Fugitive emissions are the leakage you don't see. Gas escaping past valve stems, gasket interfaces, and packing — small enough that nothing dramatic happens, large enough that across a plant it adds up to thousands of pounds per year. Regulators noticed. Now every spec sheet has an ISO 15848 line on it.
Here's what the standard actually requires, what the tightness classes mean, and how to spec without overpaying.
What ISO 15848 covers
ISO 15848 is split into two parts:
- 15848-1: Type-test the design. Verify a valve design produces low emissions under controlled conditions — a one-time qualification.
- 15848-2: Production-test individual valves. Quick leak check on each unit before shipping.
15848-1 is what you usually see on specs. The valve manufacturer takes a representative valve, instruments it, runs it through a defined number of mechanical and thermal cycles, and measures stem leakage. The result is a tightness class and an endurance class.
Tightness classes A, B, and C
Tightness is measured as helium leak rate per unit stem diameter, in millibar-liters per second per millimeter (mbar·L/s·mm). The standard defines three classes:
| Class | Max leakage (helium) | Use case |
|---|---|---|
| A (tightest) | ≤ 1×10⁻⁵ mbar·L/s·mm | Toxic, hazardous, regulated emissions service |
| B | ≤ 1×10⁻⁴ mbar·L/s·mm | Standard hydrocarbon and chemical service |
| C | ≤ 1×10⁻² mbar·L/s·mm | Less critical service — utility, water, non-VOC gases |
For comparison, EPA Method 21 (the US-side equivalent test) uses ppm at the valve interface and is generally less strict than Class B. If your spec calls out "EPA fugitive emissions compliance," you're typically looking at something between Class B and Class C.
Endurance classes CO1, CO2, CO3
The other half of the qualification is how many cycles the valve can run while still meeting the tightness class. Three endurance classes:
- CO1: 205 mechanical cycles + 2 thermal cycles. Roughly: low-cycle isolation valve.
- CO2: 1,500 mechanical cycles + 3 thermal cycles. Most control valves.
- CO3: 2,500 mechanical cycles + 4 thermal cycles. High-cycle modulating service or ESD valves.
A typical specification reads something like "ISO 15848-1, AH-CO2-SSA0-T(-29/200)". The pieces decode to:
AH— Tightness class A on HeliumCO2— Endurance class CO2 (1,500 cycles)SSA0— Stem seal adjustment class (0 = no adjustment allowed during life)T(-29/200)— Tested temperature range, in °C
What it actually takes to meet Class A
Class A on a control valve means most of the design effort goes into the stem packing system:
- Live-loaded packing with belleville washers maintains compression as packing wears.
- Multi-ring graphite or PTFE/graphite hybrid packing sets — single-ring designs rarely qualify.
- Polished stem finishes (Ra ≤ 0.4 µm typical) to minimize abrasion against the packing.
- Tight stem-bonnet bushing tolerances to prevent stem deflection that would gap the packing.
For ball valves, Class A typically requires double-stem-seal designs with a leak-detection chamber between them.
How to write the spec right
- Pick the right tightness class for the service. Toxic VOCs, HAPs, regulated hydrocarbons → Class A. General refinery and chemical → Class B. Utility services → Class C is fine.
- Pick the right endurance. ESD or control loops that cycle thousands of times per year → CO3. Block valves cycled monthly → CO1. Most general control duty → CO2.
- Specify the test temperature range. The valve's qualification only applies within the tested temperature window. Don't accept a -29/180°C qualification on a 230°C process.
- Require the type-test certificate. Not just a manufacturer claim of compliance — the actual ISO 15848-1 test report from an accredited lab.
- For Class A, require live-loading. If the spec says Class A and the supplier ships a single Belleville-stack design with a single packing follower, push back.
The bottom line
ISO 15848 isn't difficult, but it's where engineers either over-spec (and pay too much) or under-spec (and end up with measurable atmospheric leakage). Pick the class that matches the service, demand the actual test certificate, and pay attention to the temperature range it was qualified at.
If you've got a fugitive emissions spec to verify or you're not sure which class fits your service, send us the conditions. We'll review the qualification documentation against your operating window before you place the order.