Sizing up of the situation makes an initial defensive attack or a change of tactics from an offensive to a defensive operation justified.
Size-up of the fire building upon arrival is a critical, self-survival technique that must be completed prior to entering the smoke and heat of any interior operation. In the days when there were many fires that would develop a firefighter's experience level we could learn through "on the job " training so it was not necessary to train on size-up. But today, with the lower levels of experience and the explosion of quick-collapse, lightweight truss-constructed buildings, firefighters must train on size-up to survive on the fireground.
Size-up can be broken into four major factors: Construction, Occupancy, Life Hazard along with Location and Extent of the Fire. These factors are critical to understand prior to making any decisions to act on the fireground. They are also inter-related to each other. For example, upon arrival to the fire scene, we cannot get the big picture of the construction style of the fire building without also considering the location and extent of the fire. What is the construction style and where is the fire? What damage has been done to the building prior to our arrival to the scene and what damage is going to be done in the next few minutes? In other words, to understand these two related size-up factors we need to use our fireground experience and book smarts to recognize the current situation and predict what will happen next.
Many times in the distant past, as well as this year, the fire service has seen multiple firefighter deaths and injuries, which could be attributed to the lack of a good size-up. A study of these incidents is likely to reveal a poor assessment done upon arrival and continuing throughout the incident. With the study of past fires such as these we should expect that these types of incidents would stop, but with all the duties that have been given to the fire service in recent years one thing that may have been lost in our training schedules is the size-up drill for fireground survival.
Simply recognizing a deadly situation such as a truss constructed roof or floor assembly that is exposed to fire and then performing a defensive attack will often be enough to bring everyone home. Sizing up of the situation makes an initial defensive attack or a change of tactics from an offensive to a defensive operation justified. Often a change of tactics is brought about by reports made by firefighters on the scene that the incident commander (IC) would not normally be expected to have knowledge of like roof conditions.
size-up of residences can be deceiving when we arrive to the fire scene. We must always be concerned with truss construction in residential occupancies. The question if any one certain residential fire building is truss constructed is not easily answered. A prime example of this is the way that platform frame and lightweight truss built residences will present themselves on the fireground. They will look very similar, are easy to confuse in fully built form and both types are still being built today. These two building styles will also perform vastly different under the same fire conditions. Without actually witnessing the erecting of the residence it is not easy to know what holds the building up.
In these cases it is best to work on the idea that the building is in fact truss supported until we can confirm or deny it by investigating it further. In this situation the best way to determine the construction is to pull some ceiling with a pike pole at the front door and use a thermal imaging camera (TIC) to look for truss or dimensional wood joists. If a TIC is not available it is best to pull ceiling in a non-smoke filled area of the building to examine how it was built before entering. Any truss exposed to any heat or fire should tell us that at least that section and possibly the entire building is ready to collapse and we should not enter for our safety. Fire in the truss area should also be reported to the IC so everyone on the scene will know the situation.