MTVP: An Evolving Regulatory Concept

Harold Laurence, principal consultant at Trinity Consultants examines the concept of maximum true vapor pressure and how the US EPA and industry practices will impact tank owners  The US Environmental Protection Agency (EPA) developed the concept of ‘maximum true vapor pressure’ (MTVP) to identify storage vessels subject to emission standards. The MTVP concept dates to EPA’s earliest tank standards in the 1970s, and it continues to evolve with recent EPA rulemakings and newly released methods. This article explores the MTVP concept, with attention to key decisions and interpretations. Tank owners benefit from a firm grasp of EPA and industry practice for determining MTVP of stored liquids. Vapor Pressure As A Concept Vapor pressure expresses a stored liquid’s readiness to evaporate. When organic liquids are stored at the same temperature, a liquid with greater vapor pressure will evaporate in a proportionally greater amount. EPA’s AP-42 emission factor guide, Chapter 7.1 for storage tanks, defines vapor pressure as ‘the sum of the equilibrium partial pressures exerted by the components of a volatile organic liquid’ (VOL)(1) . EPA also relies on this concept when...