Montreal, Canada - Formula 1 GP organisers here have cancelled a spectators' free-access day at the Gilles Villeneuve circuit because they are scared of students' protest action disrupting the event.Sometimes violent student strike began in mid-February after the Quebec provincial government announced plans to raise tuition fees.'SERIOUS EXAMINIATION'A statement on the official ciircuit's website said there would be no Thursday "open doors" day, usually an important and popular part of the build-up to Sunday's race. The statement read, in part:"Following a serious examination of the situation, made necessary by public disruption threats and the difficulty to measure their precise validity, the organisers concluded that it was necessary to restrict access to the circuit and particularly the F1 pits lane."Francois Dumontier, president of the race, said the risks could not be ignored. "One of our primary obligations is to ensure the comfort and security of participants and spectators, something we will do as we open the turnstiles on Friday morning and again during the whole weekend."Considering the various disruption threats made public recently, the free admission and the naturally open character of the 'open doors' day revealed some risks that we could not neglect. Under these circumstances, cancelling the open day was the only action we could take."Tourism is a major source of revenues for Montreal and, according to the local tourism authority, the 2011 F1 weekend drew about 300 000 people.