API Publ 4452-1987: A Technical Review of Fugitive Emission Estimation from Petroleum Refineries

Scope and Purpose of API Publ 4452-1987

API Publication 4452-1987, titled Methodology for Estimating Fugitive Hydrocarbon Emissions from Petroleum Refinery Sources, provides a standardized technical framework for estimating volatile organic compound (VOC) and hydrocarbon emissions that escape from process equipment components. Developed by the American Petroleum Institute (API), this publication addresses the critical need for consistent, defensible emission inventories within the refining industry.

The primary scope of the document covers fugitive emissions originating from:

Valves (gate, globe, ball, and control valves)
Pump and compressor seals
Pressure relief devices
Connectors (flanges and threaded fittings)
Open-ended lines and sampling connections

Rather than imposing prescriptive regulatory limits, API Publ 4452-1987 establishes a consistent methodology for quantifying emission rates using either component screening data (e.g., organic vapor analyzer readings) or default emission factors. It serves as a key reference for refineries developing Leak Detection and Repair (LDAR) programs and for regulatory agencies requiring accurate emission reports.

Tip: API Publ 4452-1987 is often used in conjunction with API Publ 4589 and EPA’s Protocol for Equipment Leak Emission Estimates (EPA-453/R-95-017) for state-of-the-art emission inventories.

Technical Requirements for Emission Estimation

Calculation Methodology

The publication outlines two principal approaches for estimating fugitive emissions:

Correlation Approach: Uses measured screening values (in ppmv as methane) from an organic vapor analyzer (OVA) in conjunction with component-specific correlation equations.
Average Emission Factor Approach: Applies default emission factors per source type when screening data are not available or when a refinery opts for a less resource-intensive method.

Default Emission Factors and Thresholds

Table 1 summarizes the default emission factors and associated screening thresholds recommended in the publication. These values are based on extensive field studies conducted during the 1980s across multiple refineries.

Equipment Type	Default Emission Factor (kg/h/source)	Screening Threshold (ppm)	Repair Threshold (ppm)
Valves	0.0053	500	10,000
Pump Seals	0.0191	1,000	10,000
Compressor Seals	0.0650	1,000	10,000
Connectors (flanges, fittings)	0.0018	500	10,000
Pressure Relief Devices	0.0100	—	—
Open-ended Lines	0.0017	—	—

Note: Thresholds apply to screening-based programs; default factors are used when no screening is performed.

Key Technical Considerations

Hydrocarbon composition: The publication assumes the emission stream is primarily methane-equivalent; refineries handling specific HAPs (hazardous air pollutants) should adjust factors accordingly.
Correlation equations: For screening values above 10,000 ppmv, the correlation approach typically uses a zero-intercept exponential model to avoid underestimation.
Quality assurance: Periodic calibration of monitoring instruments using known methane standards is required to ensure data reliability.

Caution: Default emission factors in API Publ 4452-1987 were derived from U.S. refineries in the 1980s. Users should verify applicability to modern facility designs, process streams, and regulatory contexts. Site-specific factors may be required for HAP emission inventories under the Clean Air Act.

Implementation Considerations for LDAR Programs

API Publ 4452-1987 provides the technical backbone for many refinery LDAR programs. While the publication itself is not a regulatory standard, its methodology is widely referenced by:

U.S. EPA in the development of emission factors for the AP-42 compilation and the Electronic Greenhouse Gas Reporting Tool (e-GGRT).
State-level air quality programs (e.g., California’s Cap-and-Trade and local air district rules).
International guidance documents, including those from the European Environment Agency (EME/EEA emission factor handbook).

Integration with Modern Monitoring Techniques

Since its publication, the industry has adopted advanced monitoring approaches such as optical gas imaging (OGI) and wearable sensor networks. API Publ 4452-1987 does not directly address these technologies; however, its emission factor framework remains applicable when converting OGI-detected leaks into mass emission rates using the correlation approach.

Best Practice: Combine the default factor approach with periodic site-specific screening to reduce uncertainty. Many compliance programs permit the use of site-specific factors for non-leaking components to achieve more accurate emission totals.

Compliance and Reporting Notes

Although API Publ 4452-1987 is a technical publication, it has significant compliance implications:

Regulatory references: Several state and federal rules explicitly cite the publication as an acceptable methodology for estimating fugitive emissions. Refineries must confirm which edition is recognized (typically the 1987 version or its successors).
Data documentation: Auditors expect facilities to maintain records of component counts, screening results, instrument calibrations, and calculations using the publication’s methods.
Uncertainty management: The default factors have an inherent uncertainty of ±50% or more. For compliance reporting (e.g., Title V), refineries may need to apply a higher bounding factor or conduct additional monitoring.

Important: API Publ 4452-1987 has been superseded in some contexts by later API publications (e.g., API Publ 4616, 4697, and the Compendium of Emission Factors). Always check with the relevant authority to ensure you are using the accepted version for legal compliance.

When preparing emission reports, include a clear description of the methodology used, the basis for emission factors (correlation vs. default), and any deviations from the publication’s recommendations. Transparency is critical for regulatory acceptance and for benchmarking against industry averages.

Q: Is API Publ 4452-1987 still valid today?
A: Yes, the methodology remains a widely used foundation for fugitive emission estimates. However, many regulatory programs now prefer the updated emission factors from API Publ 4616 (2001) or the more recent Compendium. The 1987 version is still acceptable for historical comparisons or where specified by a consent decree.

Q: Can the publication be used for non-refinery sources?
A: The methodology was developed for petroleum refineries. Application to petrochemical plants or upstream oil and gas facilities requires careful evaluation of stream composition and equipment types. EPA’s Protocol (EPA-453/R-95-017) provides analogous guidance for chemical plants.

Q: What is the difference between the correlation approach and the average emission factor approach?
A: The correlation approach uses site-specific screening values (ppmv) to compute mass emissions via component-type equations, providing higher accuracy for leaking components. The average emission factor approach assigns a fixed emission rate per component regardless of leak status, which is simpler but less accurate. Most compliance programs require the correlation approach at least quarterly for valves and connectors.

Q: How do I handle emissions from components in heavy liquid service?
A: API Publ 4452-1987 primarily addresses light liquid and gas service. For heavy liquid service (e.g., > 50% BTEX by weight), the publication recommends using a separate set of emission factors or applying a correction factor. Check Section 4.2 of the document for specific guidance.

— Technical reference compiled in accordance with API and EPA guidelines. Year of article: 2026.

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