Summary of definitions and classifications of flammable liquids and combustible liquids

II. Merely from the perspective of chemical properties

The comparison of national standard classifications organized by the original poster is really useful! I’ve been working on the fire safety approval procedures for a project recently; I almost got confused by the threshold values specified in different standards😂 First of all, it’s important to note that different standards are applicable in different situations: GB50016 is the general building fire protection code, suitable for most civil and ordinary industrial buildings ； GB50160 is designed for petrochemical enterprises, while GB50074 is specific to oil depots; when selecting a standard, it is necessary to first match it to the type of project at hand. Although the logic behind classifying flash points according to the three standards is similar, there are many details that differ, such as the ranges for Class B and Class C. Do not simply copy these classifications; always refer to the original specifications to confirm the correct values. One final reminder: the application of such fire safety standards should take into account local regulatory requirements. It is advisable to consult professional fire safety experts to avoid issues with project approvals or on-site safety due to incorrect use of these standards.

III. Summary Based on the above standards and specifications, the characteristics of flammable liquids and combustible liquids are summarized as follows: 1. Regarding the classification of chemicals stored in buildings (fire hazard categories), there are three criteria. 1.1 The \"Code for Fire Protection Design of Buildings\" GB50016 (the first version was issued in 1987 as GBJ-87) does not explicitly define flammable liquids and combustible liquids, but actually classifies them based on their flash point – liquids in Categories A and B are considered flammable liquids, while those in Category C are considered combustible liquids. Furthermore, the explanatory notes to the Code for Fire Protection Design of Buildings, GB50016, detail that the drafting team for the 1987 version of this code conducted statistics and analyses on the flash points of 596 flammable and combustible liquids, taking into account the climate differences between the north and south regions; ultimately, the flash points of gasoline, kerosene, and diesel were used as the basis for classifying substances into Categories A, B, and C. Work that was extremely scientific, rigorous, and meticulous 35 years ago! The other two standards, GB50074 and GB50160, also use this classification basis. 1.2 The \"Code for Design of Oil Depots\" (GB50074) and the \"Code for Fire Protection Design of Petrochemical Enterprises\" (GB50160) consider the classification of fire hazards from the perspective of chemical storage facilities, that is, from the perspective of buildings (structures). GB50074 defines and classifies flammable liquids and combustible liquids, while GB50160 refers to both flammable liquids and combustible liquids collectively as “combustible liquids”. 2. Six standard specifications based solely on the properties of chemicals 2.1 \"Specifications for the classification and labeling of chemicals – Part 7: Flammable liquids\" (GB30000.7) is based on the United Nations’ Globally Harmonized System of Classification and Labelling of Chemicals (GHS). Flammable liquids are defined as liquids with a flash point of 93°C or less, and they are classified into 4 categories. Since GHS does not have flammable liquids, GB30000.7 also does not cover flammable liquids. 2.2 The “Catalogue of Hazardous Chemicals (2015 Edition)” and the “Classification Information Table for Hazardous Chemicals” adopt GB6944-2012 for the definition of flammable liquids (with a closed-cup flash point not exceeding 60°C), and GB30000.7 as the basis for classifying such liquids. 2.3 The \"Code for Fire Protection of Flammable and Combustible Liquids\" (SY/T6344-2017) defines and classifies flammable and combustible liquids in exactly the same manner as the \"NFPA 30 Flammable and Combustible Liquids Code\" issued by the National Fire Protection Association (**Fire Protection Committee\"). 2.4 \"Basic Classification of Flammable and Combustible Liquids\" (SY/T6460-2000) provides definitions and classifications for flammable and combustible liquids; however, since the American Fire Protection Association’s (**Fire Protection Committee) NFPA 321, which this standard is based on, was repealed in 1996 (with its contents incorporated into NFPA 30), standard SY/T6460-2000 should be considered obsolete as well (and its provisions can be replaced by the \"Code for Fire Protection of Flammable and Combustible Liquids\" (SY/T6344-2017)).

In overall layout design and equipment arrangement, these specifications can be taken into account to classify flammable liquids. What other regulations and documents need to be considered when designing pressure pipelines and installing combustible gas alarms?

According to the TSG 31-2025 Technical Regulations for Safety of Industrial Pipelines, flammable liquids refer to liquids with a flash point of 93°C or less (Class A B, Class B, and some Class C A substances). This includes liquids that contain solids in solution or suspension (such as paints, varnishes, sprays, etc.), except for substances that are classified in other categories due to their hazards, as well as liquid desensitized explosives. Flammable liquids also include liquids that are used and transported at temperatures equal to or higher than their flash point, as well as substances that are transported in liquid form at high temperatures and release flammable vapors at temperatures equal to or lower than the maximum transport temperature. Aerosols are not flammable liquids. This can guide us in qualitatively analyzing pressure pipelines.

This post was last edited by Clouds of flowing water shine on 2026-4-20 at 15:10. According to the \"Design Standard for Detection and Alarm of Flammable and Toxic Gases in Petrochemical Industries\" GB/T 50493-2019, Class A B liquids refer to flammable liquids with a flash point below 28°C, while Class B A liquids refer to flammable liquids with a flash point ranging from 28°C to 45°C inclusive. Class A B and Class B A liquids are collectively referred to as flammable liquids. This can guide us in the design of combustible gas alarms. Unfortunately, there is no list of Class B A liquids. For substances other than those in Appendix A of GB/T 50493-2019, it is necessary to seek additional information for confirmation.

Regarding leakage detection for pressure pipelines, GB20801-2025 states: 8.6.2.1.1 For pipelines transporting media with leakage hazards, a leakage test shall also be conducted after the pressure test. There are also definitions for the hazardous substances that can cause leaks: toxic substances refer to those classified as Category 1 acute toxicity substances as specified in GB 30000.18, Category 2 gaseous substances, as well as Category 2 liquid substances whose operating temperature is higher than their standard boiling point. 2 Flammable media: Flammable gases of Category 1 and Category 2, and chemically unstable gases of Category A and Category B as specified in GB 30000.3. Flammable liquid categories 1 and 2 in GB 30000.7, as well as category 3 liquid media with an operating temperature higher than their flash point. 3 Carcinogenic agents: Category 1A and Category 1B carcinogenic agents as specified in GB 30000.23. It should be noted that the range of media considered hazardous in case of leakage as defined in GB/T 20801.1-2025 differs to some extent from that specified in TSG 31-2025, the Technical Regulations for Safety of Industrial Pipelines. This difference is mainly evident in the definition of flammable liquid category 3: GB/T 20801.1-2025 requires leakage tests only for flammable liquids in category 3 whose operating temperature is above their flash point, whereas TSG 31-2025 mandates leakage tests for all flammable liquids in category 3, regardless of whether their operating temperature is above or below their flash point. This standard will come into effect on May 1, 2026, and applies to industrial pipelines covered by the Catalogue of Special Equipment. GB/T 20801.1-2025 has relaxed the requirements; it is similar to SH3501-2021, and it seems to be a more scientific approach. TSG 31-2025 is similar to older standards such as GB50235-2010 and GB50184-2011, but it is clear that these latter standards are more mandatory. So, how should we choose which standard to follow when working on a project?