Hydrochloric acid

SECTION 2: Hazards identification

MAIN HAZARDS Threshold limit values (TLVs) / American Conference of Governmental Industrial Hygienists (ACGIH) / 2002* Ceiling Exposure Limit (TLV-C) : 5 ppm (7.5 mg/m3) (*Notice of intended change: The reduction of the TLV-C to 2 ppm , 3mg/m3 ) CHEMICAL HAZARDS Hydrochloric acid may react explosively with potassium permanganate (1*,2*) or sodium, and contact of fuming hydrochloric acid with tetraselenium tetranitride is also explosive. Passing hydrogen chloride into alcoholic hydrogen cyanide in preparation of alkyliminoformate chlorides proceeds explosively (3*), and other hazard-free methods are available (4*). An extremely exothermic decomposition reaction may occur with 1,1- difluoroethylene particularly at high vessel loadings (5*). Rubidium acetylide ignites in contact with hydrochloric acid, and caesium acetylide ignites in contact with gaseous hydrogen chloride or concentrated hydrochloric acid. Hydrogen chloride also ignites in contact with fluorine, and concentrated aqueous solutions produce flame. Aluminium-titanium alloys ignite or incandesce on heating in hydrogen chloride. Hexalithium disilicide incandesces in concentrated hydrochloric acid, and silanes (which ignite) are evolved with the dilute acid. Filling a glass drying tap on a hydrochloric acid storage tank with silica gel instead of calcium sulphate resulted in fracturing of the tap (6*), and the accidental addition of concentrated hydrochloric acid to a tank of sulphuric acid caused the tank to burst violently (7*). The safe dehydration of hydrochloric acid which releases a lot of gas (8*) avoids the possibility of layer formation in an unstirred flask (9*). BIOLOGICAL HAZARDS Hydrochloric acid and high concentrations of the gas are highly corrosive to the skin and mucous membranes. Considerable variation in species sensitivity to hydrochloric acid exists (11*). The health effects of occupational exposure have reviewed (10-12*).

Potential health effects

EYES Low concentrations of vapour or mist (10-35 ppm) can be immediately irritating, causing redness.(2) Concentrated vapour, mist or splashed liquid can cause severe irritation, burns and permanent blindness.(4) - INGESTION Hydrochloric acid solutions can cause corrosive burns to mouth, throat, oesophagus and stomach. Symptoms may include difficulty in swallowing, intense thirst, nausea, vomiting, diarrhoea and in severe cases, collapse and death. Small amounts of acid which enter the lungs during ingestion or vomiting (aspiration) can cause serious lung injury and death. - INHALATION The major effects of acute exposure to hydrogen chloride are usually limited to the upper respiratory tract and are severe enough to lead to prompt withdrawal (13*). Exposure to the gas causes cough, burning of the throat and choking feeling, inflammation and ulceration of the nose, throat and larynx (14*). Exposure to higher concentrations, as may occur if a worker is prevented from escaping, may cause laryngeal spasm, and oedema of the lungs and vocal cords (15*). Prolonged or repeated exposure may cause dental discolouration and erosion (15* - 17*). Pulmonary function changes in naive but not chronically exposed workers suggests acclimatisation occurs (18*). Gastritis and chronic bronchitis have also been reported in exposed workers (19*). In humans, exposure to 50 - 100 ppm for 1 hour is barely tolerable, 35 ppm for a short while causes throat irritation, and 10 ppm was tolerable (20*), although immediate irritation has been reported at concentrations over 5 ppm (21*). Bleeding nose and gums, ulceration of nasal and oral mucosa, and painful shaving due to tender facial skin was reported in workers exposed to mists from heated metal pickling solutions (22*). In animal studies reported effects of exposure to high concentration of hydrogen chloride include damage to the lungs and blood vessels, lung collapse, and lesions of the liver and other organs(23*), coughing, wheezing, frothing, slowing of movement, increased respiratory rate, and death due to respiratory tract effects (24*). Repeated exposure to low concentrations of the gas (34 ppm) had no immediate toxic effects and produced no morphological changes (23*). Exposure to 100 ppm, 6 hours/day for 50 days caused slight unrest and irritation of the nose and eyes in several species (25*), while repeated exposure at higher concentrations caused weight loss (23*). Lesions in the nasal cavity of mice has also been reported (26*). Inhalation of weak hydrochloric acid into the bronchi of rabbits caused inflammatory processes like those occurring in "flu or due to chemical weapons (27*). Differing responses to irritant gases such as hydrogen chloride between rodents and nonhuman primates suggest that the former may be an inadequate model for evaluating the toxicity of irritant gases to humans (28*). ADDITIONAL MEDICAL INFORMATION CARCINOGENICITY No carcinogenic response was noted in inhalation experiments with rats (31*). Mortality rate from lung cancer was found to be significantly alleviated in workers exposed to sulphuric and hydrochloric acid mists during steel- pickling operations (32*). MUTAGENICITY No information is available concerning the mutagenicity of hydrochloric acid. TERATOGENICITY AND EMBRYOTOXICITY No human information is available. Insufficient information is available to evaluate an animal report. REPRODUCTIVE HAZARDS No information is available concerning the reproductive hazards of hydrochloric acid

Health Effects - Skin

Hydrochloric acid liquid can cause skin burns, and may produce keloid and retractile scarring (29*). Facial burns may result in serious and disfiguring scars. Frequent contact with the dilute acid may cause dermatitis (14*). and photosensitisation may result from industrial contact.