Dear Nozzlehead: Last spring I was at a fire conference and overheard some firefighters discussing interior attack vs. exterior attack and an Underwriter Labs (UL) study about “pushing fire.” When I talked to these firefighters about it, we all agreed that you CAN push fire with an attack line. Then later that day, a veteran firefighter argued that we CANNOT push fire and that anytime we hit fire with a hose stream, it does much more good than bad. I am REALLY confused. To me, it makes sense that fire CAN be pushed, but my research makes me wonder if it’s an old wives’ tale.
–Confused on Long Island
Dear Confused,
Let me be clear: We must stop dissing old wives. The old wives of yesteryear are certainly NOT the old wives of today. These days, many old wives look much younger than they actually are and we need to respect that.
Confused, you bring up a great issue, and you may really get people talking about this–and other hot topics. The next thing you know, we’ll start arguing about smooth-bore vs. variable fog nozzles and which one is better. Sheeesh.
The UL study is about rapidly getting water on fire, as well as ventilation issues. Its factual findings can make a HUGE difference, but only if people in leadership roles take some time to actually read and understand it.
I reached out to Steve Kerber, the lead researcher on the UL study. Steve is a fire protection engineer as well as a veteran urban-area fire officer, so he’s the perfect mix of a fire scientist and a firefighter. Also, Steve has spent much of his life in a firehouse, so he understands firehouse myths vs. scientific fact.
Several metro city fire officials participated in the study, which bases its findings on actual science, a concept not always embraced by the fire service in North America–so pay attention!
Once a hose stream is directed into an opening with fire or hot gases exiting, fire could be pushed via 1) the pressure from the stream, 2) airflow created by the stream or 3) steam expansion, which could create conditions in the house that are worse downstream.
This whole “stream application” discussion brought a lot of interest from the very seasoned fire service veterans with suburban and urban departments who were on the technical panel for the project. Interestingly, one metro department (that was a participant in the study) will commonly apply water from the outside of a structure to “reset” the fire while an attack line is being stretched to start an interior attack, so that the fire is not growing unchecked while the line is being stretched. Although this tactic has been used with success, some departments do not do this because they believe that “pushing fire” will lower tenability in the house for potential victims. Many other fire departments have instituted a transitional attack method so they can get water on the fire quickly. They then move to an interior fire attack with good results and increased survivability of their members and potential victims.
In each of the UL experiments, the fire was allowed to grow to approximately peak burning rate before water was introduced through the opening. To examine the impact of the water, temperatures were measured in each room 30 seconds before water application, during the 10 seconds of water application and 30 seconds after water application. The stream was directed toward the ceiling to cool the ceiling and was not focused directly onto any burning fuel. They attempted to push fire and/or hot gases into surrounding rooms while not putting water directly on the items burning in the room.
After examining the temperatures from the 15 burn experiments, there is no evidence of “pushing fire.” In these structural burns, the temperatures tended to decrease, and any temperature increase after water application was minimal. There were also no temperature spikes in any of the rooms, especially the rooms adjacent to the fire room. It appears that in all cases, the fire was slowed down by the water application and that external water application had no negative impact on occupant survivability. Things got better in every experiment when water was applied from the outside. This is not to say that an interior attack is not the right tactic in many situations, but when water can be applied quickly to the fire, the benefits of improving conditions inside the structure for both occupants and firefighters were measurably increased.
Although room temperatures were not affected by the use of fog patterns/streams, there was an impact on visibility or the disruption of the thermal layer in two of the experiments. Two key factors for this: 1) the air entrainment on the stream and 2) the presence of a flow path. The flow from the nozzle caused steam formation, and that steam flowed through the flow path created by the open door and windows. In both cases, the temperatures in the house decreased because the rooms were above 212 degrees F and the steam produced lowered the temperatures to 212 degrees F or below. However, using a straight stream introduced no air and did not impact the thermal layer.
Additionally, several other experiments have been conducted by UL and the National Institute of Standards and Technology (NIST) to examine the “pushing fire” concept, including one involving acquired structure townhouse fires in Chicago where members of the CFD were unable to push fire. Water puts out fire, and air can influence fire flows. But when the stream does not introduce significant amounts of air, the fire decreases in size, improving conditions.
Applying water from the outside can be an especially important tactic for departments with minimal staffing where quickly applying water can allow for other tasks to be completed, such as search and rescue, in a more survivable environment. Also, firefighters and command officers must consider how long it would take to stretch a line to the third floor of a structure. What if a coordinated stream from a deck gun was briefly flowed into the window venting fire to cool conditions while the line was being put in place? There would be no delay of interior fire attack and conditions would be better for firefighters and occupants on that floor.
The complementary piece to this: “flow” paths. If a ventilation-limited fire (which is really almost all fires) is given a vent, it will spread to that vent. Many people confuse “pushing fire” with a fire that was spreading to that vent anyway. A member who vents a window remote from the fire may see fire spread to that room while a hose stream is moving in. So the stream is not pushing the fire; the fire is simply spreading to where the air is. Without that flow path, the fire can’t move into that room because there is no oxygen and a lower pressure to flow to.
Many veteran fire officers are taken aback by this study; I know I was. I’ve been on many fires where going in and pushing it out worked great. I have also been to (and studied) many others where that didn’t work and the results were pretty bad.
Since this report came out, the interest in these findings is spreading, especially in large city fire departments. The study is being examined to help determine the BEST way to attack fires. It is expected to significantly change how we do business.
Check out some of the study details, including video, models, photos and modeling info, at http://tinyurl.com/ULstudy.
Sometimes passing stories down from generation to generation doesn’t always help. Certainly we DO want to “pass on” the good stuff that matters in how we do business; however, when the fire environment changes like it has (look around and think about what was in YOUR home 20 years ago and what is in it today!), we have an obligation to those we supervise, lead and serve, as well as our families, kids, parents and even our old (and young) wives, to re-think using facts and science to determine the best way to operate on the fireground–inside or out.
To read more from Nozzlehead, visit www.firefighternation.com/author/nozzlehead.
