Which of the following is NOT true regarding a manifold Phase I vapor-recovery system?

• A. The vent piping from two or more tanks may be manifolded
• B. 3-inch diameter piping may be used for vent manifolds
• C. Diesel tank vents and gasoline tank vents may be manifolded aboveground
• D. The aboveground vent line must not terminate less than 12 feet above grade

Answer: (C)

The statement indicating that diesel tank vents and gasoline tank vents may be manifolded aboveground is not true. In a vapor recovery system, the venting of different types of fuels is subject to strict regulations to ensure safety and prevent cross-contamination of vapors. Diesel and gasoline have significantly different physical and chemical properties, especially regarding vapor characteristics, and combining them in a manifold can create hazardous conditions. Regulations usually specify that vapor lines for different fuel types must be maintained separately to mitigate risks associated with vapor recovery and potential fire hazards.

The other statements are accurate representations of practices related to manifolded Phase I vapor-recovery systems. For instance, vent piping can be manifolded from multiple tanks to facilitate efficient vapor recovery. The use of 3-inch diameter piping for vent manifolds is permissible within the guidelines for vapor recovery systems, provided it meets the necessary flow capacity requirements. Moreover, the regulation requiring that the aboveground vent line terminates a minimum of 12 feet above grade is in place to promote safe dispersion of vapors and further reduce the risk of fire or explosion.