Modern regulations mean that if a pilot declares an emergency of any sort then all the services will attend.
Fireman attending a fuel spillage
A commercial plane is only allowed to land at an airport that has the required amount of cover available. At airports where jumbo jet can land the fire, rescue and ambulance have to be at a higher level than at a small municipal airport.
Among their many duties the fire services are responsible for fuel spillages. If you see a fire engine near your plane don’t be alarmed, their attendance is not an indication of danger. An aircraft reporting any problem with its braking system, tyres and wheels will always be accompanied to its parking place by a fire truck.
You may see the emergency vehicles moving around the airport … this does not mean that there is a problem with a plane … they may be undergoing training or vehicle maintenance.
Medical services are always available at airports and sick passengers on an aircraft will always take priority over anything else.