In a variety of fires, the fire hazards of chemical dangerous goods are serious and difficult to save. There are many special requirements for fire fighting measures. Fire-fighting measures vary depending on the combustion characteristics and combustion products of various types of chemical dangerous goods. A brief introduction to the fire characteristics and common knowledge of chemical dangerous goods within the scope of fire management is given.
First, flammable solid
A substance that exists in a solid form at normal temperature and has a low ignition point. It is a flammable solid when it is exposed to heat, impact, friction or contact with an oxidant. Such as red phosphorus, sulfur, rosin, camphor, magnesium powder and so on. The lower the ignition point, the greater the risk of flammable solids, the greater the risk of flammable solids, especially when the powdery flammable material is mixed with the oxygen in the air to a certain proportion.
The flammable solids burn rapidly and save the difficulty. For this reason, pay attention to the proper amount of flammable solids. Do not store too much in a warehouse. There must be a certain safety distance from the adjacent warehouses. In particular, warehouses storing acidic substances are not allowed to be mixed with flammable solids. . In the event of a fire, use water spray, sand, carbon dioxide or dry powder to extinguish the fire.
Second, flammable liquid
It is present in liquid form at normal temperature, and its flammable liquid with a flash point below 60 °C.
There are many kinds of flammable liquids, including chemical raw materials, fuel oil, organic solvents, additives, and adhesives. Flammable liquids generally have a small specific gravity, a low boiling point, are flammable, volatile, and easily flowable. The vapor volatilized by the flammable liquid is mixed with the oxygen in the air to a certain proportion, and an explosion occurs when exposed to an open flame.
The fire of flammable liquids is developing rapidly, often accompanied by an explosion, which is difficult to save. The fire of flammable liquids is as follows: the fire can be used for the fires of hydrocarbon-based compounds such as fuel oil, ethers, benzene and benzene which are light and insoluble in water. The fire can be saved with carbon dioxide at the beginning of the fire, but it can not be used, otherwise it will expand the fire. .
For water that is insoluble in water and larger than water, such as carbon disulfide, it can be saved by water, because water can cover the above substances and extinguish the fire.
Water-soluble flammable materials such as methanol, acetone, etc. can be used in the event of fire, misty water, chemical foam, dry powder, can also be used with 1301, 1211 halogenated alkane series fire extinguishing agent.
Third, spontaneous combustion items
A self-igniting product, which itself emits heat due to physical, chemical, or biological changes and causes self-ignition without self-fire.
Self-igniting materials are chemically active, have low ignition points, are easily oxidized, and can emit a large amount of heat when oxidatively decomposed. When the heat reaches its own ignition point, it burns by itself. For example, the white phosphorus has a burning point of 34 ° C, and it is easy to spontaneously ignite in the air. The burning point of nitrocellulose is 120 ° C to 160 ° C. Spontaneous combustion may occur under the conditions of long storage, poor ventilation and large stacking. This is the reason why table tennis self-ignition has been repeated in commercial warehouses.
When pyrophoric articles are on fire, triethylaluminum cannot be saved with water, and the rest can be saved with a large amount of water. Sand, carbon dioxide and dry powder fire extinguishing agents can also be used.
Fourth, water burning products
Anything that absorbs water vapor in the air or contacts moisture to quickly decompose and produce high temperature, and emits flammable gas to cause combustion is called water burning.
According to its characteristics can be divided into the following categories:
1. Active metals such as lithium, sodium, potassium, etc. react chemically with water to produce flammable hydrogen.
2. Hydrogen is also generated when a metal hydride such as lithium hydride, sodium hydride, calcium oxide or the like is brought into contact with water.
3. Metal carbides such as calcium carbide contact with water to produce flammable acetylene gas.
4. Even sodium sulfite (insurance powder) produces flammable hydrogen, hydrogen sulfide and sulfur dioxide when it meets water.
In addition to the action of water, the water-burning substance reacts violently with acid and oxidant, and is more dangerous.
In case of water burning, water will burn and even explode, so the fire caused by the fire is absolutely forbidden to use water and water-containing substances such as foam fire extinguishing agent. Dry sand, dry powder and stone powder can be used to extinguish the fire.
V. Oxidizer
The oxidant referred to as chemical dangerous goods refers to a substance that has a strong oxidizing ability; a decomposition reaction occurs under certain conditions to cause combustion and explosion. Such as chlorate, perchlorate, nitrate and so on.
The main feature of the oxidant is its strong oxidizing property and instability, and it reacts immediately when it comes into contact with a reducing agent, an acid or an organic substance to cause combustion. When the match head we saw every day rubbed on the outside of the matchbox, the match head burned immediately, because the main component of the match head was red phosphorus, and the outside of the matchbox was coated with a layer of oxidant potassium chlorate. After the friction, the potassium chlorate oxidized the red phosphorus to burn. . Many oxidants are extremely unstable. When they are subjected to friction, vibration, and collision, they will decompose, releasing a large amount of oxygen and heat. If they come into contact with flammable materials, they will burn or explode. To extinguish such fires, water, foam, and carbon dioxide are prohibited. Fire can be done with dry sand, dry soil, and dry powder.
6. Compressed gas and liquefied gas
In the production, the required gas is often stored in a cylinder by pressurization. Some gases also liquefy the gas when it is pressurized, which is called liquefied gas.
All compressed and liquefied gases must be packed in special pressure cylinders. Generally, the working pressure of the gas cylinder is above 150kg/cm2, so the gas is heated and the expansion pressure increases after the fire. If the gas pressure exceeds the pressure of the gas cylinder, there is a possibility of explosion. The explosion power of an ordinary oxygen cylinder is equivalent to 5 tons of TNT explosives. If it explodes, the consequences will be very serious.
When a compressed gas or liquefied gas is involved in a fire, it should be quickly saved. If it is not timely, the unfired gas cylinder must be rescued to a safe place in time. When it is impossible to move, the gas cylinder can be sprayed with mist water to cool it, prevent the gas from heating up and expanding, and explode, and extinguish the fire with carbon dioxide.
Firefighters should also pay attention to anti-virus when fighting such fires, because many high-pressure gas cylinders are poisonous. (Author Liu Beichen)
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