Benjamin Franklin was a "Renassiance Man", meaning he was a philosopher, inventor, politician, doctor, artist, writer, and much more. Benjamin Franklin created the first firehouse in Philadelphia, so his title could have been given to him for that reason. But if we look at him in more of a symbolic way, Franklin "put out fires" so to speak by being a mediator during the Constitutional Convention. He was given the title of "Peacemaker" at the Convention, since he was the sole person to mediate debates and help the two sides come together to form compromises. He was the brainchild behind the Great Compromise, which created our Congress that we still have today. Franklin was the first fireman in a way that he "put out the firey debates" and created a sense of compromise and peace among the founding fathers of our nation.
Another, more basic, reason is that Ben Franklin founded the first true fire department in Philadelphia. So in a real way, Franklin was the first fireman. This is keeping with the how the firemen and the government of Fahrenheit 451 twist history and facts to meet their own purposes.
Saminnick... Ben Franklin did not invent the first fire alarm system. Assuming you are referring to a system other than word of mouth.
In 1852, the first fire alarm telegraph system was installed in Boston. Invented by William F. Channing. The idea was taken over by John Gamewell who saw the potential and eventually cornered about 95% of the market.
As for the first fireman... Have you ever heard of "Greek fire", it is the original napalm. The Knights of St. John (back in the crusades) were attacked with this substance and many burned alive. The others ran to help save their bothers from their fiery death. These are the true first firemen. The emblem used on their shields is still worn today by firefighters all over the world. Being that these firemen were from a small island called Malta, it became known as the Maltese Cross.
However, Ben Franklin does get credit as is due in the fact that he formed the first organized fire departments focused on protection of life and property. He also researched the science of fire and fire behavior and passed this knowledge on to his firemen.
State of Florida Firefighter II, Fire Officer II, & Fire Instructor II
Concurring with the other teachers on this board, Franklin developed the alarm system that is used by fire departments; obviously technology has updated this, to alert the fire fighters to an emergency. In addition I believe he organized the idea of the bucket brigade to fight the fires.