Safety equipment for overhauling into the tank: gas detector in confined space
In the first half of 2018, more than 20 accidents occurred in confined space operations, and most of the accidents were caused by gas poisoning and suffocation in confined space. The gas detector in confined space has become an indispensable safety equipment for tank inspection and maintenance. The following is a brief introduction to the issues that should be paid attention to in the closed space, especially in the tank operation, for the chemical industry.
First, Common hazards of entering a closed space for overhaul
In the chemical maintenance, the operations in the tank are very frequent, and there are many risk factors, which are accident-prone operations. People in the air with an oxygen content of 19% to 21% behave normally; if the oxygen content drops to 13% to 16%, people will suddenly faint; if the oxygen content drops below 13%, they will die.
Confined space cannot be ventilated with pure oxygen. Oxygen is a combustion-supporting substance. In the case of sparks during operation, it will catch fire and hurt people. Operation in the confined space will be threatened by explosion and poisoning. Oxygen and toxic substances exceeding safe concentrations will cause accidents.
Due to the small activity space inside the equipment, the narrow working site, poor internal ventilation, poor lighting, difficult access for personnel, inconvenient contact, high temperature and humidity in the equipment, and the presence of residues such as acid, dust, smoke, poison, etc., combined with the thin oxygen, slightly If negligent, accidents such as burning, explosion and poisoning may occur, and it is difficult to rescue the injured. Therefore, the safety of working in the tank must be highly valued.
Second, the safety points of the closed space into the tank inspection and maintenance
(1) Establish a permit system for in-tank operations
To work in the tank, you must apply for a permit and get approval. It is necessary to clarify the content, time, and plan of the operation, formulate and implement safety measures, make the division of labor clear, and assign responsibilities to people.
(2) Safety isolation
The equipment for operation must be reliably isolated from other equipment pipelines, and the media of other systems must never be allowed to enter the equipment for maintenance.
(3) Cut off the power
Working in a confined space, frequent contact with electrical facilities, and leakage of lighting fixtures and power tools may cause electric shock and death. Therefore, the lighting power supply should be 36V, and the wet part should be 12V.
For equipment with stirring and other mechanical devices, the drive belt should be removed before the operation, and the power supply of the starting motor should be disconnected and locked so that the mechanical device cannot be started during the operation, and should be hung on the power switch. "Close" warning sign. After the above measures are taken, someone should check and confirm.
(4) Perform ventilation replacement
All equipment that has been replaced with inert gas (nitrogen) must be replaced with air before entering the confined space to prevent large amounts of dangerous gases from remaining and to ensure sufficient sample gas (oxygen content 19.5% ~ 23%). Open all access holes, hand holes, etc. during operation to ensure natural ventilation. For equipment with poor ventilation and small volume, the operator should take intermittent operation or rotation operation, and mechanical ventilation can be used if necessary.
(5) Gas detection
Before entering the tank, the oxygen content of the air in the tank must be analyzed with a closed space gas detector. For hot work in confined spaces, in addition to the content of combustibles in the air meeting the regulations, the oxygen content should be within the range. If the confined space is toxic, the content of toxic substances in the air should be analyzed to ensure that it is below the allowable concentration. Common toxic substances are hydrogen sulfide, ammonia, carbon monoxide, etc.
(6) Acid and alkali operations
When entering the acid and alkali storage tanks, a large amount of clean water should be prepared outside the tank. Human body contact with concentrated sulfuric acid must be wiped off with a cotton cloth, then quickly rinsed with large amounts of clean water and sent to the hospital for treatment. If it is rinsed with clean water first and then cleaned with a cloth, concentrated sulfuric acid will become dilute sulfuric acid, and dilute sulfuric acid will cause more severe burns.
(7) External monitoring
When working in a confined space, generally two or more people should be appointed as guardians outside the tank. The guardian should understand the various properties of the medium, and should be in a position where he can often see all the operators in the tank. His eyes should not leave the operator, and he is not allowed to leave his post without permission. When an abnormality is found in the tank, emergency personnel should be called immediately to try to rescue the victim in the tank.
All personnel who enter the tank for rescue must wear protective equipment such as gas detectors, gas masks, air respirators, and safety belts in confined spaces according to the situation on the spot. They must not be allowed to risk entering the tank to save people without taking any personal protection. To ensure the safety of operations when entering the confined space, a maintenance plan must be made, with dedicated supervision and implementation one by one.
It is worth noting that the analysis of hot work is qualified, which does not mean that no poisoning accident will occur. For example, the content of acrylonitrile in a confined space is 0.2%, which complies with the fire regulations. When the oxygen content is 21%, although it is qualified, it does not meet the sanitary regulations. The maximum allowable concentration of acrylonitrile in the air of the workshop is 2mg / m3. After conversion, 0.2% (volume fraction) is 2167.5 times the maximum allowable concentration. Working in a confined space with an acrylonitrile content of 0.2%, although there will be no fire or explosion, poisoning accidents will occur.
Third, common closed space gas detector specifications
At present, there are various types of gas detectors on the market, but for confined spaces, the selection of gas detectors needs to pay attention to the following points:
(1) Gas selection
The choice of gas depends on the gas in the enclosed space, but in general, combustible gas and oxygen are necessary, and carbon monoxide and hydrogen sulfide are more common. When other gases exist in the enclosed space, carbon monoxide or hydrogen sulfide can be replaced with corresponding gases.
(2) Selection of configuration
The gas detector in the confined space generally involves sampling and analysis before entering the tank, so it is necessary to configure a sampling pump or a pumping gas detector. Personnel should wear gas detectors for monitoring when entering the tank. Therefore, the configuration of the diffusion gas detector + sampling pump is recommended.