Hydraulic Ventilation with Fog Streams
After the fire has been knocked down and if you have decided to use hydraulic ventilation position a fog nozzle as far as possible from the chosen exit opening with the target distance being about 3-9ft away making sure to cover 80-90% of the window ensuring that the pattern is wide enough to be touching all four sides of the window leaving the corners open for smoke and heat travel. I have had better luck with this positioning because of the ability of the narrow/wide angle fog (degree of the angle depending on the size of the window) to move a great amount of air out of the window thus utilizing the Venturi effect to move the byproducts. The issue I always had with hydraulically venting was that I was originally taught to compartmentalize the room by closing the door so the space could be vented faster, through use of this tactic in the field I have found that the process is exponentially more successful by opening the room up and allowing fresh clean air to be drawn in and replace the heat and smoke. The knowledge that we gained from the recent UL stream studies detailing the amount of cubic feet of air that can possibly be moved by the narrow and wide angle fog patterns if there is an adequate flow of air available behind the nozzle to be drawn in has corroborated the effective use of this tactic. According to the study (Part II Air Entrainment) the narrow angle fog pattern from a 150gpm @ 50psi nozzle moves between approximately 5,500CFM @ 3ft from the opening and approximately 9,500CFM @ 9ft from the opening and over 12,000CFM @ 9-15ft ft from the opening. The 150gpm @ 100psi had similar results up until the 12-15ft distance and then it increased in excess of 15,000CFM. All of these studies are just vindicating everything that the trailblazers always knew and practiced in the glory days of the job, all of their writings (Warren Y. Kimball, William E. Clark, Emanuel Fried, Llyod Layman, Vincent Dunn, Harold Richman, David Fornell, John Salka, etc.) are still available to us thankfully, and I enjoy the fact that they are constantly being proven correct by updated technology and research.
(Photo credit – Nozzle Nut Photography)
(UL DHS2013_Part_II_Air Entrainment https://ulfirefightersafety.org/…/DHS2013_Part_II_Air_Entra…)