Everybody knows you need water to control fire. (And, by “everybody”, I mean firefighters, scientists, politicians, civilians, immigrants, elementary school children, your spouse and kids. Everybody.) That’s why fire apparatus are primarily designed around the need to quickly transport water to the location of a fire, engineered as they are with the capacity to carry a booster tank, hose, pump, appliances, and the personnel needed to put it all to work. It didn’t take a series of high-tech experiments to persuade us that putting water on a fire was a good idea; we’ve all been on board with that concept from the start.
Members of the North America fire service, though, had developed a rather rigid belief system regarding the ideal methods for applying water to a burning building. This approach was based on our understanding of the science, confirmed by decades of practical experience, and supported by advances in firefighting technology and equipment. Water streams were known to entrain significant volumes of air in the direction of water flow, and water that converts to steam expands tremendously (by a factor of 1,700), a combination of increased pressures that were thought to be able to spread scalding, toxic smoke beyond the area of fire involvement. This lead, understandably, to the practice of primarily flowing water in a direction that would propel heat, smoke, and steam to the exterior. With many interior fires limited to one or two rooms upon our arrival, this typically meant going inside the structure to a position between the involved and uninvolved areas in order to utilize the air movement from the hose stream to push the products of combustion, and the steam produced by the hose stream, outward. Fire resistant PPE, SCBA, and high flow handlines were brought to bear to operationalize this strategy, allowing it to become the “standard” fire attack approach for many departments. Given its inherent difficulties, with the need to first perform forcible entry, advance hoselines past multiple interior turns, and expose personnel to an IDLH environment, all the while allowing for increased fire growth, the ability to successfully execute these complex and dangerous operations became a legitimate source of pride.
Abandoned in the drive to properly position nozzles and “attack from the unburned side” were attempts to flow water from the exterior of a structure, which were seen as both ineffective, due to the frequent inability to reach the seat of the fire; and harmful, given the above-mentioned concerns regarding the “pushing” of products of combustion further into the structure. What was gained from recent fire dynamics research was a new and different appreciation of the effects of water on a structure fire, specifically the immediate and wide extent of improvement and the lack of previously-deduced ill effects, at least when proper nozzle technique is used. With a compartment fire, aiming a straight or solid stream steeply into an opening (window or door) while keeping it still (SSS) minimizes the increase in pressure from the movement of the water, while the cooling effect causes contraction of the gases that is more profound than their expansion, resulting in a net reduction in interior pressures. Bottom line: no pushing of heat or smoke further into the structure occurs. This not only provides the opportunity to use water streams directed through a window, but also supports the practice of performing gas cooling when an interior attack is chosen, spraying water into overhead smoke that is hot and combustible enough that it would be flame if only more oxygen were present. We now know that applying water to the heat emanating from a fire saps its energy, even before we reach its seat, and the sooner that process begins, the sooner occur its improvements.
While the use of exterior streams has created much controversy in the fire service, the mass of supporting data has silenced most of the debate regarding their benefits, and shifted discussions to considerations regarding how to best implement this tactical option. There are certainly a host of variables that must be factored into the decision as to the location for first water application at a specific incident, which include the size, geometry, and outside features (fences, shrubbery, grading, etc.) of the involved structure; the location of the seat of the fire, and its projected extension; and the resources available (to include personnel, appliances, and water). Research findings, though, have narrowed the general guidelines down to one key factor: speed of deployment. That is, use whatever route will most quickly get an effective amount of water on the fire.
(My emphasis of the word “effective” is intended to convey that speed alone is not the sole criteria, and that a flow into the compartment sufficient to reduce the heat output is also required. If the initiation of water flow were the only goal, flowing a deck gun would almost always be fastest, but this actually works only when the bulk of the fire is within line-of-sight and the reach of the stream; and the quickest water to deploy beyond this practical margin might be the 2 1/2-gallon water can, though this would have limited effectiveness against all but incipient blazes. While an apparatus-mounted master stream may, at times, be the best, and a portable extinguisher might, as for some Truck companies, be the only, water available, ideally we should first choose the appropriate flow, and then the shortest route to bring it to bear on the fire.)
To support the rapid initiation of water flow, it must first be conveyed to, and accepted by, department members that this is a key objective. The firefighters deploying initial hoselines have to understand that their primary goal is putting water on the fire, and not necessarily entry into the structure, the ability to perform hydraulic ventilation, or some other secondary benefit (See MFA #23: Protecting Egress - And other hoseline placement myths at https://community.fireengineering.com/profiles/blog/show?xg_source=...). Once the personnel actually tasked with initiating extinguishment are provided with this goal, they will usually be in the best position to determine the ideal course of action for its achievement. Depending upon the circumstances, initial water flow may be most effective from the exterior, the interior, or, quite commonly, the exterior and then the interior. The fact that external streams, except in situations that prevent entry due to the extent of involvement, are usually operated only long enough to achieve fire knockdown supports a sequential deployment. The point of this posting is not to advocate for one direction over another, of course, but to emphasize that we now have additional options, with associated risks and benefits, that must be considered when determining our fire attack strategy.
Fire departments have as their standard priorities the protection and life and property from fire, and the most effective method of accomplishing both is to extinguish the fire. An under-appreciated gift from fire dynamics researchers is the permission to begin water flow, and therefore improvements to interior conditions, from the first available vantage point, and any delays to accomplishing this objective must be eliminated or minimized. Faster control of fires benefits everyone.
The author can be reached at firstname.lastname@example.org