It is the job of the truck at a fire to perform ventilation tasks during an active fire fight, either inside or outside the fire building. It is common for a company officer to split his crew into multiple parts with a different task, a couple for roof ventilation, others for interior ventilation and salvage, and some others for forcible entry. Some places don't have a true truck, or understaff a truck, so they have engine company personnel performing truck tasks. This is one of the most common truck jobs at a fire, so we'll just cover the ventilation team.
The ventilation team is what most people associate truck work with, it is the removal of the smoke and heat from the fire building using heavy equipment. Those are the people you see cutting holes in roofs and setting up positive pressure fans. Ventilation is accomplished either vertically or horizontally, with the easiest being horizontal, but no less complex. When handling vertical ventilation, the crew must "go to the roof" and it is primarily natural ventilation. Horizontal ventilation can be either mechanical (or forced), natural, or hydraulic.
Successful vertical ventilation starts before you even get to the fire. You must ensure that your power saws are fueled and will start up when you need them to and your tools are in their correct places. On the scene is not the time to be running around the truck looking for tools or fueling the saw. Remember the 5 P's: Prior Preparation Prevents Poor Performance
In order to perform this task, you need ladders. Of course, this is a ladder truck we are talking about, so there should be no shortage. I learned a tip from Tom Brennan many years ago that you should pick the length of ladder that starts with the number of the floor you want to go to, starting with the 2nd floor as 1. Most single ladders of 14' will reach the roof with plenty of length to spare. From there, you should sound the roof listening and looking for instability. It is recommended that you use a roof ladder to ensure stable footing in case of collapse. If you have sure footing, you may proceed without one, but you should consult your local SOP's before attempting.
Select a site to cut that is as directly over the fire as you can safely get, and as close. In order to gain footing on the roof without a ladder, you may use a hand tool like a axe or a halligan that has been driven into the roof deck. You now have a stable platform to use a power saw or an axe to open the roof for ventilation. Text books teach you to cut a 4' by 4' hole (and many SOP's as well), but you should use judgment and make the hole large enough to effect the proper ventilation. Too small and you won't have effective smoke and gas flow upwards, so usually bigger is better. I prefer a louvered cut, where the sections of roof are cut allowing them to rotate 90 degrees. This is because of overhaul and salvage, you can close the louvers when you are finished.
Once you cut the hole to proper dimension, you should open the louvers using a pike pole. You don't want to be standing anywhere near the hole when those are opened, just due to the release of heat and gas. Fire Engineering's Training Minutes has excellent videos here on vertical ventilation under Truck Company Operations.
Sometimes you will not be able to use louvered cuts to accomplish vertical ventilation. This could be due to roof construction, fire conditions, etc. You will still need to accomplish the mission, so you will need to adapt to those circumstances.
Horizontal ventilation doesn't require as many tools, but it requires more skill. You will need to coordinate the horizontal ventilation with the interior attack and manage which openings to open and when, because if you pressurize the structure with the fan or open the wrong window at the wrong time you can push fire and smoke back towards the attack team or on to victims who may still be viable saves.
Forced ventilation is just that, forced. You will be using a mechanical means to pressurize the structure to remove smoke and heat from the structure. Positive pressure ventilation (PPV) fans are the most common sight when you are performing forced ventilation. It is typically placed at the front door or a common entry point and creates a draft through the structure that removes the smoke. The cone of air created by the fan should cover most of the opening and you should open a window at the opposite end away from the fan. The wondow should be cleaned out completely, no screen, no frame, nothing. These things can reduce the amount of air flow at the point of discharge up to 60%.
Natural ventilation is using wind and natural airflow to ventilate a structure. You should open windows on the both the leeward and windward sides of the structure and use the cross ventilation to move smoke out. This is a very slow and inefficient method because the wind speed is not constant, so you will not get a very dramatic or fast change of conditions.
Hydraulic ventilation is where you would use water to create airflow. This is only really effective when you are using a fog nozzle. This works when you are directing the stream out of an opening, forcing the air following the water to entrain smoke and heat out of the window. You can use this method when you do not have personnel to perform ventilation right away, and it is typically the initial attack line that performs it in the room of origin, to clear the air for the next arriving crews to perform salvage and overhaul.
That is a quick overview of ventilation operations and by no means inclusive, and there are definitely more than one way to accomplish this task. You should always refer to your local SOP's and perform ventilation as instructed. However, you should keep these principles in mind while working, as a technique or procedure you have practiced will save you time when it comes times to use it and give much needed relief to the companies operating inside.