GB/T 37243-2019Determination method of external safety distance for hazardous chemicals production units and storage installations (English PDF)

3.1 explosive

all explosives listed in the Catalogue of hazardous chemicals and the Classification information form of hazardous chemicals

3.2 toxic gas

gas listed in the Catalogue of hazardous chemicals and the Classification information form of hazardous chemicals, with the hazard characteristic category including acute toxicity -inhalation

3.3 flammable gas

gas listed in the Catalogue of hazardous chemicals and the Classification information form of hazardous chemicals, with the hazard characteristic category including flammable gas, Categories 1 and 2

3.4 external safety distance

distance or risk control line set between the hazardous chemicals production units and storage installations and the off-plant protected objects in order to prevent and mitigate the impact of potential accidents (fire, explosion, poisoning, etc.) of these units and installations on the protected objects

3.5 ignition source

initial energy sources that promote the combustion of combustible substance and comburants, including open flame, heat of chemical reaction, heat radiation, high-temperature surface, friction, impact, etc.

4.1

The process of determining the external safety distance for hazardous chemicals production units and storage installations is shown in Figure 1.

Figure 1 Determination process of external safety distance for hazardous chemicals production units and storage installations 4.2 The hazardous chemicals production units and storage installations involving explosive(s) shall have their external safety distance determined with the accident consequences tree (ACT) method.

4.3

The hazardous chemicals production units and storage installations involving toxic or flammable gas(es) and has the sum of the ratio of the designed maximum quantity to the threshold quantity specified in GB 18218 being greater than or equal to 1 shall have their external safety distance determined with the quantitative risk evaluation method. When the above-mentioned units and installations exist in the enterprise, all the hazardous chemicals production units and storage installations in the enterprise shall be subjected to quantitative risk evaluation as a whole to determine the external safety distance.

4.4

The external safety distance for hazardous chemicals production units and storage installations other than those specified in 4.2 and 4.3 hereof shall meet the distance requirements of relevant standards and specifications.

5.1 Calculation procedures

The process of determining the external safety distance by the accident consequences tree method is shown in Figure 2.

Figure 2 The process of determining the external safety distance by the accident consequences tree method

5.2 Foundation data acquisition

5.2.1

The process data related to explosives, including explosives data, layout plans of units and installations and process descriptions.

5.2.2

Peripheral conditions outside the units and installations that may be affected by accidents, including the use conditions of surrounding lands, terrain conditions, statistics of residents and population distribution.

5.3 Determination of the most serious accident scenario

5.3.1

Identify explosive-related elements in production units and storage installations, and refer to GB 50089-2018 to determine the maximum number of explosives that can explode simultaneously in the units and installations, and regard the simultaneous explosion of this number of explosives as the most serious accident scenario.

5.3.2

When ammonium nitrate is stored separately, the accident scenario of its explosion may not be considered. When ammonium nitrate in a unit or installation is vulnerable to other combustibles, flammables, explosives or forbidden objects in the vicinity under extreme conditions, the accident scenario of its explosion shall be considered, and half of the ammonium nitrate inventory shall be included in the maximum quantity of explosives that can explode simultaneously in the unit or installation.

5.4 Determination of external safety distance

5.4.1

According to the most serious accident scenario and the air-blast overpressure safety valve value given in Table 1, calculate the external safety distance using Formula (1):

(1) where,

deltap - - the air-blast overpressure value, Pa×105;

Q - - the TNT explosive equivalent of one explosion, kg;

R - - the distance from the explosion point to a protected object, m;

Table 1 Air-blast overpressure thresholds for different types of protected objects in: pa

Protected objects (classified according to GB 36894) Air-blast overpressure thresholda

Highly sensitive protected objects and key protected objects

Class I protected objects in the general protected objects 2,000

Class II protected objects in the general protected objects 5,000

Class III protected objects in the general protected objects 9,000 a The threshold of 2,000Pa is the upper limit of air-blast overpressure causing basically no damage to buildings; the threshold of 5,000Pa is below the medium level that causes subminor damage (2,000Pa~9,000Pa) to buildings, which may cause all glass to be broken, tiled roof to move slightly, and plaster on inner wall surface to drop slightly. The threshold of 9,000Pa is the upper limit causing subminor damage (2,000Pa~9,000Pa) to buildings, which may cause partial damage to buildings and thus uninhabitable, slight deformation of steel structures and no damage to reinforced concrete columns. The above thresholds basically will not cause direct death to outdoor personnel.

5.4.2

As for the influence of topographic conditions on the external safety distance, please refer to GB 50089-2018, Annex A to adjust the calculated external safety distance.

5.4.3

The starting points of the external safety distance are the outer edge of the outermost equipment or the outermost axis of the building, and the stopping points are the outer wall of the building at the protected object.