Checklist: Selecting Fume Extraction for Indoor Welding

Why verification comes before installation

Many procurement teams focus on fan horsepower and duct diameter when specifying welding fume extraction. This approach misses the core problem. The goal is not moving air. It is removing a specific concentration of toxic particles before they reach the worker’s breathing zone. A large fan with poor source capture will create a dangerous environment. A small, well-designed hood with proper filtration will perform better.

This checklist provides a method to verify that a proposed system meets workplace exposure limits. It is designed for buyers and engineers who need to audit a supplier’s proposal or an existing installation. Use it as a verification tool. If an item cannot be confirmed with documentation or a site test, treat it as a non-compliant risk.

The central issue is concentration. Fume extraction is a local control. It works by creating a controlled airflow path at the source of the hazard. If the path is broken, the air quality in the room remains poor regardless of how much air is exhausted from the building. Verification must therefore begin with the physical interaction between the hood and the welder. The checklist below follows the logical sequence of the airflow path: capture, filtration, fan performance, environmental interaction, and long-term maintenance. Each section highlights specific parameters, common errors, and red flags that indicate a proposal lacks engineering rigor.

Confirming source capture and hood design

The first failure point in most indoor welding air quality systems is the hood. If the fume plume escapes the capture zone before entering the duct, no amount of filtration will solve the problem.

1. Capture velocity: Confirm the hood maintains a capture velocity sufficient for the welding process. Stick welding often requires different velocities than MIG or TIG due to plume density and direction. Capture velocity is the speed of air moving across the opening of the hood. It must be high enough to pull the fume plume into the duct but low enough to avoid disturbing the welder’s view or blowing away fine slag. Stick welding produces heavier, slower-rising fumes than MIG, which can require slightly different velocity adjustments depending on the electrode diameter and the angle of attack.
2. Hood geometry: Verify the hood shape is appropriate. Conical or bell-shaped hoods generally perform better than flat plates for localized capture. Check that the opening is sized correctly for the electrode or torch. A hood that is too large allows the fume plume to dissipate before it is captured. A hood that is too small creates turbulence that can blow fume back into the workspace. The opening should be sized so the fume plume enters the hood with a margin, not just at the edge.
3. Proximity: Ensure the design assumes the hood is positioned close to the workpiece. If the proposal assumes the operator can stand back, the airflow required increases dramatically, and performance drops. The relationship between distance and required airflow is non-linear. Doubling the distance from the source to the hood often requires significantly more than double the airflow to maintain the same capture efficiency. The physical design of the arm or stand should enforce a maximum working distance.
4. Flexibility: Check if the arm or positioning mechanism allows the hood to stay close during different joint angles. Rigid fixed hoods often fail in practice because operators move away from the source. Welding joints have varying geometries. A corner joint, a flat seam, and a vertical butt joint all require different hood angles. The positioning mechanism must allow the hood face to align with the fume plume direction without excessive effort.

Red flags include generic “industrial” hoods without process-specific data. If a supplier provides a single airflow figure for all welding types, reject the proposal. Fume behavior varies by metal, process, and electrode diameter. Aluminum fume behaves differently than carbon steel. TIG fume is often finer and lighter than stick fume. The hood design must account for these specific characteristics.

Evaluating filtration media and dust collection

Welding fume extraction systems handle a mix of fine particles, metal oxides, and organic compounds. The filtration stage must be designed to capture these specific contaminants.

• Media type: Identify the filtration media. Electrostatic precipitators, bag filters, and high-efficiency particulate air (HEPA) filters serve different roles. For fine metal fumes, high-efficiency particulate filters are standard. Electrostatic precipitators are effective for fine particles but require maintenance of the high-voltage components. Bag filters are robust and handle larger volumes but can be less effective for very fine submicron particles depending on the fabric rating. HEPA filters offer the highest removal efficiency but have higher pressure drops and shorter service lives. The selection must match the fume load and the required removal efficiency.
• Differential pressure: Check the pressure drop across the filter. A high initial pressure drop indicates the design is too restrictive. A pressure drop that spikes quickly indicates the media is clogging too fast for the duty cycle. The initial pressure drop tells you about the media quality and the filter area. The rate of increase tells you about the dust loading. A good design keeps the initial drop low enough to allow the fan to operate efficiently, and the media is selected to handle the expected dust load for a reasonable period.
• Dust collection: If the process generates heavy slag or particulate dust, verify there is a pre-filtration stage or dust collection bin. Feeding coarse slag into fine filters destroys them rapidly. Slag and spatter are large, heavy particles. They act as abrasive agents and quickly reduce the efficiency of fine filters. A pre-filter or a dust bin at the bottom of the ductwork or filter housing removes these coarse particles before they reach the fine media.
• Media change interval: Request the estimated service life of the media. This should be based on the expected fume load, not just a fixed calendar. A high-production line consumes filters faster than an occasional setup. The service life estimate must be based on the total mass of fume expected to be collected. The supplier should provide a calculation or a rule of thumb based on similar applications. If the supplier only gives a calendar date, ask for the underlying fume load assumptions.

Red flags are proposals that do not specify the filtration class. “High efficiency” is vague. Look for specific micron ratings or filtration standards applicable to the local regulations. Also, ignore claims that a single filter type handles both fine fumes and heavy particulate dust. They require different approaches. A design that uses only fine filters without pre-filtration for a high-slag process will fail quickly and cost more in the long run.

Verifying airflow and fan performance

Airflow calculations must be verified against actual conditions. Suppliers often quote free delivery air, which is not the same as the air reaching the hood.

Parameter	Verification Requirement	Common Error
Hood Velocity	Measured at the capture face under load	Calculated at zero static pressure
Fan Power	Sized for total system resistance	Sized for duct length only
Static Pressure	Includes hood, duct, and filter losses	Ignored in basic calculations
Air Volume	Measured at operating conditions	Quoted at ideal standard conditions

1. Total system resistance: The fan must overcome the resistance of the hood, ductwork, bends, and filter. Ask for a breakdown of these components. The total static pressure is the sum of the pressure losses across each component. The hood, the filter, and the ductwork all contribute to this loss. A detailed proposal should list the pressure drop for each major component. This allows you to verify that the fan is capable of delivering the required airflow at the hood face when the system is fully loaded.
2. Duct sizing: Verify the duct diameter. Undersized ducts increase velocity, which creates more noise and reduces capture efficiency. Oversized ducts can allow the fume plume to dissipate before the filter captures it. The duct velocity should be within a reasonable range. Typically, velocities between 15 and 25 meters per second are common for welding fume extraction, but this depends on the system design. Too low, and the fume settles. Too high, and the noise becomes excessive and the pressure drop increases dramatically.
3. Fan curve: Confirm the fan is selected at the intersection of the fan curve and the system resistance curve. Do not accept a fan selected at the “best efficiency point” if the system resistance is higher. The fan curve shows the relationship between airflow and pressure. The system curve shows the resistance of the ductwork and filters. The operating point is where these two curves intersect. If the fan is selected at its best efficiency point but the system resistance is higher, the actual airflow will be lower than specified.
4. Variable speed control: If the process varies, check if the fan has a variable speed drive. Constant speed operation wastes energy and may over-ventilate the space, drawing in other contaminants. Variable speed control allows the fan to match the airflow to the welding activity. When the welder is not working, the fan can be slowed down or turned off. This reduces energy consumption and noise. It also prevents excessive air movement in the workspace, which can disturb other processes or draw in dust from other areas.

Red flags are fixed speed fans on variable duty processes. Also, watch for duct designs with too many bends or sharp corners. Each obstruction adds resistance. A duct run with many 90-degree bends will have significantly higher resistance than a straight run of the same length. The proposal should minimize bends and use gradual curves where possible.

Checking indoor air quality and dilution

Welding fume extraction is the primary control, but the surrounding environment matters. If the room is poorly ventilated, even a good extraction system can fail if the hood is not used consistently.

• Room ventilation: Verify that the building ventilation system is not fighting the extraction hood. If the room is under negative pressure, it may pull air into the hood from the wrong direction. Building ventilation systems are designed to maintain pressure differentials between zones. If the workshop is under negative pressure relative to the corridor or other areas, air will be drawn into the workshop from those areas. This can interfere with the hood’s capture zone and bring in fresh air that dilutes the fume before it is captured. The room ventilation system should be designed to work in conjunction with the extraction system, not against it.
• Dilution air: Some processes require a small amount of dilution air at the hood to prevent the fume from short-circuiting through the opening. Confirm if the design includes this. Dilution air is introduced at the hood face to increase the capture velocity and to push the fume plume into the hood. It is particularly useful when the hood is not perfectly aligned with the source or when the fume plume is very dense. The amount of dilution air required depends on the hood design and the fume characteristics. The proposal should specify the source and flow rate of the dilution air.
• Operator exposure: The checklist is not complete until you verify where the operator stands. If the operator stands upwind of the hood, the system is less effective. The design should dictate a safe working position. The operator’s position relative to the hood and the general airflow in the room determines their exposure. The hood captures fume at the source, but the operator’s breathing zone is still part of the environment. The design should include a marked working position or a physical barrier to prevent the operator from moving into the fume plume.
• Monitoring: Confirm that the site has a plan for air monitoring. You cannot verify exposure limits without periodic sampling. The extraction system should be designed to allow for easy sampling points. Air monitoring is a legal requirement in many jurisdictions. The system should have designated points where air samples can be taken to verify that the extraction system is performing as designed. These points should be located in the operator’s breathing zone and at the hood face.

Red flags are proposals that do not account for the layout of the workshop. If multiple welding stations are in a small room, cross-contamination is a risk. The checklist must account for the interaction between stations. Fume from one station can migrate to another if the extraction systems are not sized correctly or if the room ventilation is inadequate. The design should consider the airflow between stations and ensure that fume from one station does not become a source of exposure for another.

Maintenance, monitoring, and compliance

A welding fume extraction system is a living piece of equipment. It requires constant attention to perform.

1. Filter monitoring: Ensure the system has a differential pressure gauge or sensor that alerts when filters are clogged. A gauge or sensor provides a visual or electronic indication of the filter’s condition. When the pressure drop rises above a set threshold, the operator is alerted that the filter needs cleaning or replacement. This prevents the system from running with degraded performance, which can lead to increased energy consumption and reduced capture efficiency.
2. Maintenance log: Verify that a maintenance schedule is included. This includes checking for leaks, inspecting ducts for blockages, and testing fan performance. A written log records the date, time, and nature of each maintenance activity. It also records the readings from the monitoring instruments. This log is a key document for compliance and for tracking the system’s performance over time. It helps identify trends and potential problems before they become serious.
3. Dust disposal: Check how the collected dust is handled. Metal fume dust is often classified as hazardous waste. The system must allow for safe disposal. The dust bin or filter housing must be designed to allow for safe removal and disposal of the collected dust. The procedure for removal should be documented and included in the maintenance plan. The waste must be handled according to local regulations for hazardous materials.
4. Documentation: Request the as-built drawings and the test report. The test report should show measured airflow and pressure at the hood, not just the fan rating. As-built drawings show the actual installation, including duct sizes, fan location, and filter placement. The test report shows the measured performance of the installed system. This documentation is essential for future maintenance, troubleshooting, and compliance audits.
5. Operator training: The checklist must include a plan for training operators on proper hood placement. The best system fails if the operator does not use it. Training should cover the correct use of the hood, the importance of keeping it close to the source, and the procedure for reporting any problems. The training should be documented and repeated regularly. The operator is the first line of defense for the extraction system’s performance.

Red flags are “set and forget” claims. Fume extraction systems degrade. Dust accumulates, filters clog, and seals wear. Without a maintenance plan, the system will fail within months. The design must be robust enough to handle the expected duty cycle, but it also must be maintainable. The maintenance plan should be realistic and based on the actual usage of the system.

Final audit decision

Use this checklist to create a pass/fail record for each proposed system. Do not rely on a supplier’s word. Require measured data. If a supplier cannot provide a test report or a detailed calculation, the risk is too high.

The goal is a system that reliably removes fumes at the source. Verify the hood, the filter, the fan, and the maintenance plan. If any of these elements are missing or vague, the system is not ready for procurement.

The audit decision should be based on the completeness of the documentation and the quality of the data provided. A proposal that lacks specific data on capture velocity, filtration class, or fan performance should be rejected. The supplier must be able to justify their design choices with engineering principles and measured results. This approach ensures that the system is fit for purpose and that the risk of non-compliance is minimized. The final decision is a gate. If the checklist is not passed, the system is not approved for installation.