An MC 306/DOT 406 non-pressure liquid carrier can operate with liquids with vapor pressures below how many psi?

• A. 40
• B. 10
• C. 3
• D. 1

Answer: (C)

Non‑pressure liquid cargo tanks are designed to carry liquids that don’t generate much vapor, since there’s no internal pressurization system to manage high vapor buildup. For MC 306/DOT 406 non‑pressure tanks, the liquid’s vapor pressure must be below 3 psi at 100°F. This limit helps prevent dangerous pressure buildup as temperatures rise during transport, keeping venting simple and the tank safe without requiring complex pressure‑relief components. If a liquid has a higher vapor pressure, a different, pressurized tank design would be required.