Safety hazard of clothing fabrics in gas station safety

The level of the human body's electrostatic potential has an important relationship with clothing (including footwear). During production activities, the human body and clothing are often charged at the same time. If the electrostatic potential on the clothing reaches a certain level, electrostatic discharge will also occur, but the calculation formula of its discharge energy is different from that of the human body. The discharge formula of the conductor cannot be used, but the following formula is used:

E=1/2KσV

In the formula:     

E—discharge energy of clothing or fabric;

K—constant, in actual calculation, the constant K often takes 0.02;

σ—charge density on the surface of clothing or fabric, μC/m2;

V—Electric potential on the surface of clothing or fabric.

Scholars have conducted years of research on the ignitability of electrostatic discharge of clothing fabrics. Wilson put forward a special test report on the ignitability of electrostatic discharge of clothing fabrics in 1985. It shows that the polyester chemical fiber fabric with negative charge has a brush discharge under certain conditions at moderate ambient humidity (50% relative humidity), which is enough to ignite natural gas or a mixed combustible gas of hydrogen and air. For cotton fabrics, when the relative humidity of the environment is 15% or 33% (not at 50%), the discharge with negative charge is enough to ignite the above-mentioned combustible gas.

There have been reports in China that during the removal of nylon yarn, electrostatic discharge was caused, which caused the liquefied gas to catch fire. There are cases where the anti-gas mask (made of plastic) is released to cause burning. There are also electrostatic discharge accidents caused by clothes sorting, hat removal and other operations.

The following describes the results of a set of comparative tests by the Beijing Institute of Labor Protection Science. That is, wear ordinary clothes and anti-static clothing, stand on different grounds, conduct undressing electrification test at the same time, and then compare.

(1) The experimenter wears insulated shoes, stands on insulated ground, and wears ordinary clothes. Then take off the outer jacket and immediately use it to touch the potentiometer contacts to measure the human body potential; at the same time, put the removed jacket on the rope and measure the electric potential of the clothes. The results are shown in the table below.

Table 1  Results of ordinary clothes undressing electrification test

(2) The experimenter wears ordinary clothes inside, and wears anti-static overalls (suits) on the insulated ground, wears insulated shoes, and performs the undressing electrification test as above. The test results are shown in the table below.

Table Electrification test results of undressing for ordinary underwear and external anti-static suit

The test results show that the potential when wearing and removing anti-static work clothes is indeed much lower than that when wearing ordinary clothes, and the anti-static effect is remarkable.

However, even when wearing anti-static work clothes, do not do large-scale actions such as wearing, taking off, or squatting at any time in a dangerous place to prevent the occurrence of static accidents.

(The above content is excerpted from "Industrial Static Electricity" of China Petrochemical Press)

It can be seen that the concept of human body static electricity includes not only the static electricity carried by the human body, but also the static electricity carried by clothing fabrics. Human body discharge is a conductor discharge, and its ignition ability is stronger than the static electricity of clothes and fabrics.

The newly introduced Static Monitoring and Eliminating Device produced by Qingdao ALPTEC can detect the dangerous static power source invading the explosion-proof area in real time, and send out an alarm in time to prevent the static electricity hazard.

The following is an example of the installation of static monitors introduced by Sinopec to prevent static accidents at gas stations.

(An electrostatic monitor is installed on the top of the tanker to detect static electricity in the covered area; a static eliminator is installed in the middle of the tanker to eliminate static electricity and provide visible and audible reminders.)