// BBC UK NEWS — CRONACA
Valve failure on CalMac ferry saw uncontrolled escape of flammable gas
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 last summer, BBC Scotland News has learned.
The operator's investigation found that 700kg of the gas - enough to fill a four-bedroomed house - was vented from the side of MV Glen Sannox over the space of 12 minutes while it was 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.
While the risk of explosion is believed to have been low, 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.