Regarding the definition of gases lighter than air in GB50058
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The **Code for Design of Electrical Installations in Areas with Fire Hazards** specifies that gases with a relative density of less than or equal to 0.75 are considered gases lighter than air； Gases with a relative density greater than 0.75 are defined as gases that are heavier than air. How do people understand why gases with a relative density of less than or equal to 1 are defined as gases that are lighter than air?
This is presumably the consideration of the safety factor. In principle, gases that are lighter than air move upward relative to air, that is, they float and spread freely outward. However, when air circulation in the device (workshop) or a particular area is poor or when it is a confined space, the free diffusion of gases is restricted, thereby creating a **hazardous environment. Therefore, with reference to relevant foreign technical standards regarding the relative density of gases and taking into account national conditions, this specification sets it at 0.75 for safety purposes.