Ventilation

The primary control for welding/cutting fumes and toxic gases is appropriate ventilation. Adequate ventilation is when airflow is sufficient to control worker exposure to hazardous welding fumes and gases and exposure limits are not exceeded. OSHA Permissible Exposure Limits (PEL) and ACGIH Threshold Limit Values (TLV) are specific to the metals/gases being used in the welding application. Ventilation selection depends upon workspace volume, workspace configuration, number of welders, welding process and current, consumables used (mild steel, hardfacing, stainless, etc.), allowable levels (TLV, PEL, etc.), material welded (including paint or plating), and natural airflow.

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 advoid exposure provided that:

1. The room or welding area contains at least 10,000 cubic feet (about 22' x 22' x 22') for each welder.
2. The ceiling height is not less than 16 feet.
3. 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.
4. 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.

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.
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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.

OSHA requires this type of ventilation (or supplied air respiratory protection) when welding/cutting in a confined space involving the following substances:

Fluorine compounds (typically in fluxes and rod coatings)

Zinc (zinc-bearing base or filler materials or metals coated with zinc-bearing materials)

Lead (lead-base metals or metals coated with lead-bearing materials such as paint)

Beryllium (beryllium-containing base or filler metals)

Cadmium (cadmium-bearing or cadmium-coated base metals)

Mercury (metals coated with mercury-bearing materials, including paint)

Cleaning compounds (possible toxicity or flammability hazard)

Degreasing (chlorinated hydrocarbons)

Stainless steels (oxygen cutting using either a chemical flux or iron powder or gas-shielded arc cutting)

For assistance with selection of proper ventilation methods, contact EHSS at 231-5985.