Summary:
- A comprehensive guide to industrial valve fugitive emissions standards ISO 15848-1 and API 624 — explaining what fugitive emissions are, why they matter for environmental compliance and workplace safety, and how these standards define acceptable emission performance.
- Learn how low-emissions valves are designed and tested, including the role of live-loaded packing, precision stem machining, and emission class definitions that determine which applications require ISO 15848 or API 624 compliance.
- Understand the practical requirements for specifying fugitive emissions-rated valves in process plant, including how to write specifications that correctly invoke the standards and what documentation to require from manufacturers.
Introduction: Why Fugitive Emissions Matter
Fugitive emissions — the unintended escape of process fluids through valve stem seals, body joints, and other pathways to the atmosphere — are a significant environmental, safety, and regulatory concern in the process industries. They matter for multiple interconnected reasons that are increasingly driving tighter specifications and more sophisticated valve designs.
From an environmental perspective, fugitive emissions of volatile organic compounds (VOCs), greenhouse gases (particularly methane and CO2), and hazardous air pollutants from process plant contribute to air pollution, climate change, and human health impacts. Regulatory pressure to reduce these emissions is intensifying globally, with increasingly stringent limits and monitoring requirements driving real changes in how valves are specified, installed, and maintained.
From a workplace safety perspective, fugitive emissions of toxic, flammable, or asphyxiating process fluids create direct exposure risks for plant personnel. Even “low-level” emissions that are undetectable without instruments can represent significant cumulative exposure for workers in the vicinity of valves handling toxic substances — and the health consequences of chronic low-level exposure to many industrial chemicals are severe.
From a process and financial perspective, fugitive emissions represent direct product loss, particularly in gas and vapour services where every leaking valve is literally letting money escape into the atmosphere. In high-value product services — natural gas, petroleum products, specialty chemicals — the financial value of fugitive emissions can be substantial, and the business case for tighter-sealing valves is clear.
What Are Fugitive Emissions and How Are They Measured?
Fugitive emissions from valves occur primarily through two pathways: stem leakage (through the packing around the valve stem) and body joint leakage (through the gasket or seal between the bonnet and body, or through other bolted connections in the valve assembly). Stem leakage is typically the dominant pathway because the stem is a dynamic seal — it must move to operate the valve — and dynamic seals are inherently more challenging than static seals.
Emission measurement is performed using a portable flame ionisation detector (FID) — an instrument that measures the concentration of hydrocarbon vapours in the immediate vicinity of the valve stem or body joint. The instrument probe is held close to the emission point, and the instrument reading (in parts per million by volume, ppmv, of methane-equivalent) provides a quantitative measure of the emission rate. This technique, known as “sniffing” or “bagging,” is the standard field method for fugitive emissions surveys under programs like the US EPA’s LDAR (Leak Detection And Repair) program.
For type testing in laboratory conditions — the basis of ISO 15848 and API 624 certification — a more controlled and quantitative measurement approach is used. The valve is installed in a test rig, pressurised with a test gas (helium or methane, depending on the standard), and the emission rate from the stem seal is measured by enclosing the stem seal area in an enclosure and measuring the concentration of test gas accumulating in the enclosure over time. This gives a leak rate in mg/s/m of stem diameter — a reproducible, quantitative measure of the valve’s emission performance under defined conditions.
ISO 15848-1: The International Fugitive Emissions Type Testing Standard
ISO 15848-1 (Industrial Valves — Measurement, Test and Qualification Procedures for Fugitive Emissions — Part 1: Classification System and Qualification Procedures for Type Testing of Valves) is the primary international standard for fugitive emissions type testing of valves. It defines three emission classes (A, B, and C) with decreasing emission performance from C to A, and specifies the test procedures for qualifying valves to each class.
Class C represents the most permissive emission performance — a maximum leak rate of 1×10⁻⁴ mg/s/m at any point during the test sequence. Class C is typically specified for general chemical process applications where some emission reduction is required but the most stringent performance is not necessary. Class C valves are achievable with good-quality conventional packing designs and moderately tight manufacturing tolerances.
Class B allows a maximum leak rate of 1×10⁻⁵ mg/s/m — ten times lower than Class C. This intermediate class is appropriate for moderately hazardous services, applications with stricter regulatory requirements, and process plants committed to reducing VOC emissions below the Class C threshold. Achieving Class B requires more careful packing design — typically live-loaded graphite packing with precision-machined stems — and tighter manufacturing quality control.
Class A is the most stringent, with a maximum leak rate of 1×10⁻⁶ mg/s/m — one hundred times lower than Class C. Class A performance requires extremely careful design and manufacturing: precision-ground and polished stems with controlled surface finish, optimised packing geometries, live loading with precisely controlled spring force, and attention to every detail of the stem/packing interface. Class A valves are specified for toxic services, flammable services in sensitive environments, and applications where regulatory requirements demand the very lowest possible emissions.
The ISO 15848-1 test protocol also specifies thermal cycle classifications (CO1, CO2, CO3) defining the number of thermal cycles the valve must withstand while maintaining its emission class, and mechanical cycle classifications (CC1, CC2, CC3) defining the number of valve operating cycles. A Class A valve qualified to CO2 and CC2 has been tested to maintain Class A emission performance through thermal cycling and many thousands of operating cycles — providing assurance of long-term in-service performance, not just initial performance.
API 624: Fugitive Emissions Standard for Rising Stem Valves
API 624 (Type Testing of Rising Stem Valves Equipped with Flexible Graphite Packing for Fugitive Emissions) is the American Petroleum Institute standard for fugitive emissions type testing of globe valves, gate valves, and other rising stem valve types used in petroleum and natural gas processing. It was developed specifically for the North American oil and gas industry and has been widely adopted as a specification requirement for valves in refinery and petrochemical plant applications.
API 624 uses methane as the test gas (reflecting the predominant hydrocarbons in its target industries), with emission measurement by a sniffing technique using a flame ionisation detector. The acceptance criterion is a maximum emission rate of 100 ppmv methane-equivalent at any measurement point during the test sequence. This criterion is considerably more stringent than typical leak detection trigger levels in LDAR programs (often 10,000 ppmv) and represents genuinely low-emission valve performance.
The API 624 test protocol requires the valve to be subjected to 310 mechanical operating cycles over the course of the test, with emission measurements taken at specified intervals. The mechanical cycling represents the wear and movement that occurs in real valve service and provides assurance that the low-emission performance is maintained through the valve’s working life. This cycle count makes the test more representative of real service than a simple static leak test.
Live-Loaded Packing: The Design Foundation of Low-Emissions Valves
Live-loaded packing is the single most important design feature that enables valves to consistently achieve and maintain low fugitive emissions performance. Understanding how live loading works — and why it’s so important — is fundamental to understanding fugitive emissions valve design.
In a conventional packed gland, the packing rings are compressed by tightening the gland nuts, which pushes the gland follower down and compresses the packing rings axially. The resulting radial packing stress provides the seal around the stem. The problem is that over time — due to thermal cycling, mechanical cycling, and packing creep and consolidation — the packing volume reduces, the gland nuts “back off” under thermal cycling, and the packing compression gradually decreases. Eventually, the packing stress falls below the minimum required for sealing, and leakage begins. In a conventional gland, catching and correcting this before leakage occurs requires regular inspection and periodic gland tightening.
A live-loaded gland replaces the fixed gland nuts with a stack of disc springs (Belleville washers). These springs are pre-compressed during assembly to a defined preload force, and they maintain a continuous spring force on the gland follower regardless of packing consolidation or thermal cycling. As the packing consolidates and the gland follower moves down, the springs expand slightly and maintain the loading force. The result is consistently maintained packing compression throughout the valve’s service life — without any manual adjustment.
Specifying Fugitive Emissions-Rated Valves
When writing valve specifications for applications requiring ISO 15848 or API 624 compliance, several key decisions must be made: which standard applies, which emission class is required, what thermal and mechanical cycle requirements apply, and what documentation is required to verify compliance.
For European and international applications, ISO 15848-1 is the appropriate standard. For North American oil and gas applications, API 624 is typically specified for rising stem valves (gate and globe), with the complementary standard API 641 (Fugitive Emissions Type Testing of Quarter-Turn Valves) for ball and butterfly valves.
The emission class selection should be driven by the regulatory requirements and the nature of the process fluid. For general chemical and petrochemical service, Class B is a reasonable baseline. For toxic services, Class A is the appropriate specification. For general services where only regulatory LDAR compliance is required, Class C may be acceptable.
Conclusion: Low Emissions is an Engineering Achievement
Achieving and maintaining low fugitive emissions from industrial valves is not just a regulatory compliance exercise — it’s a genuine engineering achievement that requires careful attention to valve design, manufacturing quality, installation, and maintenance. The standards ISO 15848 and API 624 provide the framework for qualifying and verifying valve emission performance, and specifying compliance with these standards is an important tool for ensuring that your plant meets its environmental and safety obligations. Apply them properly, document compliance rigorously, and build an LDAR programme that catches and corrects developing leaks before they become significant emission sources.