Final answer:
CO₂ portable fire extinguishers are primarily used to extinguish Class B fires involving flammable liquids. Their effectiveness is related to the critical temperature of CO₂, which is 31°C. Exceeding this temperature affects the state of CO₂ in the extinguisher, and it is important to note that CO₂ extinguishers are not suitable for use on fires involving combustible metals like magnesium.
Step-by-step explanation:
CO₂ portable fire extinguishers are primarily used for extinguishing electrical fires, which are classified as Class B and commonly involve flammable liquids such as oil or gasoline. These extinguishers are ideal for such fires because CO₂ gas does not conduct electricity and can displace oxygen to smother the fire without leaving any residue.
The effectiveness of CO₂ extinguishers is also influenced by temperature. The critical temperature of CO₂ is 31°C; below this temperature, CO₂ can exist as a liquid under pressure within the extinguisher. At temperatures above the critical temperature, you would not hear sloshing in the extinguisher because CO₂ can no longer be liquefied, regardless of the pressure.
However, CO₂ extinguishers are not suitable for use on certain types of fires, such as those involving combustible metals like magnesium. Combining CO₂ with burning magnesium can result in a reaction (2Mg(s) + CO₂(g) → 2MgO(s) + C(s)) that does not extinguish the fire. Thus, CO₂ extinguishers have specific applications and must be used accordingly.