Home Podcasts THMG093 – Extinguishing Agents, Part I

THMG093 – Extinguishing Agents, Part I


In the first episode of a three-part series, Bob and Mike discuss extinguishing agents.

Complete Show Notes

4:50 History of Fire Extinguishers

  • The first fire extinguisher on record was patented in England in 1723 by Ambrose Godfrey
  • Consisted of a cask of fire-extinguishing liquid containing a pewter chamber of gunpowder
  • The soda-acid extinguisher was first patented in France in 1866 by Francois Carlier – mixed a solution of water and sodium bicarbonate with tartaric acid, which produced the propellant CO2 gas
  • Chemical foam extinguisher was invented in Russia in 1904 by Aleksandr Loran
  • In 1910, the Pyrene Manufacturing Company of Delaware filed a patent to use carbon tetrachloride (CTC or CCI4) to extinguish fires

8:10 Class A Extinguishers

  • Designed for use with combustible materials like wood, paper, fabric, and refuse
  • Most suppression techniques work
  • Symbol is a green triangle
  • Class A foams were developed in the mid-1980s for fighting wildfires
  • Class A foams lower the surface tension of the water, which assists in the wetting and saturation of Class A fuels with water
  • Aids fire suppression and can prevent re-ignition

11:55 Class B Extinguishers

  • Designed for use with flammable liquids
  • Work by inhibiting chemical chain reactions, like water mist dry chemicals
  • Symbol is a red square
  • Class B foams are designed for Class B fires
  • The use of Class A foam on a Class B fire may yield unexpected results – Class A foams aren’t designed to contain the explosive vapors produced by flammable liquids
  • Class B foams have two major sub-types:
    • Synthetic foams
      • Based on synthetic surfactants
      • Provide better flow and spreading over the surface of hydrocarbon-based liquids for faster knockdown of flames
      • Limited post-fire security and are also toxic ground water contaminants
      • Aqueous film forming foams (AFFF) are water-based and frequently contain hydrocarbon-based surfactants like sodium alkyl sulfate and fluorosurfactant (includes fluorotelomers, perfluorooctanoic acid (PFOA), or perfluorooctanesulfonic acid (PFOS))
      • Alcohol-resistant aqueous film-forming foams (AR-AFFF) are foams resistant to the action of alcohols because they form a protective film
    • Protein foams
      • Contain natural proteins that work as foaming agents
      • Unlike synthetic foams, protein foams are biodegradable
      • Protein foams spread slowly, but they provide a blanket that’s more heat-resistant and durable
      • Types include regular protein foam (P), fluoroprotein foam (FP), film-forming fluoroprotein (FFFP), alcohol-resistant fluoroprotein foam (AR-FP), and alcohol-resistant film-forming fluoroprotein (AR-FFFP)
      • Protein foam from non-animal sources is preferred due to the possible threats of biological contaminants (like prions)
      • A prion is an infectious agent composed entirely of protein material and is called PrP (prion protein) for short

24:55 Class C Extinguishers

  • Mostly used with electrical fires
  • Inhibits chemical chain reactions – like dry chemicals and halon
  • Conductive agents like water shouldn’t be used
  • Symbol is a blue circle

26:45 Class D Extinguishers

  • Dry powder usually used with flammable metals
  • Requires a suppression specialist
  • Symbol is a yellow star

28:30 Class K Extinguishers

  • Usually used with cooking oils and fats
  • Suppresses fires by removing oxygen or water mist
  • Symbol is a black hexagon

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