In an H2S environment, using CS material, what is the general maximum allowable H2S concentration?

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10 mg/m³ is the maximum allowable concentration (MAC) of hydrogen sulfide (H₂S) in workplace air, and it is applicable to industrial safety standards including those for carbon steel (CS) materials. This limit is based on China’s **Occupational Health Standard GBZ 2.1-2019 “Occupational Exposure Limits for Hazardous Factors in the Workplace”**, and it is intended to protect human health as well as reduce the risk of H₂S causing corrosion to equipment. For carbon steel materials, in a wet H₂S environment, sulfide stress corrosion cracking (SSCC) may occur when the H₂S partial pressure exceeds 0.34×10⁻³ MPa (approximately equivalent to an H₂S concentration of 20 mg/L in an aqueous solution). Therefore, to balance personnel safety and material corrosion resistance, it is recommended to keep the H₂S concentration below 10 mg/m³, and in high-risk scenarios, adopt protective measures such as using corrosion inhibitors, adjusting pH, or selecting materials resistant to sulfide stress corrosion.