A welding ventilation overview
All welding and thermal cutting operations carried on in confined spaces must be adequately ventilated to prevent the accumulation of toxic materials, combustible gases, or possible oxygen deficiency.
For processes such as welding, brazing, soldering, and torch cutting, the primary purpose of ventilation is to remove air contaminants from the worker’s breathing zone. Different ventilation strategies may be needed in each case to remove air contaminants from the welder’s breathing zone.
Ventilation is used for three general purposes:
- Remove air contaminants from a worker’s breathing zone and work area,
- Prevent the accumulation of flammable or combustible gases or vapors; and,
- Prevent oxygen rich or oxygen deficient atmospheres.
Monitoring instruments should be used to detect harmful atmospheres. Where it is impossible to provide adequate ventilation, air-supplied respirators or hose masks approved for this purpose must be used.
In these situations, lookouts must be used on the outside of the confined space to ensure the safety of those working within. Requirements in this section describe standards established for arc and gas welding and cutting.
A certified industrial hygienist should be consulted to understand the correct approach for your specific situation
Whenever ventilation is used as a means of worker protection, the ventilation system should be used and maintained in accordance with acceptable procedures.
Where ventilation alone cannot adequately protect the welder, personal protective equipment (respirators) may also be used. Select the appropriate respirator according to the hazards present, any applicable legislation, and/or to the CSA standard Z94.4 Respiratory protection.
Factor keep in mind when selecting ventilation
Ventilation selection depends upon:
- Workspace volume
- Workspace configuration
- Number of welders
- Welding process and current
- Consumables used (mild steel, hard facing, stainless, etc.)
- Allowable levels (tlv, pel, etc.)
- Material welded (including paint or plating)
- Natural airflow
Different Types of Ventilation
Ventilation strategies fall into three general categories:
- Natural Dilution Ventilation (least effective)
- Mechanical Dilution Ventilation
- Local Exhaust Ventilation (most effective)
1. Natural Ventilation
Natural ventilation is the movement of air through the workspace caused by natural forces. Outside, this is usually the wind. Inside, this may be the flow of air through open windows and doors.
According to OSHA regulations, when welding and cutting mild steels, natural ventilation is usually considered sufficient to avoid exposure 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. Note: When welding must be performed in a space entirely screened on all sides, the screens shall be so arranged that no serious restriction of ventilation exists. Screens should be mounted so that they are about 2 feet above the floor (unless work is performed at a low level and the screen must extend to the floor to protect nearby workers from welding glare.
- 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 2,000 cfm of air for each welder, except where local exhaust hoods or booths, or air-line respirators are used.
2. Mechanical Ventilation
Mechanical ventilation is the movement of air through the workspace caused by an electrical device, such as a portable fan or permanently mounted fan in the ceiling or wall.
The minimum flow rate shall be 2,000 cfm per welder, except where local exhaust hoods and booths or airline respirators are provided and used. According to OSHA 29 CFR 1910.252(c), the following spaces require mechanical ventilation:
- In a space of less than 10,000 cubic feet (about 22′ x 22′ x 22′) per welder.
- In a room having a ceiling height of less than 16 feet.
- In confined spaces, or where the welding space contains partitions, balconies, or other structural barriers to the extent that they significantly obstruct cross ventilation.
3. Local Exhaust Ventilation
Source extraction or local exhaust ventilation (LEV) is a mechanical device used to capture welding fumes at or near the arc and filters contaminants out of the air. LEV is the most effective means of removing contaminants from the welder’s breathing zone. LEV devices must be capable of maintaining a velocity of 100 fpm toward the air intake.
Examples of Local Exhaust Ventilation:
- Downdraft Bench. A downdraft bench has an open grid work surface. Air is drawn downward through the grid, drawing contaminants into exhaust ducting. Air speed must be great enough to prevent contaminants from accumulating and rising into the breathing zone. If workpieces are too large, they may block the ventilation airflow or cause pockets of high velocity air (which could affect shielding gases).
- Moveable Hood. Flexible ducting allows the capture hood to be moved where required. Provide an air velocity of at least 100 ft/min (0.5 m/s) across the welding arc. Place the hood as close as practical to the work. The optimal location for the hood is about 1 duct diameter from the arc.
- Fume Extraction Welding Guns. The contaminants are removed very close to the source of generation and are drawn through a hose into the exhaust system. They can be very effective on flat and vertical surfaces or in corners and around flanges.
Ventilation For Fluorine Compounds
In confined spaces, welding or cutting involving fluxes, coverings, or other materials in which fluorine compounds shall be done in accordance with paragraph 2-4 h, ventilation in confined spaces.
A fluorine compound is one that contains fluorine as an element in chemical combination, not as a free gas.
Maximum allowable concentration.
The need for local exhaust ventilation or airline respirators for welding or cutting in other than confined spaces will depend upon the individual circumstances.
However, experience has shown that such protection is desirable for fixed-location production welding and for all production welding on stainless steel.
When air samples taken at the welding location indicate that the fluorides liberated are below the maximum allowable concentration, such protection is not necessary.
Zinc Welding Ventilation in Confined spaces in confined spaces, welding or cutting involving zinc-bearing filler metals or metals coated with zinc-bearing materials shall be done in accordance with regulations on ventilation in confined spaces.
Indoors, welding, or cutting involving zinc-bearing metals or filler metals coated with zinc-bearing materials shall be done in accordance with local exhaust ventilation regulations.
In confined spaces, welding involving lead-based metals (erroneously called lead-burning) shall be done in accordance with guidelines on ventilation in confined spaces.
Indoors, welding involving lead-based metals shall be done in accordance with guidelines on local exhaust ventilation.
Local ventilation in confined spaces or indoors, welding or cutting involving metals containing lead or metals coated with lead-bearing materials, including paint, shall be done using local exhaust ventilation or airline respirators.
Outdoors, such operations shall be done using respiratory protective equipment approved by the US Bureau of Mines, National Institute of Occupational Safety and Health, or other government-approved testing agencies.
In all cases, workers in the immediate vicinity of the cutting or welding operation shall be protected as necessary by local exhaust ventilation or airline respirators.
Welding or cutting indoors, outdoors, or in confined spaces involving beryllium-bearing material or filler metals will be done using local exhaust ventilation and airline respirators.
This must be performed without exception unless atmospheric tests under the most adverse conditions have established that the workers´ exposure is within the acceptable concentrations of the latest Threshold Limit Values (TLV) of the American Conference of Governmental Industrial Hygienists or the exposure limits established by Public Law 91-596, Occupational Safety and Health Act of 1970.
In all cases, workers in the immediate vicinity of the welding or cutting operations shall be protected as necessary by local exhaust ventilation or airline respirators.
General. Welding or cutting indoors or in confined spaces involving cadmium-bearing or cadmium-coated base metals will be done using local exhaust ventilation or airline respirators.
Outdoors, such operations shall be done using respiratory protective equipment such as fume respirators, approved by the US Bureau of Mines, National Institute of Occupational Safety and Health, or other government-approved testing agency, for such purposes.
Confined space. Welding (brazing) involving cadmium-bearing filler metals shall be done using ventilation as prescribed in the paragraph above on local exhaust ventilation, and ventilation in confined spaces, if the work is to be done in a confined space.
Welding or cutting indoors or in a confined space involving metals coated with mercury-bearing materials, including paint, shall be done using local exhaust welding ventilation or airline respirators.
Outdoors, such operations will be done using respiratory protective equipment approved by the National Institute of Occupational Safety and Health, US Bureau of Mines, or other government-approved testing agencies.