ISO 29042-5:2010 — Safety of Machinery — Emission of Airborne Hazardous Substances — Part 5: Test Bench Method for Separation Efficiency (Unducted Outlet)

Introduction to ISO 29042-5

ISO 29042-5:2010 specifies a test bench method for measuring the separation efficiency by mass of air cleaning systems with unducted outlet. These systems — such as dust separators, filter units, and air purifiers that discharge cleaned air directly into the workplace — are commonly integrated into machinery to control airborne hazardous substances. The separation efficiency quantifies the fraction of pollutant mass removed from the airflow by the air cleaning system, which is essential for evaluating whether the system provides adequate protection.

For air cleaning systems with unducted outlets, the separation efficiency directly determines the pollutant concentration in the air returned to the workplace. A system with 99% efficiency still releases 1% of the pollutant — which may or may not be acceptable depending on the toxicity of the substance and the emission rate. ISO 29042-5 provides the standardized method for determining this critical parameter.

The standard applies to air cleaning systems used in machinery applications where the cleaned air is discharged back into the workspace rather than ducted to the outside. This includes recirculating filter units, electrostatic precipitators, and cyclone separators integrated into machines such as woodworking equipment, grinding machines, and chemical processing systems.

Test Bench Methodology

Principle of Measurement

The test bench method involves generating a test aerosol with known particle size distribution and mass concentration, passing it through the air cleaning system under test, and measuring the mass of pollutant collected by the system and the mass that penetrates through. The separation efficiency is calculated as the ratio of collected mass to inlet mass. For unducted outlet systems, special attention must be paid to collecting all penetrating emissions for accurate mass balance.

Parameter	Specification	Engineering Significance
Test aerosol	Aluminium oxide or specific test dust	Standardized particle characteristics
Particle size range	0.3 to 10 microns (respirable fraction)	Covers most health-relevant particle sizes
Inlet concentration	Specified per filter class	Represents realistic loading conditions
Face velocity	Rated airflow / filter area	Determines residence time and collection efficiency
Test duration	Until stable efficiency achieved	Accounts for filter conditioning effects
Efficiency metric	Mass separation efficiency (%)	Fraction of inlet mass removed

A critical consideration for unducted outlet systems is the measurement of penetrating particles. Since the outlet air is discharged into the test room, a total collection system (such as a HEPA filter on the outlet) must be used to capture all penetrating particles for mass balance calculation. Failure to collect all penetrating particles will result in overestimation of separation efficiency.

Test Aerosol Generation

ISO 29042-5 specifies the use of standardized test aerosols with well-defined particle size distributions. The standard references ISO 12103-1 test dusts (such as ISO 12103-1 A2 fine test dust) for gravimetric efficiency testing. The aerosol generation system must produce a stable, reproducible aerosol concentration throughout the test duration. For specialized applications, the standard allows the use of custom aerosols that represent the actual pollutant generated by the machine, but the reference test using standardized dust must also be reported for comparability.

Engineering Considerations for Air Cleaning System Design

The separation efficiency of an air cleaning system depends on multiple factors including filtration velocity, particle size distribution, filter media characteristics, and loading state. ISO 29042-5 testing provides data on initial efficiency (clean filter) and loaded efficiency (after dust loading), both of which are important for understanding system performance over its operating life. For recirculating systems that discharge into the workplace, the loaded efficiency is particularly important as it represents the worst-case condition.

Modern air cleaning systems increasingly use combined separation mechanisms — for example, a cyclone pre-separator followed by a fabric filter or electrostatic stage. ISO 29042-5 testing can evaluate each stage individually if sampling ports are provided between stages, enabling optimization of the overall system design. The standard also addresses the measurement of pressure drop across the system, which is a critical parameter for energy consumption and fan selection.

For recirculating air cleaning systems, the mass separation efficiency alone does not fully characterize health protection. Particle size-dependent efficiency and the potential for re-entrainment of collected dust must also be considered. A system with 99.9% mass efficiency may still allow significant numbers of ultrafine particles to penetrate, which may be more relevant to health effects than mass concentration.

Frequently Asked Questions

Q1: How does ISO 29042-5 relate to filter classification standards like EN 1822 or ISO 16890?
ISO 29042-5 focuses on mass separation efficiency for machinery-integrated air cleaning systems, while EN 1822 (HEPA/ULPA) and ISO 16890 (general ventilation filters) provide filter classification systems based on particle size efficiency at specific particle sizes. ISO 29042-5 complements these standards by providing a test method tailored to the specific conditions of machinery emission control.

Q2: What is the difference between mass efficiency and particle number efficiency?
Mass efficiency measures the fraction of total particle mass removed, while particle number efficiency measures the fraction of particle count removed. For a given filter, mass efficiency is typically higher than number efficiency because larger particles (which contribute most to mass) are collected more efficiently. Number efficiency is more relevant for health effects of ultrafine particles.

Q3: How does dust loading affect separation efficiency over time?
For most filter media, separation efficiency improves with dust loading as the collected dust layer itself acts as a filter medium. However, this also increases pressure drop, reducing airflow if the fan characteristic is not accounted for. ISO 29042-5 specifies testing at multiple loading states to characterize this behaviour.

Q4: Can the test bench method be used for gas-phase air cleaning systems?
The standard is primarily designed for particulate air cleaning systems. For gas-phase systems (carbon filters, scrubbers), the measurement principles may be adapted, but the specific requirements for aerosol generation and particle measurement would not apply. Gas-phase systems are better evaluated using the tracer gas method of ISO 29042-2.

The trend toward recirculating air cleaning systems in industrial environments, driven by energy cost reduction and sustainability goals, has increased the importance of accurate separation efficiency measurement. ISO 29042-5 provides the standardized methodology needed to ensure that recirculated air meets workplace air quality standards, protecting worker health while achieving energy savings compared to once-through exhaust systems that require heated or cooled make-up air.

The measurement of separation efficiency using gravimetric analysis requires attention to filter handling and weighing procedures to minimize measurement errors. Filters should be conditioned in a controlled humidity environment before pre- and post-test weighing, and electrostatic discharge effects should be eliminated using neutralization techniques. The detection limit of the gravimetric method depends on the microbalance resolution and the stability of the weighing conditions, with modern instruments achieving detection limits below 0.1 mg. For low-concentration applications, extended sampling durations may be necessary to collect sufficient particulate mass for accurate efficiency determination.