6 design considerations for localized weld fume control

Shops have a few things to consider when designing a localized fume extraction system for welding. This includes knowing which welding technologies and materials it uses, fume exposure risks, filtration requirements, the mobility of welding operations, energy savings, and spark control.

Weld shops have lots of options when it comes to designing a localized fume extraction system for manual or robotic welding. Tailoring the system to the needs of welders and the production environment will help minimize costs and energy consumption while providing maximum protection for people. Here are six considerations for system design.

1. What Welding Technologies and Materials Are Used?

The type of welding and the materials being used will have a big impact on the total volume of fume produced as well as its overall toxicity. In general, welding processes using consumables, such as gas metal arc welding, shielded metal arc welding, or flux-cored arc welding, will generate more fume than laser welding or resistance welding. Some materials are also more toxic than others; for example, welding stainless steel generates dangerous hexavalent chromium, while galvanized steel produces fumed zinc oxide.

Employers are responsible for ensuring that the weld fume collection system keeps worker exposure under the permissible exposure limits (PELs) set by the Occupational Safety and Health Administration (OSHA). The government agency has set a PEL for total weld fume concentration at 5 mg/m³ when welding mild steel, iron or aluminum, based on an eight-hour time-weighted average. However, PELs for specific elements found in weld fume, such as hexavalent chromium and lead oxides, are much lower. That means simply meeting the 5-mg/m³ standard for total weld fume is not enough.

Facility testing is a good place to start to help shops become familiar with the elements found in its weld fume and what its current exposures are.

2. Where Are People Exposed to Weld Fumes?

A localized fume collection system starts with the hood or collection device. The hood must be designed to keep weld fumes out of the breathing zone of workers. For maximum energy efficiency and minimum weld fume exposure, collect weld fumes as close to the source as possible.

Robotic welding cells can be contained under a full hood. The hood should be designed to minimize the airflow required to collect weld fumes. No one should work inside the hood. Robotic tip extraction is an alternative for applications that cannot be easily hooded or for cobots working alongside people.

For manual welding, choose an option that keeps fumes out of the breathing zone. Fume guns can be a great choice for GMAW. With proper technique, they can remove 90% to 95% of generated fumes and minimize the airflow required for collection. If using a backdraft plenum or fume arm, make sure it is positioned to pull fumes up and away from the welder’s face.

3. Should Air Be Exhausted or Filtered?

For light-duty shops with occasional welding activity, a good ventilation system with localized fume capture may be sufficient. However, high-production shops almost always require a dust collection system. These systems capture and filter weld fumes before returning air to the facility or push it outdoors. An air filtration system keeps facilities compliant with EPA rules and other regulations for exhausting contaminants to the outdoors and saves energy by keeping heated or air-conditioned air inside the facility.

A cartridge-style dust collector is recommended for most welding applications. These collectors are highly energy efficient and provide more airflow in a smaller physical footprint than baghouse collectors. They also can be equipped with higher-efficiency air cartridge filters to collect submicron particles created by thermal processes like welding. For weld fume collection, a filter with a minimum efficiency reporting values (MERV) rating of at least 15 is recommended. It is also important to size the dust collector appropriately. It must provide enough airflow to maintain required capture velocities and have enough filter media (air-to-cloth ratio) for the volume of fumes collected.

4. Is Welding Stationary or Mobile?

The right type of dust collection system depends on how many welding stations there are, the configuration of the facility, how much mobility is required by individual welders, and how much flexibility is desired for future growth or reconfiguration.

A well-designed fume extraction system will help bring a facility into compliance, reduce energy use, and maximize employee comfort and safety.

There are several options to consider:

• A centralized ducted system. This is a configuration in which multiple robotic cells or manual weld booths/stations are ducted to a single, large dust collector that is sometimes located outside. This option is best for larger facilities with many individual weld cells/stations and environments where production line configuration is relatively fixed.
• Individual, smaller dust collectors. These units can be placed on the factory floor and ducted to one or two cells/stations. This is a great option for smaller shops that only have a few weld cells/stations to support. This configuration may also be beneficial for larger shops that want more flexibility to reconfigure production lines, as the dust collectors can be moved with the cells.
• Portable hi-vac dust collector systems. These units are most typically used for manual welding (fume guns or a small portable backdraft plenum or fume arm), though some are powerful enough to support a light-duty robotic welding setup. Portable systems are great for small shops that just need to support one or two welding stations or for environments that require a lot of welder mobility. Combining a fume gun with a portable fume extractor gives welders the freedom to move around large weldments, work in semi-enclosed areas (such as a tank or ship hull), and take their welding setup from station to station.

5. What Energy-Saving Opportunities Exist?

Designing an energy-efficient system starts with selecting the right dust collector. A correctly sized cartridge dust collector is usually the most energy-efficient option.

For additional energy savings, look for these features:

• Variable frequency drive (VFD) motors ramp the motor up and down to compensate for filter loading, so the system only works as hard as it needs to. A VFD motor can decrease energy use by 20% to 40%.
• A filter pulsing system reduces energy use and maintenance by pulsing excess dust off the filters to minimize filter loading. This extends the life of the filters and decreases the energy required to push air through them. Look for a pulsing system that pulses dust across the entire length of the filter.

6. Is Spark Control Required?

Most welding processes produce a lot of sparks. Those sparks can create a fire or combustion risk inside the dust collection system. Spark control is usually necessary at the inlet of the dust collector or ductwork to prevent sparks from reaching the filter chamber.

Some dust collectors are equipped with a mesh or screen-type spark trap. These are simple devices that block sparks from entering the inlet. They must be cleaned periodically to remove soot and particulate.

A centrifugal spark arrester can provide more protection for environments where a large number of sparks are produced near the dust collection system inlet. These systems use centrifugal force to drive sparks against the chamber walls and strip the thermal envelope.

Putting It All Together

Designing a localized weld fume collection system that is both effective and efficient can be complex. It is usually beneficial to work with a qualified engineering partner who can conduct facility testing before and after installation and help you make the best decisions for your operation. The right system will keep your facility in compliance, reduce energy use, and maximize the comfort and safety of employees.

The right system will depend on the number of welding stations, the configuration of the facility, how much mobility is required by individual welders, and how much flexibility will be required in the future.