THE FOLLOWING ARTICLE APPEARED IN THE

MAY 2000 ISSUE

THE POISON SLEUTHS

DEATH BY HYDROGEN FLUORIDE

-Dr. Anil Aggrawal

"Good morning doctor. Oh, my God, what are you doing today? You have the dead body of a young man today. He is showing some burns on his body, especially on his fingers. What happened to him? Please tell me.”

“Good morning Tarun. The name of this person is Shamlal, and he worked in a sweetshop in a Delhi based shop as a sweetmaker. He had migrated from Bihar sometime back, and was living alone in his house. For some days he was having some conflict with a person named Sunder, who worked as a lab attendant in a chemistry lab in a local school. On this Holi (Holi is a traditional festival enjoyed by the Hindus about the month of March every year. Typically this festival is celebrated by throwing water and colors over the friends), Sunder reportedly came to Shamlal, and asked him to forget all past differences. You would surely agree with me that for Hindus, Holi is a festival when everyone tends to forget past enmities. Shamlal also wanted to bury the hatchet, and invited him inside and offered him sweets. After applying some color on the face of Shamlal, Sunder threw some watery liquid over Shamlal, as a gesture to play Holi. Shamlal immediately felt pain all over his body, but instead of helping him, Sunder immediately left the house. On hearing Shamlal’s hue and cries, the neighbors took him to a nearby hospital and admitted him there. He died in the hospital a day later.”

“Oh, I see. But why is his body brought to you?”

“Tarun, when Shamlal was admitted in the hospital, he told the police all the incidents. He also said that he started feeling pain after Sunder threw some watery liquid over him, under the pretext of playing Holi. The police strongly suspect that Sunder threw some corrosive substance over him, and they want me to tell them what substance it was.”

“Oh, I see. So what was it doctor?”

“Tarun, I have conducted a thorough autopsy on the dead body, and have examined his burns in detail. You can see this typical burn on his finger. I feel that Shamlal has been killed deliberately by a very deadly poison - Hydrofluoric acid.”

“Hydrofluoric acid! Never heard of this acid being used as a poison. And come to think of it, how can you be so sure?”

“Tarun, I made some discreet enquiries from the doctors who treated him at the hospital. I specifically asked them, how Shamlal described his burns. The doctors told me that he described his burns in a very strange fashion, especially those on his fingers. He said that he felt as if his fingers had been struck with a hammer! This is a very typical description of a Hydrofluoric acid burn by a patient.”

“That is very strange indeed. I think, I should know more about hydrofluoric acid, before I could be able to understand your talks more fully. Please tell me in some detail about Hydrofluoric acid.”

“Tarun, Hydrofluoric acid is also known as hydrogen fluoride and its formula is often written as HF or H2F2. It is a colorless, fuming liquid, with molecular weight 20.01. It boils at 19.40 C. It is its great solubility in water that causes it to fume strongly in moist air. HF is found extensively in industry and at home. It was first synthesized by the French chemist Edmond Frémy (1814-1894). It is one of the most important fluorine compounds, and is prepared by heating calcium fluoride in sulfuric acid. The aqueous solution of this acid, generally used commercially, is obtained by passing the anhydrous hydrogen fluoride vapors into a leaden receiver containing distilled water, thus yielding the acid in dilute form. Hydrofluoric acid is extremely corrosive and must be preserved in platic, lead or steel containers. It can not be preserved in glass bottles, as it has the property of dissolving glass (reacts with silica to form gaseous silicon tetrafluoride). In fact this property is used in a common test for the presence of a fluoride. For the same reason, hydrofluoric acid is also used extensively in various forms of glass etching, such as the marking of divisions on thermometer tubes and the etching of designs on glassware, and in other forms of ceramic etching, such as pottery decoration. It is also used for frosting and polishing glass, and for removing sand from metal castings. It is also used as a catalyst for the production of certain hydrocarbons for high-octane gasoline. Some of its other common uses are rust removal, in manufacture of dyes, plastics, germicides, tanning, solvents, fire-proofing, pottery glazing and photography. It is also used as a laboratory reagent.”

“Oh, that is interesting. What are its harmful effects on humans”

“Tarun, scientists have studied its harmful effects in animals systematically by exposing them to varying concentrations of Hydrofluoric acid vapors. This helps to study the effects in man too. When inhaled by rabbits and guinea pigs in a concentration of 15 mg/cu. meter, they could tolerate it for prolonged periods. A concentration of 24 mg/cu. meter was tolerated for a total of 41 hours without fatality, although the animals subsequently lost weight. In a concentration of 50 mg/cu. meter HF induced signs of mild irritation, such as coughing and sneezing, which appeared to lessen after 5 to 15 minutes. Inhaled in greater concentrations, it acted as a severe irritant: the eyes were kept closed, paroxysms of coughing and sneezing were frequent, the respirations were slowed, and there was a copious discharge from the nose and eyes. Concentrations below 100 mg/cu. meter could be tolerated by animals for 5 hours without causing death. When exposed to the concentration of 500 mg/cu. meter for 15 minutes or more, all animals showed signs of weakness and ill-health. Inhalation at a concentration of 1000 mg/cu. meter for 30 minutes didn’t kill any animal, but caused damage to tissues. When inhaled at a concentration of 1500 mg/cu. meter for 5 minutes, all animals died, indicating this to be the fatal dose. When necropsies were done on animals, who had survived repeated exposures of HF, increased fluoride was seen in bones. Lungs, livers and kidneys were found damaged.”

“Doctor, you said that HF is used in several industries. Does this mean, that industrial workers are also exposed to HF?”

“Yes, surely. And they can get harmful effects too. The highest concentration of HF that can be tolerated by man for 1 minute is 100 mg/cu. meter. This causes a definite smarting of skin, a definite sour taste, and some degree of eye and respiratory irritation. If the air contains 50 mg/cu. meter, the sour taste is apparent and there is irritation of the eyes and nose, but no smarting of the skin. The concentration of 26 mg/cu. meter can be tolerated for several minutes, but the sour taste becomes evident after a short time, and there is mild smarting of the nose and eyes. You may want to know that the American Conference of Governmental Industrial Hygienists has adopted 2 mg/cu. meter as the threshold limit for hydrogen fluoride. This comes to about 3 ppm (parts per million).”

“Doctor, I have seen some burns on the body of Shamlal too. Obviously they were caused by Hydrofluoric acid. Could you tell me in some more details about these burns?”

“Tarun, contact of the skin with the anhydrous liquid produces severe burns. This is the most frequently reported route of HF toxicity. If the solution is not promptly removed, the skin may be penetrated by the fluoride ion, leading to the later development of painful ulcers, which heal slowly. Solutions of less than 20% HF can produce pain and redness up to 24 hours after exposure; 20 to 50% HF produces pain and redness within 8 hours, and solutions of more than 50% produce immediate burning, redness and blister formation. Fatalities have been reported from dermal exposure to as little as 2.5% of body surface area (about the size of the sole of the foot).

HF burns range from first-degree to third-degree. The characteristic features are severe pain. Patients often describe feeling as if they had struck their fingers with a hammer! The hallmark of HF exposure is pain that is out of proportion to the burns produced. Only a few days back, I treated a case of Hydrofluoric acid burns in a young boy, on whom too, someone had thrown HF with an idea to kill him. He got severe burns on his legs. But fortunately I could save him. See this picture of his legs after one month. As you can see, he has almost recovered. His burn wounds are looking much more healthy. He became all right after a few months.”

“Doctor, how much HF can kill a person?”

“Tarun, inhalational exposure to concentrated HF for as little as 5 minutes is usually fatal, producing death within 2-10 hours. When HF is thrown on the body, the person may die in variable periods of time, usually within a day or so.”

“How does hydrofluoric acid kill doctor.”

“Tarun, you must be knowing that all acids yield free hydrogen ions or protons in solution. The more hydrogen ions an acid produces, the stronger it is considered to be. These hydrogen ions or protons exert a deleterious effects on the body in several complicated ways. That is why all mineral acids such as HCl, H2SO4 and HNO3 are so dangerous. HF is far less strong than its mineral acid cousins. It produces approximately 1000 times less free hydrogen ions or protons than an equimolar solution of hydrochloric acid, and about 450 times less free hydrogen ions than an equimolar solution of sulfuric acid. Yet it is this poor dissociation that proves so lethal to man. A poorly dissociated acid can penetrate far deeper in the tissues as it is uncharged. In fact all uncharged molecules have the ability to penetrate cells much better than charged ions. Combined with this ability is the specific ability of the fluoride ion to complex with body calcium and magnesium, even when present in exceedingly small concentrations. The combination of these two factors gives HF its unique toxicity. Free proton produced by HF does contribute to the injury (as in the case of mineral acids), but what is more important are the two factors I mentioned earlier, i.e. its unique ability to penetrate tissues, and its ability to combine with calcium and magnesium. This causes body calcium and magnesium levels to fall down. The body if affected in several other ways. I may also tell you about a unique property of the fluoride ion, which makes it very deadly. It can hold an electron more tightly than any other ion. This strong electronegativity of the fluoride ion allows it to bind tightly to any cation. These effects have the potential of disrupting all metabolic pathways, and may result in several body disorders.”

“Doctor, now I know about HF enough to follow your talks. Tell me what has happened in Shamlal’s case?”

“Tarun, I have no doubt in my mind that Shamlal has been killed by Sunder by this unique poison. Sunder worked in a chemistry lab, so HF was available to him. He offloaded some HF in a container and smuggled it home, with a view to throw it over his long adversary Shamlal. He knew that Holi was approaching soon, and he could throw it over him and leave the house quickly. As this is such a rare corrosive, he thought that he police would never be able to determine which corrosive was Shamlal killed with. But his typical findings and especially his typical description of his pain before death have given away everything. I have conducted some chemical tests on the washings which I took from Shamlal’s burnt areas, and they have tested positive for Hydrofluoric acid. Following this, I asked police to raid Sunder’s house. They did so, and found a half empty bottle containing HF. We then contacted the chemistry teacher of the school, where he was working, and asked him to check his HF supplies. He was surprised, as HF was hardly used in a routine way, and they always kept it under lock and key. But on our insistence he opened the lock and key and checked the HF bottle. To his utter surprise, it was empty. All these facts have confirmed, that Sunder stole HF from his school lab to throw it over Shamlal. Come, let us tell the police that Sunder is guilty and that the police must apprehend him.”

“That is very clever of you doctor. Without your clever deduction it would have been impossible to say how Shamlal died and Sunder may have gone scot-free. What are you going to tell me next time?”

“Tarun, next time, I would tell you about a very interesting poison - Fluorine."