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Welding and gas cutting are important processing techniques that are essential in modern industrial manufacturing and equipment maintenance. Due to process requirements, during welding, metal elements, flux, and shielding gas generate various harmful gases and welding fumes under the action of high-temperature flames, posing a threat to the health of workers (see Table 1). Table 1: Components of harmful substances generated during welding operations, health standards, sources of occurrence, and potential health hazards. Pollutants; Maximum allowable concentration in China in mg/m3: TLV-TWA*. Sources of occurrence and health hazards: Ozone – 0.3; 0.05/0.08/0.10 (for heavy, moderate, and light physical labor). It is produced as a result of ultraviolet rays generated by the arc reacting with oxygen in the air. Dryness and irritation in the respiratory tract, headache, fatigue, pulmonary congestion, and lung lesions. Nitrogen oxides: 5(NO2), 31(NO); 5.6(NO2). The ultraviolet light generated by arcs is produced when nitrogen in the air is affected by these rays. Irritation of the eyes and posterior nasal respiratory tract, pulmonary congestion, severe lung damage. Carbon monoxide: 30, 29. Produced by the combustion and decomposition of welding fluxes or shielding gases such as carbon dioxide; causes headaches, dizziness, confusion, and suffocation. Hydrogen chloride, phosgene, phosphine, hydrogen fluoride: 15, 0.5, 0.3, 1, 11; 0.4, 1.4, 2.6 (maximum allowable limit). Generated by the decomposition of chloride-containing solvents, polytetrafluoroethylene, surface coatings, etc. They vary, including both severe irritation reactions and toxicity. Aluminum 4 5, metal substrates, certain alloys, electrode metal cores. Annoying. Cadmium: 0.1, 0.005 (individual exposure limit). Metal protective coatings, certain alloys, electrode coatings. Causes severe lung irritation, emphysema, and kidney damage. Chromium: 0.05, 0.05 (hexavalent chromium)/0.5; used in stainless steel grades and alloy steels. Suspected carcinogen (hexavalent chromium); Copper – 0.1 (individual exposure limit); Nickel-copper alloys, brass, bronze, metal coatings, welding electrodes. Irritation of the nose and throat, nausea, metal fume fever. (Oxidized) iron – the main component in the welding fumes of most steel materials. Stimulation of the nose, throat, and lungs; pulmonary pigmentation (pyrrhotosis); pneumoconiosis. Fluorides 1 2.6 (maximum allowable limit) Electrode coating and flux. Irritation of the eyes, nose, and throat; pulmonary congestion; skeletal changes. Lead: 0.05 0.05 – Used in solder, brass, bronze alloys, and coatings for steel; can cause anemia, fatigue, abnormal pain, reduced fertility, kidney damage, and nerve damage. Manganese: 0.2 0.2 – Used in alloys of carbon steel and stainless steel, as well as in welding electrodes. Chills, metal fume fever, nervous system damage. Molybdenum: 4 (soluble), 6 (insoluble), 5 (soluble), 10 (insoluble); steel alloy. Metabolic disorders, irritation of the nose, eyes, and throat, shortness of breath. Nickel: 1, 0.1 (soluble), 0.2 (insoluble); stainless steel, copper-nickel alloys, chromium-nickel-iron alloys, heat-resistant nickel-chromium-iron alloys. Irritates the eyes, nose, and throat. Tin -- 2 Bronze, solder. Tin pneumoconiosis – Antimony 1, 0.5 – Stainless steel, other alloys, fluxes, coatings. Annoying. Vanadium: 0.1, 0.05 – Used in steel alloys and as the coating on welding electrodes; can irritate the eyes, nose, respiratory tract, and bronchi; may cause retinitis and pulmonary edema. Zinc: 5, 5 – Used in electroplated coatings, brass, bronze, solder, and metal fillers. Metal fume fever, chills, fever, flu-like symptoms. * TLV is a health standard recommended by the American Conference of Governmental Industrial Hygienists (ACGIH), and TWA refers to the 8-hour time-weighted average concentration. For respiratory protection of welders, appropriate respiratory protection equipment should be selected based on the characteristics of the work. Filter-type respirators, such as simple dust masks or half-face dust and gas masks, are widely used. Sparks are usually generated during welding operations, resulting in relatively high local temperatures; if the material of the respirator has flame-retardant properties, this can extend the equipment’s service life ； If a simple mask is equipped with a breathing valve that helps to effectively discharge the heat from the wearer’s exhaled air, it will make the wearer more comfortable ； The mask material should not irritate the skin due to workers’ sweating ； Wearing a mask should not prevent the use of a face shield. Electric air-supply respirators use a battery-powered motor to filter ambient air and supply it to the wearer, allowing for smoother breathing due to the high airflow. Some protective equipment is designed with the characteristics of welding operations in mind; it features goggles on the face shield or helmet, which protect both the breath and eyes while eliminating the need for a handheld face shield, thereby improving work efficiency ； Some also take into account the fact that welders often need to grind the workpiece after welding; therefore, a design that includes an elevated visor is advisable. The inner mask provides protection against spark splashes, safeguarding the eyes and skin on the head – offering triple protection for the breath, eyes, and head skin, which makes it an excellent choice. When choosing a filtering respirator, three mistakes should be avoided: First, focusing only on the rated filtration efficiency while ignoring the actual filtration performance. Since the particles in welding fumes are extremely small, usually below 1 micron, it is necessary to understand what type of particulates are used in the product standards and testing methods for the dust masks chosen. Scientific research has shown that particles with a size of 0.3 micrometers are the most difficult to filter among all types of particulate matter. Therefore, abroad, this particle size is commonly used to test the filtering efficiency of dust masks and filters. If the efficiency reaches 95%, then the efficiency in filtering particles larger or smaller than 0.3 micrometers will also be above 95%. Since this particle size of particulates is not yet included in the mandatory testing standards in our country (LD 29-92), the rated filtration efficiency of the dust masks tested cannot represent the actual filtration efficiency against welding fumes. Second, only focusing on the level of filtration efficiency while ignoring the fit between the respirator and the wearer’s face. If there is a poor fit, harmful substances will enter the respiratory tract directly through the leak, and no filter material, no matter how efficient, will be effective. Third, exhaust systems have been installed in the workplace, so individual respiratory protection is not considered necessary. Due to the characteristics of welding operations, the area around the worker’s breathing zone is where the concentrations of harmful substances are highest. Even if welding fumes can be removed using ventilation systems, this only prevents the spread of these harmful substances and reduces their concentration in the environment. However, before they are removed, these harmful substances still pass through the worker’s breathing zone; therefore, individual respiratory protection measures must be employed. Many welding tasks are carried out in relatively enclosed spaces, where oxygen deficiency can occur easily. Our country defines atmospheric conditions with an oxygen volume percentage below 18% as oxygen-deficient environments. Filter-type respirators do not produce oxygen; supply-air respiratory protection equipment must be selected. [Reference]: Zhou Guotai (ed.), *Comprehensive Book on Safety Technology for Hazardous Chemicals*, Chemical Industry Press, 1997. Shanghai Hangli Industrial Co., Ltd. Zhao Jiabin 021-64398971