What is the maximum installation distance for combustible gas alarm detectors?

This should be available in the “Code for Fire Protection Design of Buildings” or other relevant documents; go and check.

Please refer to the relevant provisions of the \"Design Code for Detection and Alarm of Flammable and Toxic Gases in Petrochemical Enterprises\".

This post was last edited by jingsan on 2009-8-11 08:34. Additional note: \"Code for Design of Detection and Alarm Systems for Flammable and Toxic Gases in Petrochemical Enterprises\": 3.0.7 Detectors should be installed on the upwind side of the wind direction corresponding to the lowest frequency of release of flammable or toxic gases. 3.0.8 The effective coverage radius in the horizontal plane of a combustible gas detector should be 7.5 m indoors ； It should be 15m outdoors. One detector can be installed within the effective coverage area. The distance between the toxic gas detector and the source of release should not exceed 2 meters in outdoor areas, and should not exceed 1 meter in indoor areas. 3.0.9 In the areas where gas detectors for flammable gases or toxic gases are required according to the provisions of this standard, fixed-type detectors are preferred; when it is not possible to install fixed-type detectors, portable detectors should be used. 3.0.10 The combustible gas and toxic gas detection and alarm system should be a relatively independent instrumentation system. 4 Determination of detection points 4.1 Process units 4.1.1 Detectors should be installed at the following sources of flammable gases and toxic gases: 1 Compressors for Class A gases or toxic gases, liquefied hydrocarbon pumps, Class A. Dynamic seals for Class B+ liquid pumps that are arranged in groups or together, as well as those for liquid pumps that can emit toxic gases ； 2 Sampling ports that may leak Class A gases, toxic gases, liquefied hydrocarbons, or Class B liquids as well as liquids that can emit toxic gases during abnormal operation, and discharge (water) ports that may carry liquefied hydrocarbons, Class B liquids, and liquids that can emit toxic gases during improper operation ； 3 Equipment or pipe flanges, valve assemblies that may leak Class A gases, toxic gases, or liquefied hydrocarbons during abnormal operation. 4.1.2 In equipment areas where the combustible gas emission sources specified in Article 4.1.1 are located in an open or semi-open environment, when the detection point is situated upwind of the direction from which the gases are emitted with the highest frequency, the distance between the combustible gas detection point and the emission source should not exceed 15 m; the distance between the toxic gas detection point and the emission source should not exceed 2 m ； When the detection point is located downwind of the wind direction corresponding to the lowest frequency of the release source, the distance between the combustible gas detection point and the release source should not exceed 5 m, while the distance between the toxic gas detection point and the release source should be less than 1 m. 4.1.3 When the combustible gas emission sources specified in Article 4.1.1 are located in enclosed or semi-enclosed buildings, a detector can be installed every 15 m, and the distance between each detector and any emission source shall not exceed 7.5 m. The toxic gas detector should not be more than 1 m away from the source of release. 4.1.4 When equipment of different fire hazard categories is installed in enclosed or semi-enclosed buildings, detectors shall be installed within 7.5 m of the combustible gas release sources specified in Article 4.1.1. 4.1.5 When the source of flammable gases lighter than air specified in Article 4.1.1 is located in a closed or semi-closed building, detectors should be installed above the source, as well as at the highest points within the building where flammable gases are likely to accumulate. 4.2 Storage and Transportation Facilities 4.2.1 Liquefied hydrocarbons, methane. For liquid-like storage tanks, detectors should be installed at the following locations: 1. Inside the fire dike surrounding the liquefied hydrocarbon tank cluster; one detector should be installed every 30 meters, and it should be no more than 15 meters away from the tank’s drainage outlet or the flanges and valves at the bottom of the tank. 2 is in A. Detectors should be installed within the fire dike of liquid-like storage tanks, and the distance between the tank’s drainage outlets, sampling ports, or bottom (side) connection flanges, valves, etc., and these detectors should not exceed 15 meters. 4.2.2 Liquid hydrocarbons, methane. For liquid-like materials handling facilities, detectors should be installed at the following locations: 1. At railway loading and unloading platforms with flexible hoses, a detector should be placed at every other loading position on the ground, and the horizontal distance between the detector and the loading/unloading port should not exceed 15 meters ； For the 2 large pipe railway loading/unloading platforms, it is advisable to install one detector ； 3 The horizontal distance between the vehicle loading/unloading jacks at the vehicle loading/unloading station and the detectors should not exceed 15 m. When buffer tanks are installed in the vehicle loading and unloading station, detectors shall be provided in accordance with Article 4.1.2 of these specifications. 4.2.3 The detector settings for the pumps or compressors in loading and unloading facilities shall comply with the provisions of Articles 4.1.1, 4.1.2, and 4.1.3 of these specifications. 4.2.4 The detector setup at liquefied hydrocarbon filling stations shall meet the following requirements: In enclosed or semi-enclosed filling rooms, the distance between the filling port and the detector should be 5 to 7.5 meters ； 2 Enclosed or semi-enclosed storage vaults shall comply with the provisions of Article 4.1.3 of these specifications ； One unit is installed every 15–30 meters around a semi-outdoor gas cylinder storage area; if the perimeter of the area is less than 15 meters, one unit should be installed ； 3 The distance between the drain outlet or valve assembly of the buffer tank and the detector should be 5 to 7.5 meters. 4.2.5 In closed or semi-closed hydrogen filling rooms, detectors shall be installed at the highest point inside the room above the filling port, where gas is likely to accumulate. 4.2.6 At loading and unloading terminals for liquefied hydrocarbons, Class A B liquids, and Class A C liquids, a detector shall be installed within 15 m of the horizontal plane of the oil transfer arm. When it is not possible to install detectors, the detection of combustible gases at loading and unloading docks shall comply with the provisions of Section 3.0.9 of these specifications. 4.2.7 Toxic gas detectors in toxic gas storage and transportation facilities shall be installed in accordance with the provisions of Articles 4.1.2 and 4.1.3. 4.3 Areas where flammable gases and toxic gases can spread and accumulate 4.3.1 Detectors should be installed at a distance of approximately 5 meters from heating furnaces, or on the outside of firewalls, between these furnaces and equipment handling Class A gases or liquefied hydrocarbons, as well as at any sources that may leak under abnormal operating conditions. 4.3.2 When the control room, power distribution room are within 30 m of the process equipment units and storage and transportation facilities for Class A gases, toxic gases, liquefied hydrocarbons, and Class N liquids, and one of the following conditions is met, it is advisable to install detectors: 1 The doors and windows face the process equipment units or storage and transportation facilities ； 2 Instrument power cable trays or conduits laid on the ground that lead into the control room or distribution room. 4.3.3 Detectors shall be installed in the on-line analysis instrument room located within Zone 2. For detecting flammable gases that are lighter than air, detectors should be installed at the highest point within the online analysis instrument room, where flammable gases are likely to accumulate. 4.3.4 Detectors should be installed in the following areas that are not within the effective coverage of the detectors: 1 the ground at the lowest level of pits and drainage ditches in process units and storage and transportation facilities where liquefied hydrocarbons and/or toxic gases are used or generated, areas where flammable gases and toxic gases may accumulate. 2 Areas prone to the accumulation of Class A gases and toxic gases, or \"dead corners\". 6 Installation of detection and alarm instruments 6.1 Installation of detectors 6.1.1 For detectors used to detect flammable gases or toxic gases that are heavier than air, their installation height should be between 0.3 and 0.6 meters above the floor (or floor slab). Note: Gases with a density greater than 0.97 kg/m3 (under standard conditions) are considered heavier than air ； Gases with a density of less than 0.97 kg/m3 (under standard conditions) are considered lighter than air. 6.1.2 For detectors used to detect flammable gases or toxic gases that are lighter than air, their installation height should be 0.5 to 2 meters above the source of emission. 6.1.3 The detector should be installed in a location free from shocks, vibrations, and strong electromagnetic interference, with a clear space of at least 0.3 m around it. The above is in electronic format and is for reference only.

There isn’t really a maximum distance of distribution; rather, there is a concept of the effective coverage radius in the horizontal plane: for combustible gas detectors, this radius is 7.5 meters indoors； It is 15m outdoors. For specific details, refer to the Design Code for Detection and Alarm of Flammable and Toxic Gases in Petrochemical Enterprises, SH3063—1999

Design Code for Detection and Alarm of Flammable and Toxic Gases in Petrochemical Enterprises SH3063—1999

There is some more information available; you can check out http://bbs.oil.hc360.com/bbs/newbbs/oil/dispbbs/12/114/117114_1.htm and http://221.11.38.175/safe/law/aq/%B1%EA%D7%BC/SY6503-2003%BF%C9%C8%BC%C6%F8%CC%E5%BC%EC%B2%E2%B1%A8%BE%AF%CA%B9%D3%C3%B9%E6%B7%B6.doc. The second one is in Word format; I’m unable to upload the doc file, so please click to download it and take a look.

Generally, according to the standards, it is 7.5m for indoor areas； It is 15m outdoors. But in actual use, it was found that 7m is better

We have always arranged them with a radius of 15 meters

I agree with the views expressed by those above. Additionally, they should be placed near the source of emission; those that are lighter than air should be installed at the top, while those that are heavier should be installed at the bottom.

Currently, the safety supervision authorities conduct inspections based on this distance