Depends what state, and sometimes city, you're in. There are presently @11 States that require a state Boiler Operator license, along with a number of municipalities, counties, etc. If you're in doubt about whether your state or city requires a license, contact the National Board of Boiler and Pressure Vessel Inspectors (614-888-8320) or the state agency that is responsible for inspecting boilers in your state. If you're in Ohio, you can go to www.steamworksllc.com and click on the Resources button, then the Boiler Operator / Stationary Steam Engineer licensing link. There's quite a bit of information there. You can also call the Ohio Division of Industrial Compliance at 614-644-2236 for details.
Here is a link for a Spokane Exam, Fee, information.
http://www.buildingspokane.org/Applications_New/Boiler%20Operator%20License%20&%20Fee%20Info.pdf
You have to be able to endure complete boredom. I enjoyed being a Boiler Operator on the Naval Ship especially when we were maneuvering, standard operation got to be a bore and when I pursued it when I got out of the Navy it was really boring as everything was auto. Jst needed a person to monitor, report and take water samples.
Good Luck
Marshall