By Warren WhitleyEditor’s note:
For more on Lloyd Layman’s theories and how they can be applied in modern-day firefighting, see “The Plug” in the March issue of FireRescue
In 1953, Lloyd Layman published Fire Fighting Tactics(1), followed by Attacking and Extinguishing Interior Fires(2) in 1955. The books complement one other, but are nonetheless useful independently. The understanding that Layman garnered about fire behavior, through extensive tests conducted during World War II at Fort McHenry, Md., and later in Parkersburg, W.Va., far exceeded that of the typical firefighter—then, as it does now, over 55 years later.
Layman’s most significant finding was that small droplets of water are the most efficient in extinguishing fires. As he noted, “The rate of heat absorption can be increased by increasing the surface exposure of a heat-absorbing substance in ratio with its volume.”(2) This means that the smaller the droplet of water, the more surface area that is exposed per volume, greatly increasing the efficiency of the water to cool gases and fuel surfaces.
This work was expanded upon by Swedish engineers starting in the 1980s, noting that water-droplet size cannot exceed .3 mm in diameter for optimum efficiency. Giselsson and Rosander, Taylor, Grimwood et al, and the U.S. Air Force(3-7) have all carried Layman’s work further, proving that water fog is an excellent and efficient extinguishing agent.
So, why has the use of fog nozzles fallen out of favor in many places? Why has Layman’s work been discounted when his findings are still valid?
The Case for Smooth-Bore
Smooth-bore nozzles certainly have their place, but they’re not the ideal tool for every fire. In many situations, water fog will be more efficient and use less water to achieve favorable results. Photo Cary Ulrich
Some firefighters argue that smooth-bore nozzles have greater reach, and that’s hard to dispute. Other smooth-bore proponents claim that bouncing the stream off the ceiling breaks up the stream into droplets, increasing the efficiency of the application. Although that’s also true, the droplet sizes achieved by the stream breaking up on the ceiling are not very efficient; they greatly exceed a .3-mm diameter.
Some advocates also point to studies that show virtually no difference in the extinguishing properties of fog and smoothbore applications and that the application of fog could push the fire throughout the structure, but in both cases, the under- and over-pressure areas of the air track were not understood and ignored.(8) As mentioned earlier, for the stream to be at peak effectiveness, the droplet size must be .3 mm in diameter or smaller. Physics has not changed since Layman’s studies, and the smaller droplets are able to travel along the air track to the fire and are much more efficient at heat absorption.
Some smooth-bore proponents rest their arguments on the Iowa Formula(9), forgetting that the formula was based on the application of water fog and conversion of the water droplets to steam. Substituting flows from smooth-bore nozzles will result in much more water being necessary for extinguishment and the potential for a lot more water damage to the structure and its contents.
The bottom line: Smooth-bore nozzles certainly have their place, but they’re not the ideal tool for every fire. In many situations, water fog will be more efficient and use less water to achieve favorable results.Beyond Nozzles
Layman also commented on how the air flows feeding a fire and the gases exiting the burn area are like a solid fuel stove; there needs to be an air inlet and an exhaust.(2) By changing the inlet (damper) and/or the exhaust (vent), you can control the rate of combustion in the stove. The same principle works in a burning structure; if you control the air, you control the fire.(5)
The lesson: Limiting openings can reduce the amount of air getting to the fire. Opening doors and breaking windows with reckless abandon is generally something that doesn’t help the situation on the fireground because it allows gases that may have previously been too rich to burn to lean out and ignite.
John Taylor, author of Smoke Burns, notes that Layman would have had the entire fire behavior picture if he had closed the top opening of the “stove” during his experiments with indirect fire attack. Had he done so, he would have noticed a change in the inlet and exit point for the fire gases. In fact, he would have noticed that the opening for the inlet and the exit was being shared by both air tracks. The inlet would be at the bottom of the opening and the exhaust would be above it, with the neutral plane close to halfway.
Layman then might have deduced that he could apply his water fog into the intake (negative air track) and his small droplets of water would have done exactly as he said, followed the air to the fire and back through the positive track of fire gases, rapidly extinguishing the fire and greatly improving conditions for potential victims and rescuers alike.Worth Revisiting
When we couple Layman’s fire behavior knowledge and proper application of water fog with his excellent tactical mnemonic tool for the fireground, RECEO(1), there’s a lot that his books still have to offer the fire service as foundational material for new and experienced firefighters. In short, the NFPA should reconsider reissuing Layman’s work. When linked to the other seminal works published since then (some of which are referenced in this article), Layman’s work provides valuable insight into fire behavior.
This knowledge can help firefighters operate more safely by making better risk assessments and applying appropriate, coordinated tactics to mitigate the situation. Warren Whitley is a 30-year veteran of the Prince William County (Va.) Department of Fire and Rescue and currently serves as an assistant chief. He is a member of the IAFC and the U.S. Branch of the IFE and holds an MPA from Virginia Tech and an MA from the Naval War College. REFERENCES
- Layman L: Fire Fighting Tactics. NFPA: Boston, 1953.
- Layman L: Attacking and Extinguishing Interior Fires. NFPA: Boston, 1955.
- Handell A: Utvärdering av dimstrålrörs effektivitet vid brandgaskylning. Lund University: Lund, Sweden, 2000.
- Giselsson K and Rosander M: The Fundamentals of Fire. Norrköping, Sweden, year unknown.
- Taylor J: Smoke Burns. Self-published: York, 2008.
- Grimwood P, Hartin E, McDonough J et al: 3D Fire Fighting: Training, Techniques and Tactics. Fire Protection Publications: Stillwater, Okla., 2005.
- Menchini C et al: The Development and Design of a Prototype Ultra-High Pressure P-19 Firefighting Vehicle. USAF: Tyndal AFB, 2006.
- Clark W: Firefighting Principles and Practices. PennWell: Saddle Brook, N.J., 1991.
- Royer and Nelson: “Water for Firefighting—Rate of Flow Formula.” Iowa State University Bulletin #18. Ames, Iowa: Iowa State University, 1959.
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