Occupational hazards and protection against tetraethyl lead

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Tetraethyl lead is an organometallic compound in which a lead atom is bonded to 4 ethyl molecules; it is a colorless and transparent oily liquid with a slightly fruity sweet taste, containing approximately 64% lead. It is highly volatile at room temperature; even at 0°C, it can produce large amounts of vapor. It has high lipophilicity, is insoluble in water, but soluble in organic solvents. Tetraethyl lead was widely used as a gasoline additive to increase the octane rating of fuel and prevent knocking in engines, thereby allowing for higher compression ratios and improving engine efficiency and power. By the 1970s, as environmental awareness grew, the Environmental Protection Agency of the United States enacted the Clean Air Act. In the late 1970s and early 1980s, the United States began a complete ban on the use of leaded gasoline in vehicles. On January 1, 2000, the China **Quality and Technical Supervision Bureau issued the mandatory standard GB 17930-1999 \"Lead-free gasoline for vehicles\" (which has since been replaced by GB 17930-2013 \"Gasoline for vehicles\"), thereby banning the use of lead-containing gasoline in vehicles across the country; however, tetraethyl lead is still used in aviation gasoline. 　　Tetraethyl lead is flammable and can catch fire and explode in the presence of an open flame or high heat. Releases toxic and corrosive gases when exposed to water or heat. The main combustion (decomposition) products are: carbon monoxide, carbon dioxide, and hydrogen chloride. Toxicological characteristics and hazards: Tetraethyl lead can be absorbed through the respiratory tract, digestive tract, and skin. Tetraethyl lead vapor is absorbed into the lungs very quickly; therefore, the lungs are the main route of entry for tetraethyl lead. Secondly, since tetraethyl lead is a lipophilic compound, it is also relatively easily absorbed by the skin and mucous membranes. If the skin is exposed to tetraethyllead gasoline for an extended period, there is a risk of poisoning, as the absorbed tetraethyllead can easily cross the blood-brain barrier and accumulate in large amounts in the brain. In the environment, tetraethyl lead is gradually degraded into triethyl lead under the action of light and heat, and further degraded into inorganic lead. Tetraethyl lead in human tissues is completely metabolized into inorganic lead after 14 days. 　　Tetraethyl lead is a potent neurotoxin that readily affects the central nervous system. 　　Acute poisoning: Initial symptoms include sleep disorders, general weakness, emotional instability, and autonomic nervous system dysfunction; low blood pressure, body temperature, and pulse rate are often observed. In severe cases, toxic encephalopathy occurs, with symptoms such as delirium, mental disorders, coma, and seizures; cardiac and respiratory dysfunction may also arise, and death can occur immediately at high concentrations. 　　Chronic poisoning: It is mainly characterized by a neurasthenic syndrome and autonomic nervous system dysfunction. There may be low blood pressure, body temperature, pulse rate, as well as EEG abnormalities. Causes of poisoning and preventive measures: Occupational exposure to tetraethyl lead mainly occurs during its manufacturing, packaging, and transportation. Accidental leaks or spills often result from failure to follow operating procedures and from the chronic neglect of equipment and pipelines. Some poisoning incidents are also caused by entering storage tanks that once held tetraethyl lead-containing gasoline for cleaning or maintenance without adequate protection or even without any protection at all, or by mistakenly using tetraethyl lead-containing gasoline as ordinary solvent gasoline and applying it in large quantities in poorly ventilated areas. 　　Measures to prevent occupational poisoning: 1. Effective ventilation systems should be installed in the production workshops for tetraethyl lead. Clean contaminated walls, floors, and related equipment at any time using bleach solution or potassium permanganate solution (metal equipment is not suitable for this). Wastewater and exhaust gases must be purified. 　　2. The packaging, mixing, transportation, and loading/unloading of tetraethyl lead must be carried out in a sealed, piped, and mechanized manner to prevent leaks and spills, and to avoid any skin contact. Direct oral syphoning for repackaging is strictly prohibited. 　　3. Ethyl gasoline should be colored in a distinctive way for easy identification, and the containers holding it must be labeled with the word “Highly Toxic.” It is strictly prohibited to use it as an industrial solvent or for cleaning equipment. 　　4. Before transporting ethyl gasoline, it is necessary to routinely check the strength and shock resistance of the joints as well as the fuel tanks. Various components of the oil tanker must not be modified or replaced arbitrarily to prevent accidents. 　　5. Strengthen personal protection. After work, one should take a shower and change clothes; if the skin comes into contact with tetraethyl lead, it must be scrubbed with kerosene within 15 minutes and then washed clean with soapy water. When entering oil tanks and oil holds, it is necessary to strictly follow safety procedures: wear protective clothing, as well as air-supplied gas masks, rubber gloves, and long rubber boots. Drivers are strictly prohibited from sucking on the oil hose with their mouth. 　　6. Contaminated work clothes and materials must be stored separately, and dedicated personnel should use specific methods for cleaning them. They can be washed with a 1%–5% chlorine gel solution, or scrubbed and soaked in a 20% bleach solution, followed by rinsing with clean water. 　　7. Workers handling tetraethyl lead, ethyl liquid, and ethyl gasoline should undergo pre-employment and annual health examinations. Persons suffering from various mental and neurological disorders, as well as severe liver, kidney, and endocrine diseases, should not be assigned to work. Principles for emergency rescue and response: In the event of a tetraethyl lead leakage, personnel on site should promptly evacuate from the contaminated area to a safe zone, and the area should be isolated with strict restrictions on access. Eliminate the ignition source. Emergency responders must wear positive-pressure respirators and protective suits. Do not come into direct contact with the leak; try to shut off the source of the leak as much as possible. Prevent entry into confined spaces such as sewers and drainage ditches. Minor leaks can be absorbed or trapped using sand or other non-flammable materials. In the event of a large-scale leak, dikes should be built or pits dug to contain it ； Cover with foam to reduce vapor damage. Transfer with a pump into a tank truck or specialized collector, and recycle or transport to a waste disposal facility for disposal. 　　In case of a fire, firefighters must wear gas masks and full-body firefighting suits. The extinguishing agents used include: fogged water, foam, carbon dioxide, and sand. 　　First aid measures and treatment for poisoned persons: 1. Quickly move the poisoned person from the site of exposure to a place with fresh air. Keep the airway clear. If there is difficulty breathing, administer oxygen. If breathing stops, perform artificial respiration immediately. Be admitted to the hospital for treatment as soon as possible. 　　2. Those whose skin is contaminated with tetraethyl lead liquid should immediately remove the contaminated clothing, shoes, and hats, clean the affected area with pure gasoline or kerosene first, and then thoroughly wash the skin, nails, hair, etc. with soapy water or clean water before seeking medical attention at a hospital. 　　3. After admission, the antidote dimercaprol (β-mercaptoethylamine, cysteamine) should be administered promptly. When conditions permit, early treatment with hyperbaric oxygen therapy or photodynamic blood oxygenation therapy can help mitigate secondary hypoxic damage to brain tissue. Case of poisoning – Case 1: In November 2003, an acute tetraethyl lead poisoning incident occurred at a chemical plant in Henan Province. A total of 18 people were poisoned; among them, 11 had mild poisoning and 7 had moderate poisoning (2 of whom died). The sequence of events was as follows: In July 2003, the factory built a new pilot production line for manufacturing the fuel additive tetraethyl lead. Trial production began intermittently in September, and bulk production started after successful trial production on October 20. Production was halted on November 5, with a total of about 200 kg of tetraethyl lead being produced. After working continuously for 2–3 days, workers experience noticeable irritation in the upper respiratory tract, discomfort or a feeling of a foreign body in the throat, dizziness, insomnia, and so on. As the duration of exposure increases, most workers develop symptoms such as irritability, severe insomnia, frequent nightmares, and fear; they may also experience hallucinations, mental stress accompanied by headaches, dizziness, nausea, loss of appetite, fatigue, and excessive sweating. On November 4, 2003, a worker exhibiting psychotic-like symptoms was admitted to the hospital. On November 5, four more poisoned workers were admitted; one of them was already in a coma. After that, 13 more people were admitted to the hospital for treatment one after another. 　　According to the on-site occupational health investigations conducted by the local health supervision authorities, it was found that the tetraethyl lead simulation production line in this factory had not undergone evaluation, assessment, or completion inspection regarding occupational disease hazards associated with construction projects. It was designed and installed by the factory itself; the equipment is rudimentary, and there are serious problems of leaks and spills. The production process is outdated and does not meet safety and hygiene standards; chemical reactions are monitored only by visual inspection. Adding materials and filling the containers are done manually in an open manner, which leads to inhalation of toxic substances through the respiratory tract and skin contamination. Workers who enter the reaction vessels to remove residues come into direct contact with these toxins. The workshop lacks specialized personal protective equipment, as well as facilities for sealing, ventilation, and toxin removal; there are also no warning signs indicating the presence of toxic or hazardous operations. Workers are equipped only with ordinary work clothes, rubber gloves, and rubber shoes while working; activated carbon protective masks are provided and replaced every 2–3 days. The changing rooms and showers in the workshop are not in use. The factory has weak occupational health management and has not established operational procedures for occupational health and safety. Enterprise managers and workers lack awareness of safety precautions; they know very little about the toxicity of tetraethyl lead and the potential harm it can cause. No pre-employment training or occupational health checks are provided for workers during their employment. The main cause of this accident was the workers’ illegal operations, carried out without understanding the properties of the toxins, lacking awareness of self-protection, and without wearing appropriate personal protective equipment. Case 2: A 42-year-old male patient, a laborer at an oil refinery. At around 8 o’clock one day, the person entered the gasoline storage tank wearing plastic sandals and cloth gloves, with their legs submerged in the sludge; they used an iron shovel to remove the sludge from inside the tank. After about 2 hours, symptoms such as dizziness, headache, nausea, vomiting, palpitations, and abdominal distension appeared, so they went home to rest. At around 2 p.m., they went back into the tank to work for about 2 hours; the aforementioned symptoms worsened, so they went to the hospital. The hospital administered metoclopramide, diazepam, and other treatments. The next morning, after working inside the tank for about 2 more hours, the patient experienced dizziness, headache, increased abdominal distension, unsteady gait, and confusion. Upon returning to the hospital, treatment with domperidone, multienzyme tablets, and diazepam was administered, but there was no improvement. A week later, the condition gradually worsened: the patient became excited, talkative, and forgetful; there were involuntary tremors in both lower limbs, weakness in those limbs, muscle twitching, severe insomnia, nightmares, and easy waking up, with only about 1 hour of sleep per night. After that, they went to a local occupational disease hospital for treatment. 　　An investigation of the patient’s workplace revealed that the gasoline tank was of metal construction and typically stored around 300 tons of No. 7 gasoline (with less than 1.00 g/kg of tetraethyl lead). The oil tank had not been cleaned for 8 years; during the cleaning process, no ventilation equipment was available, and only the patient was involved in the task of removing more than 3 tons of sludge from the tank. After the accident, the average concentration of tetraethyl lead in the air measured in similar empty oil tanks was 0.75 mg/m3; the sludge contained 16% tetraethyl lead. The patient was diagnosed with acute mild tetraethyllead poisoning. He returned to normal after 5 months of hospital treatment. 　　This case suggests that when cleaning gasoline storage tanks, it is necessary to first flush them and fill them with a large amount of compressed air. Workers should wear positive-pressure or passive gas masks, rubber gloves, protective clothing, and long rubber boots, and the duration of each entry time should be limited. There should be a dedicated person to supervise outside the tank; after working, one should take a shower to clean oneself, and any residual materials must be disposed of properly in order to effectively prevent poisoning incidents.