The Geometry of Fire
To grasp the practicality of throwable fire extinguishers, it helps to consider what goes into fighting a fire.
At its most basic, fire is just a fast, hot form of oxidation, the same basic chemical reaction that rusts old bumpers and turns cut fruit brown. It entails four elements -- fuel, heat, oxygen and an uninhibited chemical reaction -- that together form what firefighters call the fire tetrahedron: Heat something to its ignition temperature in an oxygen environment, and you get fire, which throws off more heat as it burns, which then sets new and interesting stuff ablaze or feeds back into the system and keeps the reaction rolling [source: NFPA].
At its core, firefighting means playing Yoko Ono to this Fab Four of Fire, but just what that means varies from fire to fire and can require great expertise to figure out. One key element in that calculation, so basic that it defines how the United States and other countries classify fires, involves the fuel's composition [sources: NFPA; OSHA]:
- Class A: familiar combustibles, such as wood, cloth, paper, rubber and many plastics
- Class B: flammable liquids (which burn at room temperature) and combustible liquids (which are defined as having a flash point at or above 100 F, or 37.8 C), including petroleum greases, oils, solvents, lacquers, alcohols and flammable gases
- Class C: Class A or B fuels, combined with the tangy zip of energized electrical equipment
- Class D: combustible metals, such as magnesium, titanium, zirconium, sodium, lithium and potassium (some of which tend to crop up in car fires)
- Class K: cooktop and industrial fryer fires composed of the delicious-but-deadly things we cook food in, such as vegetable oil, animal oils and fats
In truth, fighting any but the most basic fires takes years of training and experience in how fire spreads, affects structures, builds pressure in tanks, or changes moods in an instant. For instance, water, which cools fire and creates steam to crowd out oxygen, works well on Class A fires but makes grease fires and Class Cs more hazardous. Fighting Class B fires typically means establishing a smothering foam barrier, while Class D materials, which can churn out their own oxygen and hydrogen while burning, require sand or salt-based powders to smother (a salt is a compound formed from an acid-base reaction in which the acid's hydrogen is replaced by a metal or other positive ion) [sources: Encyclopaedia Britannica; NFPA].
Throwable fire extinguisher and balls don't avoid this problem; you still need to know the limited subset of fires covered by a given product. But, as we'll see in the next section, they do overcome other limitations of canister extinguishers, including bulk, upkeep and complexity of use.