Why CAFS is better than water or
water / foam solution
The fire triangle illustrates the three elements a fire needs to exist: heat, oxygen and fuel. When fire is burning, it is generating heat. When there is no flame, it is dissipating. Plain water only attacks one side of the fire triangle – heat. When water is sprayed onto a fire, it turns to steam which removes a tremendous amount of heat from the fuel and atmosphere.
When foam solution is added to the water, it acts like soap added to water dramatically lowering the surface tension of the water. By lowering the surface tension, a smaller water droplet can be formed which allows these droplets to turn to steam quicker when applied to fire. The smaller the water droplet, the quicker it turns to steam. This also explains the advantage of using a straight stream nozzle to reach into an area and hit an object, bursting the water stream into smaller water droplets allowing them to turn to steam quicker.
CAF (compressed air foam) adds a third element to the water / foam solution mixture – air. When pressurized air is added to the mixture, it creates a very small bubble. The smaller the bubble of the mixture, the more surface area of moisture (skin of the bubble) is available to heat up and turn to steam within the mixture. A bubble will get hot and turn to steam faster than a water droplet, while more efficiently using the moisture of the water to cool the fire and atmosphere. A good CAF looks like shaving cream.
Additionally, because CAF has the consistency of shaving cream it does not run off quickly. It acts like a blanket covering the fuel. This blanket separates the fuel from oxygen and heat. It attacks the heat in the fuel and atmosphere because the blanket is made up of water bubbles steaming off. It stays on the fuel, cooling it quickly below the flashpoint.
CAF attacks all three sides of the triangle at the same time.
It consists of small bubbles which turn to steam quicker than water droplets, cooling the fire faster.
It acts as a blanket over the fuel, separating the fuel from oxygen.
The CAF blanket is made up of water bubbles which stay on the fuel, steaming off to cool the fuel and atmosphere.
It more effectively uses water resources, using bubbles instead of just water droplets, which nearly eliminates runoff and water damage.
If there is an outgassing concern, the CAF acts as a blanket to hold in the harmful fumes or vapors.
An experiment was performed with a superheated room at 1200 degrees Fahrenheit. The amount of water applied to the room was measured and the room had a center drain to measure water runoff. Plain water, water / foam solution and CAF were all tested with the same conditions. The amount of time to cool the room was recorded. The cooling rate results were as follows:
Plain water with a fog nozzle cooled the room at a rate of 4 degrees per second. (The fog nozzle was used to make the water droplets as small as possible)
Water / foam solution with its decreased surface tension cooled the room at a rate of 12 degrees per second.
CAF cooled the room at a rate of 38 degrees per second.
The effective water usage results were as follows:
Plain water used roughly 3% of the water applied to the room.
Water / foam solution used roughly 9% of the water applied to the room.
CAF water usage couldn’t be measured because there wasn’t any runoff out of the room.
To summarize, for every 1000 gallons of plain water sprayed into a room, only about 30 gallons actually get used to cool the fire and atmosphere. For water / foam solution, the actual water usage rises to just 90 gallons. The rapid knockdown and minimal water damage that CAFS (compressed air foam system) provides is far superior to plain water or water / foam solution.
A fire truck with 500 gallons of water and CAFS has more firefighting capability than a fire truck with 5000 gallons of plain water and any size pump in a structure type fire. CAFS has the capability to knockdown fires quicker with minimal water damage than would be possible with plain water or water / foam solution which is very desirable from the standpoint of home and business owners. For instance in an attic fire, the water damage is dramatically minimized as opposed to plain water because there isn’t water and mineral residue draining through all the floors to the lowest level due to minimal CAF runoff. CAFS gives the fire department and the community it’s protecting an incredible safety and tactical advantage over traditional plain water or water / foam solution methods.