A heath trust has apologised to any patients who had their appointments delayed by a incident with a nitrogen canister yesterday.

The dermatology unit at Watford General Hospital was evacuated for a short period while firefighters removed the leaking cylinder.

A spokesman for West Hertfordshire Hospitals NHS Trust said: "The fire brigade attended Watford Hospital to dispose of a small nitrogen cylinder which was leaking. The leak posed no risk to patients, visitors or staff and it is standard practice for the fire brigade to be called because they have the expertise to deal with this kind of problem.

"In order to make it easier for the fire brigade to deal with the leak, we asked the patients, visitors and staff in our dermatology outpatients’ clinic to leave the department for a short time. Appointments were unfortunately delayed by approximately 15 minutes and we apologise for any inconvenience caused.

"Nitrogen is used to treat various skin conditions like warts."