Home Podcasts THMG095 – Extinguishing Agents, Part III

THMG095 – Extinguishing Agents, Part III

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In part three of this three-part series, Bob and Mike conclude their discussion of extinguishing agents.

Complete Show Notes

2:10 Novec 1230

  • Also known as dry water or SAPPHIRE fluid
  • Fluorinated ketone that works by removing massive amounts of heat
  • Unlike other clean agents, Novec 1230 has the advantage of being liquid at atmospheric pressure – this means it can be discharged either as a stream or a rapidly vaporizing mist

5:45 Sodium Chloride

  • Examples include Super D, Met-L-X, M28, and Pyrene Pyromet
  • Melts to form an oxygen-excluding crust over the metal
  • Thermoplastic additives like nylon are added to allow the salt to more readily form a cohesive crust over the burning metal
  • Works on most alkali metals, including sodium and potassium – can also be used on magnesium, titanium, aluminum, and zirconium

10:00 Graphite Based

  • Examples include G-PLUS, G-1, Lith-X, and Chubb Pyromet
  • Contains dry graphite that smothers burning metals
  • Unlike sodium chloride powder extinguishers, graphite powder extinguishers can be used on very hot metal fires like lithium
  • These extinguishers don’t stick to and extinguish flowing or vertical lithium fires, though (unlike copper powder extinguishers)

12:20 Sodium Carbonate Based

  • One example is Na-X
  • Used where stainless steel piping and equipment could be damaged by sodium chloride-based agents
  • Designed for use with sodium, potassium, and sodium-potassium alloy fires
  • Smothers and forms a crust

14:10 Fire Grenades/Bombs

  • These are manually operated and designed to be rolled or thrown into the fire
  • Self-destruct once it comes into contact with the flames and disperses a cloud of ABC dry chemical powder over the fire to extinguish it
  • This technology isn’t new – in the 1800s, glass fire grenades filled with suppressant liquids were popular

17:35 Wetting Agents

  • Detergent-based additives break the surface tension of water and improve penetration for Class A fires
  • Usually involves emulsification and uses a surfactant to make the oil and water “shake hands”
  • Not designed for use with alcohol events

20:30 Class A Foams

  • Basically a simple foam with a surfactant added to it
  • Used to be very popular for rural firefighting because it stuck to trees and grass
  • Commonly used for structural firefighting due to the quick drain time and its ability to soak into materials that would resist water (i.e. petrochemicals)

23:15 Decontamination (Decon) Foam

  • Spray-on cleaning solution that has a longer residence time on contaminated surfaces than regular liquids
  • As a result, it provides more efficient decontamination of biological and chemical contaminants

24:30 How Firefighting Foams Work

  • Clean agents extinguish fire by displacing oxygen – i.e. CO2 or inert gasses
  • Some foams remove heat from the combustion zone – i.e. Halotron I, FE-36, and Novec 1230
  • Other foams inhibit the chemical chain reactions – i.e. Halon

25:25 Foam Expansion Ratings

  • Low-expansion foams (like AFFF) have an expansion ratio that’s less than 20 – they’re low-viscosity, mobile, and can quickly cover large areas
  • Medium-expansion foams have an expansion ratio of 20-100
  • High-expansion foams have an expansion ratio of 200-1,000 – suitable for enclosed spaces like hangars where quick filling is necessary

28:05 Adding Antifreeze to Foams

  • Chemicals are added to water to lower its freezing point to around -40 degrees Fahrenheit
  • This has no appreciable effect on extinguishing performance and is a solid choice for cold areas

29:30 Low-Frequency Sound

  • In 2015, researchers announced that high-volume sound in the 30-60 hertz range drives oxygen away from the combustion surface, which can extinguish fires
  • Might be used to extinguish fires in outer space, since there’s no clean-up required (unlike mass-based systems)

32:55 Foams and Quarter Life

  • Important to know that the water makes the magic in foam, not the bubbles – all foams lose their water from the bubbles (some faster than others)
  • For example, Class A foam starts losing its water content almost immediately after leaving the nozzle
  • Drain time refers to roughly how much surfactant is in the finished foam and how well it’s aerated
  • So, if you double your proportion from 3% to 6%, the foam will take twice as long to drain
  • Quarter life refers to the time it takes for 25% of the foam’s water weight to drain
  • Quarter life is the industry standard for when you should refresh your foam application
  • This is particularly important when dealing with volatile, un-ignited spills or extinguished spills that may have leached into the earth
  • The longer the quarter life, the less frequently you have to reapply foam, the less water you need on-scene, and the less you have to clean up afterward

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