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How To Classify Major Hazards Of Hazardous Chemicals
- Sep 04, 2018 -

The Interim Provisions on the Supervision and Administration of Major Hazardous Sources of Hazardous Chemicals (Order No. 40 of the State Administration of Work Safety) clearly sets out the requirements for grading major hazard sources and specifies specific grading methods. According to its regulations, the major hazard source of hazardous chemicals is divided into first, second, third and fourth grades.

First, the grading index

The ratio of the actual presence (on-line) of various hazardous chemicals in the unit to the critical amount specified in the Identification of Major Hazardous Sources of Hazardous Chemicals (GB18218), and the sum of the ratios corrected by the correction factor, R, is used as the grading index.

Second, the calculation method of R

In the formula:

Q1, q2,...,qn — the actual (online) amount of each hazardous chemical (unit: tons);

Q1, Q2, ..., Qn - the critical amount (unit: ton) corresponding to each hazardous chemical;

11, β2..., βn—correction coefficients corresponding to each hazardous chemical;

α—The correction factor for the exposed personnel outside the plant where the hazardous chemical is a major hazard.

Third, the value of the correction coefficient β

Set the correction factor β value according to the type of hazardous chemicals in the unit, see Table 1 and Table 2:

Table 1 Correction coefficient β value table

Hazardous Chemicals

Category toxic gas explosives, flammable gases, other types

Hazardous Chemicals

β see Table 221.51

Note: The categories of hazardous chemicals are determined according to the classification criteria in the Dangerous Goods Product Name List.

Table 2 Common Toxic Gas Correction Coefficient β Value Table

Toxic gas name

Carbon dioxide

Sulfur ammonia epoxy

Ethane hydrobromide


Toxic gas name hydrogen sulfide hydrogen fluoride

Nitrogen cyanide hydrogen carbonyl chloride phosphine hydrogen isocyanate


Note: The toxic gases not listed in Table 2 can be taken as β=2, and the highly toxic gases can be taken as β=4.

Fourth, the value of the correction coefficient α

According to the boundary of the plant boundary of the major hazard source, the number of permanent residents within 500 meters is extended, and the correction coefficient α of the exposed personnel outside the factory is set. See Table 3:

Table 3 Calibration coefficient α value table

Number of people exposed outside the factory alpha

100 or more 2.0

50 to 99 people 1.5

30 to 49 people 1.2

1 to 29 people 1.0

0 people 0.5

Five, grading standards

Based on the calculated R value, determine the level of major hazard source for hazardous chemicals according to Table 4.

Table 4 Correspondence between major hazard source levels and R values of hazardous chemicals

R-value of major hazard source level of hazardous chemicals

First level R≥100

Secondary 100>R≥50

Level 3 50>R≥10

Four levels R<10

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