Overhaul can be divided into pre-control overhaul and post-control overhaul. Knowledge of building construction to take advantage of the paths of least resistance is critical to both operations. Knowing where to open the building ahead of a spreading fire is the first and most important portion of pre-control overhaul. For instance, knowing where a basement fire in a balloon frame dwelling is likely to spread will cause lines to be positioned in the attic early in the firefight, a strategy not usually pursued in buildings of other type construction. Likewise, in ordinary construction, the building may be a maze of honeycomb-like voids, inviting many different ways for fire to spread in many directions at once. Sometimes, fires will not spread as easily vertically and have to move relatively great distances horizontally before finding a vertical channel. One fire that started in a ceiling light fixture spread through the space above the ceiling, passing over room partitions to the other side of the apartment, where it found a vertical void adjacent to the chimney. It then spread to the upper floors and the cockloft. While it is usually best to check around suspected and known vertical openings (paths of least resistance), don’t be lulled into neglecting horizontal paths of least resistance. Checking above drop and tin ceilings, checking inside soffits, cornices, and facades, pulling ceilings in exposures, and exposing barrier penetrations are all ways to check for horizontal fire spread based on building characteristics.
Post-control overhaul tactics should take advantage of the same building openings as pre-control overhaul. In addition, man-made openings such as light fixtures, plumbing and wiring areas, ductwork, and outlets are all paths of least resistance and must be checked. In addition, the area directly over the fire may allow fire to spread into upper floors even where no man-made openings exist. Conduction, convection, and radiation will be the culprits here. The objective of post-control overhaul is to make sure the fire is out. Keeping in mind the most effective paths of least resistance regarding fire travel will assist in ensuring this objective is met.
Damage can be categorized into two areas. Primary damage is the damage done by the fire. Secondary damage is that damage done by firefighting operations. This includes structural and contents damage conducted as part of fire control as well as water damage suffered as a direct result of suppression agent application. Forecasting the most effective paths of least resistance for fire travel and then moving combustibles from those areas before they can become involved not only reduces the available fire load, but also saves property. Take for example a building that is exposed to a fire occurring in an adjacent building via a shaft between the two. The exposed building is of ordinary construction. It is a warm day so many windows may be open. The most effective path of least resistance for exposure ignition from both radiated and convected heat will be via the open windows. Closing the windows and removing combustibles as well as venting windows opposite the fire to dissipate heat are passive ways to lessen the heat’s impact on the building. Coating the building with water and stretching lines via the interior to the window areas of the exposed rooms is a more dynamic method. Why do we do this? The reason is because the window represents the most effective path of least resistance for fire travel into the building. Therefore, in this case, it must be the first area protected in the exposure.
As stated earlier, water will always seek the paths of least resistance, but in a downward and opposite manner when compared with heat. When planning a property conservation strategy, the officer in charge of the Salvage Group must think like water. He or she must consider all the paths of least resistance in order to divert the water or place equipment aimed at limiting or eliminating water damage prior to the water arriving there. In other words, identifying the most effective paths of least resistance for water runoff before the water actually gets there is a proactive method of reducing secondary damage.
All collapses are gravity-dependent. Once the pull of gravity is stronger than the integrity of the building’s connections, collapse will occur. Buildings will always fall in the path of least resistance. For instance, a building that is connected on one side, but not the other will likely fall into the area where no resistance is given. Lean-over collapses are a perfect example of this principle. The building is likely to lean and collapse into the path of least resistance, which is the adjacent lot or street. Although no one can predict exactly how and when a building will fail, determining the likely paths of least resistance can help establish both collapse zones and safety perimeters.
Collapse rescue is another area where an awareness of the paths of least resistance may pay dividends when developing a rescue plan. Chief Officers developing strategies to rescue collapse victims must, however, take into very serious consideration that the most effective paths of least resistance are oftentimes not the safest paths. Secondary collapse, fire involvement, and utility hazards are just a few of the problems that can complicate a rescue operation and make the most effective path of least resistance unacceptable as a rescue route. Remember that when life is involved, the rule of thumb MUST be to utilize the safest, most effective path of least resistance to accomplish the objective. If the seemingly most effective path of least resistance is unsafe, it no longer satisfies the rule of thumb.
The Incident Commander or Rescue Group Supervisor must weigh the risk of rescuing via unsafe, albeit most effective paths of least resistance versus the time it might take to access victims via safer, but more time-consuming access route. This is a difficult decision to make. Rescuers who become victims are no longer rescuers, but now part of the problem. This same mentality must also apply to confined space, high angle, trench rescue, and other technical rescue incidents. Command must never, under any circumstances, let the risks outweigh the potential gains.
· UNINTENDED CONSEQUENCES
It is interesting (and not surprising) to note that in direct contrast to proper tactics and their relation to the paths of least resistance, improper tactics will also take advantage of paths of least resistance and may lead to unintended consequences. For example, misunderstanding of building construction and the associated dangers of compromised structural components has led to death and injury when failing building components unexpectedly fall. Misplaced hoselines due to improper tactics, lack of training, or lack of information in regard to the location of the fire can push fire into uninvolved areas. Improper and misplaced ventilation operations will also pull fire into uninvolved areas, possibly jeopardizing rescue and attack operations. In addition, improper and uncoordinated positive pressure ventilation will push fire into paths of least resistance, often burning the building down. There are many examples of misuse of the most effective paths of least resistance that have resulted in outcomes quite different than those intended. They must be learned from.