Fog Oil Smoke Composition
Credit: Phil Hardass
Fog oil smokes rely on vaporization of mineral oil into the atmosphere, and subsequent condensation of the oil particles to form very small droplets suspended in air, as a result creating thick smoke. Traditional techniques of vaporizing the oil with a heater as in "fog pots" go back decades, as used in the military for screening troops. The effectiveness of a fog pot can now be be captured in the form of portable, handheld cartridges or canisters described in this article.
Mechanism of Operation:
The fog oil smoke compositions work in a similar manner as that of a fog machine - creating heat, gas, and a vaporized fluid that condenses after being exposed to the cooler atmosphere. Configured in the form of a portable canister, the operation is similar to that of a conventional colored smoke grenade. The heat and gas are generated from a pyrogen mixture, composed of potassium nitrate and sugar, creating hot water vapor and carbon dioxide. The fluid vapor is mineral oil, which vaporizes from the heat of combustion of the pyrogen and then condenses after being ejected from the vent holes above the canister. The composition, once initiated, sustains a steady burn rate and creates a very dense, oil-based fog.
Heavy Mineral Oil.................23%
All percentages in wt %. KNO3 is ground fine in an electric coffee grinder. The powdered sugar and potassium nitrate are placed inside a Ziploc baggie and shaken and smeared together to completely mix the oxidizer and fuel together, to a uniform consistency. This forms the pyrogen mixture.
77% Pyrogen and 23% Mineral Oil (wt %) are added to another Ziplok baggie and mixed together until a consistency of soft modeling clay is obtained. This is the smoke composition. The pyrogen without the oil (KNO3 + sugar) is used as an igniter for the smoke composition in canisters.
An example of a useful smoke composition as employed in a smoke canister is described below.
60g KNO3, finely ground
40g Sugar, powdered
30g Mineral Oil
Shake and smear the smoke composition components together in a Ziploc baggie until mixture is completely mixed. TIP: A dash of airfloat charcoal into the composition can aid as a visual indicator to make sure the sugar and potassium nitrate are completely mixed together, mixing until a uniform grey colored paste is obtained. The composition should feel like a clump of modeling clay or hard toothpaste inside the baggie when done.
Press the composition into the bottom of an empty canister, with sufficient headroom to allow the hot gasses to cool and condense as they make their way up to the top of the can.
A good rule of thumb is to use a canister where the composition takes up no more than half the volume inside the canister when pressed in. If the composition is filled to the top, the fog oil may flare up from excessive heat. Keep sufficient headroom for condensation to occur. Next, is the igniter.
0.8g Sugar, Powdered
With the 2g of pyrogen (mixed together in a baggie), place it in a pile in the middle of a little square of aluminum foil. Cut a length of fuse to extend from the middle of the foil out to a sufficient length above the canister. A good length would be approx 5" if a can of 5" tall is used. Wrap the aluminum foil square around the pyrogen and fuse, making a little sack of pyrogen with a fuse sticking out of it.
There should only be a single layer of aluminum foil containing the pyrogen ignition mixture. This little device will act as an igniter for the smoke composition in the canister.
Press the pyrogen igniter into the middle of the smoke composition contained at the bottom of the canister.
Tear off about a square foot of aluminum foil and fold it in half twice, creating a 4-layer square of foil. Make a little hole in the middle of it. Place the foil piece over the top of the canister, with the fuse protruding out of the hole of the foil.
Wrap the foil tightly around the top edge of the canister, and secure it with tight wire (not tape, it will melt off).
Use a shish-kabob skewer to poke holes through the top foil layers, to let the smoke out.
Done. Ready for use.
Place on level ground away from combustibles. Light fuse and get away. Do not use in confined areas - a high concentration of this smoke may be harmful to your health.