VII. How to Prepare Specification Documents for LEV Designers
Employers do not necessarily need to understand all the technical details of LEV design – that is the engineer’s job. However, employers must be able to provide designers with a clear specification document, which serves as the basis for communication between both parties. A good specification document is like a good architectural design brief: the more detailed it is, the closer the final outcome will be to expectations.
The core content of the standard document includes the following aspects:
Pollutant information: What is the substance? If it is a mixture, what are the main components and their proportions? What is the approximate concentration – estimated value, empirical value or historical detection data? Where does the pollutant come from – specifically which equipment, which part, and which action? Attach the Safety Data Sheet (SDS), with particular attention to the occupational exposure limit (OEL/WEL) and toxicological information.
Process conditions: The specific location of the pollution source – three-dimensional coordinates, size, and shape. The temperature of the pollution source – ambient or high? If it is high, what is the approximate temperature range? The spray speed and direction – does the pollutant spray out at a certain speed from a certain direction? Is the workstation fixed – do the operators work at a fixed position or need to move within a large range? The operation frequency – how many hours per day? How many days per week? How many workstations are operating simultaneously?
Operation mode: Where do the workers stand – relative to the position and orientation of the pollution source? How do the workpieces enter and exit – where do they come from and where do they go? Which actions generate pollutants – continuously or intermittently? Where are the operator’s hands, head, and torso – the exhaust hood should not block these positions.
Control target: What is the expected exposure concentration? The common practice is to set a certain proportion of the occupational exposure limit as the target, such as 50% or 30% of the limit. This “safety margin” is to cope with fluctuations in the production process and degradation of the Local Exhaust Ventilation (LEV) performance. If the target is “exactly at the limit”, then once the production load slightly increases or the system slightly deteriorates, it will exceed the limit.
Constraints: What are the space limitations in the workshop – where do the pipes go and where are the equipment placed? Are there noise restrictions – will the noise from the fan and airflow affect nearby offices or residential areas? Is there a heat source for winter make-up air – if the air drawn from outside is not replenished, the workshop will become cold. Explosion-proof requirements – if the pollutant is combustible dust or flammable vapor, the equipment and electrical systems need explosion-proof design. Installation time window – when can the equipment be shut down for installation and how many days are needed?
Additional requirements: Is remote monitoring and alarm required – automatic alarm when the filter material pressure difference exceeds the limit? Are there any special requirements for the format of the logbook and user manual? Acceptance criteria and testing methods – which standards are adopted (such as HSG258)? Which indicators are tested (hood face velocity, duct static pressure, workstation concentration)? Who will perform the tests – a third party or the supplier?
The time employers invest in preparing normative documents will be repaid many times over in the subsequent design, installation, acceptance and operation stages. This is not dispensable “paperwork”, but the crucial first step to ensure the success of the LEV project.
VIII. Information to be Communicated to the LEV Supplier
The more information the employer proactively provides, the more accurate and timely it is, the more reliable and practical the solution offered by the supplier will be. Conversely, when the information is insufficient, the supplier can only make designs based on assumptions – and if these assumptions do not match the actual situation, problems will only surface during the installation and commissioning stage, by which time the cost of making corrections will be very high.
Employers should at least inform suppliers of the following:
A complete list of pollutants: Different welding processes, types of welding materials and parameters produce significantly different smoke dust components, particle size distributions and generation rates. For wood dust, it is necessary to specify the type of wood, as the dust characteristics and health hazards vary among different types of wood. For foundry dust, the content of silica in the molding sand should be specified, as it determines the risk level of silicosis.
The actual production load: It is necessary to clearly state how many hours the equipment operates daily, how many days a week, and how many workstations/equipment operate simultaneously. What are the future expansion plans? The design air volume should cover the maximum operating conditions. The more comprehensive the production load coverage, the more reasonable the LEV design plan.
Workshop environmental conditions: The temperature range, humidity, whether there are corrosive gases, and whether there are explosion-proof requirements should all be clearly specified. These factors directly affect equipment selection and cost.
Budget range: Honest communication about the budget helps suppliers find a reasonable balance between performance and cost. If the budget is too low, suppliers can directly inform the employer that “this budget cannot produce a system that meets your needs” instead of forcing a reduced version that ultimately dissatisfies both parties. If the budget is sufficient, suppliers can recommend higher performance, longer lifespan, and lower operating cost solutions. The purpose of budget communication is to align expectations, not to let suppliers “take advantage” of the employer.
Expected performance verification methods: After installation, how to prove the system is effective? Is it by measuring the face velocity of the hood (performance indicator at the equipment outlet)? Or by measuring the air quality at the workstation (final effect indicator)? It is recommended to combine both: first confirm that the equipment itself meets the design parameters through the face velocity and duct air volume, and then confirm that the pollutant concentration in the breathing zone of the workers has dropped below the target value through air sampling at the workstation (or real-time detection). The acceptance criteria should be specified in the contract, including the detection method, detection points, and pass/fail criteria.
Maintenance and support expectations: How long is the warranty period provided by the supplier? Which items are free for repair or replacement during the warranty period? Is operator training provided? Is a logbook template and checklist provided? What is the supply cycle and price for subsequent spare parts (filters, activated carbon, etc.)? These may seem like “after-sales issues”, but they should be clarified during the procurement stage.
The supplier’s responsibility is to provide a “fit-for-purpose” system – not the most expensive or the cheapest, but one that can truly control pollutants, meet the actual needs of the employer, and be used by the operators. In manufacturing enterprises in Stuttgart and its surrounding areas in Germany, professional air filter suppliers such as TrennTech usually require employers to fill out a detailed on-site investigation questionnaire when providing air filtration solutions. This questionnaire covers dozens of items of information such as pollutant parameters, process conditions, operation modes, and maintenance expectations. Based on this, they design the system and select filter materials to ensure that the LEV system precisely matches the on-site conditions.
Employers should also require suppliers to provide complete documentation – including design calculation sheets (proving the basis for the selection of air volume and air pressure), commissioning reports (proving that all parameters meet standards after installation), user manuals (operating methods and key points for daily checks), and logbook templates (formats for recording daily checks and maintenance). These documents are not optional attachments but are the basis for subsequent maintenance and compliance checks. Without these documents, three years later when filter materials need to be replaced and fans need to be overhauled, you may have forgotten the original design parameters.
Deciding to adopt the LEV solution means that the employer has recognized that air pollution is an issue that needs to be addressed. However, between “recognizing the problem” and “solving the problem” lies the above-mentioned eight matters.
LEV is not a commodity that is purchased and then forgotten. Instead, it is a system that requires design, commissioning, operation and maintenance. The role of the employer is not that of a “payer”, but that of a “system owner” – from proposing requirements, preparing specifications, to design review, acceptance and delivery, and then to daily management, regular testing and annual compliance checks, the employer must be involved throughout the process. Only when the employer truly understands and assumes this role can the LEV system remain effective continuously and the health of workers be truly guaranteed.