said by Fat City:
Good thing about Halon is no residue afterwards.
This is true in test scenarios where you deploy halon absent of any real fire. In that scenario halon is non-toxic (it will still kill due to lack of oxygen but it won't poison you) and mostly inert to any items present in the room.
However under the influence of heat and flame in a real fire scenario halon forms toxic substances some of which are causing aggressive reactions with the materials present in the vicinity. In those cases a hazardous materials cleanup may be required afterwards.
That doesn't mean that halon is a bad choice of fire suppression, just that it isn't as perfect as it was thought to be when it first became popular. To some extend this also applies to modern halon substitutes but to a lesser degree. See FM200 for example (this is Heptafluoropropane which is also used as propellant in medical aerosols).
Despite the mess that they are making, powder based fire extinguishers are a better choice to carry in the car. Gas based extinguishers (CO2, halon, FE36) don't work well in even slightly windy conditions (fresh supply of oxygen).--
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