Final answer:
The capacity of a CO₂ extinguisher is more about pressure and temperature rather than weight. Below its critical temperature of
, CO₂ can exist as a liquid in a high-pressure cylinder. Above this temperature, it cannot be liquified, and safety precautions must be observed to prevent over-pressurization.
Step-by-step explanation:
When considering what is the maximum capacity, by weight, of a portable CO₂ extinguisher, it's important to understand the properties of carbon dioxide under different temperatures, rather than a specific weight limit for an extinguisher. As we examine the behavior of CO₂ in a fire extinguisher, we can observe that on a cool day with temperatures below its critical temperature of
, CO₂ remains in liquid form due to the high pressure inside the cylinder. This is why we can hear the liquid CO₂ sloshing around.
Conversely, on a hot summer day when the temperature rises above
, CO₂ exceeds its critical temperature and, regardless of pressure, cannot remain in liquid form. Hence, there is no sloshing sound as there is no liquid present. Understanding the gas behavior at different temperatures also informs safety precautions, such as the one stating that the extinguisher should be stored at temperatures below
(
) to prevent dangerous pressure build-up or possible explosion. This is evident from an exercise where a CO₂ extinguisher pressurized at
at
increases its pressure when left in a closed automobile where the temperature reaches
, potentially compromising the integrity of the cylinder.