ISO 29042-9:2011 — Safety of Machinery — Decontamination Index

Introduction

ISO 29042-9:2011, developed by ISO/TC 199, specifies a method for measuring the decontamination index (IA) of pollutant control systems installed on machinery. This Type-B standard under the ISO 12100 framework covers capture devices including local exhaust ventilation, water spray systems, and separation equipment. The decontamination index quantifies how effectively a pollutant control system improves ambient air quality compared to operation without the system.

The decontamination index ranges from 0 (no effect) to 1 (complete decontamination to background level), providing a simple yet powerful metric for comparing pollutant control system performance.

Measurement Principle and Three-Phase Procedure

The method uses the real pollutant and can be performed in room or field environments. The measurement involves three distinct phases repeated twice, evaluating concentrations at predetermined points around the machinery.

Phase	Machine State	Control System	Measured Value
Phase 1	Shut down	Not in operation	Cfi (background level)
Phase 2	In operation	In operation	Cmi (with control)
Phase 3	In operation	Shut down/removed	Cai (without control)

The decontamination index is calculated as: IA = (1/n) × Σ[(Cai – Cmi) / (Cai – Cfi)], where n is the number of measurement points.

Engineering Design Insights

Measurement Point Selection and Influencing Factors

Measurement points are determined by pre-testing to ensure they are in zones of measurable emission. The number and precise positions should be specified in Type-C standards. Many factors influence results: machine data, type of working process, type of product, operational duration, surrounding machinery conditions, exhaust air flow rate, room dimensions, and general ventilation characteristics. Cross-draught velocities and ambient temperature/humidity should also be recorded.

Practical Considerations and Methodological Challenges

The measurement is most accurate when background levels are low. Surrounding machinery should ideally be shut down during testing. A key challenge is the potential heterogeneity of pollution in both space and time, which may require a large number of measurements. Special attention must be paid to minimizing fluctuations in exhaust air flow rate or air flow patterns, particularly during transitions when machines or ventilation systems are switched on or off.

WARNING: Switching off or altering the pollutant control system during Phase 3 can lead to exposure to hazardous pollutant levels. Appropriate preventive measures must be taken to minimize risk to operators and occupants.

Interpreting the Decontamination Index

When IA = 0, the control system has no effect (Ca = Cm). When IA = 1, the system brings pollution down to background level (Cm = Cf). For each measurement point and each of the three measurements, the index is calculated individually. The mean value for each measurement point serves as the test result. When background levels are negligible, the formula simplifies to IA = 1 – (1/n) × Σ(Cmi/Cai).

FAQs

Q1: What types of pollutant control systems can be evaluated?
A: The method covers capture devices including local exhaust ventilation, water spray systems, and separation equipment installed on machines.

Q2: Can this test be performed in the field?
A: Yes, unlike Parts 7 and 8 which are laboratory-based, ISO 29042-9 can be conducted in room or field environments, making it suitable for in-situ evaluation.

Q3: How is the background level accounted for?
A: Phase 1 measures the background concentration Cfi with the machine shut down and its control system off. This value is used in the IA calculation to isolate the machine’s contribution from ambient pollution.

Q4: What does IA = 0.7 mean in practice?
A: An IA of 0.7 indicates the control system reduces the pollutant concentration to 30% of the level that would exist without the system, representing a 70% improvement in air quality.