Why must a plain water stream extinguisher never be used on energized electrical equipment?
- The stream can carry current back to the operator
- Water makes the insulation burn faster
- The stream breaks into hydrogen and oxygen
- Water lowers the voltage and damages the equipment
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A. The stream can carry current back to the operator
Ordinary water conducts electricity, so a solid stream gives the current a path to the person holding the extinguisher. That is why plain water units carry only a Class A rating.
Reference: NFPA 10: extinguisher types and agents
A water mist extinguisher can carry a Class C rating even though a standard water extinguisher cannot. Why?
- It uses a plastic shell that does not conduct current
- It adds a dry chemical to the water charge to stop current flow
- It uses deionized water discharged as fine separate droplets
- It discharges at a much lower pressure than plain water
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C. It uses deionized water discharged as fine separate droplets
Deionized water has very low conductivity, and the fine mist does not form a continuous conductive stream. The shell material has nothing to do with it; the test is on the discharge.
Reference: NFPA 10: extinguisher types and agents
A stored-pressure water extinguisher is to hang in an unheated warehouse where winter temperatures fall well below freezing. What is the right answer?
- Add automotive antifreeze to the water charge
- Use a unit and charge listed for low temperatures
- Add calcium chloride to the stainless steel shell
- Reduce the water charge to leave room for ice
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B. Use a unit and charge listed for low temperatures
Only an antifreeze charge or a different extinguisher type listed for the temperature may be used. Home-made mixes change performance, and chloride salts attack stainless steel shells.
Reference: NFPA 10: recharge agents; temperature range