FE Extinguishing Agent Properties & Chemistry 2 — Questions and Answers
Question 1: Which extinguishing agent is specifically recommended for Class K fires involving cooking oils and fats in commercial kitchens?
- ABC dry chemical powder
- Carbon dioxide (CO2)
- Wet chemical potassium acetate solution (Correct answer)
- AFFF aqueous film-forming foam
Correct answer: Wet chemical potassium acetate solution
Wet chemical agents (potassium acetate, potassium carbonate, or potassium citrate) are designed for Class K fires because they react with hot cooking oils to form a soapy foam layer via saponification.
Question 2: AFFF (Aqueous Film-Forming Foam) creates a suppression layer on flammable liquid fires by which mechanism?
- Chemically reacting with hydrocarbon vapors
- Forming a thin aqueous film that seals the fuel surface (Correct answer)
- Cooling the fuel below its flash point through water absorption only
- Releasing CO2 gas from the foam bubbles
Correct answer: Forming a thin aqueous film that seals the fuel surface
AFFF works by spreading a thin aqueous film over the fuel surface that seals vapors, preventing them from reaching the flame, while also cooling the fuel with water.
Question 3: What minimum temperature limitation is a critical operational concern for CO2 extinguishers during discharge?
- The discharge creates temperatures as low as -110°F (-79°C) at the horn (Correct answer)
- The agent freezes in the cylinder below 32°F (0°C)
- CO2 becomes liquid above 87°F (31°C)
- The discharge pressure drops below effective range above 100°F (38°C)
Correct answer: The discharge creates temperatures as low as -110°F (-79°C) at the horn
CO2 expands rapidly during discharge, dropping to approximately -110°F (-79°C) at the horn, which can cause frostbite if the horn is held improperly during use.
Question 4: Monoammonium phosphate (MAP), the active ingredient in ABC extinguishers, melts on contact with burning Class A materials. Why is this significant?
- It increases the discharge range of the extinguisher
- It forms a vitreous coating that seals the fuel surface and prevents re-ignition (Correct answer)
- It absorbs moisture from the air to dilute combustion
- It lowers the burning point of ordinary combustibles
Correct answer: It forms a vitreous coating that seals the fuel surface and prevents re-ignition
When MAP contacts hot Class A surfaces, it melts and forms a glassy (vitreous) coating that seals oxygen away from the fuel, which is why ABC extinguishers are effective on ordinary combustibles.
Question 5: Which clean agent is most widely used as a replacement for Halon 1301 in fixed suppression systems?
- Nitrogen (IG-100)
- FM-200 (HFC-227ea) (Correct answer)
- CO2
- AFFF foam
Correct answer: FM-200 (HFC-227ea)
FM-200 (HFC-227ea) is the most widely used halon alternative for total-flooding applications because it has zero ozone depletion potential and extinguishes fires at low concentrations.
Question 6: Which dry chemical extinguishing agent is considered the most effective pound-for-pound on Class B flammable liquid fires?
- Sodium bicarbonate
- Monoammonium phosphate (ABC)
- Potassium bicarbonate (Purple-K) (Correct answer)
- Calcium chloride
Correct answer: Potassium bicarbonate (Purple-K)
Potassium bicarbonate (Purple-K) is approximately twice as effective as sodium bicarbonate on Class B fires because potassium ions are more efficient at interrupting combustion chain reactions.
Question 7: The 'saponification' reaction relevant to Class K extinguisher agents describes which chemical process?
- Oxidation of potassium ions releasing heat
- Alkaline solution reacting with fatty acid oils to form soap and glycerol (Correct answer)
- Reduction of CO2 at high cooking temperatures
- Hydrolysis of foam concentrate in water
Correct answer: Alkaline solution reacting with fatty acid oils to form soap and glycerol
Saponification is the reaction between the alkaline wet chemical agent and the fatty acid cooking oils to form a soap-like emulsion that blankets the surface and prevents vapor release.
FE Extinguishing Agent Properties & Chemistry 2
Which extinguishing agent is specifically recommended for Class K fires involving cooking oils and fats in commercial kitchens?