Metal fabrication: why the welders are rarely one exposure group

Fabrication shops are where the most common air monitoring mistakes are made. The work itself is not unusual. The trouble is that “the welders” get treated as a single similar exposure group (SEG), meaning workers who do the same job the same way, when they are usually four.

Welding fume is not one substance

Welding fume is a mixture, and which components matter depends on what you weld and what you weld it with.

• Manganese is in nearly all steel filler metals, and it is the component that should concern you most, as the next section explains.
• Hexavalent chromium shows up on stainless and high-alloy work and mostly does not on mild steel. The same welder in the same booth with a different wire or rod has a completely different exposure and falls under a different OSHA standard.
• Nickel and iron oxide
• Ozone and nitrogen dioxide on aluminum welded with gas metal arc welding (GMAW)
• Zinc on galvanized metal
• Cadmium in some silver solders
• Fluorides from flux-cored electrodes and shielded metal arc welding (SMAW) electrodes

→ Welding fume air monitoring · Hexavalent chromium air sampling

The manganese gap

OSHA's permissible exposure limit (PEL) for manganese fume is 5 milligrams per cubic meter of air (mg/m³), a ceiling limit on total dust and fume that was set in 1971. A ceiling limit must not be exceeded at any time.

ACGIH, the professional body that publishes the threshold limit values (TLVs), adopted its current TLV of 0.02 mg/m³ in 2013. That value is an 8-hour time-weighted average (TWA) for the respirable fraction, the finest dust that reaches deep into the lungs.

That is a ratio of 250 to 1. Even on a like-for-like comparison, against ACGIH's inhalable TLV of 0.1 mg/m³, the gap is still 50 times. The NIOSH recommended exposure limit (REL) sits in between, at 1 mg/m³ as a shift average.

A shop can demonstrate compliance with the OSHA limit and still expose welders well above every current health-based limit, and the harm at stake is to the nervous system. Sampling against both limits costs exactly the same, because it is the same filter and the same laboratory analysis.

→ OSHA PELs and ACGIH TLVs compared

Exposure groups among welders in a fab shop

Treating welders as a single exposure group is where air monitoring in fabrication shops most often goes wrong. These are the factors that actually separate them:

• Process. Gas metal arc (GMAW), gas tungsten arc (GTAW), shielded metal arc (SMAW) and flux-cored arc (FCAW) welding generate very different amounts of fume, and flux-cored is generally the highest.
• Base and filler metal. Whether the work is stainless or mild steel determines whether you have a hexavalent chromium problem at all.
• Position and confinement. Welding inside a vessel is a different exposure from welding at an open bench with the same wire or rod.
• Time on the arc. A fitter who welds 90 minutes a day and a production welder with 6 hours of arc time do not belong in one group.
• Ventilation. A booth with a working local exhaust hood is not the same as a fan pointed in the general direction.

→ How many air samples do you actually need?

The article exemption trap in TRI reporting

The Toxics Release Inventory (TRI) is the annual toxic chemical release report filed with EPA, and fabrication shops are the facilities most likely to claim its article exemption incorrectly.

To qualify, an “article” must not release a listed chemical under normal conditions of processing or use. If machining, grinding, cutting or welding the item generates dust, fume or fines, article status is at risk.

EPA allows a narrow margin: if total releases from all like items are 0.5 pounds or less per year, the items keep article status. Above that line the exemption fails for that item entirely, and the whole amount of the chemical in the item counts toward your threshold, not only the part released.

That lopsided rule is what makes the mistake expensive, because a few pounds of release can pull tons of chemical into your threshold determination.

→ Do you have to file a Form R?

The rest of the shop

• Noise. Grinding, plasma and air tools routinely put fabrication shops above the 85 decibel (dBA) action level for noise.
• Respirable silica in abrasive blasting, depending on the blast media.
• Solvents in degreasing and parts washing.
• Isocyanates if you spray polyurethane coatings.

Most of this can be measured in one or two days on site if the survey is planned properly. An air monitoring survey covers the airborne exposures, and a noise survey covers the noise exposure of each job.