Which type of extinguisher does not require hydrostatic testing?

The correct answer is CO₂ extinguishers because they are not subject to the same hydrostatic testing requirements as other types of fire extinguishers. Hydrostatic testing is typically required for extinguishers that are pressurized with gases, particularly those that store liquid agents under pressure, such as water or AFFF (Aqueous Film-Forming Foam) extinguishers.

CO₂ extinguishers, which contain carbon dioxide under pressure, operate differently because they rely on the release of gas to extinguish fires. Their construction and the materials used are such that they do not corrode or deteriorate in the same way that liquid-based extinguishers might. Consequently, the operational and safety characteristics of CO₂ extinguishers allow for a longer inspection interval without the need for frequent hydrostatic testing. The regulations specify that they only require testing every five years and detailed maintenance checks, rather than hydrostatic tests.

This distinction is crucial for understanding the maintenance and safety requirements for fire extinguishers used in various environments.