GB/T 50493-2019 in English

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This standard is revised from GB 50493-2009 Specification for design of combustible gas and toxic gas detection and alarm for petrochemical industry by Sinopec Guangzhou Engineering Co., Ltd. jointly with organizations concerned according to the requirements of Document JIANBIAO [2015] No.274 issued by the Ministry of Housing and Urban-Rural Development of the People's Republic of China - Notice on Printing and Distributing the ‘Development and Revision Plan on Engineering Construction Standards and Codes in 2016’.

During the revision of this standard, the standard drafting group made extensive investigations and studies on the problems encountered in the design of combustible gas and toxic gas detection and alarm for petrochemical industry, summarized the experience in the use of combustible gas detectors and toxic gas detectors in petrochemical enterprises in recent years, and finalized this standard after examination finally by reference to the European standard EN 60079-29-2 Explosive atmospheres - Part 29-2: Gas detectors - Selection, installation, use and maintenance of detectors for flammable gases and oxygen and on the basis of soliciting opinions from design, production, scientific research, detector manufacturing enterprises and other relevant parties.

The main technical contents of this standard are: general provisions, terms, basic requirements, location of detection points, design of combustible gas and toxic gas detection and alarm system, installation of combustible gas and toxic gas detection and alarm system, etc.

The main technical contents of the revision of this standard are: 1. The scope of application of the standard is revised from “construction, extension and renovation engineerings of petrochemical industry" to "construction and extension engineerings of petrochemical industry"; 2. The scope of toxic gases is expanded from toxic gases listed in the Catalogue of highly toxic articles to common toxic gases; 3. The requirements for design compatibility, independence and reliability of combustible gas and toxic gas detection and alarm system (GDS) are added; 4. The requirements for separately setting the combustible gas and toxic gas detection and alarm system (GDS) and the fire fighting and fire automation system are added; 5. Open-path (laser, infrared) detectors, noise detectors and other contents are added, and the detection point and layout requirements of detectors are further improved; 6. Guide for the selection of common gas detectors as well as the arrangement plan of combustible gas and toxic gas detection and alarm system are added.

The Ministry of Housing and Urban-Rural Development of the People's Republic of China is in charge of the administration of this standard, China Petrochemical Corporation is responsible for the routine management, and Sinopec Guangzhou Engineering Co., Ltd. is responsible for the explanation of specific technical contents. During the process of implementing this standard, you are kindly requested to send your opinions and advice (if any) to Sinopec Guangzhou Engineering Co., Ltd. (Address: F20, Tower A, Guangzhou Sinopec Building, No.191, West Tiyu Road, Tianhe District, Guangzhou City, Guangdong Province, 510620, China).


Contents

1 General provisions 1
2 Terms 2
3 Basic requirements 4
4 Location of detection points 6
4.1 General requirements 6
4.2 Process units 7
4.3 Storage and transportation facilities 7
4.4 Other places where combustible gases, toxic gases diffuse and accumulate 8
5 Design of combustible gas and toxic gas detection and alarm system 10
5.1 General requirements 10
5.2 Selection of detector 10
5.3 Selection of field alarming units 11
5.4 Selection of alarm control unit 12
5.5 Measurement range and setting of alarm value 13
6 Installation of combustible gas and toxic gas detection and alarm system 15
6.1 Installation of detector 15
6.2 Installation of alarm control unit and field alarming unit 15
Annex A Properties of common combustible gases and vapors 16
Annex B Properties of common toxic gases and vapors 21
Annex C Arrangement plan of combustible gas and toxic gas detection and alarm system 22
Annex D Technical performance table of common gas detectors 23
Annex E Guide for selection of common gas detectors 25
Explanation of wording in this standard 26
List of quoted standards 27



1 General provisions

1.0.1 This standard is formulated with a view to ensuring the personal safety and production safety of petrochemical enterprises, monitoring combustible gases or toxic gases leaked during the production process and in storage and transportation facilities and timely alarming to prevent personal injury and fire and explosion accidents.

1.0.2 This standard is applicable to the design of combustible gas and toxic gas detection and alarm system for construction and extension engineerings of petrochemical industry.

1.0.3 In addition to the requirements of this standard, the design of combustible gas and toxic gas detection and alarm system for petrochemical industry shall also comply with those stipulated in the current relevant standards of the nation.

 
2 Terms

2.0.1 combustible gas
combustible gas or vapour formed after gasification of Class A gas or Classes A and BA combustible liquids, which is also known as flammable gas

2.0.2 toxic gas
toxic gas or vapor that may cause death or permanent health injury of workers through skin contact or breathing during professional activities

2.0.3 source of release
location or place where explosive gas atmosphere and toxic gas atmosphere may be released and formed

2.0.4 detector
an electronic device that converts the concentration of combustible gas, toxic gas or oxygen into electrical signals

2.0.5 open-path gas detector
an open type gas detector for detecting combustible gas or toxic gas clouds in a straight path. Commonly used open-path gas detectors include: infrared gas detectors, laser gas detectors, etc.

2.0.6 field alarming unit/audible and visual alarm unit
an electronic device installed on the site to alert personnel on or near the site by sound, light, or optical rotation. Common ones include: the integrated audible and visual alarm unit on the detector, and the field alarming unit set by zone

2.0.7 alarm control unit
an electronic device that receives the output signal of the detector, displays and records the concentration of the detected gas, emits audible and visual alarm signals, and can send gas concentration alarm signal and alarm control unit fault information to equipment such as graphic display device in the fire control room. When the combustible gas alarm signal is involved in the fire control linkage, the alarm control unit usually adopts a special combustible gas alarm controller that is manufactured according to the product standard for the special combustible gas alarm controller and has been provided with the detection report

2.0.8 sensible range
the concentration range of the detected gas that the detector can detect, which is also called measurement range

2.0.9 alarm set point
the preset alarm concentration value, which is divided into primary alarm set point and secondary alarm set point

2.0.10 response time
the time from the detector contacting the detected gas to reaching stable indication under test conditions. Usually, the response time is the time required for reaching 90% of the stable indication, and the recovery time is the time required for returning to 10% of the stable indication

2.0.11 vertical height
vertical distance from the suction inlet of the detector sensor to the specified reference

2.0.12 lower explosion limit (LEL)
the lower concentration (V%) limit of a combustible gas when it explodes

2.0.13 upper explosion limit (UEL)
the upper concentration (V%) limit of a combustible gas when it explodes

2.0.14 occupational exposure limit (OEL)
the allowable exposure level of a worker that will not cause harmful health effects on the majority of contacts during his/her long-term repeated exposure in the occupational activities. The occupational exposure limits of chemical factors can be divided into three types: maximum allowable concentration, permissible concentration-short term exposure limit and permissible concentration-time weighted average

2.0.15 maximum allowable concentration (MAC)
the concentration of toxic chemicals that cannot be exceeded at workplace at any time within a working day

2.0.16 permissible concentration-time weighted average (PC-TWA)
the average permissible exposure concentration for 40h per working week (i.e., 8h per working day), with time as the weight

2.0.17 permissible concentration-short term exposure limit (PC-STEL)
the permissible short term (15min) exposure concentration subject to the permissible concentration-time weighted average (PC-TWA)

2.0.18 immediately dangerous to life or health concentration (IDLH)
certain dangerous level of the concentration of air pollutants in the environment at workplace, which may cause death or permanent health damage, or may make human immediately lose escape ability

 
3 Basic requirements

3.0.1 In the areas of the process units producing or using combustible gases and toxic gases and the storage and transportation facilities for combustible gases and toxic gases, when the concentration of combustible gas in the leaked gas may reach the alarm set point, the combustible gas detector shall be set; when the concentration of toxic gas in the leaked gas may reach the alarm set point, the toxic gas detector shall be set; in case of the single-component gas medium that belongs to both combustible gas and toxic gas, the toxic gas detector shall be set; in case of the multi-component mixed gas containing both combustible gas and toxic gas, when the concentration of combustible gas and that of toxic gas may reach the respective alarm set points at the same time during leakage, combustible gas detector and toxic gas detector shall be set respectively.

3.0.2 Two-level alarm shall be adopted for detection and alarm of combustible gas and toxic gas. When an alarm is sent for the toxic gas and combustible gas at the same level at the same time, the alarm level of toxic gas shall take precedence.

3.0.3 The detection and alarm signals for combustible gas and toxic gas shall be sent to the attended field control room and central control room for display and alarm. The secondary alarm signal of combustible gas and the fault signal of alarm control unit in combustible gas and toxic gas detection and alarm system shall be sent to the fire control room.

3.0.4 The operation area of the control room shall be provided with audible and visual alarm for combustible gas and toxic gas; the field alarming unit should be set according to the occupied area of the unit, the layout of equipment, buildings and structures, the physical and chemical properties of the source of release and the field air flow characteristics, which shall have audible and visual alarm functions.

3.0.5 The combustible gas detectors must be provided with the type approval certificate for measuring instruments, the explosion-proof certificate and the type inspection report for fire-fighting products issued by the organization designated by the nation or its authorized inspection unit; the alarm control unit involved in fire control linkage shall be the special combustible gas alarm controller that is manufactured according to the product standard for the special combustible gas alarm controller and has been provided with the detection report; the toxic gas detectors required by the national regulations must be provided with the type approval certificate for measuring instruments issued by the organization designated by the nation or its authorized inspection unit. Toxic gas detectors installed in explosive hazardous areas shall also be provided with the explosion-proof certificate issued by organization designated by the nation or its authorized inspection unit.

3.0.6 Where combustible gas and toxic gas detectors need to be set, stationary detectors should be adopted. Where it is necessary to temporarily detect the combustible gas and toxic gas, transportable gas detectors should be equipped.

3.0.7 Field workers entering explosive gas atmosphere or toxic gas atmosphere shall be equipped with portable combustible gas and (or) toxic gas detectors. When explosive gas and toxic gas coexist simultaneously in the atmosphere entered, the multi-sensor type portable combustible gas and toxic gas detectors may be adopted.

3.0.8 The combustible gas and toxic gas detection and alarm system shall be set independently of other systems.

3.0.9 The gas detectors, alarm control units, field alarming units, etc. in the combustible gas and toxic gas detection and alarm system shall be considered as particular important power supply loads among Class I electrical loads, and should be powered by UPS device.

3.0.10 The occupational exposure limit of toxic gas shall be selected in priority order of the maximum allowable concentration, the permissible concentration-time weighted average and then the permissible concentration-short term exposure limit.

3.0.11 The properties of common flammable gases and vapors shall be adopted according to Annex A hereto; and the properties of common toxic gases and vapors shall be adopted according to Annex B hereto.

1 General provisions
2 Terms
3 Basic requirements
4 Location of detection points
4.1 General requirements
4.2 Process units
4.3 Storage and transportation facilities
4.4 Other places where combustible gases, toxic gases diffuse and accumulate
5 Design of combustible gas and toxic gas detection and alarm system
5.1 General requirements
5.2 Selection of detector
5.3 Selection of field alarming units
5.4 Selection of alarm control unit
5.5 Measurement range and setting of alarm value
6 Installation of combustible gas and toxic gas detection and alarm system
6.1 Installation of detector
6.2 Installation of alarm control unit and field alarming unit
Annex A Properties of common combustible gases and vapors
Annex B Properties of common toxic gases and vapors
Annex C Arrangement plan of combustible gas and toxic gas detection and alarm system
Annex D Technical performance table of common gas detectors
Annex E Guide for selection of common gas detectors
Explanation of wording in this standard
List of quoted standards