx and SOx emissions. However, the technology proved challenging for the Ferguson shipyard, adding weight and complexity to the design. The congested engine room, dubbed the 'snake pit' by workers, highlighted operational difficulties. Ferguson fell into administration due to disputes over extra costs, but CalMac insisted on delivering ships with LNG systems fully commissioned. The first LNG ship of its kind ever built in the UK, Glen Sannox, introduced regulatory uncertainties. The sister ship, MV Glen Rosa, is due for delivery later this year with retrofitted safety sensors.
Source: BBC
