The job assigned to an Engine Company at a fire is determined by the arrival sequence of the engine. For example we will consider an assignment, to a report of a house fire. This type of assignment would include four engines, two ladders, a rescue unit and one deputy chief (also knows as battalion).
The first engine company (called first due engine) to arrive on the scene of a working fire is charged with extinguishment. The City Of Mount Vernon Fire Department policy is for a quick interior attack on the fire whenever possible. This includes making quick entry to the fire building to find and extinguish the source or seat of the fire. Throwing water at smoke from outside a window will not put out the fire. Of course every fire is different, there is no such thing as a normal fire. Initial fire line placement, method and location of the entry point, and fire line size are just a few of the variables that must be considered on every scene.
The second engine company to arrive on the scene of a working fire is charged with water supply to the first engine and then backup for the first crew in the building. The "usual" procedure for the second engine company is to stop at a hydrant closest to the fire and lay a 5 inch diameter supply line on the way to the fire building. This size supply line should be large enough to supply the first truck with water to spare. Once the second engine is at the fire building part of the crew will complete the hook up of the supply line to the first engine. The third engine is assigned to fill in any gaps, often stretching a 2nd line or back up attack hose.