Foam Stored Pressure Fire Extinguisher
The fire extinguisher is a portable device used to put out fires of limited size. Such fires are grouped into four classes, according to the type of material that is burning. Class A fires include those in which ordinary combustibles such as wood, cloth, and paper are burning. Class B fires are those in which flammable liquids, oils, and grease are burning. Class C fires are those involving live electrical equipment. Class D fires involve combustible metals such as magnesium, potassium, and sodium. Each class of fire requires its own type of fire extinguisher.
Foam extinguishers use an aqueous film forming foam (AFFF) agent that expels a layer of foam when it is discharged through a nozzle. It acts as a barrier to prevent oxygen from feeding the fire. Although each class of fire has a specific extinguisher, the foam extinguisher is useful for both Class A and Class B fires; however, it is best suited for Class B.
This description explains to the general homeowner the structure, assembly, and operating principle of the foam fire extinguisher.
Fire extinguishers come in many sizes depending on the preference of the buyer. Foam fire extinguishers consist of a metal cylinder filled with an aqueous film forming foam usually under pressure of some form of non-flammable gas. A siphon tube directs the foam up through an assembly consisting of a handle and operating lever, which is secured during any period of non-use by a safety pin. The operating lever, when depressed, allows the foam to spray out of a hose connected to the siphon tube. Most extinguishers are replaced after a single use in order to assure dependability and to lessen the possibility of malfunction.
The foam fire extinguisher contains five interlocking parts:
(See Figure 1 on following page)
Figure 1 Parts of a foam stored pressure fire extinguisher.
Description and Function of Parts
The handle is usually a solid, unmovable piece of metal that stretches horizontally above the cylinder. Attached securely to the metal cylinder, the handle is the part by which the fire extinguisher is meant to be carried and held while in use.
The operating lever is connected to the handle above and to the siphon tube below. After the safety pin has been removed, the operating handle can be depressed, allowing the foam inside to be released into the hose.
The safety pin is...