Understanding Fire Department Staffing

Recently I was tasked with conducting some research on minimum staffing levels per apparatus for the fire department. Many people are used to seeing fire trucks responding to calls with 4 guys on board. You typically wouldn't question it as I never did thinking there must be some logic behind this. Firefighters will tell you its an NFPA (National Fire Protection Association) standard and required by federal regulation. In actuality, that federal regulations (CFR 1910.134 paragragh g) and clarification by the regulating agency behind it, OSHA, states the opposite.
OSHA established what is known as the 2-in,2-out rule in 1998. In summary, it requires that there be at minimum two firefighters outside of a burning structure when conducting interior structure firefighting. That is to say if two guys are inside a house with fire hoses putting out a fire from the inside, two guys need to be outside ready to go in case the inside guys need rescue. Makes sense. The rule makes exceptions when conducting search and rescue operations when people are trapped and lives are endanger inside a building. This also doesn't prevent firefighters from fighting a fire from the outside until additional aid arrives.
So where am I going with all this, firefighters make the case that they need 4-four man crews on a truck to fight fires and respond to medical calls. This gets expensive real quickly. They will also say that failure to have 4-man crews will affect insurance ratings. No where in the the rating schedule used by ISO which provides such insurance ratings does it say that the number firefighters affects the rating. It specifically states that the number of engine companies affects the ratings. This is because the more engine you have at fire the more water pumps are available and the more water you can put on a fire more quickly. Many cities across the country and in the valley send two fire engines to a structure fire already. Additionally mutual aid agreements can provide additional fire companies from other cities.
I can go on and on about this as I found this research very interesting. I'll leave you with this note, many of the cities that operate 4-man crews do so because of union agreements yet cities that operate 3-person crews have the same if not better ISO ratings. Additionally 70-90% of calls firefighters respond to are medical calls where only the on-board paramedic and another firefighter are realy only ones doing anything until an ambulance arrives.