GB/T 50493-2019 (GB 50493-2009) PDF English
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GB 50493-2009: Specification for design of combustible gas and toxic gas detection and alarm for petrochemical industry
---This is an excerpt. Full copy of true-PDF in English version (including equations, symbols, images, flow-chart, tables, and figures etc.), auto-downloaded/delivered in 9 seconds, can be purchased online: https://www.ChineseStandard.net/PDF.aspx/GB50493-2009
NATIONAL STANDARD
OF THE PEOPLE’s REPUBLIC OF CHINA
p GH 50493-2009
Specification for Design of Combustible Gas
and Toxic Gas Detection and Alarm for
Petrochemical Industry
Issued on: MARCH 19, 2009
Implemented on: OCTOBER I, 2009
.Jointly Issued by Ministry of Housing and Urban-Rural Construction of the
People’s Republic of China
General Administration of Quality Supervision, lns1•ection
and Quarantine of the People’s Republic of China
Table of Contents
General Provisions... 1
2 Terms ... 2
3 General Requirements ... 4
4 Determination of Detection Points .. 6
4.1 General Rules ... 6
4.2 Process Unit ... 6
4.3 Storage and Transportation Fa巳iliti巳s ... 7
4.4 Other Combustible Gas or Toxic Gas Diffusion and Accumulation Site ... 8
5 Combustible Gas And Toxic Gas Detection Alarm System ... 9
5.1 Technical Performance... 9
5.2 Selection of Detector... 9
5.3 Selection oflndication Alarm Device ... 1 0
6 Detectors and Indication Apparatus Installation ... 1 2
6.1 Detector Installation ... 1 2
6.2 Indication Appara饥is and Onsite Alarm Installation ... 12
Appendix A Properties of General Combustible Gas and Vapor ... 1 3
Appendix B Properties of General Toxic Gas and Vapor ... 1 7
Appendix C Technical Performance Table of Detector for General Gasses ... 18
Explanation of Wording in This Code ... 19
1 General Provisions
1.0.1 This standard is formulated with a view to preventing personal injury, and fire and
explosion accidents, and ensuring the safety of petrochemical enterprises.
1.0.2 This standard is applicable to the combustible gas and toxic gas detection and alarm
design of new, expended or rebuilt works for petrochemical enterprises.
1.0.3 Besides the provisions of this standard, the combustible gas and toxic gas detection and
alarm design for petrochemical industry shall meet the requirements of the current related
national standards.
2 Terms
2.0.1 Combustible gas
It is referred to Class A combustible gas or the combustible gas generated after Class A and
B flammable liquid gasi马ring.
2.0.2 Toxic gas
It is referred to the Gasses which cause acute or chronic health harms on workers by body
contact in the employment activities. The scope of toxic gas in this standard is toxic vapour
toxic gas listed in “ acute toxic substances" (Wei Fa Jian Fa [2003] No.142). The general toxic
vapours or toxic gases are as. nitrogen dioxide, hydrogen sulfide, benzene, hydrogen cyanide,
ammonia, chlorine gas, carbon monoxide, acrylonitrile, vinyl chloride and phosgene.
2.0.3 Source of release
It is referred to the Position or site which releases explosive gas mixture or toxic gas.
2.0.4 Detector
It is referred to the electronic unit which can convert the concentration of combustible gas
and toxic gas into electrical signal, and it is composed of sensor and transducer.
2.0.5 Indication apparatus
It is referred to the electronic devices which receive the output signal of detector and send
Indication, alarm and control signals.
2.0.6 Sensible range
It is referred to the range of the detected gas that can be detected by detector under the test
condition.
2.0. 7 Alarm set value
It is referred to the pre-set alarm concentration value of warning device.
2.0.8 Response time
It is referred to the time from detector contacting gas to stably indicating value under test
condition. 90% of the time to reach the stable indicated value is adopted as response time; 10%
of the time to restore to stable indicated value is adopted as recovery time.
2.0.9 Vertical height
It is referred to the vertical distance from the detection opening of detector to the appointed
reference object
2.0.10 Lower explosion limit (LEL)
It is re也rred to the concentration value (V %) of combustible gas at lower explosion limit
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
prov1s1ons.
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 ent巳r
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.S 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.
3.0.6 Combustible gas detector shall be the products which the measuring instrument
production certification, explosion protection performance certification and fire control
certification are approved by the institution designated by the country.
3.0. 7 Toxic gas detector specified by the laws of the country shall be the products which the
measuring instrument production certification is approved by the institution designated or
4 Determination of Detection Points
4.1 General Rules
4.1.1 The detection points of combustible gas and toxic gas detectors shall be arranged on the
positions where gas is easy to accumulate and sampling or detection is convenient, according
to the following conditions. gas physicochemical property, characteristic of release source,
production yard layout, geographic conditions, environmental climate and operating and patrol
examining route.
4.1.2 Detection points shall be arranged for the following release sources with possible
combustible gas or toxic gas leak.
1 Sealing of gas compressor and liquor pump;
2 Liquid and gas sampling ports;
3 Liquor drainage opening or vent;
4 Flange and valving for equipment and pipes.
4.2 Process Unit
4.2.1 When release sources are located on the equipment sections of open-Air or open-type
facility Layout, the distance from detection point and release source shall meet the following
requirements.
1 When the detection point is located on windward Side of the all-the-year least
frequency wind direction, the distance from combustible gas detection point to release source
should not be larger than 1 Sm, and the distance from toxic gas detection point to release source
should not be larger than 2 m;
2 When the detection point is located on leeside of the all-the-year least 仕equency wind
direction, the distance from combustible gas detection point to release source should not be
larger than Sm, and the distance from toxic gas detection point to release source should not be
larger than 2 m;
4.2.2 When combustible gas release source is located on semi-open workshop building of
closing or imperfect local ventilation, a detector may be ranged per I Sm, and the distance from
the detector to any release source within this coverage should not be larger than 7.Sm. The
distance from Toxic gas detector to the release source should not be larger than lm.
4.2.3 When lighter-than-air combustible gas or Toxic gas release source is located on semi-
open workshop building of closing or imperfect local ventilation, detector shall be arranged
over the release source, beside combustible g...
......
Source: Above contents are excerpted from the full-copy PDF -- translated/reviewed by: www.ChineseStandard.net / Wayne Zheng et al.
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