Core Viewpoint - The article addresses concerns regarding the carbon dioxide (CO2) levels in high-speed trains, clarifying that the reported levels do not exceed the established safety standards [1] Group 1: CO2 Standards and Regulations - The standard limit for CO2 concentration in passenger trains in China is set at a maximum of 2500 ppm according to TB/T 3493-2017, which is specific to rail vehicles [1] - In Europe, the standard limit for CO2 concentration in passenger trains is 5000 ppm as per EN13129-2016 [1] - The reported passenger measurements referenced a standard from GB 50736-2012, which is applicable to civil buildings and not to passenger trains [1] Group 2: Air Quality Management in Trains - High-speed trains are designed with a fully sealed car body, and air exchange is managed entirely by the air conditioning system, providing a fresh air volume of over 15 m³/h per person [1] - The air exchange rate in these trains ranges from 6 to 12 times per hour, ensuring that CO2 levels typically do not exceed 1500 ppm during normal operation [1] - During transit through continuous tunnel sections, the train implements pressure protection measures that temporarily restrict air exchange with the outside, which may lead to a short-term increase in CO2 levels, but this is not harmful to passenger health [1]

Core Viewpoint - The reported CO2 concentration levels in high-speed train carriages have been clarified by experts, indicating that the standards for rail vehicles differ from those for civilian buildings, and the levels observed do not pose health risks to passengers [1][2]. Group 1: CO2 Concentration Standards - The standard limit for CO2 concentration in passenger trains in China is set at a maximum of 2500 ppm according to TB/T 3493-2017, while European standards allow up to 5000 ppm [1]. - The viral claims regarding CO2 levels were based on GB 50736-2012, which applies to civilian buildings and is not relevant to passenger trains [1]. Group 2: Air Quality Management in Trains - High-speed trains are designed with a fully sealed car body, relying on air conditioning systems for ventilation, providing over 15 m³/h of fresh air per person, with air exchange rates of 6 to 12 times per hour [1]. - During normal operation outside tunnels, CO2 levels typically do not exceed 1500 ppm, but can temporarily rise above 2000 ppm when passing through tunnels due to pressure protection measures [2]. Group 3: Public Reaction and Observations - A video showing CO2 levels rising in a second-class carriage sparked public discussion, with initial readings around 880 ppm increasing as passengers boarded, leading to a perception that high-speed travel induces drowsiness [2].

Core Viewpoint - The reported CO2 concentration levels in high-speed train carriages do not exceed safety standards set by relevant regulations, and the standards for rail vehicles differ from those for buildings [1][2]. Group 1: CO2 Concentration Standards - The CO2 concentration control standard for passenger trains in China is set at a maximum of 2500 ppm according to TB/T 3493-2017, while European standards allow up to 5000 ppm [1]. - The reported values circulating online reference the GB 50736-2012 standard for civil buildings, which is not applicable to passenger trains [1]. Group 2: Air Quality Management in Trains - High-speed trains are designed with a fully sealed body, and air exchange is managed entirely by the air conditioning system, providing a fresh air volume of over 15 m³/h per person, with air exchange rates of 6 to 12 times per hour [1]. - During operation in non-tunnel sections, CO2 levels typically remain below 1500 ppm; however, when passing through tunnels, pressure protection measures may temporarily increase CO2 levels without impacting passenger health [2].