Fume management: Know your hierarchy of controls

Managing welding fumes has become a topic discussed with greater frequency since the American Conference of Governmental Industrial Hygienists (ACGIH®) updated its guidance on Threshold Limit Values (TLVs®) and Biological Exposure Indices (BEIs®) in 2013. At that time it created a new TLV of 0.02 mg/m3 for respirable manganese – a tenfold reduction from the former 0.2 mg/m3 TLV. This followed on the heels of similarly dramatic changes in exposure indices for hexavalent chromium.

Many Canadian provinces follow the ACGIH guidance, which has required fabricating shops to review their welding and air management processes.

Fume management can be particularly challenging when a shop has a weldment that involves working in tight spaces. Speaking to a number of experts on the subject, Canadian Fabricating & Welding asked how managing fume in tight spaces differs or is similar to typical weld management. Ultimately, the critical point that everyone came back to was following OSHA’s hierarchy of controls to ensure as much fume as possible is removed from a welder’s vicinity. Almost always, this requires a combination of anywhere from three to five approaches.

Process Modification and Substitution

“With any welding shop, the No. 1 thing we want to consider is what material the customer is working with,” said Chrissy Klocker, applications engineering manager at Donaldson’s Torit product business. “Is the material hazardous or not? If you are working with carbon steel, typically that does not raise concerns about hazardous particulates. But if you are working with stainless steel, that includes hexavalent chromium and could be more hazardous. Understanding the particulate you are working with is going to drive the discussion of how you are going to manage that fume.”

Miller Electric Mfg. LLC’s Brian Bellile recommends engaging an industrial hygienist to determine the particulate levels in your facility to understand precisely what the hazard level is.

“From there we will usually walk through OSHA’s hierarchy of controls to determine the best way to manage a shop’s needs,” said Bellile, product manager for Miller’s weld environment category.

The first issue that has to be addressed in the hierarchy of controls is process modification or substitution. Switching to a lower-manganese consumable is one option, as that decreases risk right at the source.

A challenge with reducing the manganese in the welding wire is that, for many jobs, the manganese is there for a very specific reason: to increase toughness of the weld. This may not be appropriate for every application.

Pulsed gas metal arc welding (GMAW) machines are becoming a more popular response to fume management. The major advancements in pulsed machines have come from technology that allows much tighter arc lengths while maintaining arc stability. This is done through high-speed manipulation of the electrical output of the power source. It is a comparatively spatterless process that typically runs at lower voltages and heat inputs, which can lead to lower fume levels.

“If you compare a robot to a human in welding terms, the one thing a human does better than a robot is run a bead,” said Lincoln Electric’s Rob Ritchot. “The robot can position the part quickly and properly, and given the right parameters ahead of time, the welding power source can provide the settings.” Here we see Lincoln Electric’s combination of its Weld Sequencer® technology and a part positioner to create the Smart Positioner™ welding system. Basically, this simplified approach to optimizing weld placement for each operator and their position combines process modification/substitution and work practice controls.

The pulsed GMAW process works by forming one droplet of molten metal at the end of the electrode per pulse. Then, just enough current is added to push that one droplet across the arc and into the puddle. The machine drops the current at times when extra power is not needed, thereby cooling off the process. This allows it to weld better on thin materials, control distortion, and run at lower wire feed speeds with arc stability.

According to Rob Ritchot, district manager for Lincoln Electric, the slower travel speed of pulsed units is something that made many hesitate to invest in the technology when it first appeared, for very good reasons.

“Some companies that tried pulse machines 10 years ago often did not implement the solution because the pulse mode had a lower travel speed compared to CV,” said Ritchot. “But we’ve come a long way since then. Computing power is more robust, and the new waveforms are so precise that they allow us to control larger-diameter wires, which in turn gives us the ability to weld faster. Our newest Low Fume Pulse™ waveform makes it possible to achieve up to 60 per cent lower fume generation in some applications. This is situation-dependent. And we’re often able to use one size wire diameter larger because we are running lower voltages and maintaining our amperage. This makes it possible to increase productivity by 5 to 10 per cent.”

Engineering Controls: Fume Extraction

The second hierarchy of control is engineering controls, such as fume extraction. This relates to any physical means of separating the operator from the fume. It could refer to a physical barrier such as a robotic cell, an ambient fume extractor, or actual fume extraction at the arc.

“If you’re working in a confined space, it is likely that the main device used for extracting fume would be a fume extraction gun,” said Bellile.

Fume extraction guns are a popular source extraction approach because it removes fume very close to the source.

“In a confined space you would pair the extraction gun with a high vacuum fume extraction system,” said Jeremy Bruesewitz, field application engineer for fume extraction at Miller. “This type of system provides higher static pressure, so you can run the fume through a flexible hose into whatever area you have to work in and not lose any of that suction, which can happen with a low-vac system.”

However, a shop can’t count on a fume extractor gun to remove all particulates.

“That’s why we really rely on the industrial hygienist to keep testing the air,” said Bellile. “If the fume extraction gun isn’t able to get particulates below the required threshold, or if you’re not using GMAW, that’s when a fume extraction arm or some other external device needs to be used to capture the fume.”

Fume extraction guns are a popular source extraction approach because they remove fume very close to the source.

As Klocker explained, for proper fume mitigation with a dust collection system, you want to use a hood that draws the fume away from the breathing zone of the welder.

“If you are working on a piece of equipment in front of you, you want to have the hood either down and away from the weld or in front of you to draw that contaminant away,” said Klocker. “If you’re left with no other option but ambient capture away from the weld, an overhead hood or extraction arm could be used. This may be positioned above the welder if there’s no other option, but that’s not ideal because you are drawing the fumes up past the employee. But again, work with your industrial hygienist, depending on the material, [to determine what] might be acceptable. Regardless of your solution, you just want to avoid having the extractor behind the employee. Weld fume is hot, so it’s going to want to rise. The key is to keep the fume away from the welder’s breathing zone as much as possible.”

In small spaces, Klocker said that sometimes having an extraction arm that can be manoeuvred is preferred so that you have the ability to modify placement of the hood to maintain source control. She recommended referring to the book Industrial Ventilation: A Manual of Recommended Practice for guidance on placement if you are adjusting equipment already in your shop.

Determining the capture velocity necessary on a fume hood is something you will likely work on with your supplier, but Klocker said it’s important to keep two things in mind: the type of material being welded, and the distance from the weld to the extractor.

“The distance is a big driver in terms of how much airflow you need for your system,” she explained. “If your hood is located 6 in. from the weld, you are not going to have to draw as much air as if you’re 18 in. away. The latter distance will require a lot more energy. If that’s not taken into account when sizing your dust collection system, you may end up with a system that doesn’t have sufficient capacity to remove the contaminant.”

Sizing a system also requires considering how often you are welding. A continuous-duty system, for instance, could run for 18 to 24 hours a day, but there are also intermittent, point-of-use collectors that work best when run for a couple hours or so.

“With intermittent collectors, to clean the filters you have to shut the collector down,” said Klocker. “A continuous-duty system, on the other hand, will pull the same amount of airflow consistently and is able to clean its filter while still running. This obviously allows you longer operating hours.”

For weld systems, Klocker said Donaldson recommends a cartridge dust collector, which uses compressed air to clean the filters.

“A continuous-duty collector has a gauge that indicates the pressure drop across the filters, and when that pressure drop reaches a certain level, it signals to the cleaning system to start cleaning the filters,” she said. “An intermittent-duty collector requires you to manually trigger the cleaning process after the collector has been shut down.”

Klocker noted that if you plan to recirculate the air in your facility, you might need ancillary equipment.

“If you are working with stainless steel, for instance, where hexavalent chromium is an issue, you may require an afterfilter,” she said. “Those are static filters that will capture dust released in an upset condition. Having this secondary filter will also add resistance to your fan, so that also has to be considered when sizing your system during the design process.”

Work Practice Controls

The third hierarchy of controls is work practice controls.

“That’s essentially training,” said Bellile. “But it’s a challenge to address this sometimes because you have to figure out what your target is. Are you re-training your operators to encourage better form or parameters for managing weld fume? Are you simply trying to figure out a way to get the welder’s head farther away from the arc? That might be a training issue, or it might be an equipment consideration.”

Bellile pointed out that lens technology in newer welding masks, such as his company’s ClearLight technology, allows welders to see the weld better, which can help encourage them to move their head farther from the weld plume and, in essence, reduce their exposure.

Simple adjustments to an operator’s posture can make a difference as well.

“One of our customers did a study; they basically had the operator stretch his arms out an extra 3 or 4 in. from the welding plume,” said Ritchot. “By doing so, it reduced his exposure significantly.”

It is possible to encourage better welding using advanced positioners that can optimize welding and operator position. Optimizing these positions for every weld can maximize weld productivity while minimizing operator exposures, if done right. That sort of review of welding basics can be valuable to any welder. However, computing and robotics technology is now allowing companies to take this all a step further.

“If you compare a robot to a human in welding terms, the one thing a human does better than a robot is run a bead,” said Ritchot. “The robot can position the part quickly and properly, and given the right parameters ahead of time, the welding power source can provide the settings. Robots are going to continue to dominate the welding industry, but there are a lot of parts that are not robot-friendly, usually due to part tolerance issues, and require the skills of a person. We want to make people more productive.”

To make this a reality, Lincoln Electric has created a welding system that combines Weld Sequencer® and a part positioner into the Smart Positioner™ welding system.

“The Weld Sequencer is a software tool that displays visual work instructions for the operator on a monitor,” said Michael Relko, product manager at Lincoln Electric. “As it’s displaying the image, it’s also controlling the settings on the power source. So when the welder makes the weld, it detects that the weld has been made. You can also set parameters to make sure it will alert you if the weld is out of specification. For example, if it notices the volts are too high, or the amps are too low, it can alert an inspector. But after the welder makes the weld and the system validates that it’s good, it will move on to the next weld in the sequence.”

The Smart Positioner combines with the Weld Sequencer so that the part can be shifted into a position that is relatively comfortable for the welder. Ideally, if positioned correctly, it optimizes the position of the assembly for weld fume management as well.

“At FABTECH® Atlanta we will be demonstrating a new feature in this product that interacts with the Smart Positioner so that when an operator scans their badge to log in, the sequencer will know that person’s height so that weld placement can be optimized for every operator,” said Jay Latchic, marketing communications specialist at Lincoln.

Basically, this simplified approach to optimizing weld placement for each operator and their position combines process modification/substitution and work practice controls.

“All of this is in aid of helping the welding industry make it to the next level of productivity,” said Ritchot.

Personal Protection

The final level in the hierarchy of controls is personal protection. If personal protection in the form of a PAPR helmet is required, it can make a big difference to the operator if that personal protection is comfortable while effectively protecting him. A number of improvements to PAPR units have been made over the past few years to improve in these areas.

Lincoln Electric, for instance, updated its PAPR unit so that it can be supplied with an extended battery option. It also signals through a sound and a vibration when the battery is low and when the filter requires changing.

Miller’s Bellile noted that some air respirators can supply both hot and cold air to the operator’s face depending on the environment in which they are working. Miller’s newest design, meanwhile, pushes air out to six different areas of the face at once to provide even cooling/heating.

“Personal protection is considered a last resort in terms of the hierarchy of controls for weld fume management, but we think of this in terms of heat stress in the environment as well, and really encourage the use of this equipment if the shop is consistently hot or if you are working in a confined space where oxygen levels and heat may become an issue,” said Bellile. “Productivity can be directly linked to comfort. If people aren’t comfortable, productivity will suffer.”

Editor Robert Colman can be reached at [email protected].

Donaldson Torit, www.donaldson.com

Lincoln Electric Canada, www.lincolnelectric.ca

Miller Electric Mfg. LLC, www.millerwelds.com