There is a difference between the airport being 'closed' and commercial airlines being unable to land or depart due to lack of fire cover.
...err no there isn't. If the fire crew are engaged in a response callout and the residual equipment/staff is below required fire cat for the airport; or at the discretion of the airport management any ensuing emergency situation in progress otherwise impedes on the capacity of the airport to operate safely, then the word is closed, period. Any other interpretation of closed would probably be DISUSED or ABANDONED.
...err, sorry, there's a huge difference.
In the UK, pretty much the only reason that an airport is closed is if the runways are covered in snow. In other parts of the world there are other criteria which require the airport to be promulgated as closed.