Stack testing, from the port to the report.

Stack testing is how a facility proves what comes out of its exhaust. This guide walks through the EPA reference methods in the order a test crew runs them, with live diagrams you can adjust to see why each step matters.

Start the course Browse the methods

Short on time? Watch the whole test in a three-minute movie.

A Method 5 probe working through a 12-point traverse. At each point the crew reads the pitot Δp and sets the meter box ΔH so the nozzle samples at the same speed as the gas around it.

What a stack test measures

A stack test, also called a source test or performance test, measures the pollutants leaving a stationary source such as a boiler, kiln, turbine, or incinerator. A crew climbs to sampling ports on the stack, pulls exhaust gas through carefully controlled sampling trains, and follows the EPA reference methods to the letter so the numbers hold up in front of a regulator.

Almost every answer a test produces is a concentration multiplied by a flow. Methods 1 through 4 work out how much gas leaves the stack. Method 5 and the instrumental analyzers work out how much pollutant is in each cubic foot. Multiply them and you have an emission rate you can compare to a permit limit.

Why facilities test: to show compliance with permit limits, New Source Performance Standards (40 CFR 60) and NESHAP rules (40 CFR 63); to measure control device efficiency; and to certify continuous emission monitors.

How much gas

1Where to measure 2How fast it moves 3What it’s made of 4How wet it is

How much pollutant

5Particulate catch 7EGas analyzers
Flow rateQ_{sd}dry standard ft³/hr
ConcentrationCgr/dscf or ppmvd
Emission rateE = C \times Q_{sd}lb/hr, compared with the permit limit

The methods

Each lesson covers what a method answers, the equipment, the procedure, the acceptance criteria, and the field mistakes that void runs. Every one has at least one model you can adjust.

1 Traverse points Choose a sampling location and lay out points that represent the whole cross-section. Site planner, equal-area layout, cyclonic flow check 2 Velocity and flow rate Turn the pressure difference across an S-type pitot tube into gas velocity and volumetric flow. Pitot and manometer, velocity profile, flow calculator 3 Gas composition Measure O₂ and CO₂ to get the dry molecular weight and excess air. Composition mixer, molecular weight calculator 4 Moisture Condense and weigh the water vapor to find what fraction of the gas is water. Impinger train, saturation check 5 Particulate matter Pull a sample isokinetically through a heated filter and weigh what it catches. The method that ties the first four together. Sampling train explorer, isokinetic simulator, nozzle and K-factor calculator 7E Instrumental analyzers Continuous analyzers for O₂, CO₂, NOₓ, SO₂, CO and hydrocarbons, and the checks that keep them honest. Calibration, bias and drift simulator, stratification test + More methods Condensable PM, acid gases, metals, dioxins, VOCs, FTIR, and visible emissions. Method finder by pollutant

A test, in order

A compliance test is weeks of planning around a few long days on the platform. The first lesson walks through each stage.

  1. Weeks beforePlan and notifyTest protocol, agency notification, site survey
  2. ArrivalRig upPlatform setup, calibrations, leak checks
  3. Before run 1PreliminariesTraverse points, cyclonic check, velocity and moisture estimates
  4. Test dayThree runsUsually about an hour each, with the process at representative load
  5. Between runsRecoveryRinse, seal and label every sample fraction
  6. Back at baseLab and mathGravimetric analysis, calculations, QA review
  7. Weeks afterReportResults against limits, submitted to the agency