Metal fume fever: measuring zinc oxide and copper fume

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.

Metal fume fever clears up in 24 to 48 hours, and that one fact is why most shops that have it do not know they have it.

A welder cuts galvanized (zinc-coated) steel in the afternoon and that evening develops chills and a fever, a metallic taste, aches and a headache. Two days later the welder is fine.

It looks like the flu and gets called in as the flu, so it never reaches the OSHA 300 log and never reaches the safety manager. The pattern is Monday and Tuesday, the same three people, the same job, and no one sees it unless somebody is looking for it.

Ask your welders directly whether they get flu-like symptoms the evening after galvanized work. In shops that cut and weld coated metal, the answer is often yes, and the question has rarely been asked.

Where we find it

• Welding and thermal cutting on galvanized steel: structural steel, ductwork, guardrail, trailers and tanks. The zinc coating vaporizes well below the temperature of the arc.
• Hot-dip galvanizing kettles: skimming dross, fluxing and work at the kettle edge.
• Zinc die casting: furnace tending, ladling and trim.
• Brass and bronze foundries. Melting and pouring release zinc from the alloy, and copper comes with it.
• Thermal spray and metallizing with zinc and zinc-aluminum wire arc, a process that generates fume at a high rate by design.
• Scrap cutting and demolition torch work on coated and mixed-metal material.
• Brazing and silver soldering. Copper and zinc come from the filler alloys. Some silver solder also contains cadmium, which has its own OSHA standard and a far tighter limit.

→ Cadmium air sampling

Exposure limits

The table shows limits from three sources: OSHA's permissible exposure limits (PELs), NIOSH's recommended exposure limits (RELs), and the threshold limit values (TLVs) published by ACGIH. The PELs are legal limits, while the RELs and TLVs are recommendations.

All values are in milligrams per cubic meter of air (mg/m³). In the table, “TWA” means a time-weighted average over a full work shift, and “STEL” means a short-term exposure limit.

“Respirable” refers to the finest particles, the ones that reach deep into the lungs. A ceiling limit is a level that must not be exceeded at any time.

Iron oxide is in the table because it is in the fume, but it does not cause metal fume fever. Its effect is siderosis, a benign lung condition that comes from dust settling in the lungs over a long time, which is a different exposure question on a different time scale.

Three points in that table deserve attention.

The 10 mg/m³ STEL for zinc oxide that gets quoted everywhere comes from NIOSH and ACGIH, not from OSHA. OSHA has no STEL for zinc oxide. The number is often quoted as if OSHA could enforce it, and OSHA cannot. A program built on meeting it is meeting a recommendation, which is acceptable as long as everyone knows which is which.

Copper has two separate entries in Table Z-1, OSHA's general table of air contaminant limits, with a tenfold gap between them. Fume is at 0.1 mg/m³, and dusts and mists are at 1 mg/m³. Which entry applies depends on whether the copper became airborne through heat or through mechanical action, and the lab cannot tell you that.

The lab reports micrograms of copper on a filter, and whether that result passes or is ten times over depends on a judgment about the process that is made in the field. That judgment has to be documented at the time of sampling, and a copper result should state which entry it was evaluated against.

Copper fume is the rare case where ACGIH is less strict than OSHA. The ACGIH TLV is 0.2 mg/m³, which is twice the OSHA PEL of 0.1. For most substances the health-based value is the tighter one, so you cannot use the ACGIH number as a shortcut here. A result of 0.15 mg/m³ meets the ACGIH TLV and exceeds the OSHA PEL.

How we sample for it

You may see another OSHA analytical method, ID-206, listed for this work. It was written for dust and fume from soldering, and it covers silver, beryllium, cadmium, copper, lead, antimony, tin and zinc. Iron is not on that list, so the method cannot give a full set of welding fume metals on its own.

One conversion decides the answer: the lab reports zinc, but the PEL is for zinc oxide. To convert, multiply by 1.245. A zinc result of 4.0 mg/m³ is 4.98 mg/m³ as zinc oxide, so the same measurement can look comfortable or sit right at the PEL, depending on whether that step was done.

It is worth checking any zinc result you already hold. If the report says “zinc” and compares it to 5 mg/m³ without mentioning 1.245 or zinc oxide anywhere, the comparison comes out low by about a quarter.

The other issue in the field is how much of the shift the work takes, because galvanized work is rarely all day. Take a welder who cut coated metal for 90 minutes: the full-shift TWA is genuinely low, yet the 90-minute exposure still caused symptoms.

Both numbers are true, and they answer different questions. If the complaint is metal fume fever, the full-shift TWA will not explain it. Sample the task.

→ Welding fume air monitoring

There is no standard to meet here, and that is the point

None of these metals has a substance-specific OSHA standard. They appear only in Table Z-1, which means:

• No action level
• No required monitoring schedule
• No deadline for notifying workers
• No required medical surveillance

Nothing in the regulations will ever prompt you to look, so the prompt has to come from the pattern of symptoms, and that pattern is disguised as seasonal illness.

In that situation a survey is not mainly a compliance record. It answers practical questions: whether the exhaust hood on the cutting bay is doing anything, and whether moving the work or changing the exhaust actually reduces the exposure.

That can be measured in a day, and unlike most of what we do, the fix is usually inexpensive once you know where to aim it.

Over the long term, the fever is not the whole story

Metal fume fever resolves on its own, which is the reassuring part and also the reason shops tolerate the exposure.

The long-term side does not clear up in 48 hours. Welding fume is a mixture, and manganese, hexavalent chromium and nickel can come along with the zinc, depending on the base metal and the welding wire or rod. Ongoing exposure to that mixture is the reason an analysis for a set of metals tells you more than zinc alone.

→ Hexavalent chromium air sampling