More Information On Controlling Welding Fume, A Total Systems Approach
Tom Pumphrey, Production Manager, Environmental Systems, The Lincoln Electric Company, Cleveland, Ohio, May, 1998.

Fume Extraction Technology

The one method of fume control effective for almost any welding process is ventilation. Since the operator's breathing zone is the critical area, localized ventilation, usually called "fume extraction," is the preferred method. Fume extraction technology falls into two categories: low vacuum/high volume, or high vacuum/low volume.

Low Vacuum/High Volume

Regular building ventilation systems are low vacuum, high volume systems, sometimes called "low static, high flow." When industry needed better ventilation solutions, many companies modified low vacuum systems for localized ventilation. Hoses 6 to 9 inches (160 - 200 mm) in diameter were added for flexibility and eventually structures were designed to support the hoses and make it easier to position them. Manufacturers began to make these arms with different designs and features, and they are still used in many industries, including the welding industry.

The articulated arms generally move between 600 and 900 cubic feet (900 - 1500 m3/hr) per minute (CFM) of air, but use low vacuum levels (3 to 5 inches water gauge [750 - 1250 Pa]) to minimize power requirements. Water gauge (WG) is a measure of negative pressure: higher numbers mean more negative pressure (more "suction"). With this volume of airflow, the end of the arm can be generally 10 to 15 inches (250 - 375 mm) away from the arc and still capture the fume. Articulated fume extraction arms are produced by a wide range of manufacturers, using 6 inch or 8 inch hose, or hose and tubing combinations. Lengths are typically 7, 10, or 13 feet (2, 3 or 4 m), with boom extensions available. The arms may be wall mounted, attached to mobile units, or incorporated into a centralized system.

For greater capture distances, a larger volume of air is required to achieve the necessary "capture velocity" and capture the fume. In practice, however, longer capture distances may mean that breathing zone exposure is compromised. Overhead hoods, for example, capture most of the fume, but only after it has passed through the breathing zone of the operator.

Cross draft ventilation is a variation of overhead hood technology. These systems use a plenum with openings to the side of the work space, rather than above it. Therefore, the fume moves sideways, away from the operator's breathing zone. These systems can be effective for small booths when small parts are being welded. The CFM required for effectiveness varies depending upon the installation design, but frequently can be 1,000 CFM or higher.

There are, however, certain disadvantages associated with the low vacuum systems. For example, in systems incorporating articulated fume extraction arms, the operator must stop to reposition the arm over each weld area, which diminishes productivity. These arms also have limited reach, commonly 10 to 13 feet. The high volume of air flow requires large hoses, and ductwork ranging from 8 to 36 inches in diameter or more, depending upon the installation. Exhausting air outside often requires make-up air systems and make-up air heaters. Filtration systems are large due to the high air volume being processed.

High Vacuum/Low Volume

High vacuum/low volume fume extraction systems are much more specific to point-source applications such as welding. Their chief advantage: they remove the fume directly at the source, within inches of the arc. This means that fume is captured before it can reach the operator's breathing zone or disperse into the room. Because of the close proximity to the source, fume extraction can be achieved with lower airflow rates, typically 80 to 100 CFM for suction nozzles, depending upon the design, and 35 to 60 CFM for integrated fume extraction guns. The vacuum level is high (40 to 70 inches WG), permitting the use of hose featuring longer lengths (10 to 25 feet) and smaller diameters (1.25 to 1.75 inches). High vacuum equipment ranges from small, portable units to mobile three-phase systems, to large, centralized systems.

There are two methods of high vacuum extraction: welding guns with built-in extraction, or separate suction nozzles of various designs. (Photo.) Suction nozzles are positioned near the weld, typically with magnets, and commonly use capture distances of less than four inches. Fume extraction guns use fume capture nozzles built into the gun tube and handle. Therefore, no repositioning is required, since the suction automatically follows the arc.

High vacuum extraction, like other solutions, has its limitations. Although manufacturers have greatly improved designs, fume extraction guns are larger than regular welding guns. Furthermore, fume guns do not control residual fume and smoke, since the gun is moved away immediately after welding is completed. Finally, unless they are set in weld fixtures, high vacuum suction nozzles also require repositioning.

Nevertheless, high vacuum/low volume methods of fume extraction offer significant advantages to welding fabricators. Of chief importance is the removal of fume right at its source, before it can reach the operator's breathing zone. Since fume guns eliminate the repositioning required by articulated arms or suction nozzles, productivity is not directly reduced.

Many other advantages come from reducing the total amount of airflow required. A lower volume of air means smaller ductwork, smaller hoses, much smaller filter systems, and less strain on make-up air systems if the air is exhausted outside. This translates into lower material, installation and maintenance costs. A typical low vacuum system for twenty stations, for instance, might require an airflow rate of 12,000 CFM, whereas a high vacuum system serving the same facility could require an airflow rate as low as 1,200 CFM.


After fume is removed from the source, it is either exhausted directly to the atmosphere or is passed through an electrostatic or cartridge filter. Because electrostatic filters lose efficiency if they are not frequently washed, the welding industry primarily uses more easily maintained cartridge filters. Most cartridge filters have a high efficiency level, usually 98% or higher. Although cartridges classified as "HEPA" have extremely high efficiency when new, they are expensive and have shorter life. HEPA filters are normally not necessary in fume extraction equipment, since capture efficiency has a much greater impact on breathing zone exposure than filtration efficiency.
CommentAuthorRobCommentTimeNov 22nd 2009
More Information on Controlling Welding Fume, A Total Systems Approach
Tom Pumphrey, Production Manager, Environmental Systems, The Lincoln Electric Company, Cleveland, Ohio, May, 1998.

Regulatory Bodies

Two major types of organizations study and regulate exposure to welding fume and other particulates in the workplace: industrial health organizations, and government regulatory agencies. In the U.S., two major industrial health organizations are the American Conference of Governmental and Industrial Hygienists (ACGIH) and the National Institute of Occupational Safety and Health (NIOSH). They set exposure limits for a variety of materials, including those found in welding fume. The ACGIH calls their limit the Threshold Limit Value (TLV). The TLV is influential in industry and is a standard followed by most insurance companies. As important as the TLV is, however, it is not enforceable by law. The Occupational Safety and Health Administration (OSHA) is the only organization that can establish legally enforceable limits for exposure to chemicals in the workplace. At both state and federal levels, OSHA's mandatory Permissible Exposure Limits (PEL) place tough demands on the welding industry.

Exposure Limits

The limits for fume exposure set by OSHA and others are measured in milligrams of particulate per cubic meter of air (mg/m3). The total amount of fume produced is not limited, but rather the concentration of fume is limited. During facility testing, a sampling device is placed in the breathing zone of the operator (e.g., the welding hood, not on the lapel). At the end of the operator's shift, a number is calculated that reflects an 8-hour Time Weighted Average (TWA) of the fume concentration in the operator's breathing zone, in mg/m3.

Since this method focuses on breathing zone exposure, the results are highly unpredictable, even when the process, procedure and other influences are consistent. Therefore, to ensure compliance with exposure limits, companies should test their own operators while they are welding in everyday applications to obtain an accurate concentration value. The results can then be compared to benchmarks such as the TLV or PEL. If the number is higher than the standard, then that company is out of compliance.

Listed in Table 1 are the current welding fume exposure limits as specified by OSHA and ACGIH. Note that the table does not contain a PEL for total welding fume. The PEL of 5 mg/m3 established in 1989 was challenged in a lawsuit, and is no longer enforced.

Exposure Guidelines for Materials Sometimes Found in Welding Fume
Table 1.
Exposure Guidelines for Materials Sometimes Found in Welding Fume
Welding Fume ACGIH(1)
TLV (mg/m3)
PEL (mg/m3)
5.0 ..
Iron Oxide, as Fe 5.0 10.0
Manganese (all forms 0.2 1.0(3) 5.0 (c)
Chromium III compounds 0.5 0.5
Chromium VI compounds, sol 0.05 0.05 (c)
Chromium VI compounds, insol 0.01 0.5 (c) NIC.0005 - .005
(both forms)
Nickel, insol compounds, as N (1.0) 0.5 NIC 1.0
Aluminum, Welding Fumes, as Al 5.0 ..
Zinc Oxide, fume 5.0 10.0 (c) 5.0
Barium compounds, sol, as Ba 0.5 0.5
Beryllium & compounds, as Be 0.002 .01(c) 0.002 .005(c)
Cadmium Oxide, as Cd 0.002 0.005
Cobalt oxide, as Co 0.02 0.1
Copper fume, as Cu 0.2 0.1
Flourides, as F 2.5 2.5
Magnesium oxide fume 10.0 15.0 total particulate
Molybdenum, insol compounds, as Mo 10.0 15.0 total particulate
Tin oxide 2.0 2.0
Vanadium pentoxide, as V2O5 0.05 0.1(c)

Manganese and chromium are two examples of materials which have strict time exposure limits as well. When limits are measured on an 8-hour TWA, an operator may be exposed to high concentrations in the morning, but the facility may still be in compliance if concentrations are lower in the afternoon. The limits for certain forms of chromium are "ceilings," meaning that any overexposure during the day will cause the facility to fail compliance.
Welding Fume Exhaust Systems

The following is a helpful guide in helping design an efficient and reliable welding fume exhaust system. Our design criteria follows that of The American Conference of Governmental Industrial Hygienists and some of the following are excerpts from the ACGIH Manual of Recommended Practice 22nd Edition as well as clips from various Welding Journal magazine articles.

Engwald is proud to be a member of the newly formed N.A.O.V.E.R.M. National Association of Vehicle Exhaust Removal Manufacturers, which has as one of its goals, the development of standards and specifications for the industry and to present them to other national organizations such as BOCA and ASHRAE.

Studies have compared the lungs of heavy duty welders without proper ventilation, to lungs of people who smoke. The findings were that these welders had the lungs of people who smoke about 25 Cigarettes a day.

A common problem with general ventilation systems in regards to welding fumes is that welding smoke particles stay in the air a lot longer than grinding particles (therefore, a larger spread throughout the workplace). For example, it takes 4 hrs. for a welding smoke particle to hit the floor from a height of 3 ft. whereas, it takes only 3 min. for a grinding particle from the same height.

All of Engwalds' fume exhaust systems are based on the principal of Source Capture, in other words, capturing the contaminant as close to its source as possible, thereby not allowing it to get into the general atmosphere where the worker can breath it in. The main objective is to keep the welder's breathing area as clean as possible. Welding smoke consists of fine particles and gases, which spread at a relatively low speeds from the point of welding and are fairly easy to capture, so why not capture them at the source.

Design Guidelines:

The ACGIH Manual defines Capture Velocity as the minimum hood-induced air velocity necessary to capture and convey a contaminant. It offers the following table:

Condition of Dispersion Containment Example Capture Velocity, fpm
Released with practically no velocity into quiet air. Evaporation tanks,degreasing 50-100
Released at low velocity into moderately still air. Spray booths, container filling, welding, plating, pickling 100-200
Active generation into zone of rapid air motion. Spray painting in shallow booth, barrel filling, conveyor loading 200-500
Released at high initial velocity into zone of very rapid air motion. Grinding, abrasive blasting,tumbling. 500-2000

The formula used for converting this capture velocity to required cfm is:

Q = V(5X2 + A) where.

Q= Required Exhaust Air Flow, cfm.
X= Distance From Hood Face To Point Of Contaminant Release, Feet.
A= Hood Face Area, Sq. Ft.
V= Capture Velocity, fpm, T Distance X.

Using this formula for various hose sizes, we come up with the following cfm requirements for cone shaped hoods. (Assuming a face velocity of 1500 fpm and a distance of 9-12 inches from the source.

Condition of Dispersion Containment Example Capture Velocity, fpm
Released with practically no velocity into quiet air. Evaporation tanks,degreasing 50-100
Released at low velocity into moderately still air. Spray booths, container filling, welding, plating, pickling 100-200
Active generation into zone of rapid air motion. Spray painting in shallow booth, barrel filling, conveyor loading 200-500
Released at high initial velocity into zone of very rapid air motion. Grinding, abrasive blasting,tumbling. 500-2000

NOTE: These are suggested airflows for welding fumes only. Applications such as dust or grinding collection require higher airflow and capture velocities.

The Engwald Fume Exhauster Line

Our fume exhaust line is comprised of two main components, counterbalanced fume arms and suspended flexible hoses with magnetic suction hoods that sit directly on the welding surface. Both types are available as stationary mounted portable units.

The counterbalanced stationary mounted fume arms are our W-200, W-300, and W-600 Series in 4", 5", and 6" diameters respectively. The W-200 and 300 Series are available in 9 ft, 12 ft, and 15 ft. models and the W-600 Series comes in 5 ft, 7 ft, 10 ft, and 14 ft. models. all types can be either wall or ceiling mounted and can have direct mounted fans.

Special W-800 series fume arms with 8" hose available on request.

The W-400 Series are our suspended flex hose models with aluminum suction hood, magnetic base with screen and swivel. These units are designed to be used where a counterbalanced arm assembly may not be feasible perhaps because of tight quarters. These units are available in 4" thru 12" diameter models with a standard hose length of 10 ft. Customized hose lengths and diameters are also available.

We also manufacture a line of portable and stand type fume exhausters perfectly suited to eliminate smoke, fumes and toxic gases from confined spaces.

The Engwald Series W-200-75 Welding Booths control fumes, smoke and flashes from arc and acetylene gas welding by the use of high velocity suction. These welding booths are ideal in the training of students in welding techniques without exposing students to dangerous fumes and toxic gases. We offer a wide variety of booth sizes to suit many applications such as Schools, Machine Shops and Manufacturing Plants.