1. What are the main components of the fumes produced during welding galvanized coils? Why is special protection necessary?
A: During welding galvanized coils, the zinc layer rapidly vaporizes at high temperatures and reacts with oxygen in the air, generating fine fumes primarily composed of zinc oxide, along with small amounts of metal oxides such as iron and manganese. Inhalation of zinc oxide fumes can cause "metal fume fever," manifesting as fever, chills, a metallic taste in the mouth, and nausea. Symptoms typically appear within hours of exposure and last for several hours to a day. Long-term exposure can also lead to chronic respiratory irritation. Therefore, more stringent protective measures than those for welding ordinary carbon steel are required.
2. What is the most effective engineering control measure for galvanizing welding fumes?
A: The most effective engineering control measure is to use a local exhaust ventilation system (i.e., a welding fume purifier). The air intake should be as close as possible to the welding point to ensure that the fumes are captured before they spread. For fixed workstations, high-negative-pressure or central fume purification units can be used, equipped with high-efficiency filters (HEPA filtration efficiency ≥99.97%) targeting submicron-sized zinc oxide particles. For non-fixed on-site operations, mobile fume purifiers should be used, along with fire-resistant suction arms and dust hoods. Furthermore, when conditions permit, welding should be prioritized outdoors or in large workshops with overall ventilation to avoid fume accumulation.
3. What type of respiratory protective equipment should operators wear? Are ordinary dust masks sufficient?
A: Ordinary dust masks (such as KN90/KN95 levels in GB 2626-2019) are insufficient for effectively filtering nano-sized zinc oxide fumes, and their poor fit to the face makes them prone to leakage. It is recommended to use a filtering half-face or full-face respirator that meets at least N95 or higher standards (such as N100, P100), ensuring a good fit to the face. For confined spaces or prolonged high-concentration work, a powered air-purifying respirator (PAPR) or a positive pressure long-tube respirator must be used to provide clean air. Note: Activated carbon masks are only effective for adsorbing organic gases and are ineffective against zinc oxide fumes.
4. Besides respiratory protection, what other personal protective measures should be taken?
A: Operators should wear flame-retardant or burn-resistant welding protective clothing, gloves, and goggles or welding masks. Since zinc vapor condenses into white zinc oxide powder on low-temperature surfaces after cooling, which easily adheres to hair and skin, it is recommended to wear a dust cap and a one-piece work suit. Change clothes and shower immediately after welding. Eating and smoking are prohibited in the work area to prevent ingestion of fumes through the hands and mouth. Drinking milk or beverages rich in vitamin C before and after work, while not providing direct protection, can help alleviate subjective discomfort for some personnel.
5. How can welding processes be improved to reduce fume generation and thus lower protection pressure?
A: Galvanized welding fumes mainly originate from the high-temperature evaporation of zinc. Therefore, reducing heat input or changing the heating method can reduce zinc evaporation. Specific process improvements include: prioritizing pulsed gas metal arc welding (pulse MIG) over conventional MIG to reduce total heat input; using welding wire with a smaller diameter and containing deoxidizer; employing short arc operation and increasing welding speed; for thin plate lap joints, resistance spot welding or seam welding can be considered, as the fumes generated by localized instantaneous heating are far lower than those from arc welding; in addition, removing the zinc layer in the area to be welded before welding (e.g., through mechanical grinding or acid etching) can fundamentally eliminate the source of fume generation at that location, but it should be noted that zinc-containing dust generated during grinding should also be treated separately.