To access the remainder of this piece of premium content, you must be registered with Firehouse. Already have an account? Login
Register in seconds by connecting with your preferred Social Network.
Complete the registration form.
The answers usually include the desire to hydraulically ventilate, the need for the extra protection, or just in case. Fog streams flowing 150 to 180 gpm produce over 6,000 to 10,000 cfm compared to a solid-tip 15/16 that produces 510 cfm, but our main focus here is fire suppression. If our main focus is stretching the initial attack line for ventilation purposes, we need to reevaluate our thinking. Let’s leave the ventilation to the truck companies. Our main focus for the initial stretch should be proper extinguishment.
We have been fooled for many years believing that a curtain of water between you and the fire is protection. What is occurring is you are pushing heat, fire, smoke and other products of combustion out in front of you, which is not a bad thing if you are fighting a vehicle fire outside. The pushing effect gives you a false sense of security because what you have pushed away is likely to return to you. Fire, heat and smoke will seek the path of least resistance and potentially extend your fire vertically and laterally.
We should not depend on flow rates any less than 150 gpm for interior structural fires. Flow rates below 150 gpm are inadequate to overwhelm compartments that are filled with synthetic materials. The HRR given off by these synthetics must be controlled with the correct stream and volume of flow to overwhelm such rapid fire events.
You want to enter a structure with a 200-foot pre-connected handline combination nozzle set on straight stream flowing 150 gpm, with a 170 psi at your pump panel. Before making entry, your captain wants the engineer to just back the pressure down to 130 so you can move it around easier. (Sound familiar?) Now, are you really receiving adequate flow? You have just dropped your psi by 25%, so what have you done to your gpm? You now have 115 gpm. This gpm is woefully inadequate and not a safe practice. You may be merely containing the fire and not extinguishing it.
I have witnessed in several training evolutions combination nozzles advanced into structures and rotated accidentally on whatever they come in contact with. One would not like to be on the receiving end of the fog stream that has been injected into the thermal layer. While I personally advocate the use of solid streams, if a combination nozzle is the only option, it should be used in a straight-stream position with an adequate rate of 150 gpm. A solid or straight stream will provide a rapid knockdown with less violent disruption of the thermal layer, and is more likely to reach the seat of the fire due to less premature conversion to steam or carried away by convection currents.
Although their use in direct attack is similar, straight and solid streams have distinct differences. A straight stream, in essence, is a very narrow fog stream. It is produced by a combination nozzle and is made up of millions of tiny water droplets divided by air entrained within the stream. Narrow streams produced by combination nozzles are not “solid streams.” A solid stream is produced by a smooth bore orifice and is a compact, solid cylinder of water as it leaves the nozzle. Proper tip pressure will allow this stream to remain compact for a considerable distance before friction with the air; gravity and other factors destroy the quality of the stream. One important reason solid streams are more effective than straight streams in interior fire attack concerns the water droplets.
When a solid stream is deflected off the walls and ceiling, it produces droplets of sufficient mass and size to reach the burning fuel without being carried away by the thermal currents or prematurely vaporized by the heat. Straight streams created by fog nozzles are the result of changing the direction of water travel inside the nozzle by striking the stream against the deflector. This consists of countless droplets that are now even smaller when colliding with the ceiling and upper walls. These small droplets are drawn into and propelled out of the thermal column of the fire, never to reach the burning fuel.
Ready for battle
We must be ready for battle with effective hoseline selection, nozzle selection and flow rates to overwhelm this driving force of fuel. It is our duty to be proactive when it comes to the constant changes our profession brings. We owe this to ourselves and to the citizens we serve.
I want to stress that the information and recommendations here are related to interior structural firefighting and are techniques that are proven to be effective and provide the greatest chance for survival and extinguishment.