Nineteen deep-level stations had to shut, because they are served by lifts, and passengers were being warned to allow extra times for their journeys.
However, the early signs were that fewer Tube staff were refusing to work on safety grounds than they did in the last fire strike, which caused severe disruption. So far today 18 drivers and one member of station staff have refused to work citing safety fears. During the first 48-hour fire strike last week around 100 drivers and some 250 other staff refused to carry out duties.
A LU spokeswoman said those not working today had been sent home and would not be paid for their shifts, and this was currently the limit of disciplinary measures to be taken against them.
"The number refusing to work may change during the day as different shifts start," she said, adding that LU was hoping to run as "normal a service as possible".
The Rail, Maritime and Transport Union (RMT) gave formal notice to LU on Wednesday that it would ballot its tube members for industrial action, and was seeking assurances that those not working on safety grounds should not be disciplined. Ballot papers will be sent out next week and voting will finish on December 12.
On the safety issue, LU today passed on this joint statement from the Health and Safety Executive and Her Majesty's Railway Inspectorate: "We have carefully considered the consequences of FBU [Fire Brigades Union] over the past 11 weeks and we are content that we are taking adequate measures to mitigate any additional risk that this action may pose for customers and staff.
"Our customers and the majority of our staff agree with this view and are happy to work and travel as usual. We have listened to the concerns of the 350 staff who have refused to work on the grounds of safety and we do not believe that our staff have been placed in "serious or imminent danger" by the FBU's strike action and that by refusing to work they are in breach of their contracts of employment. We have now made it clear that if they continue to refuse to work normally they will not be paid."
During the first 24 hours of the first dispute, some lines had only a handful of trains running, although services were less affected during the second half of the strike.
A London Underground station was evacuated today after smoke was spotted on a platform. Green goddess crews were called out to Bank station at around 9.40am in what British transport police said appeared to be a minor incident.
The stations shut today because of the dispute were Edgware Road, Regent's Park, Holland Park, Queensway, Lancaster Gate, Goodge Street, Russell Square, Covent Garden, Wapping, Borough, Lambeth North, Elephant and Castle, Kennington, Hampstead, Tufnell Park, Holland Park, Belsize Park, Chalk Farm and Mornington Crescent.
In addition, there were only limited services at Shadwell, Gloucester Road and Camden Town. The dispute also caused the closure of Essex Road main line station on the West Anglia Great Northern route.
But the Association of Train Operating Companies said it expected to run a normal service during the strike. Some main line trains were making extra stops to help passengers affected by the tube station closures.
