Requirements regarding the installation location of gas probes in industrial enterprises

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Gentlemen, regarding the installation height of gas detectors, there are several standards in use currently: (1) According to GB/T 50493-2019 \"Design Standards for Detection and Alarm Systems of Flammable and Toxic Gases in Petrochemical Industries\", section 6.1.2 states that when detecting flammable or toxic gases that are heavier than air, the detector should be installed at a height of 0.3m to 0.6m above the floor (or floor level); whereas when detecting flammable or toxic gases that are lighter than air, the detector should be installed within 2.0m above the source of emission. When detecting flammable gases or toxic gases that are slightly heavier than air, the installation height of the detector should be between 0.5 m and 1.0 m below the source of emission; when detecting flammable gases or toxic gases that are slightly lighter than air, the installation height of the detector should be between 0.5 m and 1.0 m above the source of emission. (2) Article 10.8.2 of the «Code for Design of Urban Gas» stipulates that the installation of gas concentration detection alarms shall meet the following requirements: 1. When detecting gases that are lighter than air, the horizontal distance between the detection alarm and the gas appliance or valve shall not exceed 8 m; its installation height shall be within 0.3 m of the ceiling, and it shall not be installed above the gas appliance. 2. When detecting gases that are heavier than air, the horizontal distance between the detection alarm and the cooking appliance or valve must not exceed 4 m, and its installation height should be within 0.3 m above the ground. (3) CJJ/T 146-2011 Technical Specifications for Urban Gas Alarm Control Systems, 3.3.3: When the gas source is a gas with a relative density of less than 1 and the vertical distance from the source of gas release to the ceiling exceeds 4 m, a gas collection hood should be installed or detectors should be arranged in layers, in accordance with the following provisions: 1. When a gas collection hood is used, it should be located approximately 4 m above the source of gas release; the area of the hood must be at least 1 m², and the height of its skirt edge must be at least 0.1 m. The detectors should be placed inside the hood. 2. If no gas collection hood is used, detectors should be arranged in two layers – the topmost detector should be at a vertical distance of less than 0.3 m from the ceiling, while the bottommost detector should be located above the source of gas release, with a vertical distance of no more than 4 m. For example, in one of my factories, the distance between the emission source and the ceiling is more than 4 meters; so which standard should be followed and what should be the appropriate installation height?