Staff at Truro’s Royal Cornwall Hospital called 999 yesterday evening after a gas cylinder “exploded” in part of the hospital.

Three fire crews from Truro and Tolvaddon were sent, along with a senior officer as incident commander, after the call came in just before 8.30pm yesterday.

A Cornwall Fire and Rescue Service spokesperson said: “We received a 999 call from RCH Treliske reporting a gas cylinder had exploded.

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“Upon arrival crews found that the cylinder had been dropped and the contents released.”

Firefighters confirmed the UN Number on the cylinder with Critical Control, which has access to ChemData, a comprehensive database of hazardous materials that gives advice to emergency services on how to resolve an incident.

The gas was confirmed as nitric oxide in the form of medical-grade Entonox, used for pain relief.

Crews wearing breathing apparatus investigated and found that all the contents had been released.

They ventilated the area before handing back control to the hospital.