Precautions for sewage treatment safety accidents

1、 Common toxic and harmful substances in sewage well / pool

1. Hydrogen sulfide

It is the main cause of acute poisoning accidents in this industry. Hydrogen sulfide exists in the form of colorless gas with rotten egg odor under normal temperature, which can be dissolved in water, and can explode when the concentration in the air reaches 4.3% – 45.5%. This gas is not only a kind of irritant gas, but also a kind of asphyxiating gas of strong neurotoxic poison. Low concentration (30-300mg/m3) can cause tears, cough, dizziness, headache, chest tightness, fatigue, nausea, vomiting and other symptoms after exposure. Medium concentration (300-700mg/m3) can cause limb dyskinesia and transient disturbance of consciousness after exposure, except for dizziness, headache, chest tightness, fatigue, nausea, vomiting and other symptoms. High concentration (above 700mg/m3) can directly affect the brain nerve center through the chemical receptors in the human body after exposure, resulting in respiratory paralysis or further stop, abnormal heartbeat and further stop, resulting in delirium, convulsion, rapid coma, etc., resulting in “lightning like” coma or death (above 1000mg/m3), and at the same time. Accompanied by pulmonary edema. In addition, hydrogen sulfide also has cytotoxic effect, producing symptoms similar to cyanide poisoning. After being sent to hospital for treatment, it may also aggravate the disease and cause death.

2. Methane

It is the main cause of acute poisoning accidents in this industry. Methane exists in the form of colorless and odorless gas at normal temperature, which is lighter than air and can explode in air. This gas is a kind of simple asphyxiating gas with anesthetic like effect. When the air concentration reaches 25% – 30%, brief inhalation may cause dizziness, headache, chest tightness, fatigue, nausea, vomiting and other symptoms. After continuous inhalation, besides dizziness, headache, chest tightness, fatigue, nausea, vomiting and other symptoms, it may cause limb dyskinesia, temporary disturbance of consciousness, etc. When inhaled in large quantities, it can directly act on the brain nerve center through the chemical receptors in the human body, resulting in respiratory paralysis or further stop and abnormal heartbeat and further stop, resulting in delirium, convulsion, rapid coma, etc., resulting in “lightning like” coma or death.

The acute poisoning caused by the sewage treatment tank and the construction motor well is not only caused by the above two gases floating out of the sewage during daily accumulation and agitation, but also caused by hypoxia caused by the above gases.

3. Carbon dioxide

It is the secondary cause of acute poisoning safety production accidents in this industry. Carbon dioxide exists in the form of colorless and odorless gas under normal temperature, which is heavier than air and has no flammability and explosion. This gas is a kind of simple asphyxiating gas. Its content in natural air is 0.03%. It can excite the respiratory center at low concentration and inhibit the respiratory center at high concentration. Acute poisoning is often accompanied by hypoxia. Therefore, the daily so-called carbon dioxide poisoning is not simple, but actually caused by hypoxia. High concentration short-term inhalation can cause dizziness, headache, chest tightness, fatigue, nausea, vomiting and other symptoms. Continuous inhalation may cause limb dyskinesia, temporary disturbance of consciousness, etc,. When inhaled in large quantities, it can directly act on the brain nerve center through the chemical receptors in the human body, resulting in respiratory paralysis or further stop, abnormal heartbeat and further stop, resulting in delirium, convulsion, rapid coma, etc., leading to death.

4. Cyanide, hydrogen cyanide

It is the secondary cause of acute poisoning safety production accidents in this industry. Sodium cyanide (Shannai) and potassium cyanide in cyanide are highly toxic substances; Potassium ferrocyanide (yellow blood salt), iron ferrocyanide (Prussian blue), potassium ferrocyanide (red blood salt) and other low toxicity, but release highly toxic cyanic acid in case of acid; Cyanide generally does not cause poisoning unless it enters the eyes by mistake or damages the skin. Hydrocyanic acid is a colorless, bitter almond flavored liquid that releases steam and is highly toxic. Hydrogen cyanide exists as a colorless, bitter almond flavored gas at room temperature. All inorganic cyanogens are asphyxiating substances with strong blood toxicants. A very small amount can cause dizziness, headache, chest tightness, fatigue, nausea, vomiting and other symptoms. Severe poisoning will immediately lead to death. Inhale high concentration hydrogen cyanide gas (300mg/kg) for a short time and die immediately.

5. Arsenide, hydrogen arsenide

It is the secondary cause of acute poisoning safety production accidents in this industry. Arsenic trioxide (arsenic) in arsenide is highly toxic. Arsenic pentoxide, arsenic disulfide (orpiment) and arsenic disulfide (realgar) are low toxic. Arsenide releases highly toxic hydrogen arsenide in the presence of acid. Highly toxic arsenic generally does not cause poisoning unless it accidentally enters the mouth and eyes or damages the skin. Hydrogen arsenide exists as a colorless, garlic smelling gas at room temperature. Arsenic is a kind of strong hemolytic poison, which mainly causes kidney damage, heart, liver and skin damage. Inhalation of a small amount of hydrogen arsenide can cause dizziness, headache, chest tightness, fatigue, nausea, vomiting and other symptoms. Severe poisoning will immediately lead to death. Inhalation of high concentration hydrogen arsenide gas (250PPM) for a short time will lead to immediate death, and inhalation of 25-50 ppm for 30 minutes will also lead to death.

6. Ammonia gas

It is the secondary cause of acute poisoning safety production accidents in this industry. Ammonia gas exists in the form of colorless, urine odor and irritating gas at normal temperature, which mainly causes upper respiratory tract irritation and corrosion, and seriously leads to chemical pneumonia, pulmonary edema, even acute pulmonary hemorrhage, pneumothorax, emphysema, etc., and burns damage to eyes and skin. Inhalation of a small amount of ammonia (more than 100mg/m3) can cause upper respiratory tract irritation symptoms, such as cough, tears, runny nose, chest tightness, fatigue, nausea, vomiting, laryngeal edema, dyspnea, etc. severe (1750-4500mg/m3) will immediately produce chemical pneumonia and pulmonary edema, and may lead to death.

The above content is about the damage caused by toxic substances in the sewage pool. You must pay attention to protective measures when cleaning the sewage pool.

2、 How to clean the sewage well / pool correctly?

Suffocation and poisoning in cleaning up the pool are also the most common accidents in sewage treatment. Summer is the peak season for toxic gas production in sewage treatment plants, and it is also the season for high incidence of accidents in sewage treatment plants. Previously, the author also suggested that we should not do something irrelevant to production such as desilting in summer. If production is indeed affected, underwater operations such as frogmen can be used to replace it, However, some managers have weak safety awareness and can not achieve effective safety protection, resulting in the disappearance of many lives!

（1） Cleaning steps and precautions of sewage tank

1. The sewage inlet valve shall be closed before the sewage tank is cleaned, and the sewage in the tank shall be drained as far as possible to maintain natural ventilation for more than 24 hours. If mechanical cleaning can be adopted, manual cleaning shall not be adopted as far as possible.

2. Operators working in the pool must be healthy and conscious. Persons under the age of 18, persons with respiratory, cardiovascular, allergic or skin allergies, and women shall not engage in this type of work.

3. The sewage pool cleaning operation sheet must be filled in for the sewage pool cleaning operation. The person in charge of safety shall designate the site safety personnel. The on-site safety officer must make technical and safety disclosure to the decontamination personnel, and both sides of the disclosure shall sign on the sewage pool cleaning operation sheet.

4. During the operation in the pool, the on-site safety officer must be present to supervise the implementation of safety measures in the whole process, and more than 2 supervisors must be appointed.

5. The personnel entering the pool must wear corresponding protective equipment (gloves, helmet, safety belt, safety rope, oxygen tank and toxic gas alarm), and the on-site safety officer shall check the safety measures before operation.

6. Before entering the pool, a multi-functional gas detector must be used to detect harmful gas. The oxygen content in the air of the workplace should be 19.5% ~ 23%. If the oxygen content in the air is lower than 19.5%, there should be an alarm signal. The concentration of toxic substances shall comply with GBZ 2.1 and GBZ 2.2. If it is confirmed that the dangerous gas alarm does not exceed the standard, the safety officer shall be responsible for the supervision on site and report to the first safety responsible person for signature before going down to the pool for operation.

7. The multi-functional gas detector is used for gas detection. When the alarm of dangerous gas exceeding the standard is determined, the multi-functional gas detector is used for detection after 15 minutes of forced ventilation by the blower. If the alarm of dangerous gas not exceeding the standard is detected, it shall be implemented according to Article 6.

8. After the blower is used for mechanical ventilation, the multi-function detector monitors and gives an alarm when the blower exceeds the standard, and immediately informs the safety competent department to send personnel to the site to check the safety measures. After the factory director in charge of production signs and agrees, he can go down to the pool only after wearing gloves, safety helmet, safety belt, safety rope and isolation breathing mask, and make a record of the operation. The time of the operation shall not exceed 30 minutes.

9. After lowering into the pool, tools and accessories must be hoisted with tool bags. Throwing is strictly prohibited. There shall be no stones, bricks and other objects that may cause damage within one meter around the operation well. The personnel on the pool shall do all the safety work for the personnel on the pool.

10. A restricted area shall be marked out on the ground of the construction area, and construction signs shall be hung to prevent unauthorized people from entering. Safety ladders shall be set at the pool side.

11. It is strictly forbidden to smoke or carry inflammables and explosives into the pool for operation. If hot work is required and the conditions for hot work are met, ventilation equipment must be used, fire-fighting equipment must be equipped, and the hot work permit must be issued by the safety authority before operation into the pool.

12. Open flame lighting and non explosion-proof equipment are not allowed to be used in the clean-up area with combustible gas.

13. If the production and business operation unit does not have the cleaning operation conditions, it shall contract the operation items to the construction unit with corresponding qualifications, and sign the contract and safety production agreement.

14. If the cleaning operation takes a long time, the operators shall go down to the pool in turn. If the operators under the pool feel dizzy, weak legs, suffocation, nausea and other discomfort, they must leave the pool immediately for rest.

15. During the cleaning operation, the on-site safety officer and supervisor must stick to their posts, concentrate on their work, do not engage in other operations, keep in touch with the underground operators, pay attention to observing and identifying the status of the underground operators, find problems in time, and avoid safety accidents.

16. In case of any dangerous operation, the operators shall be rescued immediately and leave the site for rescue, and the competent safety department and relevant leaders shall be notified at the same time.

（2） Accident rescue measures

The accident rescue personnel shall take personal protection and necessary preventive measures, and then quickly put into the risk elimination work. Irrelevant personnel within the dangerous range shall be evacuated and evacuated from the site quickly. The rescue personnel must obey the command, understand the toxic substances and site conditions, and wear complete protective equipment. The rescue personnel must rescue under the premise of ensuring their own safety. More than two rescuers must be grouped to enter the toxic gas area. Rescue the injured to a safe area in time.

（3） First aid measures for accidents

1. First aid treatment for hydrogen sulfide poisoning: quickly remove the patient from the poisoning site to a place with fresh air, remove foreign bodies in the mouth and contaminated clothes, immediately inhale oxygen, untie the tie and trouser belt to keep the respiratory tract unobstructed, and call 120 for help at the same time. In case of cardiac arrest and respiratory arrest, artificial respiration should be performed immediately (chest compression artificial respiration should be used, mouth-to-mouth artificial respiration should not be used, and several layers of wet gauze should be separated from the patient as a last resort) and extracorporeal cardiac compression should be performed to enhance respiratory capacity until they are delivered to the hospital.

2. First aid treatment for ammonia poisoning: quickly remove the patient from the poisoning site to a place with fresh air, remove foreign bodies in the mouth and contaminated clothes, thoroughly wash the contaminated eyes and skin, call 120 emergency telephone for help, untie the tie and trouser belt, and keep the respiratory tract unobstructed.

3、 How to prevent explosion of sewage treatment

（1） Hazard of sewage treatment system

1. Presence of explosive gas mixture

Soluble and combustible gases often exist in the sewage discharged by chemical enterprises. Under certain circumstances, these gases and liquids are easy to form explosive mixtures, which are manifested in several aspects: first, if the equipment system is damaged or overflowed due to violation of operation, flammable and explosive gases are easy to enter the sewage, which brings adverse reactions to the safety production of the system. Second, after high-temperature steam and sewage enter the sewer, the temperature of sewage will rise, and the flammable liquid evaporated may cause security. Third, in the process of gas absorption and desorption, if flammable liquid or flammable gas is encountered, these gases will be resolved when the temperature rises. At this time, flammable liquid will continuously overflow from the outlet.

2. Hazardous substances will be generated

Various substances discharged into the sewer will react with each other, which is likely to produce flammable, explosive and even spontaneous combustion substances.

3. Fire spread

Sewage pipelines are all over the enterprise area, and the explosion or fire often spreads along the sewage treatment system. If it is not stopped in time, it is likely to cause chain damage.

4. Ignition source

There are various ignition sources in sewage treatment sources, including mechanical expansion, friction sparks, welding sparks, lighted cigarette butts, and sparks in vehicle exhaust pipes.

（2） Safety measures for sewage treatment system

1. Set up sewage pipeline

The water channel of the enterprise is strictly prohibited to pass through the residential area, tank group and production device. The sewage channel of the workshop must be provided with open ditches and pipelines. When the open ditches are open for treatment, purified water is required to prevent secondary pollution. For outdoor sewer pipelines, they need to be closed and covered with soil and concealed pipes.

For domestic sewage, it is strictly prohibited to connect directly with other waterways. If it is impossible to avoid mixing domestic sewage with chemical sewage, the pump station can be used for transportation, but flammable and explosive gases should be avoided from entering.

2. Prevent potential safety hazards caused by mixed contact

During the actual operation, it is forbidden to mix the inflammable and explosive substances decomposed into one time. At the same time, clean water must be used to clean the workshop floor and the pipes and wells of cleaning equipment to prevent the accumulation of inflammable and explosive substances in the pipes. When cleaning up the sewage from dangerous goods equipment, it is necessary to conduct purification treatment first to discharge the hazardous substances, flammable and explosive substances. The sewage can be discharged only after the discharge meets the standard requirements.

3. Avoid explosive gas mixtures

It is strictly forbidden to directly discharge the waste water discharged from the process equipment into the sewer. Before discharge, it is necessary to completely remove the flammable gas and liquid in it. This can be achieved by setting up a local degassing and evaporation system in the workshop and installing a plant wide sewage degassing system. In addition, it should be noted that direct discharge of sewage exceeding 40 ℃ should be avoided, and flange and liquid sealing equipment should be set in the drainage pipeline from process equipment to sewer.

4. Avoid combustion and explosion spreading along the pipeline

For the sewage treatment system, it is necessary to set water seal well to avoid combustion and explosion extending along the pipeline. When setting water seal, the following problems should be noted:

Each production sewage discharge system needs to be equipped with corresponding water seals. If the length of the pipeline between the two water seals exceeds 300m, it is necessary to add water seal wells. Water seal shall be set for furnace, pump, tower and heat exchange equipment in process unit. A water seal shall be added to the inlet and outlet pipes of the oil separator, and the inspection well shall use the closed mode. If the production facilities need to design an open ditch for drainage, a water seal well shall be used to separate the open ditch, and the length shall be controlled within 20m.

5. Prevent damage to the sewage treatment system

In order to prevent water wells, sewer pipelines and water chambers from corrosion, it is necessary to select materials with high corrosion resistance. For large-diameter water pipes, reinforced concrete pipes can be used, and for medium and small-diameter pipelines, acid resistant ceramic pipes can be used. Buildings can be coated with asphalt. For equipment for transfer and sewage treatment, alloy steel or carbon steel can be used.

In order to prevent sediment from blocking pipelines, water pipes and facilities, grit chamber and clarification tank shall be used for purification before sewage discharge to eliminate suspended particles. At the same time, in order to prevent solid particles from settling in sewer pipelines, inclined design method shall be adopted to prevent sewer pipelines. The specific inclination can be calculated by formula.

6. Eliminate ignition source

For the sewers with accumulated steam and combustible gas, it is strictly prohibited to operate before the danger is eliminated. It is strictly prohibited to set exhaust pipes within 15m from the places where sparks and open flames are emitted. For the buildings and equipment of the sewage treatment plant, the fire separation shall be set according to the code for fire protection design of petrochemical enterprises. If the combustible gas and liquid cannot be discharged normally during production and maintenance is required, the emergency alarm must be raised to prevent the discharged combustible gas and liquid from detonating the fire source.