How are explosion-proof zones distinguished and defined?

For reference: GB 50058-92 Code for Design of Electrical Installations in Explosive and Flammable Environments

The following is excerpted from: GB 50058-92 Code for Design of Electrical Installations in Explosive and Fire-Hazardous Environments, Chapter 2 Classification of Areas with Explosive and Fire Hazards, Section 1 Classification of Explosive Mixtures and Fire-Hazardous Substances, Article 2.1.1 The following mixtures shall be classified as explosive mixtures: 1. Explosive mixtures formed by combustible gases and air (hereinafter referred to as gas explosive mixtures)； II. Explosive mixtures formed by the vapors of flammable liquids, and by the vapors of combustible liquids with a flash point equal to or lower than the ambient temperature in the area, and air ； When the operating temperature is above the flash point of the flammable liquid and a leak is possible, an explosive mixture formed by the vapor of the flammable liquid and air (hereinafter referred to as a vapor explosive mixture) ； III. Explosive mixtures formed by suspended combustible dusts or fibers and air (hereinafter referred to as dust or fiber explosive mixtures). Article 2.1.2 The following combustible substances shall be classified as fire-hazardous materials: 1. Combustible liquids with a flash point higher than the ambient temperature of the area; combustible liquids for which, when the operating temperature is above their flash point, leakage may occur but no explosive mixture will be formed ； II. Suspended or piled combustible dusts or fibers that cannot form explosive mixtures, as well as other solid combustible substances.

Section 2: Grades of Areas at Risk of Explosion and Fire Article 2.2.1 The grades of areas at risk of explosion and fire shall be classified into three categories and eight grades based on the likelihood and consequences of accidents, as well as differences in the degree of danger and the state of the substances present. This classification enables appropriate measures to be taken to prevent accidents caused by sparks, arcs, or dangerous temperatures generated by electrical equipment and circuits. The classification into three categories and eight grades is as follows: I. Explosive hazard areas for gaseous or vapor explosive mixtures in Category 1 are divided into three grades. 1. Areas of Class Q-1 where explosive mixtures can form under normal conditions ； 2. Areas of Category Q-2 that under normal conditions cannot form explosive mixtures, but can do so under abnormal conditions ； 3. Areas of Category Q-3 that under normal conditions cannot form explosive mixtures, but in abnormal conditions have a low likelihood of forming such mixtures. For example: the amount of explosive substances in that location is small, the density of such substances is low making it difficult for them to accumulate, the lower explosion limit is high, and these substances have a strong odor. II. Explosive hazard areas for Class II dust or fiber explosive mixtures are divided into two grades: 1. G-1 grade areas – areas where an explosive mixture can be formed under normal conditions ； 2. Areas of Grade G-2 that under normal conditions cannot form explosive mixtures, but can do so under abnormal conditions ； III. Third-class fire-hazardous areas are divided into three grades: In Grade H-1 areas, flammable liquids with a flash point higher than the ambient temperature of the area are generated, used, processed, stored, or transported during the production process, in terms of both quantity and arrangement. Places posing a fire hazard ； 2. H-1 class locations where, during the production process, suspended or accumulated combustible dusts or fibers cannot form explosive mixtures, but where their quantity and arrangement can pose a fire hazard ； 3. Class H-3 areas: Areas where solid combustible materials, in terms of quantity and arrangement, pose a fire hazard. Note: ① Normal conditions refer to normal driving, operation, stopping, etc. (such as open loading and unloading) ； ②Abnormal conditions refer to accidental damage, misoperation, improper maintenance, as well as disassembly and repair of devices or equipment. Article 2.2.2 For the classification of certain locations, in addition to complying with the provisions of Article 2.2.1 of these specifications, the following rules shall also be followed depending on their specific circumstances: 1. For open or partially open buildings and structures, as well as outdoor installation areas with good air circulation, the classification level may be reduced by one tier after taking into account various factors such as specific gravity, flash point, and explosion limits. II. Under normal conditions, a gas or vapor explosive mixture can only be formed in localized areas of the premises, and such localized areas should be classified as Q-1 level ； The remaining areas should be classified into different grades based on the range that explosive mixtures may reach under abnormal conditions. III. Poorly ventilated corners, deep pits, and other recessed areas in explosion-hazardous zones where explosive mixtures of gases or vapors can accumulate should be classified as Q-1 level. This post was last edited by QQ Ai on 2009-3-2 20:53.]