What classes require excess flow control or approved means of leak detection above 15 PSI?

In the context of fuel-oil piping and storage systems, excess flow control and approved means of leak detection are critical safety measures that help prevent incidents related to overpressure and potential leaks. Classes of fuel oil systems are typically categorized based on their pressure and the associated risks.

When considering the specific classes that require excess flow control or approved means of leak detection above 15 PSI, it is essential to understand the characteristics of those classes. Class 3 systems, often involving additives and higher pressures with specific operational conditions, demand robust safety mechanisms to prevent spills or over-pressurization. Additionally, Class 4 systems generally include more complex configurations that also necessitate stringent oversight and safety controls due to their operational parameters.

Thus, identifying that Classes 3 and 4 require these specific safety features aligns with regulatory standards aimed at minimizing risks associated with high-pressure fuel systems. Therefore, this recognition of risk management for Classes 3 and 4 is the reason why the selection aligns with the correct answer.