Ryanair pilots were forced to wear oxygen masks as they made an emergency landing in Barcelona today after a fire extinguisher went off in the cockpit. Passengers said the pilot and first officer were unable to breathe without the masks as halon - a liquefied, compressed gas - filled the confined space as the plane flew from London Stansted Airport to Valencia. TV presenter and professional sailor Hannah White said that passengers suspected there was a serious problem, but they did not know the reason for the emergency landing until they arrived at Barcelona-El Prat Airport. Ryanair flight FR8321 was met by fire trucks when it landed at Barcelona-El Prat Airport . Hannah spoke to told MailOnline Travel as she and other passengers sat on the plane while the pilot and co-pilot were checked over by medical staff. She said: ‘One of the fire extinguishers in the cockpit went off and it’s got halon gas, which is very dangerous, and as a result the pilot and first officer couldn’t breathe.' Ryanair described it as a minor fault involving a fire extinguisher and said the flight crew followed standard procedure by putting on their masks. Hannah added: ‘The oxygen masks deployed [for the flight crew] and we dropped down to a very low altitude. ‘When [the pilot] came over the tannoy to talk to us you could hear them breathing through the oxygen masks. Passengers said they were unaware of the reason for the emergency landing but knew it was serious . TV presenter and professional sailor Hannah White tweeted a photo of fire trucks on the tarmac . ‘The first thing we heard was “emergency landing”, said three times by the captain, which indicates a massive issue.’ Hannah said the announcement didn’t send immediate panic through the cabin as the passengers had no idea why flight FR8321 was diverting. She said: ‘It was clear that something was wrong. I would have to say the whole situation was dealt with amazingly and professionally.’ One of the flight attendants became anxious and oxygen masks did not deploy for passengers in the cabin, she added. Passengers hailed the crew for their professionalism while the plane diverted to Barcelona . Several passengers tweeted updates while the plane was on the ground and the pilots were checked over . Fire trucks greeted the Boeing 737 when it touched down shortly after 10:15am local time as passengers began to grasp the nature of the emergency. Hannah, 31, said: ‘We had very limited information until we were about to land. It was fairly calm on board, I have to say.’ Once people learned of the reason for the emergency landing they became agitated that they weren’t told sooner, she said. ‘It’s hot [on the plane], and people are pretty keen to get off or find out what’s going on.’ The flight crew declared an emergency over southern France and changed their flight path . Hannah, from London, and her coach were travelling to Valencia for a training session as she prepares to attempt to set a new world record for women’s speed sailing. After the plane had been on the ground for about 30 minutes, passenger Josh Adler tweeted: '@Ryanair it sounds like the faulty equipment has been replaced and you expect us to re-journey soon, thanks again to the pilots and crew.' A Ryanair spokeswoman said: 'This flight from London Stansted to Valencia diverted to Barcelona due to a minor fault with a cockpit fire extinguisher. 'The aircraft landed normally and was inspected by a Ryanair engineer, who replaced the fire extinguisher and cleared the aircraft to return to service. 'Customers remained on board and this flight has since departed to Valencia. Ryanair apologised sincerely to all customers affected by this diversion and short delay. 'Both pilots followed standard procedures and all crew continued to Valencia.'
Plane was flying from London Stansted Airport to Valencia, Spain . Pilot heard breathing through oxygen mask while making announcement . Plane was met by fire trucks when it landed at Barcelona-El Prat Airport . Pilot and first officer were taken off plane to be checked for injuries . Ryanair said plane departed for Valencia after a brief delay . Carrier described it as a minor fault involving a fire extinguisher .