A faulty valve on the CalMac ferry MV Glen Sannox caused a sudden and uncontrolled release of highly flammable methane gas last summer. An investigation by the operator found that 700kg of methane was vented from the side of the vessel over 12 minutes while carrying 82 passengers from Arran to the mainland.
The release was significant enough that some methane was drawn into a ventilation intake, triggering gas alarms in the ship's generator room. CalMac described the event as a "critical failure" in the gas fuel system.
The incident on 3 June 2025 involved the 15:10 sailing from Troon to Brodick, and then the 17:20 return journey to Troon. The valve, designed by Wartsila, failed during the flushing process when switching from LNG to diesel, allowing high-pressure LNG fuel to escape.
Since the incident, CalMac has not operated the MV Glen Sannox's main engines on LNG. The ship's methane tank was completely emptied in November 2025.