Which type of vaporizers do NOT require pressure relief valves if their capacity is less than 1 quart?

Atmospheric vaporizers do not require pressure relief valves if their capacity is less than 1 quart because they operate at ambient pressure. These vaporizers take liquid propane and convert it to gas without the need to maintain a high-pressure environment. Since they rely on atmospheric pressure, any excess pressure would naturally dissipate, making additional pressure relief measures unnecessary for smaller capacities.

In contrast, other types of vaporizers, such as direct and indirect vaporizers, can create or maintain gas under pressure, thus requiring pressure relief valves to ensure safety and manage potential over-pressurization. High-pressure vaporizers, by their nature, are designed to operate at elevated pressures and would always necessitate pressure relief systems for safety reasons. Hence, atmospheric vaporizers are uniquely suited for situations where pressure management is minimal, particularly in low-capacity applications.