GB 50493-2009 Specification for Design of Combustible Gas and Toxic Gas Detection and Alarm for Petrochemical Industry (Text of Document is in English) - Beijing translation compay

3 General Requirements

3.0.1 When possible combustible gas and toxic gas leak is detected in the area for process unit producing or using combustible gas and toxic gas, and for storage and transportation facilities, combustible gas and toxic gas detector shall be arranged according to the following provisions:

1 Combustible gas or combustible gas with toxic gas is leaked, and the concentration of combustible gas may reach 25% of the lower explosion limit nut the toxic gas cannot reach maximum allowable Concentration. at this time, combustible gas detector shall be equipped;

2 Combustible gas or combustible gas with toxic gas is leaked, and the concentration of combustible gas may reach the lower explosion limit nut the toxic gas cannot reach 25% of maximum allowable Concentration. at this time, toxic gas detector shall be equipped;

3 In the place where combustible gas and toxic gas are stored together, the concentration of combustible gas may reach 25% of lower explosion limit, and the concentration of toxic gas may also reach maximum allowable Concentration. At this point, combustible gas and toxic gas detectors shall be all equipped;

4 When a gas is both combustible gas and toxic gas, only toxic gas detector shall be equipped.

3.0.2 Two-level alarm shall be adopted for the detection system of combustible gas and toxic gas. When the toxic gas and combustible gas detectors simultaneously alarm in same detection area, the following principles shall be complied with:

1 In same level alarm, toxic gas alarm shall be preferential;

2 Level 2 alarm has priority over level 1 alarm.

3.0.3 If the process has special requirements, or runs normally, staffs must not enter hazardous area, continual detection, Indication and alarm should be taken for the release source of combustible gas and toxic gas, and alarm should be recorded and printed.

3.0.4 Alarm Signal shall be sent to site warning device and indication apparatus at attended control room or site operation room, and audible and visual alarm shall be available.

3.0.5 The arrangement of the site warning devices in equipment zone shall be determined according to the following factors: area of equipment zone, arrangement of equipment and structure, physico-chemical properties of release source and site air flow character. Site warning device may be sounder or alarm lamp.