Hazard and protection of nitrogen
Ren Jianqing
Sinochem International Ministry of Safety and Environmental Protection
The proportion of nitrogen in the atmosphere is 78% because nitrogen is inactive and does not support combustion or react directly with other substances at normal temperatures. When the nitrogen content in the environment gradually increases and the oxygen content gradually decreases to 19%, people tend to be dizzy. As the proportion of oxygen continues to decline, it will cause simple asphyxia. Its main performance is the body's lack of oxygen, dizziness, headache, difficulty breathing, rapid, rapid heartbeat, weak and fast pulse, mental uneasiness, general weakness, muscle coordination and movement disorders. If you enter a device or container that is completely filled with nitrogen, people will faint and suffocate immediately until they die. In the usual chemical production, nitrogen is often used to evacuate the combustible gas in the pipeline. Because nitrogen is colorless and odorless, the low-oxygen environment generated by nitrogen purge is often ignored by workers and even grassroots managers.
Let's take a look at the hazards of nitrogen by the following two cases of workers entering the confined space in the Varel refinery in Delaware, USA.
CSB conducted a detailed analysis of the incident and issued a security bulletin. The accident occurred on a facility that processed 180,000 trucks of crude oil a day, and the contractor personnel installed the pipeline. The tank below the staff's location has just been purged with nitrogen, and the metal column at the top of the tank is also wrapped around a warning band that is prohibited from entering, and is affixed with a warning sign that is “dangerous†and is not allowed to enter. However, there is no indication of the existence of a nitrogen hazard. The maintenance work ticket did not safely cover the presence of nitrogen. The operator found a roll of tape at a position 5 feet from the bottom of the tank during the tank cleaning. The tape must be taken out before the pipe is installed. They could choose to have the professional limited space working group come to clean the tape, but the process took several hours and the time for them to change the bend was not much. In order to avoid delay, an operator was Near the opening, I tried to hook the tape with a wire, but it didn't work. An operator sits on the edge of the boot and two legs reach into the can, but he still can't remove the tape. At this time, there are two kinds of accidents. The operator, under the supervision of the person next to him, tried to quickly enter the tank, pick up the tape and go out. Or it is because of the high concentration of nitrogen in the tank and suddenly stuns and loses consciousness and falls into the tank. Immediately after seeing the outside, the guardian who set up the ladder set up the ladder into the tank to help the fainted worker. However, this is a tragedy that has worsened. Because there is no air respirator, he has fallen. Other personnel on the site immediately pressed the emergency alarm button and used the intercom to inform the situation. When the rescuer arrived, the hand-held tester on the hand of the fainted worker showed that the oxygen content was less than 1%. Professional rescuers put on air breathing apparatus and set up hinges to enter the tank for ambulance, but this time has passed 10 minutes, and finally 2 workers died and died. The accident occurred because the employee believed that he could quickly enter the tank and take out the tape and leave quickly. American security experts pointed out that this is a wrong idea. Holding your breath and getting in and out quickly is a very unreliable thing, because the time you breathe is not enough to accomplish this. Inhalation of high concentrations of nitrogen in the confined space inlet can also cause oxygen deficiency and fainting. It is important to point out that after a colleague is in distress, other people will be very eager to rescue, even if the PPE equipment is not worn, they will enter and die. This is not a question of the staff's judgment of the accident, but a question of training. This will not happen if the staff are properly trained and exercised.
This case shows that in the position close to the opening of the confined space, when hypoxic air is inhaled into the lungs, affecting the judgment and coordination of the person, the person will eventually fall, stun, or die without finding an exit. As can be seen from the accident, the rush into the confined space and other workers entering the tank without protective measures reflect the lack of understanding of the dangers of nitrogen. Otherwise, this tragic accident can be completely avoided.
Precautionary measures: Identify the risk of nitrogen. Locations with high concentrations of nitrogen must be clearly identified and alerted. All employees and temporary workers should be strengthened in education and exercises to enter the restricted space knowledge, and they can be employed after passing the examination.
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