Flammable liquid (2)

(2) Steam explosion

Another major hazard characteristic closely associated with high flammability is the explosive vapour of flammable liquids

The larger the explosion limit range and the lower the lower explosion limit, the greater the risk, as shown in Table 15-1

According to the flammable and explosive characteristics of flammable liquids, the basic protective measures are: ① reduce volatilization; ② increase the number of air replacements for supply and exhaust; ③ avoid fire sources (including high heat, static electricity, collisions, etc.

(Three) easy to generate static electricity

Many flammable liquids are non-polar substances.

1.

The internal cause of static electricity generated by flammable liquids is a small dielectric constant and a large resistivity

The dielectric constant represents the degree of polarization of the dielectric, that is, the ability to bind the charge.

Resistivity is a physical quantity used to express the resistance characteristics (conductivity) of a substance

Generally speaking, the dielectric constant is less than 10F/m, especially the liquid with small 4F/m and resistivity greater than 10 ⁶ Ω·cm has the ability to generate static electricity

Table 15-2 Dielectric constant and resistivity of commonly used flammable liquids

Whether or not static electricity is generated, or how much static charge is generated, there is no critical value in the dielectric constant and resistivity.

2.

1) Flow rate

When the liquid is flowing (straight, opposite or turbulent) molecules collide with each other, it is easy to generate static electricity, the faster the speed, the more static charge is accumulated, and the higher the static voltage

2) Material of contact surface

If the inside of the container or pipe wall that is in contact with flammable liquid is made of insulating material, static charge is easily generated

3) Roughness of the contact surface

If the inside of the container or pipe wall in contact with the flammable liquid is rough, or there are many elbow valves, it will greatly increase the turbulence of the flammable liquid, that is, increase the chance of collision between molecules and the inner wall of the molecule, resulting in a large increase in electrostatic charge

4) Humidity of the environment

The amount of static electricity generated by flammable liquids is also related to the humidity of the medium air.

No matter which of the above-mentioned conditions generates static electricity, when it accumulates to a certain level and reaches a certain voltage, a discharge phenomenon will occur
.
If the environment where the electrostatic sparks are released reaches the explosive limit, it is enough to cause combustion or explosion
.

3.
Highly fluid diffusivity

Flow is the continuity of liquids, and the molecules of flammable liquids are mostly non-polar molecules with low viscosity.
Not only are they very easy to flow, but also due to the effects of penetration, infiltration and capillary phenomena, even if the container has only very small cracks, Flammable liquid will also seep out of the container wall, expand its surface area, and continuously volatilize, increasing the concentration of flammable liquid vapor in the air, thereby increasing the risk of combustion and explosion
.

4.
Thermal expansion

The expansion coefficient of flammable liquid is large, and the volume is easy to expand after being heated.
At the same time, its vapor pressure also increases, which increases the internal pressure in the sealed container, causing "drums" or even bursting, which will occur when the container bursts.
Sparks cause combustion and explosion
.
Therefore, flammable liquids should be stored away from heat, and there should be more than 5% of the gap in the container during filling, and it should not be filled
.

5.
Avoid oxidants and acids

Some flammable liquids come into contact with oxidants or oxidizing acids (especially nitric acid ), which can react violently and cause combustion and explosion
.
This is because flammable liquids are all organic compounds, which can react with oxidants and generate a lot of heat, causing the temperature to rise to the ignition point and cause combustion and explosion
.
For example, ethanol will burn when it comes in contact with the oxidant potassium permanganate , and it will burn when it comes in contact with an oxidizing acid such as nitric acid .
Turpentine will burn immediately when it meets with nitric acid
.
Therefore, flammable liquids must not come into contact with oxidants and oxidizing acids, and they must not be stored in the same warehouse, cabinet or shelf
.

6.
Toxicity

Most flammable liquid and vapor in varying degrees of toxicity, such as methanol , benzene, carbon disulfide and the like
.
Not only inhalation of the vapor will cause poisoning, and some absorption through the skin can also cause poisoning accidents
.

Even if flammable liquids such as alkanes are not very toxic, if they are inhaled or absorbed for a long time without paying attention to labor protection, there will be a risk of chronic occupational diseases and even acute poisoning
.
Therefore, it is necessary to avoid extensive operations and operate strictly in accordance with regulations.
While doing personal protection, increase the number of air replacements for supply and exhaust to ensure the health and safety of the operating environment
.

Related Links: Flammable Liquids (1)