I would guess that as it was some time after the end of the race,
all pit crew and others had stood down and taken off all the protective
clothing they wear.
You only have to look at the photos of pit crew in action to see
that everyone is wearing full suits including what looks like fire
retardant clothing underneath.
However that doesn't negate the fact that fire services didn't
seem to respond.
The 2nd last photo, left hand side on the page in the link below shows fire hoses being used but by F1 crew, not fire fighters.
Spanish Grand Prix 2012 horror: 16 injured when fire broke out in Williams team's garage | Mail Online