Overview
ISO 29042-4:2009 - "Safety of machinery - Evaluation of the emission of airborne hazardous substances - Part 4" defines a tracer method for measuring the capture efficiency of an exhaust system installed on a machine. The standard applies in test-bench, room or field environments and is only valid when the chosen tracer exhibits aerodynamic behaviour comparable to the real pollutant. Capture efficiency is measured as the ratio of tracer mass collected by the exhaust to the uncontrolled tracer emitted from the machine.
Key Topics and Requirements
- Principle: Emit a tracer to simulate the pollutant and measure tracer flow collected by the exhaust vs. tracer flow emitted at the source; capture efficiency is the percentage ratio of collected to emitted tracer.
- Test environments: Applicable to test bench, room or on-site (field) testing as referenced in ISO 29042-1.
- Test procedure:
- Typical sequence includes background measurement, tracer emission into the duct, tracer emission at the source (simulating pollutant), and post-test background check.
- At least three tests are required to establish repeatability.
- Assumes the tracer is well mixed in the duct; mixing devices may be used to shorten mixing length.
- Concentration measurement and statistics:
- Concentrations are averaged after reaching the first quasi-equilibrium time constant; the measuring-system time constant should be adjusted to 10 s.
- Results should include statistical treatment (e.g., minimum capture efficiency, relative standard deviation) and state the measurement uncertainty (typical reporting confidence 95%; Annex A gives uncertainty calculation guidance).
- Tracer selection criteria:
- Low or negligible toxicity, chemical stability at process temperature, non-interference with existing pollutants, and low background concentration.
- Consider tracer density and whether dilution is required to emulate real pollutant behaviour.
- Limitations: Only valid if tracer aerodynamic behaviour matches that of the hazardous substance under consideration.
Applications
- Evaluating performance of machine exhaust systems
- Verifying improvements to an exhaust design
- Comparing and ranking exhaust systems for machines of similar design
- Determining required exhaust airflow to achieve a target capture efficiency
- Establishing state-of-the-art performance for machine exhaust systems
Who Should Use This Standard
- Machine designers and OEMs assessing exhaust controls
- Safety and occupational hygiene engineers
- Test laboratories and certification bodies performing emission and capture-efficiency tests
- Regulatory agencies and compliance assessors evaluating control measures for airborne hazardous substances
Related Standards
- ISO 29042 series (Parts 1–3 cover method selection and emission-rate measurements)
- ISO 12100-1 (basic safety concepts; this part is classified as a type-B standard)
- EN 1093-4 (basis for ISO 29042-4)
Keywords: ISO 29042-4:2009, tracer method, capture efficiency, exhaust system, safety of machinery, airborne hazardous substances, tracer gas, measurement, test bench, field testing.