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Requirements for preservatives due to rising temperatures

1. The temperature rise increases the volume of dangerous chemicals and increases the pressure.


Thermal expansion and contraction are the general physical phenomena of objects. The flammable liquid has a relatively large expansion coefficient and is stored in a closed container. The volume is easily expanded after being heated, and the vapor pressure is increased to increase the internal pressure of the container. If the pressure exceeds the pressure of the container, the container may be damaged. Even bursting. The phenomenon of "drums" in the iron drums containing flammable liquids during the hot season and the bursting of the glass containers are all due to thermal expansion. If the container is open, the liquid will expand beyond its capacity and overflow, causing run, run, drip, and leak. For example, the volume expansion coefficient of liquefied petroleum gas is 11 to 17 times that of water, and its volume is greatly affected by temperature. Therefore, when using liquefied petroleum gas in the home, it is forbidden to use boiling water to heat or bake. In order to prevent this from happening, in addition to taking measures to prevent heat and temperature, it is necessary to control the filling amount, that is, to fill according to the specified filling factor.


As far as gas is concerned, its coefficient of expansion is even greater. The gas is usually packed in a cylinder, and as the temperature increases, the pressure inside the cylinder increases. For example, when the oxygen cylinder is at 0 ° C, the pressure inside the bottle is 150 kg / cm; when the temperature is raised to 54.6 ° C, the pressure is raised to 180 kg / cm 2 . If the pressure is too high, the cylinder will be in danger of explosion.


2. The temperature rises to accelerate the evaporation of the liquid


The ability of the flammable liquid to evaporate is not only related to the nature of the liquid itself, but also to the surrounding environment, where temperature is more important. The higher the temperature, the faster the flammable liquid evaporates, the greater the vapor concentration on the liquid surface, the greater the possibility of forming an explosive mixture with air, and the greater the risk of fire and explosion. The evaporation rate of different liquids varies with temperature, boiling point, specific gravity, and pressure. The ease with which a flammable liquid evaporates is expressed by the boiling point, and the lower the boiling point, the stronger the evaporability of the liquid. Some flammable liquids have a very low boiling point. For example, at normal pressure, the boiling point of gasoline is 50 ° C. If the ambient temperature exceeds its boiling point, it is dangerous.


3. Temperature rise accelerates oxidative decomposition and spontaneous combustion


Due to environmental factors such as temperature and humidity, many dangerous chemicals are easily decomposed after being heated, releasing oxygen or even oxygen atoms, causing other substances to oxidize and releasing a large amount of heat. If the ventilation is poor, the heat will not accumulate, causing the temperature to rise, which will accelerate the oxidation rate and generate more heat, which will cause the temperature to continue to rise. When the temperature reaches the spontaneous ignition point of the substance, the substance will spontaneously ignite. Some substances with low self-ignition point, such as yellow phosphorus (spontaneous ignition point is 30 °C), if not properly stored, when the summer temperature exceeds its spontaneous ignition point, it will spontaneously ignite when exposed to air.


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