Around here there are regulations that say the employer has to allow volunteer firefighters to go for emergencies and he has to allow them to get some sleep if the emergency required him to stay up all night. The volunteer must tell an employer that he is volunteer when applying for a job.
It is affordable if there is a critical mass so the volunteers can take shifts. A first squad comes on moments notice the reinforcements or second shift has time to prepare.
Some employers actually like to have volunteers. It means they have trained staff in case of an emergency at their place. It also means that insurance companies rate them as a lower risk. That has direct impact on their insurance fees.
And don´t forget: Viewed from the right angle it is a satisfying hobby where guys get to play with heavy machinery they could not even dream to afford from their own salary . Sometimes entire families get integrated in the community so even the problem of lonely wife and kids at home is solved.