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Operator Health and Safety: Laser Cutting Fumes and Dust

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Hazardous substances in laser cutting of metals

During thermal processing — in our case, gas-assisted laser cutting — the air becomes saturated with hazardous gases and very fine dust from oxides of the cut metal. Cutting is accompanied by sparks, spatter, and high-frequency noise. Let us look at the harmful substances.

Fine particulate matter (dust)

Laser cutting of metal generates a large amount of dust. Some particles exceed 1 µm, but a special class is fine particulate matter (particles smaller than 10 µm — PM10). Humans cannot see or feel it, yet it poses the greatest hazard because it penetrates deep into the respiratory tract.

  • Contaminant particles settle on the walls of blood vessels, gradually narrowing them and slowing blood flow. The result is an increased risk of thrombosis.
  • Many fine dust particles are carcinogenic, so their regular inhalation can cause lung cancer.
  • Continuous inhalation produces a cumulative effect, which can lead to serious diseases such as bronchial asthma, chronic obstructive pulmonary disease (COPD), and others.
  • Dust can trigger allergies. During flare-ups, severe coughing, frequent sneezing, watering eyes, swelling, and reddening of the eyes occur.

Dust harms not only the operator but also the laser itself: it attenuates the laser beam and reduces cutting accuracy.

Aerosols (fume)

Aerosols are air or gas containing suspended solid or liquid particles smaller than 1 µm. Aerosols are conventionally divided into dust, smoke, and mist. Dusts and smokes are systems of air or gas with suspended solid particles; mists are systems of air or gas with liquid particles.

In our case, condensation aerosols are hazardous: they form when metal is cut, heated, and cooled. Microscopic particles end up suspended in the air.

The volume of substances released depends on:

  • cutting speed;
  • assist-gas pressure;
  • type and grade of metal;
  • cutting parameters.

Mild steel produces far fewer emissions than materials containing CrNi (chromium-nickel) alloys or galvanized steel sheet. When cutting alloy steels and non-ferrous metals, condensation aerosols are released into the working zone; the most toxic ones are aerosols of manganese, zinc, vanadium, and nickel oxides and many other metals and their compounds.

Laser cutting produces fume and dust in which 97 % of particles have a diameter below 5.7 µm.

Effects of substances released during thermal cutting on the human body

  • Chromium oxides. Inhalation causes coughing, breathing difficulty, shortness of breath, sore throat, and stertorous (rattling) breathing. Skin contact causes redness, burns, and physical pain. Eye contact causes redness, pain, permanent vision loss, and severe deep burns. Ingestion causes abdominal colic.
  • Nickel and its compounds. At elevated concentrations they typically cause allergies (dermatitis, rhinitis, etc.), anaemia, increased excitability of the central and autonomic nervous systems, and possible neoplasms including cancer. Nickel has no direct skin irritant effect, but nickel platers have experienced "nickel itch" (nickel eczema), swelling, blisters, etc.
  • Aluminium oxide. No negative effect on skin contact. Short-term high-concentration exposure to the dust irritates the eyes and upper respiratory tract. Long-term or repeated exposure can affect the central nervous system.
  • Carbon monoxide. Inhalation causes headache and dizziness, ringing in the ears, shortness of breath, palpitations, visual flickering, facial flushing, general weakness, nausea, vomiting, convulsions, loss of consciousness, and coma.
  • Nitrogen oxides. Affect the body more strongly than carbon monoxide. Disrupt lung and bronchial function, the nervous system, the gastrointestinal tract, and cardiac activity. Cause coughing, headache, burning sensation, nausea, drowsiness, clouded consciousness, bluish skin, convulsions, and loss of consciousness.
  • Magnesium oxide. Fumes cause redness, pain, digestive upset, respiratory tract irritation, headache, coughing, increased sweating, nausea, and fever (metal fume fever symptoms may not appear during the first 4–12 hours after exposure).

Thermal cutting of metals releases large volumes of harmful substances. Some negatively affect the human body and, with prolonged exposure, create the conditions for cancer. To prevent illness, personnel must use personal protective equipment (PPE), and the shop must be equipped with general (ambient) ventilation and local exhaust ventilation (LEV / fume extraction).

Also keep in mind that workers are affected by such factors as indoor air temperature, air movement, relative humidity, hazardous emissions, etc.

Typical air contaminants

  • emission dust;
  • carbon monoxide;
  • oil mist (aerosols);
  • smoke;
  • products of thermal decomposition of organic matter;
  • metal aerosols;
  • metal oxides;
  • fluoride compounds;
  • phenols;
  • organic acids;
  • organosulphur compounds;
  • pungent odour, etc.

Gases used for cutting stainless steel

Although the gases used in laser cutting of stainless steel are not toxic, they can be potentially hazardous. The associated risks include smoke and gas itself.

  • The amount of smoke generated during oxygen cutting was 100 times greater than during nitrogen cutting.
  • Particle size from oxygen cutting was smaller — predominantly below 6 µm, which is considered the most problematic from a hygiene standpoint.
  • Chemical analysis of the smoke from both processes showed that the percentage of hexavalent chromium — Cr(VI) — a known carcinogen — was lower when cutting with nitrogen.
  • There is a danger to life if the oxygen concentration in the ambient air drops below 18 %.
  • Under oxygen-enriched conditions, many materials become combustible.
  • Operating high-pressure nitrogen cutting in a confined space creates a risk of oxygen displacement (asphyxiation).