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bg2.png01. Combustion can be divided into flaming combustion and non-flaming combustion. For combustion to occur and develop, three necessary conditions must be present: a combustible material, an oxidizer (a substance that facilitates combustion), and temperature (a source of ignition). 02. Common ignition sources: open flames, electric arcs, electrical sparks, lightning strikes, high temperatures, and self-igniting substances (white phosphorus and aluminum alkyls can ignite spontaneously in air) ； Metals such as potassium and sodium catch fire when they come into contact with water ； Flammable and combustible substances catching fire upon contact with oxidizers or peroxides, etc.). 03、The lower the flash point, the greater the fire hazard; conversely, the lower it is, the smaller the fire hazard. The flash point is related to the saturated vapor pressure of flammable liquids; the higher the saturated vapor pressure, the lower the flash point. When the temperature of a liquid is above its flash point, it can be ignited by a fire source at any time or may catch fire spontaneously; if the temperature is below the flash point, the liquid will not ignite, let alone catch fire. 04. The flash point of gasoline is -50°C, while that of kerosene is 38–74°C. Based on these flash point values, it is possible to determine the fire hazard category of locations where flammable liquids are produced, processed, or stored: those with a flash point below 28°C fall into Category A ； Those with a flash point of ≥28°C to <60°C are classified as Category B ； Those with a flash point of ≥60°C are classified as Class C. 05. The ignition point of flammable liquids is generally 1–5°C higher than their flash point, and the lower the flash point, the smaller this difference is; in particular, it is difficult to distinguish between the flash point and the ignition point in open containers. Therefore, when assessing the fire hazard of such liquids, the flash point is generally used. 06. The lower the auto-ignition temperature, the greater the risk of a fire. 07. Gas combustion methods are divided into diffusion combustion (such as using gas for cooking, lighting, or welding) and premixed combustion (the combustion in gas lamps). 08、Liquid combustion: flash point (lowest temperature), boiling over, splashing. 09、Under normal circumstances, boiling over occurs much earlier than splashing. The time at which boiling over occurs is related to the type of crude oil and its moisture content. According to experiments, oil containing 1% moisture will experience boiling over after being burned for 45–60 minutes. The timing of splashing is related to the thickness of the oil layer, the speed of propagation of the heat wave, and the burning speed of the oil. 10. Solid combustion: evaporative combustion, decompositional combustion, surface combustion, smoldering (slow combustion), and dynamic combustion (explosion). 11. Complete combustion products refer to CO2 (gas) formed by the oxidation of C in combustibles, H2O (liquid) formed by the oxidation of H, SO2 (gas) formed by the oxidation of S, and so on. 12. Products of incomplete combustion refer to CO, NH3, alcohols, aldehydes, ethers, etc. 13. The boiling points of volatile metals are generally lower than the melting points of their oxides (except for potassium), whereas for non-volatile metals, the melting points of their oxides are lower than those of the metals. 14. Hazards of combustion products: toxicity and light absorption. The wavelength of visible light is typically between 0.4 and 0.7 μm, while the particle size of smoke particles in fire smoke ranges from a few μm to several dozen μm. Since d > 2λ, these smoke particles are opaque to visible light. 15. Class A fires: Fires involving solid materials ； Class B fire: Fires involving liquids or fusible solid materials. Such as fires involving gasoline, kerosene, crude oil, methanol, ethanol, asphalt, paraffin, etc ； Class C fire: Gas fire ； Class D fire: Metal fires ； Class E fire: Fire involving electricity ； Class F fires: Fires involving cooking materials in cooking appliances (such as animal and vegetable fats and oils). 16. Classification based on the degree of disaster damage caused by fire accidents: (1) Extremely serious fires: These are fires that result in 30 or more deaths, 100 or more severe injuries, or direct property losses exceeding 100 million yuan ； (2) Major fire: refers to a fire that results in 10 to 30 deaths, or 50 to 100 serious injuries, or direct property losses ranging from 50 million yuan to 100 million yuan ； (3) Major fire: refers to a fire that results in 3 to 10 deaths, or 10 to 50 serious injuries, or direct property losses ranging from 10 million to 50 million yuan ； (4) Ordinary fire: refers to a fire that results in 3 or fewer deaths, 10 or fewer serious injuries, or direct losses of less than 10 million yuan. Note: “Above” includes the current value, while “Below” does not include it. 16. Common causes of fires: electrical issues, smoking, careless use of fire in daily life, careless handling during production processes, equipment failures, playing with fire, arson, and lightning strikes. 18. There are three ways of heat transfer: conduction, convection, and radiation. 19. The driving forces for smoke flow include the stack effect caused by the temperature difference between indoors and outdoors, the effect of external wind, and the influence of ventilation and air conditioning systems, etc. 20. At the onset of a fire, the speed at which smoke spreads horizontally is 0.3 m/s; when the burning is intense, this speed can reach 0.5 to 3.0 m/s ； The speed at which smoke spreads through stairwells or other vertical ducts can reach 3.0–4.0 m/s. The walking speed of a person on flat ground is approximately 1.5–2.0 m/s, while the speed when climbing stairs is about 0.5 m/s. Thus, the speed at which a person climbs stairs is **lower than the vertical flow speed of smoke. Therefore, when a building is on fire, it is dangerous for people to run upstairs. 21. Several stages in the development of building fires: initial growth stage, full development stage, and decay stage. 22. Basic principles and methods of fire extinguishing: cooling, isolation, smothering (combustion cannot continue when the oxygen concentration is below 15%), and chemical suppression (common fire extinguishing agents used for chemical suppression include dry powder and heptafluoropropane). 23. A combustible dust explosion requires three conditions: the dust itself must be explosive, it must be suspended in the air and mixed with air to reach an explosive concentration, and there must be a source of fire sufficient to trigger the dust explosion. 24. The characteristics of dust explosions mainly include the following points: (1) Continuous explosions are the most prominent feature of dust explosions, as the initial explosion lifts the accumulated dust, creating more explosive mixtures in new areas that lead to further explosions ； (2) The minimum ignition energy required for dust explosion is relatively high, generally exceeding several tens of millijoules; moreover, it is difficult to ignite dust using hot surfaces ； (3) Compared to combustible gas explosions, dust explosions exhibit a slower rise in pressure; the high-pressure state lasts longer, and they release a large amount of energy, resulting in great destructive power. 25. The higher the moisture content in the air, the higher the minimum ignition energy of the dust ； As the oxygen content increases, the limit range of the explosion concentration expands ； The presence of flammable gases in an environment with dust **increases the risk of dust explosions.** 26. Different substances have different explosion limits due to their varying physical and chemical properties ； Even for the same substance, its explosion limit varies under different external conditions. The explosion limit in oxygen is wider than that in air, with the lower limit decreasing. 27. The greater the energy of the ignition source for the combustible mixture, the wider the explosion range of that mixture, and the greater the risk of explosion. 28. An increase in the initial pressure of the mixture leads to an enlarged explosion range, thereby increasing the risk of explosion. It is worth noting that as the pressure of a mixture of dry carbon monoxide and air increases, its explosive range narrows. 29. The higher the initial temperature of the mixture, the wider its explosive range, and the greater the risk of explosion. 30. Adding an inert gas to a combustible mixture narrows the explosion limit range; generally, the upper limit decreases, while the lower limit changes in a more complex manner. Once the amount of inert gas added exceeds a certain level, mixtures in any proportion can no longer undergo explosion. 31. As the concentration of flammable gas or liquid vapor in the explosive mixture increases, more heat is generated by the explosion, and the pressure rises. When the concentration of combustible substances in the mixture increases to slightly above the stoichiometric concentration, the combustible substances react fully with the oxygen in the air; as a result, the most heat is released during the explosion, and the pressure generated is at its highest. When the concentration of combustible substances in the mixture exceeds the stoichiometric concentration, the heat released and explosion pressure decrease as the concentration of combustible substances increases. 32. The common ignition sources that can cause explosions include mechanical ignition sources, hot fire sources, electrical ignition sources, and chemical ignition sources. 33. The minimum detonation energy required for a certain ** is its sensitivity. 02. Flammable gases are those for which, at a temperature of 20°C and a standard atmospheric pressure of 101.3 kPa, the lower explosion limit is ≤13% (by volume), or the flammability range is at least 12 percentage points (the difference between the upper and lower limits of the explosion concentration). 34. Flammable gases are divided into two categories. Grade I: Blast lower limit < 10% ； Or, regardless of the lower limit for explosions, the upper limit range for explosions is ≥12 percentage points ； Grade II: 10% ≤ lower explosion limit < 13%, and the explosion margin is < 12 percentage points. In practical applications, gases with a lower explosion limit of <10% are generally classified as Class A fire hazards, while gases with a lower explosion limit of ≥10% are classified as Class B fire hazards. 35. Generally speaking, gases composed of simple components, such as hydrogen (H2), are more flammable than those made up of complex components like methane (CH4) and carbon monoxide (CO); they burn faster, have higher flame temperatures, and pose a greater risk of explosion. 36. Flammable gases with unsaturated valence bonds pose a greater fire hazard than flammable gases with corresponding saturated valence bonds. 37. For flammable gases, at constant pressure, the temperature of the gas is directly proportional to its volume ； When the temperature remains constant, the volume of a gas is inversely proportional to its pressure; that is, the greater the pressure, the smaller the volume ； At constant volume, the temperature of a gas is directly proportional to its pressure; in other words, the higher the temperature, the greater the pressure. 38. The more liquid or solid impurities are present in the gas, the more static charge is generated in most cases ； The faster the gas flows, the more static charge is generated. 39. Materials are manufactured using high-pressure alloy steel along with certain amounts of rare metals such as chromium and molybdenum, and their pressure resistance and other properties are regularly tested. 40. Flammable liquids are divided into three categories. (1) Grade I. Initial boiling point ≤35℃ ； (2) Class II. Flash point < 23°C, and initial boiling point > 35℃ ； (3) Class III. 23℃ ≤ flash point ≤ 35℃, and initial boiling point greater than 35℃ ； Or with a flash point greater than 35°C and ≤60°C, and a boiling point greater than 35°C with continuous combustion. In practical applications, liquids with a flash point of <28°C are generally classified as Class A fire hazards, while liquids with a flash point of ≥28°C and <60°C are classified as Class B fire hazards.