Popular science on hazardous chemicals: Hydrogen sulfide

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In this issue of our series on hazardous chemicals, we’ll be discussing hydrogen sulfide. Those of you who work with this substance should pay close attention. I. Physical properties: Hydrogen sulfide is an inorganic compound. Under normal conditions, it is a colorless, flammable acidic gas. At low concentrations (0.13 ppm–4.6 ppm), it has a rotten egg odor ； At concentrations higher than 4.6 ppm, there is no odor (because high concentrations of hydrogen sulfide can numb the olfactory nerves). It is soluble in water; at 0 °C, 1 mole of water can dissolve about 2.6 moles of hydrogen sulfide. An aqueous solution of hydrogen sulfide is called hydrosulfuric acid; it is a weak acid. When heated, hydrogen sulfide escapes from the water. http://p3.itc.cn/images01/20201202/ea25defb9ed1419eaef4f01bf5c47854.png II. Chemical properties: instability, flammability, precipitability, strong reducibility III. Hazards of hydrogen sulfide Hydrogen sulfide gas is a highly toxic gas that can be fatal; it is second only to cyanides in terms of toxicity. Its toxicity is 5 to 6 times that of carbon monoxide (CO), and 7 times that of sulfur dioxide (SO2). Its lethal concentration for the human body is 500 ppm, while under normal conditions, the safe critical concentration for humans should not exceed 20 ppm. It binds with alkaline substances in human tissues to form sodium sulfide, thereby causing tissue damage. Inhaling a small amount of high-concentration hydrogen sulfide can be fatal in a short time. When exposed to extremely high concentrations of hydrogen sulfide (above 1000 mg/m3), the human body may experience a \"electric shock-like\" death, meaning sudden collapse, as if struck by electricity. The main targets of hydrogen sulfide toxicity are the central nervous system and respiratory system; damage to organs such as the heart can also occur. It is inhaled into the body, passes through the respiratory tract and lungs, and is then transported by the blood to various organs in the body. First, it irritates the respiratory tract, causing a dull sense of smell and coughing; in severe cases, it can cause burns ； Eyes become irritated; in severe cases, blindness may occur ； It stimulates the nervous system, causing dizziness, loss of balance, and difficulty breathing ； The heart beats faster, and in severe cases, the heart suffers from oxygen deficiency leading to death. IV. Its main uses are in the synthesis of phosphors, as well as in the manufacture of electroluminescent devices, photoconductors, and photometric exposure meters. Reducing agents in organic synthesis. Used for metal refining, pesticides, pharmaceuticals, and catalyst regeneration. General reagents. Various sulfides are produced. It is used to manufacture inorganic sulfides, as well as in chemical analysis such as the identification of metal ions. V. Personal protection
Personal protection and engineering controls against hydrogen sulfide (H₂S):
Respiratory protection: When the concentration in the air exceeds the permissible limit, wear a filtering gas mask (half-mask). During emergency rescue or evacuation, it is recommended to wear an oxygen respirator or an air respirator. Eye protection: Wear chemical safety goggles. Physical protection: Wear anti-static work clothes. Hand protection: Wear chemical-resistant gloves. Other precautions: Smoking, eating, and drinking are prohibited at the workplace. After finishing work, take a shower and change clothes. Change work clothes promptly. Operators should learn self-rescue and mutual rescue. When entering tanks, confined spaces, or other areas with high concentrations, supervision must be provided. Engineering controls: Ensure strict sealing, and provide adequate local exhaust ventilation as well as general ventilation. Provide safety showers and eye wash stations. VI. Emergency response in case of leakage: In the event of a sudden leakage, the personnel on site should promptly report it to the relevant authorities. Rapidly evacuate personnel from the leak-contaminated area to upwind locations, and establish a perimeter based on the circumstances of the incident. For minor leaks, isolate an area of 150m; for major leaks, isolate 300m, and strictly restrict access. Ventilation should be carried out before entering a confined space. Cut off the source of fire. It is recommended that emergency responders wear self-contained positive-pressure breathing apparatus and anti-static work clothes. Enter the site from the upwind side. Seal the source of leakage as much as possible. Ensure proper ventilation to accelerate dispersion. Dilute and dissolve with spray water. Construct dikes or dig pits to contain the large amount of wastewater generated. If possible, use an exhaust fan to send the residual gas or escaping gas to a scrubber tower or a fume hood connected to the tower. Or pass it through an iron(III) chloride aqueous solution, with a check valve installed in the pipeline to prevent the solution from flowing back. Leaking containers must be properly handled, repaired, and inspected before being used again. Emergency response after a hydrogen sulfide fire: In the event of a fire or explosion, personnel on site should immediately alert the relevant authorities. Evacuate unrelated personnel to the upwind area in a timely manner, and establish a safety zone depending on the circumstances of the accident. In the event of a fire during transportation and the tank truck is located in the fire area, immediately establish a 800-m exclusion zone around it. Fire extinguishing method: Firefighters must wear full-body fire and gas-resistant suits and extinguish the fire from the upwind direction. Cut off the gas supply. If the gas supply cannot be cut off, it is not allowed to extinguish the flame at the leak site. Use water spray to cool the container; if possible, move the container away from the fire to an open area. Extinguishing agents: fogged water, alcohol-resistant foam, dry powder. VIII. Early rescue measures and general nursing principles for hydrogen sulfide poisoning: timely and effective rescue, correct and feasible methods, comprehensive and meticulous measures, and scientific medical monitoring. Before entering the area contaminated by toxic gases to rescue those poisoned, rescuers must wear appropriate protective clothing, including masks, goggles, rubber boots, and rubber gloves. Immediately move the poisoned person from the area where hydrogen sulfide is present to a place with fresh air. If the poisoned person has stopped breathing and their heart has stopped beating, cardiopulmonary resuscitation should be performed immediately and continuously. If the poisoned person does not stop breathing, keep them in a resting position, and oxygen therapy can be administered if conditions permit. Skin contact: Remove contaminated clothing and rinse with running water. Seek medical attention. Eye contact: Immediately lift the eyelids and rinse thoroughly with plenty of flowing water or saline for at least 15 minutes. Seek medical attention. Inhalation: Quickly move to a place with fresh air. Keep the airway clear. If there is difficulty breathing, administer oxygen. If breathing stops, perform artificial respiration. Seek medical attention. http://p7.itc.cn/images01/20201202/75d3a3454a7246c8a7f0a6953a43a2f7.png 9. Operations and handling must be carried out in a strictly enclosed environment; sufficient local exhaust ventilation and general ventilation should be provided. Operators must receive specialized training and strictly adhere to operating procedures. It is recommended that operators wear filter-type gas masks (half-masks), chemical safety goggles, anti-static work clothing, and chemical-resistant gloves. Stay away from sources of fire and heat; smoking is strictly prohibited in the workplace. Use explosion-proof ventilation systems and equipment. Prevent gas from leaking into the workplace air. Avoid contact with oxidizers and alkalis. During transfer, cylinders and containers must be grounded and bonded to prevent the generation of static electricity. Handle with care during transportation to prevent damage to the cylinders and accessories. Equip with appropriate types and quantities of fire-fighting equipment and leak emergency response equipment. X. Precautions for storage: Store in a cool and well-ventilated warehouse. Keep away from flames and heat sources. The storage temperature should not exceed 30°C. Keep the container sealed. It should be stored separately from oxidizers and alkalis; mixed storage must be avoided. Use explosion-proof lighting and ventilation facilities. The use of mechanical equipment and tools that can generate sparks is prohibited. The storage area should be equipped with emergency equipment for dealing with leaks. XI. Packaging precautions for steel gas cylinders ； Ordinary wooden boxes for frosted-mouth or threaded-mouth glass bottles ； Ordinary wooden box outside the ampoule bottle. XII. Precautions for transportation
During railway transportation, loading must be carried out strictly in accordance with the dangerous goods stowage table specified in the “Regulations on the Transport of Dangerous Goods” issued by the Ministry of Railways. When transporting in a gas cylinder, the safety cap on the cylinder must be worn. Gas cylinders should generally be placed flat, with their openings facing in the same direction; they must not be crossed ； The height must not exceed the vehicle’s side rails, and it should be secured with wooden wedges to prevent rolling. During transportation, the vehicle should be equipped with fire-fighting equipment of the appropriate type and in sufficient quantity. The exhaust pipes of vehicles transporting this item must be equipped with flame arresters. The use of mechanical equipment and tools prone to generating sparks is prohibited for loading and unloading. It is strictly prohibited to load and transport together with oxidizers, alkalis, food chemicals, etc. During summer, transportation should take place in the early morning or late evening to avoid exposure to sunlight. During stops, keep away from open flames and heat sources. When transporting by road, it is necessary to follow the designated routes; stopping in residential areas and densely populated zones is prohibited. When transporting by rail, letting the train roll away uncontrolled is forbidden. That’s all the information regarding hydrogen sulfide. Hydrogen sulfide is highly toxic, so relevant workers must be especially careful.