(Trivia) Hazard analysis of oils and fuels, risk factors that generate ignition sources

(Trivia) Hazard analysis of oils and fuels. China Work Safety Network: http://images.cworksafety.com/templates/101804/images/top-08.gif 1) Flammability: The vapors emitted by oils and fuels combine with air to form flammable mixtures; when these mixtures reach a certain concentration, they will catch fire upon contact with an ignition source. The lower the flash point of a flammable liquid, the greater the risk of combustion. Gasoline has a very low flash point of -50°C; at room temperature, its flammable vapor can easily evaporate, and it requires very little energy to catch fire, making it highly flammable. 　　2) Explosivity Oil vapors can form explosive mixtures with air. When a certain range of mixing ratios is reached, an explosion can occur upon exposure to a fire source; the risk of explosion depends on the lower explosion limit and the explosion range. The lower the explosion threshold or the wider the explosion range, the greater the danger of an explosion. For example, gasoline has an extremely low lower explosion limit; when the concentration of gasoline vapor in the mixture reaches 1.3%, the mixture can explode with even a very small amount of ignition energy. 　　3) Toxicity Oil vapors possess a certain degree of toxicity. Oil vapors enter the respiratory system through the mouth and nose, causing damage to human organs and leading to acute and chronic poisoning. When the gasoline vapor concentration in the air is 0.28%, people will start to feel dizzy after 4 to 12 minutes; when the concentration reaches 1.13% to 2.22%, acute poisoning occurs, making it difficult for people to stay conscious ； When the oil vapor content is higher, it can cause people to faint immediately, lose consciousness, and even put their lives at risk. Chronic exposure to oil vapors can cause symptoms such as dizziness, fatigue, and drowsiness. Skin that is in frequent contact with oils may suffer from degreasing, dryness, dermatitis, and localized nerve numbness. 　　4) Volatility  Oils can evaporate at relatively low temperatures; for example, about 0.4 cubic meters of gasoline vapor can be produced from 1 kg of gasoline. Kerosene and diesel evaporate more slowly at room temperature. As the temperature rises, the evaporation rate increases. These evaporated oil vapors have a high relative density and are not easy to disperse; they accumulate in areas with poor air circulation or in low-lying spots. When oil vapors and air reach a certain concentration, they are highly prone to combustion and explosion in the presence of an ignition source. 　　5) Electrostatic properties Oil is a non-polar substance with a high resistivity (the resistivity of gasoline and diesel is generally between 1010 and 1015 Ω·cm); it has poor electrical conductivity but a strong ability to accumulate charge. During processes such as pipeline transportation and filling, static electricity is likely to be generated due to friction. When the static charge accumulated in the oil reaches a certain level, electric sparks are generated. If the energy of these static sparks is equal to or greater than the minimum ignition energy of the oil vapor, combustion and explosion will occur immediately. For example, the minimum ignition energy of gasoline is 0.1–0.2 millijoules. During operations such as loading, unloading, filling, and pumping, static electric field strengths and oil surface potentials generated due to flow, spraying, filtering, impact, and other factors can often reach 20,000–30,000 volts. It has been determined that a static voltage of 350–450 V is sufficient for the discharge sparks produced to cause combustion or explosion of flammable gases. 　　6) Flow diffusivity The viscosity of gasoline and diesel is generally very low, allowing them to flow and penetrate easily; moreover, as the temperature rises, viscosity decreases and flow diffusivity increases. When oil tank containers have extremely minor cracks, the oil will seep out of the container walls due to penetration, wetting, and capillary action, evaporating continuously and increasing the vapor concentration in the air, which raises the risk of fire and explosion. 　　7) Thermal expansion: When gasoline and diesel in storage tanks are heated, some of the liquid evaporates into vapor, causing the volume to increase and the vapor pressure to rise. When stored in a sealed, fixed tank such as a diesel dome tank, if the tank is overfilled or if there are hazards such as damaged tank vents or pressure relief valves, the volume of the tank will expand rapidly when heated, exceeding the maximum allowable pressure limit of the container, which can lead to an explosion of the container. 　　Hazard analysis of loading, unloading, and storage processes: In oil depots and oil terminals, during processes such as receiving oil, storing it, transporting it, and loading it onto vehicles for delivery, potential accidents include fires and explosions. The main risk factor leading to fires and explosions is the leakage of oil, which creates flammable and explosive gases. In the presence of ignition sources such as open flames, electrical sparks, static electricity sparks, impact sparks, lightning, or high temperatures, the vaporized oil can catch fire and cause a blaze ； When oil and gas mix with air to reach a certain concentration, an explosive mixture is formed, which can explode upon encountering a source of ignition. 　　According to the receiving and dispatching processes in oil depots, the main risk factors for the generation and accumulation of oil and gas are as follows: 1) Oil unloading operations at the dock. (1) During the process of loading and unloading oil from tankers, large amounts of oil vapor are released from the unloading connections, resulting in the formation of flammable and explosive gases in the area around the unloading points. 　　(2) Loosening of components such as shaft seals, flanges, and valves on oil pumps like unloading pumps and loading pumps, as well as damage to welds and expansion joints in the oil transfer pipelines, can lead to oil leaks; near these leak points, flammable and explosive gases are formed in combination with air. 　　(3) Errors in the operations of the loading/unloading personnel led to oil leakage, resulting in the formation of flammable and explosive gases. 　　2) Oil storage 　　(1) Oil tanks and their surrounding areas are classified as explosion-hazardous zones. The oil in the tank evaporates and leaks through tank accessories such as breather valves, vent holes, light-transmitting holes, and manholes, where it mixes with air to form flammable and explosive gases. 　　(2) Corrosion and perforation of oil tanks, corrosion and perforation or accidental breakage of oil transmission pipelines, as well as leaks in flanges, valves, and other components, result in the leakage of oil. 　　(3) Measurement errors or improper operations lead to the tank being filled beyond its capacity, resulting in oil leakage from the tank and spillage of the liquid. 　　3) Vehicle fueling operations 　　(1) During the process of filling fuel into a vehicle’s tank, large amounts of oil vapor are released from the filling port, creating an explosive hazard zone around the fuel tanker and its vicinity. 　　(2) Failures in the tank body and valves and other accessories of the truck tanker result in oil leakage during loading. 　　(3) Measurement or operational errors result in the amount of oil filled exceeding the capacity of the tank truck, causing the oil to spill out of it.