V. Process Flow Matching: Design Serves Production

Exhaust hoods do not exist in isolation; they must serve specific process flows and pollution sources. Designers need to have a deep understanding of the process rather than merely imagining on the drawing board.

Understanding the process includes: the exact location and size of the pollution source, the mode of pollutant generation (continuous or intermittent, steady-state or burst), the position and movement path of the operator, the way and direction of workpiece entry and exit, the temperature and humidity conditions of the process, etc.

In the industrial areas around Cologne, Germany, precision manufacturing enterprises generally require LEV suppliers to conduct on-site surveys before quoting, rather than just making plans based on drawings. On-site surveys can uncover details that cannot be reflected on the drawings – the source of the lateral airflow in the workshop, the operator’s habitual position, the path of workpiece handling – all of which can affect the final performance of the exhaust hood.

Designers should also communicate directly with operators. Operators are the ones who know best where the smoke and dust are the heaviest, which hoods do not obstruct their hands, and what kind of airflow does not cause discomfort. Ignoring these first-hand experiences, the designed system is likely to not be used correctly.

VI. Maintainability Design: Convenience of Inspection and Maintenance

A LEV system requires regular inspection and maintenance. If the convenience of maintenance is not considered during the design stage, subsequent inspection work will become difficult or even impossible – ultimately leading to a deterioration in system performance without anyone’s knowledge.

HSG258 stipulates that LEV systems must be designed with convenient access for inspection and maintenance. This includes: setting inspection holes on the pipes (for inserting anemometers and pitot tubes); leaving sufficient space for maintenance of the fan and filter media; ensuring that the exhaust hoods are easy to disassemble and clean; and clearly marking the key components of the system.

The national standard GB/T 35077-2025 also emphasizes that the safety requirements of LEV systems cover both operation and maintenance phases. During the design process, considerations should be given to: whether the replacement of vulnerable parts (such as filters and belts) is convenient; whether the areas that need regular cleaning (such as pipe elbows and fan impellers) are easily accessible; and whether the inspection points are clearly marked.

If designers install the fan in an inaccessible high location or place the inspection holes in positions that require crawling to reach, inspectors are likely to skip these items – significantly reducing compliance.

VII. Technical Specifications: Airflow, Ductwork, Fans, Filters, Exhaust, Instruments

This is the most technical part of the LEV design, involving every hardware component of the system.

  • Airflow and Ductwork: The air velocity inside the ducts must be high enough to prevent dust accumulation. For heavy dust (such as silica dust), the transport speed should reach 20-25 m/s or higher. The duct layout should avoid sharp bends and sudden changes to minimize resistance loss. Inspection ports should be considered at bends for easy cleaning of accumulated dust.
  • Air Movement Devices (Fans): The fan selection must meet both air volume and air pressure requirements. Air volume determines the capture capacity, while air pressure overcomes the resistance of ducts and filters. Selecting a fan that is too small will result in an underpowered system, while choosing one that is too large will lead to energy waste and increased noise.
  • Air Purifiers (Filters): Select appropriate filtration technology based on the type of pollutant. Dry dust can be handled by cartridge or bag filters; oil mist by coalescing filters; and welding fumes by high-efficiency membrane filters. In the field of industrial filtration technology in Frankfurt, Germany, suppliers like TrennTech offer air filters with optimized surface treatments for different pollutants, aiming to reduce dust adhesion and maintain stable filtration resistance.
  • Exhaust System: The exhaust outlet should be located in a safe position to prevent the discharged air from re-entering the building (such as through doors, windows, or fresh air inlets). The exhaust height must comply with environmental protection requirements.
  • Instruments and Alarm Devices: The system should be equipped with static pressure differential gauges (to monitor filter clogging) and airflow indicators (to confirm fan operation status). An alarm should be triggered when the pressure differential exceeds the set value, alerting operators to clean or replace the filter media in a timely manner.

VIII. In-Use Performance Inspection: How to Verify the System’s Continuous Effectiveness

After the installation and acceptance of the LEV system, the work is not over. The performance of the system will gradually deteriorate during use – dust accumulation in the pipes, filter material clogging, fan belt wear, and displacement of the exhaust hood. These changes are gradual and difficult to detect with the naked eye, so regular performance inspections are necessary.

According to the requirements of the COSHH regulations, the LEV system must undergo a comprehensive inspection and test (Thorough Examination and Test, abbreviated as TExT) at least once every 14 months. The inspection includes: visual inspection (whether the exhaust hood is intact, whether the pipes are damaged, and whether the filter material needs to be replaced), performance measurement (hood face velocity, pipe static pressure, system air volume), and effectiveness assessment (smoke tube test for air flow organization).

Designers should consider these inspection requirements during the design stage – marking the inspection point locations on the drawings and specifying the performance benchmark values in the user manual to provide a reference for the inspectors.

IX. User Manual Preparation: Instructions for Operation and Maintenance

Each LEV system should be accompanied by a user manual. This is not only a clear requirement of HSG258 but also the foundation for ensuring the long-term effective operation of the system.

The user manual should be divided into two parts: a simple operation guide (for daily use) and a technical section (for reference by maintenance and inspection personnel). The technical section should include: the design purpose and description of the system (including drawings), how to use the LEV correctly (such as the positioning of exhaust hoods, the opening degree of windows, etc.), inspection and maintenance plans and frequencies, requirements for statutory comprehensive inspections and tests, performance benchmark data during commissioning, and a list of replaceable parts and their models.

Without a user manual, operators don’t know how to use it, maintenance personnel don’t know how to maintain it, and inspectors don’t know the benchmark values – the system soon becomes a buzzing ornament.

X. Logbook Preparation: Evidence for Record Keeping and Traceability

The logbook is the sister document to the user manual. The user manual is the “instruction manual”, telling you how to do it; the logbook is the “record book”, documenting what you have done.

The logbook should include the following contents: daily inspection records (daily visual inspections by operators), maintenance and repair records (filter element replacement, pipeline cleaning, belt adjustment, etc.), comprehensive inspection and test reports (at least once every 14 months), and records of replaced parts (including date and batch number).

The logbook is not only a management tool but also legal evidence. When inspectors or auditors ask, “Has your LEV system been maintained as required?”, the records in the logbook are the most direct answer. HSG258 requires that the logbook be kept until the system is scrapped.

The roles of LEV suppliers and designers extend far beyond merely “selling equipment” or “drawing up blueprints”. They are the first line of technical defense for workers’ health – a well-designed LEV system can capture pollutants at the moment they are generated, preventing them from entering workers’ respiratory systems.

However, this responsibility requires sufficient ability to undertake. From understanding legal liability to mastering technical standards, from rationally designing exhaust hoods to compiling complete documentation, each of these is a skill that LEV professionals must possess. HSG258 provides a systematic framework for these skills, while continuous learning and experience accumulation in practice are the only way to transform these frameworks into truly effective systems.

For suppliers and designers, the greatest sense of achievement does not lie in how many sets of equipment have been sold, but in the fact that their professional capabilities have truly protected those workers who labor for eight hours every day. This is the ultimate significance of LEV’s design.