Purple-K, also known as PKP, is a dry-chemical fire suppression agent used in some dry chemical

fire extinguisher A fire extinguisher is a handheld active fire protection device usually filled with a dry or wet chemical used to extinguish or control small fires, often in emergencies. It is not intended for use on an out-of-control fire, such as one which ha ...

s. It is the second most effective dry chemical in fighting class B (flammable liquid)

fire Fire is the rapid oxidation of a fuel in the exothermic chemical process of combustion, releasing heat, light, and various reaction Product (chemistry), products. Flames, the most visible portion of the fire, are produced in the combustion re ...

s after Monnex (potassium allophanate), and can be used against some energized electrical equipment fires (USA class C fires). It has about 4–5 times more effectiveness against class B fires than

carbon dioxide Carbon dioxide is a chemical compound with the chemical formula . It is made up of molecules that each have one carbon atom covalent bond, covalently double bonded to two oxygen atoms. It is found in a gas state at room temperature and at norma ...

, and more than twice that of

sodium bicarbonate Sodium bicarbonate ( IUPAC name: sodium hydrogencarbonate), commonly known as baking soda or bicarbonate of soda (or simply “bicarb” especially in the UK) is a chemical compound with the formula NaHCO3. It is a salt composed of a sodium cat ...

. Some fire extinguishers are capable of operation in temperatures down to −54 °C or up to +49 °C. Dry chemical works by directly inhibiting the chemical chain reaction which forms one of the four sides of the

fire tetrahedron The fire triangle or combustion triangle is a simple model for understanding the necessary ingredients for most fires. The triangle illustrates the three elements a fire needs to ignite: heat, fuel, and an oxidizing agent (usually oxygen). A fir ...

(heat + oxygen + fuel + chemical chain reaction = fire). To a much smaller degree it also has a smothering effect by excluding oxygen from the fire. "Dry chemical" extinguishers, such as Purple-K, are different from "dry powder" extinguishers that are used to fight Class D (flammable metal) fires. Purple-K was developed by the United States Naval Research Laboratory in 1959, as an improvement over sodium bicarbonate for extinguishing oil and gasoline fires. It was named due to the characteristic lavender tint imparted to flames, owing to the potassium (chemical symbol "K") content. "Purple K Powder", "Naval Aviation News", September 1959, page 19,

Characteristics

Purple-K powder has an acrid taste and odor, is free-flowing, floating on most liquids, non-abrasive, does not wet with water and is compatible with most foam concentrates. It has violet color, to distinguish it from other dry agents. Its principal component is

potassium bicarbonate Potassium bicarbonate ( IUPAC name: potassium hydrogencarbonate, also known as potassium acid carbonate) is the inorganic compound with the chemical formula KHCO3. It is a white solid. Production and reactivity It is manufactured by treating an ...

(78–82% by weight), with addition of

(12–15%),

mica Micas ( ) are a group of silicate minerals whose outstanding physical characteristic is that individual mica crystals can easily be split into fragile elastic plates. This characteristic is described as ''perfect basal cleavage''. Mica is co ...

(1–3%),

Fuller's earth Fuller's earth is a term for various clays used as an absorbent, filter, or bleaching agent. Products labeled fuller's earth typically consist of palygorskite (also known as attapulgite) or bentonite. Primary modern uses include as absorbents ...

(1–3%), amorphous

silica Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , commonly found in nature as quartz. In many parts of the world, silica is the major constituent of sand. Silica is one of the most complex and abundant f ...

(0.2–%), and is made

hydrophobic In chemistry, hydrophobicity is the chemical property of a molecule (called a hydrophobe) that is seemingly repelled from a mass of water. In contrast, hydrophiles are attracted to water. Hydrophobic molecules tend to be nonpolar and, thu ...

by methyl hydrogen polysiloxane (0.2–1%).Fire extinguishing powders. A. E. Finnerty US. Army Research Laboratory, L. J. Vande Kieft. Halon Options. Technlcal Working Conference 6-8 May 1997

/ref> Purple-K is normally non-toxic, but ingestion of a large amount can cause

alkalosis Alkalosis is the result of a process reducing hydrogen ion concentration of arterial blood plasma (alkalemia). In contrast to acidemia (serum pH 7.35 or lower), alkalemia occurs when the serum pH is higher than normal (7.45 or higher). Alkalosis ...

Uses

Purple-K is commonly used in oil refineries, airport ramps, service stations, military facilities, naval warships, power plants, and other places where large volumes of flammable liquids are handled. It is often paired with foam in twin agent systems, usually found fitted to airport fire appliances. Purple-K is used in many forms, from small handheld fire extinguishers to large mobile and stationary units, including fixed-nozzle piping systems. Cleanup of spent agent can be difficult, as it forms a residue when discharged. If the spent agent is dry it can be removed by suction, but when combined with water, hydrocarbons and other liquids, it forms a thick crusty scum that can be challenging to remove. Purple-K should never be mixed with

phosphate Phosphates are the naturally occurring form of the element phosphorus. In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthop ...

-based fire suppression agents (

ABC dry chemical Monoammonium phosphate, ABC Dry Chemical, ABC Powder, tri-class, or multi-purpose dry chemical is a dry chemical extinguishing agent used on fire classification, class A, class B, and Electrical fires. It uses a specially fluidized and siliconize ...

), as the resulting chemical reaction will destroy its efficiency.

References

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External links

* U.S. Naval Research Laborator
Purple-K-Powder

MSDS for Purple-K powder
Fire suppression agents