API Publ 325-1994: A Guide to the Evaluation of Hydrocarbon Vapor Emissions from Marine Vapor Collection and Recovery Systems

Scope of API Publ 325-1994

API Publication 325, first released in 1994, is a guidance document developed by the American Petroleum Institute to assist operators, engineers, and regulatory agencies in evaluating hydrocarbon vapor emissions from marine vapor collection systems (VCS) and marine vapor recovery systems (VRS). While not a mandatory standard in the traditional sense (it is classified as a Publication), API Publ 325 presents methodologies widely adopted by the industry for assessing emission levels, verifying system performance, and supporting compliance with volatile organic compound (VOC) regulations at marine loading/ unloading terminals.

The document focuses on three key areas:

• Quantification of vapor emissions during marine loading operations, including both displaced vapors and fugitive releases.
• Performance evaluation of vapor collection and recovery systems, including vapor tightness, recovery efficiency, and emission factors.
• Guidance on test protocols, instrumentation, and data analysis methods for emission measurements.

API Publ 325 applies to crude oil, gasoline, and other volatile liquid cargoes handled at marine terminals, and covers both ship-to-shore (loading) and shore-to-ship (discharge) operations, though loading scenarios are the primary focus. The publication complements other API works such as API RP 2217 (Vapor Recovery Systems) and API MPMS Chapter 19 (Evaporative Loss Measurement).

Technical Requirements and Key Provisions

Emission Estimation Methodologies

API Publ 325 provides two principal approaches for estimating vapor