Welding fume: sampling for what is actually in it

This page explains what the rules and common practice call for. Every site is different, and what a survey or a filing needs at your facility is something we work out with you after we see it.

Welding fume is not one substance but a mixture, and which constituents matter depends on what you weld and what you weld it with.

That is why “we sampled for welding fume” means nothing on its own, and why quotes for the same shop vary so widely. The question is always: fume containing what?

What is actually in it

The manganese gap

This is the part of the welding fume rules that catches people off guard, and it deserves a plain explanation.

The OSHA permissible exposure limit (PEL) for manganese fume is 5 milligrams per cubic meter of air (mg/m³). It is a ceiling limit on total particulate, set in 1971. A ceiling limit must not be exceeded at any time, and total particulate means all the airborne dust and fume.

ACGIH is the professional body that publishes the threshold limit values (TLVs), which are recommended limits.

The current ACGIH TLV is 0.02 mg/m³, as an 8-hour time-weighted average (TWA) of the respirable fraction of the fume. The respirable fraction is the finest particles, the ones that reach deep into the lungs. ACGIH adopted this TLV in 2013, and the limit the year before was 0.2 mg/m³.

Set OSHA's 5 mg/m³ against ACGIH's 0.02 mg/m³ and the ratio is 250 to 1.

Those two numbers measure different things, so compare them with care. One is a ceiling on total particulate at any single moment, and the other is an 8-hour TWA of the respirable fraction.

The closest match is a better comparison. ACGIH has an inhalable TLV of 0.1 mg/m³, which covers all the particles a person can breathe in through the nose or mouth. Set that against OSHA's 5 mg/m³ and the gap is still 50-fold.

The NIOSH recommended exposure limit (REL) is 1 mg/m³ as a full-shift TWA, with a 3 mg/m³ short-term exposure limit (STEL). That sits between the other two and well below OSHA's number.

However you frame the comparison, the conclusion holds. A welding shop can meet the OSHA PEL comfortably, and be able to prove it, while still exposing welders to many times the level that every current health-based limit treats as protective.

The health effect behind the ACGIH change is harm to the nervous system, a Parkinson's-like illness caused by manganese, and the research behind it is not thin.

We are not going to tell you what to do with that, but we will tell you three things:

1. It is the gap most likely to lead to a General Duty Clause citation. OSHA can and does use the General Duty Clause where a recognized hazard exists and a feasible means of abatement is available, even where the PEL is met. A documented gap of this size, across ACGIH and NIOSH, is about as clear a record of a “recognized hazard” as exists.
2. It is the gap most likely to lead to an injury lawsuit. “We met the 1971 limit” is a weak position when the current health-based limit came out in 2013 and is widely known.
3. Sampling to both limits costs the same. The lab work is identical, with the same filter and the same analytical run, and what differs is which number you compare the result against. Knowing where you stand against the ACGIH TLV tells you a great deal.

How we sample welding fume

The cyclone ahead of the filter is what lets only the respirable fraction reach it.

Note what that table means. You cannot get a set of metals and a fume weight from the same filter. The metals method, NIOSH 7300, uses a mixed cellulose ester filter, while methods 0500 and 0600 are gravimetric and need a pre-weighed PVC filter. Hexavalent chromium needs its own filter again.

If you want all three on one welder, that means more than one pump on one person, and a quote that shows a single pump for each welder does not cover all three.

Under the helmet or outside it? Both are valid, and they answer different questions. Sampling outside the helmet shows the exposure in the workplace, and it is what most rules have in mind.

Sampling inside the helmet shows what the welder actually breathes, and it is the right measurement for evaluating how well a powered air-purifying respirator works. A survey report should state which one was done and why.

Why the welders are rarely one exposure group

For sampling, workers are sorted into similar exposure groups (SEGs), meaning workers who do the same job the same way. “The welders” are rarely one SEG, and these are the factors that split them:

• Process. MIG, TIG, stick and flux-cored welding (GMAW, GTAW, SMAW and FCAW) generate fume at very different rates, and flux-cored is generally the highest.
• Base and filler metal. Stainless or mild steel is the difference between having a hexavalent chromium problem and not having one.
• Position and tight spaces. Welding inside a tank or vessel is a different exposure from welding on an open bench, even with the same welding wire or rod.
• Arc time. The time the arc is on varies a great deal, so a fitter who welds 90 minutes a day and a production welder with 6 hours of arc time are not in the same SEG.
• Ventilation. A booth with a working exhaust hood is one thing, and a portable fan that someone points in the general direction is another.

→ How many air samples do you really need?