HCl refers to both hydrogen chloride gas and aqueous hydrochloric acid. Hydrogen chloride gas is a colorless gas formed from the reaction of hydrogen with chlorine. It forms white fumes of hydrochloric acid upon contact with atmospheric humidity. Hydrochloric acid is a highly corrosive, strong mineral acid with many industrial uses. Hydrochloric acid is found naturally in gastric acid. Hydrogen chloride gas and hydrochloric acid are important in technology and industry. For example, hydrochloric acid is used in the chemical industry as a chemical reagent in the large-scale production of vinyl chloride for PVC plastic, and MDI/TDI for polyurethane. It has numerous smaller-scale applications, including household cleaning, production of gelatin and other food additives, descaling, and leather processing. Hydrogen chloride is less widely used, although even in the absence of water, hydrogen chloride can still act as an acid. For example, hydrogen chloride can dissolve in certain other solvents such as methanol, protonate molecules or ions, and serve as an acid-catalyst for chemical reactions where anhydrous (water-free) conditions are desired. Hydrogen chloride is corrosive, particularly in the presence of moisture. Likewise hydrochloric acid is also extremely corrosive. Most hydrochloric acid is sold or is available as a 38% aqueous solution.
belongs to the class of inorganic compounds known as halogen hydrides. These are inorganic compounds in which the heaviest atom bonded to a hydrogen atom is a halogen.
Both hydrogen chloride gas and hydrochloric acid are highly corrosive. Many strong acids cause tissue burns through the denaturation of proteins and partial hydrolysis of proteins. Most proteins denature at pH values of less than 3-4. The large-scale denaturation of proteins, de-esterification of lipids and subsequent desiccation of tissues leads to chemical burns. Symptoms include itching, bleaching or darkening of skin or tissues, blistering and burning sensations.
3, not classifiable as to its carcinogenicity to humans. (1)
Uses/Sources
Hydrochloric acid is found naturally in gastric acid. Most hydrogen chloride gas is used in the production of hydrochloric acid. HCl gas is also an important reagent in other industrial chemical transformations. For example, the hydrochlorination of rubber and the production of vinyl and alkyl chlorides. In the semiconductor industry, it is used to both etch semiconductor crystals and to purify silicon via trichlorosilane (SiHCl3). It may also be used to treat cotton to delint it, and to separate it from wool. In the chlor-alkali industry, brine (mixture of sodium chloride and water) solution is electrolyzed producing chlorine (Cl2), sodium hydroxide, and hydrogen (H2). The pure chlorine gas can be combined with hydrogen to produce hydrogen chloride in the presence of UV light.
Minimum Risk Level
Occupational exposure limits for hydrogen chloride (gas) have been set at 5 ppm
Health Effects
Hydrogen chloride forms corrosive hydrochloric acid on contact with water found in body tissue. Inhalation of the fumes can cause coughing, choking, inflammation of the nose, throat, and upper respiratory tract, and in severe cases, pulmonary edema, circulatory system failure, and death. Skin contact can cause redness, pain, and severe skin burns. Both hydrogen chloride gas and hydrochloric acid may cause severe burns to the eye and permanent eye damage. Severe and rapid corrosive burns of the mouth, gullet and gastrointestinal tract will result if hydrochloric acid is swallowed. Symptoms include burning, choking, nausea, vomiting and severe pain. Concentrated hydrochloric acid (fuming hydrochloric acid) forms acidic mists. Both the mist and the solution have a corrosive effect on human tissue, with the potential to damage respiratory organs, eyes, skin, and intestines irreversibly. Upon mixing hydrochloric acid with common oxidizing chemicals, such as sodium hypochlorite (bleach, NaClO) or potassium permanganate (KMnO4), the toxic gas chlorine is produced. Chronic exposure to hydrogen chloride can lead to liver damage, bleeding of nose and gums, nasal and oral mucosal ulceration, conjunctivitis, yellowing of teeth and erosion of tooth enamel as well as dermatitis.
Symptoms
Inhalation of HCl fumes can cause coughing, choking, inflammation of the nose, throat, and upper respiratory tract, and in severe cases, pulmonary edema, circulatory system failure, and death. Skin contact can cause redness, pain, and severe skin burns. Hydrogen chloride may cause severe burns to the eye and permanent eye damage. Severe and rapid corrosive burns of the mouth, gullet and gastrointestinal tract will result if hydrochloric acid is swallowed. Symptoms include burning, choking, nausea, vomiting and severe pain.
Treatment
The mainstay of treatment of any acid burn is copious irrigation with large amounts of tap water. To be most effective, treatment should be started immediately after exposure, preferably before arrival in the emergency department. Remove any contaminated clothing. Do not attempt to neutralize the burn with weak reciprocal chemicals (i.e. alkali for acid burns), because the heat generated from the chemical reaction may cause severe thermal injury.
