There is an age old debate in the fire service about which firefighting nozzle is better, fog or smooth bore. I have been a part of many of these arguments myself, often listing all the pros and cons of each nozzle in hopes that I can prove that my favorite nozzle puts out fire the best. The thing is, both of the structural firefighting nozzles that we are arguing over extinguish fire, and they have been doing it for many, many years. With that said, the debate is really more about which nozzle puts out fire better, or is more efficient, or is easier to use, and it often comes down to the fact that each type of nozzle has its place in firefighting. So how do you choose which to use?
Well, I propose that you look at nozzle selection a bit differently, and very simply. Choose your nozzle based on the type of fire attack that you are using. Forget all the pros and cons momentarily, and instead understand that both of these nozzles we DESIGNED for a specific method of fire attack;
The smooth bore nozzle was “designed” at the beginning of modern firefighting as a way to allow firefighters and civilians alike to apply a solid stream of water directly to burning buildings from a distance, since modern protective gear did not exist. Direct attack, as we call it, was born; applying water to solid fuels to cool them to the point where they no longer are being broken down and liberating combustible gases (pyrolysis), and extinguishing the fire.
The fog nozzle, from a structural firefighting standpoint, was developed on the deck of a naval ship. Confined fires in ship compartments were hard to extinguish using direct attack, so a creative captain decided to keep the fire contained and instead use a spray nozzle to inject small drops of water into the fire compartment via ventilation ducting, in hopes of using steam conversion to absorb heat and displace oxygen. It worked, and it worked well for shipboard firefighting.
With this new method of suppressing fires working so well on ships, it was thought that it might work equally well in buildings. The findings from these ship fires were presented at FDIC, and shortly thereafter spray nozzles were being developed to create tiny drops of water that produced a fog of water, and they were given the name fog nozzle. Experiments were done with this new nozzle, and it was found that introducing water fog into a confined building fire and letting steam conversion work for 10-15 minutes would suppress these types of fires enough to allow for easy entry into the building for final extinguishment. Indirect attack was born.
From a design standpoint, Smooth Bore nozzles have not changed over the years. The fog nozzle however, has. After indirect attack was introduced to the fire service, someone decided that combining both methods of fire attack, direct and indirect, would create a method that uses the best of both worlds, and the combination attack came to exist. This caused the creation of the modern adjustable fog nozzle, a design that allows both wide and narrow fog streams to come from the same nozzle so that it could be used for either indirect and direct attack, or a combination of the two. So now that we understand that a smooth bore nozzle is designed for direct attack, and a modern fog nozzle is designed to do it all, wouldn’t it make sense to just go with the fog nozzle? Well not quite.
The primary design of the adjustable fog nozzle is to provide the tiny drops of water and wide fog patterns necessary for indirect attack. The problem is when adjusted to a narrow pattern, or straight stream as it is called, you are simply just changing the shape of the fog stream. It is still made up of tiny drops of water entrained with air and is not a solid stream of water. For small fires, this is acceptable for direct attack. The problem comes with larger, hotter fires that have entered pre and post flashover (and other hostile event) stages. The fires of today produce such a high thermal output that premature water evaporation is a concern when trying to slow or stop, let alone extinguish compartment fires that are reaching or have reached peak thermal output.
With direct attack, we want as much water as possible to land on the solid fuels that are burning, at the same time producing as little stream as possible to keep from disrupting and over-pressurizing the fire compartment. The small drops of water and air from a fog nozzle, even when in a straight stream, are evaporated easily when compared to a solid stream. Sure, some of the water will get to the seat of the fire, but not the same amount as a solid stream. Simply stated, what we really want is for all the water that we are spraying to not be evaporated or effected by thermal columns and to land on all the solid fuels in the fire compartment and cool them all down, so the fire goes out and flammable gas emission ceases.
So yes, a straight stream can work to directly put water on the burning solids, but not as efficiently as a solid stream from a smooth bore. The solid stream from the smooth bore nozzle is inherently designed to do this best, and is therefore the best choice when wanting to perform direct attack on both confined and unconfined fires.
What is the point of all this? Well, after being involved with many nozzle debates as our organization began to make changes in the nozzles we use, I learned that it is not the nozzle that we were arguing about. When broken down, it was all about what fire attack method is preferred. By being able to articulate which method you think works best, is the safest, or most efficient, then nozzle selection comes automatically.
– If you choose to use indirect attack and want to use steam to snuff confined fires, there is only one real choice. The fog nozzle.
– If you choose to use direct attack and be able to extinguish both confined and unconfined fire, especially large and more developed fires, the smooth bore nozzle is made for this and is the most efficient.
– If you want the option to do both, the adjustable fog nozzle will give you that ability, but will not provide the same level of effectiveness and efficiency for direct attack as the smooth bore.
If you can alter your perspective on what a nozzle is used for, then hopefully you will choose your firefighting nozzle based on the fire attack method that you or your department chooses to use, or better yet the method that the fire dictates you to use.