Metal Fume Exposure

When you weld, cut or braze metal, some of it boils off and condenses into tiny particles in the air. That smoke is fume, and it is small enough to reach deep into your lungs. What it does to you depends on what you are heating, so the same torch can be low risk on one job and dangerous on the next.

What You Will Be Able to Do

• Name the metals of most concern and where they come from.
• Recognize metal fume fever and know what to do.
• Explain how an OSHA exposure limit works.
• Choose controls in the right order, from removing fume to wearing a respirator.
• Spot jobs that need extra protection before you start.

What Fume Is

Fume is made of solid metal particles, mostly metal oxides, that are much smaller than you can see individually. It comes from the base metal, the filler, the electrode coating, and any paint, plating or oil on the surface. The arc or flame also creates gases, such as ozone, nitrogen oxides and carbon monoxide.

In 2017, the International Agency for Research on Cancer classed welding fume as a known cause of cancer in humans. Fume from plain carbon steel is not harmless just because it does not contain chromium.

Some jobs make more fume than others:

What Each Metal Does

Manganese

Manganese is in nearly all steel welding, and welding wires and rods often add more. Long-term exposure can damage the nervous system. It can cause a condition like Parkinson's disease, with slow movement, stiffness, tremor and mood changes. Studies have also found smaller changes in brain function and motor skills at low exposures. These effects do not always go away after exposure stops. Enclosed spaces raise the risk because fume builds up.

Hexavalent Chromium

Chromium in stainless steel is safe as a solid. The heat of welding or cutting changes some of it into hexavalent chromium, written Cr(VI). It causes lung cancer, can damage the lining of the nose, and can cause skin ulcers and allergic rashes. Stick and flux-cored welding on stainless usually produce more than TIG or MIG.

Zinc and Metal Fume Fever

Heating galvanized steel makes zinc oxide fume. Breathing a lot of it causes metal fume fever, a flu-like illness. You may get fever, chills, muscle aches, a metallic taste, nausea, headache and a dry cough. It usually starts a few hours after exposure, often that evening, and clears in a day or two.

Metal fume fever is not a badge of honor, and milk does not prevent it. Tell your supervisor and get medical care, especially if you have chest pain or trouble breathing. Severe exposures, such as in an enclosed space, can be more dangerous. Also, other metals can cause similar symptoms: cadmium fume can feel like the flu at first, then cause fatal lung damage a day later.

Warning: Do not heat a part with a yellow or gold plating, or an unknown coating, until you know what it is. Cadmium plating looks harmless and its fume can kill. Check the Safety Data Sheet or ask your supervisor.

How OSHA Limits Work

A Permissible Exposure Limit (PEL) is the most of a substance you may legally breathe, usually averaged over an 8-hour shift. Limits are measured with a sampling pump worn on your body, with the sample taken inside your helmet if you wear one. The air you breathe is what counts, not the general shop air.

A microgram is one-thousandth of a milligram, so the chromium limit is very low. For hexavalent chromium, OSHA also sets an action level of 2.5 micrograms per cubic meter. At or above that level, your employer must keep monitoring, and if you are exposed for 30 or more days a year you must be offered medical checks. Construction work has its own matching standards in 29 CFR 1926.

The manganese limit is a ceiling, meaning it should never be exceeded, even briefly. That limit is old. The National Institute for Occupational Safety and Health (NIOSH) recommends 1 milligram per cubic meter, and the American Conference of Governmental Industrial Hygienists recommends far less, at 0.02 for the respirable part of the fume. Many employers work to these tighter numbers. Being under the OSHA limit does not prove that an exposure is safe.

OSHA does not simply say "use a fume extractor." It sets the limits and requires your employer to meet them, with engineering and work practice controls first in most cases. Your employer must also tell you what you are exposed to. Your state may have stricter rules.

Controlling Fume

Work down this list, starting at the top. A respirator is the last line of defense, not the first.

1. Remove the source. Strip paint and coatings back from the weld with the right method. Clean oil off the metal. Choose a lower-fume process or consumable if the procedure allows.
2. Capture fume at the arc. Use a local exhaust hood, fume arm or fume-extraction gun. A capture hood usually has to be close to the arc to work, so reposition it as you move. Follow the maker's distance. Downdraft tables and water tables do the same job for cutting.
3. Dilute what is left. General ventilation with fans and open doors helps, but it does not stop what you breathe directly from the plume. Make sure the airflow pulls fume away from you and not across your face.
4. Position your body. Keep your head out of the plume. Move to the side, or stand upwind when you are outdoors. Outdoor work is not automatically safe.
5. Wear a respirator when controls cannot keep you below the limit, or for the jobs below. Your employer must run a program with medical clearance, fit testing and training. A particulate filter does nothing for gases, so the type must match the hazard.

Ventilation has to be maintained to work. A clogged filter, a crushed duct or a hood pushed aside gives you false comfort. Check that the air is actually moving before you start.

Jobs That Need Extra Care

• Stainless steel and high-chrome alloys. Expect exposure monitoring and local exhaust.
• Galvanized or coated steel. Grind the coating back from the joint where possible, and use local exhaust. The same goes for torch or plasma cutting it.
• Old painted steel. Assume lead until a test says otherwise. OSHA has specific rules for cutting and welding lead-coated metal.
• Enclosed or confined spaces. Fume, gases and shielding gas build up fast. Mechanical ventilation and air monitoring are needed, and you should never use oxygen to ventilate a space.
• Anything near chlorinated degreasers. Arc light can turn the vapor into phosgene gas.

Reading the Warning Signs

Tell your supervisor if you notice a visible haze at face height, a metallic taste, repeated flu-like illness after shifts, new coughing or wheezing, or shakiness or stiffness that you cannot explain. You have a right to know the results of air sampling done for your job, and you can file a confidential complaint with OSHA without being punished.

Common Mistakes

• Trusting the shop fan. A fan may push fume through your breathing zone.
• Leaving the hood behind. A fume arm 3 feet from the arc captures little.
• Welding galvanized "just this once." A short job in a closed room is what causes metal fume fever.
• Assuming clean steel means clean air. Manganese and iron oxide are still in the plume.
• Wearing a dust mask. A loose paper mask is not a fitted respirator.

Check Your Understanding

You feel feverish and achy at 9 p.m. after welding galvanized brackets all afternoon. What is probably going on, and what do you do?

It sounds like metal fume fever. Tell your supervisor and get medical advice, especially if your chest hurts or you cannot catch your breath. Next time, grind the coating back and use local exhaust.

Your shop switches from carbon steel to stainless with the same fan and no hood. Is that a problem?

Yes. Stainless fume contains hexavalent chromium, which has a very low OSHA limit. Your employer needs to assess exposure, and local exhaust is the normal first step.

A coworker says the job is fine because he is working outside. What is wrong with that?

Air movement helps but does not make it safe. If he is leaning over the plume or the wind blows it at him, he still breathes it. Position, local capture or a respirator may still be needed.

A part has a shiny yellow plating and no paperwork. What should you do?

Stop and find out what it is. It may be cadmium, and that fume can kill. Get the Safety Data Sheet or ask a supervisor before you heat it.

Key Takeaways

• Fume comes from the base metal, filler and coatings, so what you are heating decides the hazard.
• Manganese damages nerves, hexavalent chromium causes cancer, and zinc causes metal fume fever.
• OSHA limits apply to the air you breathe, and some are far looser than current science supports.
• Control fume at the source first. A respirator comes last.
• Keep your head out of the plume, every time.
• Enclosed spaces, stainless and coated metals need extra controls.