Whether or not you will be presented with a bill when you have called in the assistance of the Spanish Fire Brigade, depends on the region you are in, and the kind of incident.
In general, the costs for the Bombero services is divided in one part for the Administration, and one part ´tasa´ like you have to pay for all kinds of services, from obtaining documentation, registrations, permits etc.
In many cases that ´tasa´ will be taken care of by your insurance company. But in some autonomous regions the ´consumers´ will get the bill presented instead.
In several autonomous regions they make a difference between call outs to extinguish fires and assistance with natural disasters and call outs for other kinds of services, like unblocking drains, cleaning up the road after an accident, saving hikers from a mountain etc. The first not being charged to private indivuals, the latter being billed.
In all cases, when you ask the bomberos to be present at an event, as part of the obligatory safety measures, you will have to pay for their services.
We would advise to make a call to your house insurance company to enquire after the regulations for your area.