This section comes from Lincoln Electric's Arc Welding Safety Brochure on Lincoln Electric's website.
There are many methods which can be selected by the user to provide adequate ventilation for the specific application. The following section provides general information which may be helpful in evaluating what type of ventilation equipment may be suitable for your application. When ventilation equipment is installed, you should confirm worker exposure is controlled within applicable OSHA PEL and/or ACGIH TLV. According to OSHA regulations, when welding and cutting (mild steels), natural ventilation is usually considered sufficient to meet requirements, provided that:
- The room or welding area contains at least 10,000 cubic feet (about 22' x 22' x 22') for each welder.
- The ceiling height is not less than 16 feet.
- Cross ventilation is not blocked by partitions, equipment, or other structural barriers.
- Welding is not done in a confined space.
Spaces that do not meet these requirements should be equipped with mechanical ventilating equipment that exhausts at least 2000 cfm of air for each welder, except where local exhaust hoods or booths, or air-line respirators are used.
Important Safety Note:
When welding with electrodes which require special ventilation such as stainless or hardfacing (see instructions on container or MSDS) or on lead or cadmium plated steel and other metals or coatings which produce hazardous fumes, keep exposure as low as possible and below exposure limit values (PEL and TLV) for materials in the fume using local exhaust or mechanical ventilation. In confined spaces or in some circumstances, for example outdoors, a respirator may be required if exposure cannot be controlled to the PEL or TLV. (See MSDS and Supplement 3 of this brochure.) Additional precautions are also required when welding on galvanized steel.
Source Extraction Equipment
Mechanical ventilation is an effective method of fume control for many welding processes. Because it captures fume near the arc or source of the fume, which is more efficient in most cases, local exhaust, also called "source extraction", is a very effective means to control welding fume.
Source extraction of welding fumes can be provided by mobile or stationary, single or multi-station, exhaust and/or filtration equipment designed with adjustable fume extraction arms nozzles or guns, by fixed enclosures, booths or tables with extraction canopies also known as down-draft, or by back-draft or cross-draft tables/booths. Source extraction of weld fume falls into two categories: low vacuum/high volume, or high vacuum/low volume.
Low Vacuum/High Volume
Mobile or stationary, single or multi-station, large centralized exhaust and/or filtration equipment designed with adjustable fume extraction arms are usually low vacuum/high volume systems. When correctly positioned, the capture rate of adjustable fume extraction arms is suitable for all position welding and cutting. For more difficult to reach work areas, flexible hose may be used in place of adjustable fume extraction arms.
These arms generally move between 560 and 860 cubic feet per minute (CFM) (900 – 1400 m3/hr) 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 placed 6 to 15 inches (160 – 375 mm) away from the arc and still effectively capture weld fume.
Fume extraction arms generally use a 6 or 8 inch diameter hose, or hose and tubing combinations. Arm 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.
In general, the farther the extraction hose is from the arc, the more volume of air movement is required to effectively capture welding fume. Overhead hoods (canopies), for example, capture most of the fume, but care must be taken to be sure fume is not pulled through the breathing zone of the operator.
Fixed enclosures, booths or tables with extraction canopies also known as down-draft, back-draft or cross-draft booths/tables are a variation of overhead hood technology and can be used as source extraction equipment. A booth is a fixed enclosure that consists of a top and at least two sides that surround the welding operation. These systems use a plenum with openings to the side, back or bottom of the work space rather than above it to capture the weld fume. The weld fume is extracted through the plenum and away from the breathing zone of the operator that is welding or cutting. Down-draft or backdraft booths/tables can be mobile or stationary, single or multistation, exhaust and/or filtration systems. They are particularly suitable for in-position bench welding or cutting jobs and can be effective when small parts are being welded. The airflow required for effectiveness varies depending upon the installation design, but may be 1,000 CFM or higher.
There are advantages and limitations associated with low vacuum/high volume source extraction systems.
|Source extraction with large volume of air being extracted from welder breathing zone.||If not using filtration unit, exhausting air to outside requires make-up air systems and make-up heaters (ie. large volumes of displaced air need to be replaced, resulting in increased utility costs).|
|Auto-stop delay assists with removal of residual fumes.||Welder must stop to reposition arm over weld area(s).|
|Low noise level.||Filtration systems larger due to volume of air flow.|
|Flexible arm for repositioning.||Depending on design, ductwork can be large.|
|Low installation costs (ductwork).|
|Low energy consumption (small fan unit with low rpm).|
|Adjustable arms suitable for all position welding.|
High Vacuum/Low Volume
High vacuum/low volume fume extraction systems are designed for close proximity (2 to 4 inches) positioning. High vacuum/low volume weld fume extraction is achieved with lower airflow rates than those encountered when utilizing low vacuum/high volume systems. There are two methods of high vacuum extraction: welding guns with built-in extraction (fume extraction guns), or separate suction nozzles of various designs.
Fume extraction guns
Use fume capture nozzles built into the gun tube and handle. The extraction airflow is approximately 35 to 60 CFM (60 – 100 m3/hr) for integrated fume extraction guns. Therefore, no repositioning is required, since the suction automatically follows the arc. The vacuum level is high (40 to 70 inches WG [9.96 X 103 to 1.74 X 104 Pascal]) permitting the use of hose featuring longer lengths (10 to 25 feet) and smaller diameters (1.25 to 1.75 inches). Fume extraction gun designs have been improved to be more ergonomic and user friendly. Depending upon the type of welding, particularly "in position" welding, extraction guns may be a good solution.
Suction nozzles are positioned near the weld, and commonly use capture distances of less than four inches. Depending upon the design, airflow of suction nozzles is typically between 80 to 100 CFM (135 – 170 m3/hr). Suction nozzles must be kept near the arc to be used effectively. The capture rate for fume extraction guns or nozzles is highest when used in flat and horizontal welding positions. High vacuum equipment ranges from small, portable, mobile units to stationary, single or multi-station, large centralized filtration systems.
There are advantages and limitations associated with high vacuum/low volume source extraction systems.
|When using a fume extraction gun, welder does not need to stop and reposition extraction device.||Required when using a suction nozzle. Welder may need to stop to reposition extraction device.|
|Low volume of air is displacedresults in energy efficiency and conservation.||High noise level due to increased air velocity and high motor rpm of the fan unit.|
|Ductwork smaller in diameter (3 to 10 inches) vs. low vacuum systems.||Possible removal of shielding gases affecting weld integrity if nozzle or gun placed too close to source.|
|Low obstruction of welder vision.||Greater energy consumption (large fan unit with high rpm).|
|Suitable for heavier particulate (ie. grinding dust).||Residual fumes not extracted.|
|Suitable option for confined, difficult to reach work spaces.||Less effective in out-of-position welding.|
|Smaller filter systems due to less volume of airflow.|
Fume extraction is only one component in reducing welding fume. Users should also consider the selection of the welding process, welding procedure, or consumable. Many times a combination of fume extraction, training, process change, and/or consumable change is needed to reduce the amount of fume to acceptable levels. Solutions to a particular application may involve one or all of these factors and the user must determine which solution best fits their application.
OSHA regulations include specific requirements for exhaust systems which should be reviewed when selecting fume extraction systems.
Exhaust vs. Filtration
Source extraction exhaust equipment captures and extracts weld fumes from the source and exhausts the fumes to the outside atmosphere. This technique removes welding fume from the breathing zone of the welder but can also displace large volumes of conditioned air which may lead to increased utility and heating costs.
Source extraction filtration equipment captures and extracts weld fumes from the source and filters the fumes by passing them through a cellulose and/or polyester filter cartridge or electrostatic filter. Depending on the weld application, environment, federal or local regulations, and filtration efficiency levels, filtered air may be re-circulated back into the facility or exhausted to the outside atmosphere. By re-circulating filtered air back into the work environment compared to exhausting to the outside, source extraction filtration equipment can be more economical to operate. Particularly in winter months, substantially lower heating costs may be recognized, as less replacement air is required with filtration versus exhaust systems.
Using a cellulose or polyester filter cartridge or electrostatic filter will depend upon the weld application. Electrostatic filters may also be used however, they lose efficiency if they are not frequently washed.
Regardless of the type of mechanical ventilation (exhaust or filtration) source extraction system used, the important factor is that it is a tool designed to control exposure to welding fume and its constituents. All forms of mechanical ventilation or source extraction equipment require routine maintenance. In addition, when using weld fume source extraction equipment, sparks from welding, cutting or grinding processes can cause fire within the equipment. To control this potential fire hazard, operation, service and maintenance instructions for source extraction equipment should be followed.
It is the equipment owner and operator’s responsibility to comply with Occupational Safety, Health Administration (OSHA) Permissible Exposure Limits (PELs) or American Conference of Governments Industrial Hygienists (ACGIH) TLVs for welding fume. It is the responsibility of the equipment owner to research, test and comply with regulations which may apply to filtered air recirculated inside the facility or unfiltered air is exhausted outside of the facility.