【Chemical Science Popularization】There is a type of poisoning that prevents you from smelling anything

Thread Content

In the laboratory, many chemical substances have odors, and some of these odors are so unpleasant that they make people want to avoid them at all costs. For example, isovaleraldehyde has the smell of smelly feet; proline has the scent of semen; hydrogen sulfide has the odor of rotten eggs; allyl isothiocyanate has the distinct taste of mustard; and isopentyl acetate has the classic banana fragrance. But sometimes, extremely high concentrations of the foul smell can actually numb your sense of smell, preventing you from detecting it, and that can be dangerous. Once, 6 people died in a pesticide factory warehouse in a city in southwestern China. Judging from everyone’s position at the scene, those 6 people were taking shelter from the rain. That warehouse stores sodium sulfide, packed in knitted cotton bags. The autopsy determined that the cause of death was hydrogen sulfide poisoning. Those who have done chemical experiments know that hydrogen sulfide is a gas with a strongly pungent odor, similar to that of rotten eggs; even low concentrations of this gas can be unbearable to breathe. How could those 6 people die from hydrogen sulfide poisoning? Couldn’t they have detected such a foul smell? Yes, they couldn’t! Low concentrations of hydrogen sulfide gas do have a strong, pungent odor, but high concentrations are odorless, as the olfactory nerves are instantly paralyzed. The reason why the 6 workers hid in the warehouse that day was because it was pouring outside, and there were leaks in the warehouse that allowed water to soak the bags containing sodium sulfide. Sodium sulfide is a substance that readily absorbs moisture, which led to the release of large amounts of hydrogen sulfide. It instantly paralyzed the olfactory nerves of 6 workers until they collapsed from acute poisoning. Is hydrogen sulfide really that toxic? Yes, hydrogen sulfide is known as the “mysterious killer”. On June 12, 2008, Anning Qitian Fertilizer Co., Ltd. in Kunming, Yunnan Province, suffered a hydrogen sulfide poisoning accident during the pilot production of arsenic-free refined phosphoric acid, resulting in 6 deaths and 29 people being poisoned. At the time of the incident, the operator was adding a sodium sulfide aqueous solution to the phosphoric acid tank. When adjusting the bottom valve, it was found that the valve could not be closed; as a result, the sodium sulfide solution continued to flow into the phosphoric acid tank, causing an excessive amount of sodium sulfide to accumulate in it. The large quantity of hydrogen sulfide gas generated escaped from the upper part of the unsealed phosphoric acid tank, leading to poisoning of some of the workers on site as well as those who came to provide assistance. At around 5:10 on March 3, 2019, an hydrogen sulfide gas poisoning incident occurred in the phosphate filling area of the logistics department at Wengfu Dazhou Chemical Co., Ltd., resulting in 3 deaths and 3 injuries. According to the investigation, the direct cause of the accident was that there was still residual liquid in the transport vehicle operated by the beacon company (Wengfudazhou Chemical Co., Ltd.’s transportation service provider) after the liquid sodium sulfide was unloaded. When the driver of the transport vehicle used low-pressure steam to clean the tank inside the vehicle, the remaining sodium sulfide flowed into the gutter along with the steam-water mixture; it then reacted chemically with the phosphoric acid already present in the gutter, producing hydrogen sulfide gas, which caused nearby people to be poisoned by inhalation. The harm caused by hydrogen sulfide to the human body, as well as the disasters it triggers, are astonishing and have shocked the whole country. Hydrogen sulfide is a toxic chemical. In chemistry, toxicity is mainly classified into four categories: non-toxic, low toxicity, toxic, and highly toxic. Although hydrogen sulfide is not classified as a highly toxic chemical, its danger is greater than that of many highly toxic chemicals because it is a gas at room temperature and has the effect of paralyzing respiration. Besides hydrogen sulfide, another common chemical gas also has this property of paralyzing the respiratory nerves. That is ammonia. Unlike hydrogen sulfide, low concentrations of ammonia can cause olfactory fatigue quite quickly, while high concentrations of ammonia can alert you instantly. However, if the concentration of ammonia in your working environment is low, it can still be very dangerous, as olfactory fatigue means you will no longer be able to smell anything. By the time you notice symptoms such as difficulty breathing, coughing, or chest tightness, it may already be too late. To summarize, the two types of gases that paralyze the respiratory system are hydrogen sulfide: at low concentrations it has a strong odor that can serve as a warning signal, while at high concentrations it paralyzes the respiratory system instantly, to the point where no odor can be detected. Ammonia, at low concentrations, can rapidly cause olfactory fatigue, paralyze the sense of smell, and lead to poisoning ； At high concentrations, it can actually serve as a warning. Therefore, when coming into contact with or using these two chemicals, it is essential to wear a gas mask; do not rely on your sense of smell.