Automatic dry powder fire extinguishers

How dry powder fire extinguishers work:
Dry powder fire extinguishers smother fires by forming a barrier between the fuel and the source of oxygen.
As they do not cool the fire, there is a small risk of re-ignition.
NaOH+AlCl3+2NaHCO3====Al(OH)3↓+2CO2↑+3NaCl

Pros and Cons of dry powder fire extinguishers:
Pros: work on most types of fire; they suppress fires very quickly; specialist dry powder extinguishers are the only extinguishers that work on flammable metals.
Cons: slight danger of the fire re-igniting; when discharged, the powder can spread over a large area leaving a residue; can obscure vision when discharged, and can be inhaled if used in enclosed areas.

Who needs dry powder fire extinguishers?:
Dry powder fire extinguishers are ideal for open or outdoor environments with the risk of several different types of fire, especially those involving chemicals, fuel, or vehicles. 
Examples include:
• Garage forecourts
• Large, commercial boiler rooms
• Flammable liquid storage facilities
• Large workshops
• Fuel tankers and other vehicles