First off, let’s revisit the reason for our existence — fire suppression. That means we are putting out fire, not playing with it, not looking to prolong it or sustaining long attacks that tax personnel and equipment. An old adage, “the first five minutes dictate the next five hours” is a very realistic statement. Basically, we use the most appropriate agent — in this case water — to counteract the natural forces of nature, the fire tetrahedron, creating combustion. As combustion produces heat (BTUs) that transfers multiple ways to other fuels, we as firefighters intervene in this process with a cooling agent (water) that absorbs quite a bit of heat. This is our battlefield, folks; and our battlefield changes regularly.
Let’s look at heat production and distribution. Since World War II, society has changed significantly from solid wood and natural products used to build and furnish those lifestyles to lightweight, engineered and synthetic materials that build and furnish our lifestyles. These products are manufactured to make the most from the least amount of material.
Most of our traditional residential, and some other construction methods, — furnishings and coverings — are made of synthetic materials and engineered wood products such as glue and sawdust in some cases, that now exhibit faster burning patterns that what was seen by our “grandfathers” doing the same job. BTU outputs, because of these materials, have tripled, yet we try to use the old, tried-and-true methods of low GPM, highly mobile attack lines. That’s not to say this tactic is a bad one to use. We have become most efficient with this attack style, up to a point. At some point, GPM input must override BTU output in order for fires to extinguish and we win this day’s battle.
Gallon per minute flows are crucial in battle. We must begin to realize those BTU outputs (some being over two million BTU) are increasing exponentially as more fuels are exposed and the fire progresses. Progressions with line flows have increased from 40 to 60 GPM booster line interior attacks of yesterday to 125 to 200 GPM one and three-fourth inch and two inch attack lines of today and up to 328 GPM through an one and one-fourth inch smooth bore tip on a two and one-half inch hose (if used). In the 19th century, attack lines of approximately 210 GPM through two and one-half inch hose and one inch tips at approximately 50 psi were quite common, as it was the only attack line ever used. Today, we must be able to put those needed gallons of water in the appropriate place to absorb the given amount of heat the fire is producing. When that is accomplished, we win that battle as well.
Placement of attack
Placement of attack lines are as crucial as the flows themselves. Those 19th century attack lines were outside the structures for the most part, relying on pure brute force of the smooth-bore nozzle and pump pressures generated (by hand or by steamer) to reach the seat of the fire. 20th century technology brought internal combustion engines, automotive chassis, centrifugal pumps, better hose and combination fog nozzles. Canvas coats and hip-wader style boots began allowing firefighters to attempt interior fire attack over their double-breast cotton shirts and denim dungarees uniforms. Breathing apparatus improvements attributed from mine safety movements. Mine Safety Appliances (MSA) gave the “smoke eaters” an option of attempting to breathe clean air. Ventilation methods also improved the attack line placement as firefighters can get to the seat of the fire without massive amounts of heat and smoke delaying the attack. During the 1970s, improvements in turnout gear from cotton duct and canvas to Nomex® then to PBI in the 1990s allowed firefighters to put the whole package together and advance further into heated atmospheres than any time in our collective past.
Those “smoke eaters” also found their two and one-half inch hose was unmanageable within the smaller confines of single family structures. That also brought along the development of smaller attack lines and different hose construction methods. One inch booster hose and one and one-half inch hose led the way — quick, personnel economy (minimal compliment to put in place) and mobile. FDNY began the use of one and three-fourth inch because of staffing cutbacks and attempts to flow more water than one and one-half inch hose or as much as the two and one-half inch lines in use already. Two inch lines utilize the same principles as the one and three-fourth inch lines did when they were inducted into use — to flow more than one and three-fourth inch hose and as much as two and one-half inch while still being mobile with a minimal compliment of firefighters to mobilize the hose. Still, the larger the hose diameter equals more people to maneuver it into place.
Smooth-bore nozzles (operating at 50 psi) have their place within the tactical placement of attack lines. Their use was widespread, before the innovation of the fog nozzle. Smooth-bores do not have streams that heat can readily break apart; nor do they interrupt the thermal balance created inside burning compartments. Past generations of firefighters, because they did not do aggressive interior attacks, did not have to deal with this bit of information. Conversely, if the seat of the fire can be reached, these flows can be very effective in quenching fires. Contrary to popular belief — one does not need to be in the same room as the fire in order to put it out or chase it back into the room/area of origin. Nozzle manipulation of smooth bore nozzles is becoming a lost art that I feel needs to be saved.
With the combination fog nozzles operating at 100 psi traditionally (50 or 75 psi for low-pressure nozzles) — either automatic or selectable flows — one must understand that water in droplet form will easily convert to steam. The wider the pattern used within burning confined spaces, the more water droplets that convert to steam. This condition has burned numerous firefighters through their protective clothing, including me. Realize that this tactic was developed from US Navy shipboard firefighting by utilizing steam within a sealed compartment to suppress fires within that tightly sealed application area. With automatic nozzles, the nozzle attempts to maintain the pressure intended and balance that with pattern output. One would never know what pressure the nozzle has, because the pattern would look the same, feel the same and act the same way either under pumped or properly pumped.
Understanding the fire flow
The figuring of a fire flow is more than just pulling lines until the fire is finally overwhelmed. Being able to determine the size and construction features of a building, amount of fire anticipated and potential water supply to sustain the attack are integral parts of the whole picture.
The National Fire Academy formula of length x width/100 equals needed GPM is a good fireground formula to determine GPM to flow and extinguish fires. Keep it simple and use round approximates. The ability to anticipate water supply needs early allows that initial Incident Commander and the Relieving Commander(s) to have resources enroute and/or in place for effective firefighting streams and the staffing to handle the lines used for that incident.
We’ve lulled ourselves into pulling mobile one and three-fourth inch lines for just about everything we contact in suppression. I’ll grant that particular line is a very user-friendly line with lots of abilities to perform admirably daily. Recent events have placed a new respect on tactical decision-making as to fire attack line deployment. Take the time to pull all the lines your agency can (and eventually will) put into service. See what it will take to make the most of the best punch you have available. Sometimes the “sucker punch” of a large caliber line will “put the lights out” of our enemy — the uncontrolled fire. Wouldn’t you rather win early than stay for the whole fight?