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How clean is the air in your manufacturing facility?

Understanding air quality and how to clean it up

Figure 1
Many older manufacturing workers probably expect a haze of cutting and welding fumes to hang over the shop floor, as seen in the top photo, but if the industry expects to recruit a new generation of workers, it will need to provide work environments with better indoor air quality. Proper ventilation can help to clear the air, as the photo at the bottom shows.

Anyone who has been in a metalworking plant knows it can be a dirty place. Welding and other metalworking operations generate not just nuisance debris, but also dangerous pollutants that can pose serious health threats to workers. These pollutants include oil mist, dust, and fumes containing manganese, lead, hexavalent chromium, and other toxic elements.

Those health threats are the primary reason the Occupational Safety and Health Administration (OSHA) monitors metalworking plants and, as the agency does with other industrial workplaces, regulates the quality of indoor air. Like all workplaces, plants must comply with OSHA’s General Duty Clause, which states that each employer “shall furnish to each of his employees … a place of employment which [is] free from recognized hazards that are causing or likely to cause death or serious physical harm to … employees.”

Specific to air quality, industrial operations must comply with air contaminant requirements outlined in 29 CFR 1910 Subpart Z. They also must be aware of other OSHA standards that apply to welding in specific industries. For example, welding, cutting, and heating operations in the shipbuilding industry must comply with ventilation and protection requirements in 29 CFR 1915 Subpart D. Construction operations, meanwhile, must comply with 29 CFR 1926 Subpart D relating to employee exposure to gases, vapors, fumes, dusts, and mists.

Workplaces that don’t comply with these OSHA regulations may be subjected to fines like the almost $350,000 fine issued to a plating company in 2014 for violations that exposed workers to hexavalent chromium.

While compliance with OSHA regulations is mandatory, some metalworking plants may decide to take steps to meet even more stringent indoor air quality (IAQ) guidance. The American Conference of Governmental Industrial Hygienists (ACGIH) suggests a time-weighted average (TWA, measured over an eight-hour shift) threshold limit value (TLV) for respirable manganese particles of 0.02 mg/m3. This means a person should not breathe in more than 0.02 mg/m3 of air containing manganese particles over an eight-hour work period. ACGIH also offers guidelines for inhalable manganese—particulate from grinding activities that can be inhaled into the nose and mouth but are not likely to be inhaled deep into the lungs because of size. This recommended TLV-TWA for inhalable manganese is 0.1 mg/m3.

Indeed, manufacturers have several good reasons to exceed minimum performance standards, but one of the biggest reasons is to provide the safest and healthiest workplace possible to protect employees. Focus on workplace health and safety has increased over recent decades. Baby boomers who long served in the metalworking trades are retiring and being replaced by younger millennial workers, many of whom have quite different notions than their elders of what makes for a good place to work (see Figure 1).

Superior IAQ helps attract and retain employees while keeping them healthier (which means reduced liability and lower workers’ compensation costs for the employer) and more productive. It also can help to attract and retain OEM customers that expect supply chain partners to achieve sustainability targets through responsible manufacturing.

In addition, superior IAQ can improve product yields. For example, in laser welding, too much smoke can diffuse the beam delivery and intensity to the part, possibly affecting overall part quality. With fewer airborne particles to settle on surfaces, including on sensitive electronics and equipment where dust can wreak havoc, superior IAQ helps make facility cleaning and maintenance easier and less costly, keeping the focus on production.

Air Quality Problems: Sources and Effects

Most air quality problems in metalworking plants can be traced to weld smoke and fumes, which vary in their toxicity based on the type of welding process, base metal, filler metals used, and welding rod composition. For example, gas tungsten arc welding (GTAW) produces less fumes than flux-cored arc welding (FCAW) or shielded metal arc welding (SMAW).

Of all the fumes generated in welding, 85 percent comes from the electrode, with particle sizes ranging from 0.1 to 5.0 microns. A good rule of thumb is that for every 1,000 pounds of weld wire used, 10 to 20 lbs. of particles can be generated. During welding, about 1 to 2 percent of the weld-join metal in carbon steel converts to collectable particulate. For welding aluminum, that figure is 6 to 8 percent. Steel particulate tends to be oilier because of upstream processing. Weld fumes also are hot (about 750 to 1,000 degrees F), especially when close to the welding arc, and rise relatively slowly from the weld work zone.

Figure 2
Applications such as welding large and awkward-shaped fabrications are good candidates for portable ventilation products. They can be moved to the point where welding is taking place and easily be repositioned for the next job.

According to OSHA, acute exposure to welding fumes can result in eye, nose, and throat irritation; dizziness; and nausea. Prolonged exposure to welding fumes may cause lung damage and various types of cancer, including lung, larynx, and urinary tract. Health effects from certain fumes may include metal fume fever, stomach ulcers, kidney damage, and nervous system damage. Gases such as helium, argon, and carbon dioxide displace oxygen in the air and can lead to suffocation, particularly when welding in confined spaces. Carbon monoxide gas also can form, posing a serious asphyxiation hazard.

Three airborne hazards common to welding operations are of specific concern:

1. Oil mist is a natural byproduct of metalworking processes and poses slip-and-fall dangers. In addition, exposure to these airborne substances has been shown to cause respiratory illness, allergies, skin ailments, and even cancer.

2. Hexavalent chromium, or Cr(VI), is formed during the welding process from the chromium component found in welding consumables. Cr(VI) fumes are produced when the electric arc hits the shiny metal. The fume is highly toxic and can damage the eyes, skin, nose, throat, and lungs. It also has been linked to cancer.

3. Manganese is a trace element found in virtually all types of welding. It can cause a condition called manganism, which is similar to Parkinson’s disease. In extreme cases, overexposure to manganese fumes can affect the central nervous system and change neuropsychological and neurobehavioral function.

So What Does Clean Look Like?

“Clean” is a subjective term and may mean different things to different facilities. If someone walks into a plant and sees a blue haze around the lights, he or she can surmise quickly that the facility has an air quality problem. But some problems aren’t as easy to spot, which is why manufacturers need to know exactly where their plant stands.

All manufacturing facilities have two physical areas where air quality measurements must be taken: in the worker’s breathing zone and in the facility’s ambient air.

Hiring a third-party inspection firm or industrial hygienist (IH) accredited by the American Industrial Hygiene Association (AIHA) is the best way to measure air quality. The IH sets up monitors throughout the facility and on selected employees. Over an eight-hour period, the monitors gauge air quality. Upon completion of air monitoring, the IH inspects air filters and analyzes their contents. From that, areas of concern can be identified and strategies for fixing problems can begin.

OSHA has established permissible exposure limits (PELs) on a number of toxic elements, with exposure to cadmium and chromium being most restrictive:

  • Cadmium: 0.005 mg/m3
  • Chromium: 0.005 mg/m3
  • Lead: 0.05 mg/m3
  • Nickel: 1.0 mg/m3
  • Manganese: 5.0 mg/m3

The ACGIH has more stringent guidelines related to manganese, with a recommended TLV-TWA of 0.020 mg/m3—about 250 times lower than the OSHA limit. It is widely expected that OSHA will follow the ACGIH recommendations at some point, raising the bar considerably for weld fume control systems.

Figure 3
In this setup, ductwork is used to pull welding fumes and dust from the individual booths to a central collection unit several feet away.

Welding plants need to decide if they simply will meet standard regulations or take the extra steps and go beyond current expectations.

Improving Air Quality

Metalworking plants should take a three-pronged approach to improving their IAQ:

  1. Eliminate or reduce fumes and dangerous particles through process or engineering controls.
  2. Extract fumes and particulates from the breathing air through capture and ventilation systems.
  3. Filter particulates and fumes from any air returned to the facility or discharged outside.

Process and engineering controls may include:

  • Cleaning welding surfaces of any coating that could potentially create toxic residue, such as solvent residue, oil, or paint.
  • Positioning workers to avoid breathing welding fumes and gases.
  • Substituting a lower fume-generating or less toxic welding type or consumable.

Short of using giant fans and opening a plant’s doors to let smoke and fumes escape, manufacturers have many options for extracting fumes, gases, and particulates from the breathing air inside welding operations. Examples include localized units that remove these air pollutants at the source (see Figure 2) and powerful systems that ventilate large, complex processes (see Figure 3). In the case of these systems, one size and one design do not fit all. A well-designed dust collector should integrate every component needed to make it operational: cabinet, motor, blower, control panel, safety features, and filters.

Some localized units mount directly over the welding cell to capture fumes at the source and remove them. Without ductwork, these localized units can be moved with the cell for greater flexibility and less downtime on the plant floor when relocation of the cell is required. Other localized units can be placed on the floor next to the welding cell and connected to the cell with ductwork.

It is crucial that canopies of local exhaust systems fit correctly—with a custom fit if necessary—to contain dirty air properly. A downward airflow reduces air turbulence and significantly reduces re-entrainment or reblowing dust within the collection unit.

Cabinet construction also is important. Seams and joints should be fully welded and engineered to create a perfect seal.

Facility-wide systems are suitable when source capture is not possible (see Figure 4), such as when overhead cranes are used for welding large products. These ambient systems can be placed on the plant roof, with a circuit of ductwork back to the welding cell. The systems need not be big and bulky; compact models are available with fans contained internally, protected from inclement weather and moisture. Such roof-mounted systems eliminate downtime for the plant during installation, maintenance, and filter cleaning and changeouts.

Here are some additional tips for evaluating dust and fume collectors:

  • Consider the welder’s position. If smoke forms a plume behind the welder, the system may extract it by pulling it across the welder’s breathing space, which defeats the system’s purpose.
  • Also consider the difference between manual and robotic welding. The average person can keep the arc on up to 30 percent of the time during a shift. For a robot, that figure rises to 90 percent, meaning more fumes are produced.
  • Make sure you don’t allow open plant doors to overwhelm the system. A moderate breeze moves air at about 700 feet per minute (FPM), which is no match for a fume collection system designed to collect slow-moving welding smoke at 80 to 150 FPM.
  • Beware of electrostatic units. They may effectively collect smoke, but tend not to remove all the particles of the smoke. In turn, those particles get returned to the airflow in the plant and stick to walls, ceilings, and equipment.
  • If a plant processes multiple metals on the same equipment, make sure the ventilation equipment has spark arrester controls and explosion vents to reduce the risk of explosion and fire, especially if paper-based filters are used.
  • To free plant workers for production tasks, look for a ventilation system that can automatically monitor filter performance and track maintenance, ideally through an electronic control panel that allows the system to start and stop instantaneously as a welder or machine operator works.

Effective particulate filtration also is critical for creating a safe, efficient welding environment.

Figure 4
If fabricators elect to go with facility-wide filtration systems instead of localized units attached to individual cells, they often choose to put the collection units outside the building, keeping floor space free for manufacturing activities.

Most modern dust collectors use cylindrical, self-cleaning cartridge filters that can be cleaned by pulse cleaning. In this process, pulses of compressed air are blown periodically outward from the centers of the cylindrical filters. This effectively sheds the accumulated debris, which then falls into a collection bin for easy removal.

A filtration process in which air flows in a downward path is more efficient at air cleaning than a horizontal process. A downward, or vertical, filter design allows for better separation and deposition of larger, heavier particles during pulse cleaning, which reduces the load on the filter cartridge for longer filter life. With horizontal filters, dirt and debris tend to fall off only the bottom two-thirds of the filter, rendering the top of the filter ineffective as it becomes clogged with debris.

Oil mists also affect the cleanability of the chosen filter. Once oil impregnates many filters, they can’t be cleaned by pulse cleaning and must be replaced. If oil mists are present, it’s best to use a filter with media that’s pretreated to resist the gummy smoke and fumes that result from oil and antisplatter solutions.

Filters vary in their filtration efficiencies, depending on the filter media used inside. Be sure to match the filter’s minimum efficiency reporting value (MERV) to the size of particles that the operation generates. In addition to checking a filter’s MERV, also check its efficiency against submicron particles, looking for a 99.99 percent efficiency rating on particles of 0.3 micron. Also remember that some filter media is designed for dry particulates, while other filter media can handle oil mists. Typically, a filter with synthetic media outperforms one made with cellulose media.

Don’t forget to check the filter’s air-to-media ratio. In most welding operations, it should be 2-to-1. Keep in mind that a higher ratio may reduce initial investment, but the filter loads much faster as it struggles to keep up with dust and fumes generated. This requires the filters to be cleaned and/or replaced more frequently. Six months to one year is considered a good, long life for a cartridge filter.

A filter’s filtration media also has an impact on the system’s energy use. Filter media with a higher differential pressure causes your ventilation system to work harder to drive the required air through the unit.

After polluted air is removed from the breathing space and filtered, it needs to be replaced. The best way to do that is by recirculating clean air through the system rather than blowing it outside and drawing make-up air from the outside. This saves both heating and air-conditioning costs and makes for a more comfortable work environment. Additionally, it may help plants avoid Environmental Protection Agency issues because the indoor air is not being released outside.

Final Considerations

When evaluating ventilation and air filtration systems, look at operational costs and performance levels in addition to purchase price and unit cost. Plants may end up paying more in the long run for a seemingly less expensive system.

Also, don’t forget about personal protective equipment, including respirators. These devices may be required to provide adequate worker protection, especially in confined-space welding.

About the Author

Jim Reid

General Manager

37900 Mound Road

Sterling Heights, MI 48310

888-762-6836