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Epidemiologic Notes and Reports Chlorine Gas Toxicity from Mixture of Bleach with Other Cleaning Products -- California

From October 1987 through November 1989, five episodes of chlorine gas exposure with toxicity to at least 14 persons occurred at two state hospitals in California. Each hospital provides inpatient treatment to approximately 1000 forensic psychiatric patients. As part of their rehabilitation programs, selected patients perform cleaning duties under the supervision of janitors or nursing staff. Each incident occurred during the performance of these duties and involved the mixture of bleach (sodium hypochlorite) and a phosphoric acid cleaner by inpatients. This mixture produced chlorine gas and other chemical byproducts (Figure 1a and 1b), and resulted in temporary illness in exposed persons. Hospital A

Episode 1. On October 18, 1987, a patient poured an undetermined amount of a 4% phosphoric acid cleaner into a bucket containing diluted bleach. A chemical reaction occurred immediately, releasing an irritating gas. The patient was assisted from the room, and the cleaning solution was diluted with water and poured down a drain. Windows were opened to ventilate the area, and the ward was evacuated. The patient complained of anxiety, chest tightness, difficulty breathing, and heartburn; physical examination revealed scattered bibasilar pulmonary rhonchi. He was treated with supplementary oxygen, and most symptoms subsided after 1 hour.

Episode 2. On December 19, 1987, a patient mopped a bathroom floor with a 4% phosphoric acid solution, then rinsed the floor with water. Immediately after he applied a bleach and water solution to the floor, a noxious gas with a strong odor was emitted. The mixture was poured down a drain, and the floor was again rinsed with water; however, because the room's exhaust fan was inoperative and windows had been sealed shut, the gas dispersed throughout the ward and caused symptoms in other patients. The ward was evacuated; patients and staff returned after 1-1/2 hours when the odor had dissipated. Within an hour of their return, additional patients and staff complained of symptoms including nausea, eye irritation, tearing, sore throat, headache, cough, and chest tightness; one patient had an acute exacerbation of asthma. The ward was reevacuated until the following day. The local fire department assisted with ventilation.

Episode 3. On December 25, 1987, a patient mixed approximately 1/2 L of bleach and 1 L of a 4% phosphoric acid cleaner in a bucket, creating a noxious gas. The patient rapidly developed eye irritation followed by fatigue; four employees developed symptoms that included a lightheaded dizziness, nausea, eye and nose irritation, headache, and chest tightness. The ward was evacuated until chemical residues on the bathroom floors had been rinsed and air exchange had been completed using the existing exhaust fan system. For some persons, symptoms persisted for several hours. More than an hour after the episode, two employees entered an enclosed nursing office 50 feet from the gas release site; despite the absence of a detectable chlorine odor, both promptly experienced recurrent symptoms.

Following these three incidents, patients and employees were interviewed to establish policies to prevent recurrences. Each incident involved the same phosphoric acid formulation. The three patients had been supervised by different staff; they denied mixing the chemicals intentionally to create a disturbance, denied knowing each other, and denied knowledge of previous episodes. Each incident occurred on a weekend or holiday, when janitors were off duty and the patients were cleaning bathroom floors while being supervised by ward nursing staff without constant observation.

Beginning December 29, controls were instituted on the storage and use of the phosphoric acid cleaner at hospital A. The cleaner was dispensed by housekeeping supervisors to janitors, who kept it locked in storage areas accessible to employees only.

Episode 4. Despite more stringent controls over the use of cleaning products, a fourth episode occurred. On November 3, 1989, a patient supervised by a new employee was allowed in a locked storage area and poured an undetermined amount of 4% phosphoric acid cleaner into a bucket containing bleach and water, immediately producing a cloud of noxious vapor.

The employee assisted the patient from the area, then returned to the area and poured the contents of the bucket down a sink. The employee, who was exposed to the vapors for less than 1 minute, reported immediate throat and nasal burning that persisted for more than 24 hours, as well as transient dizziness and nausea. Supplemental oxygen was administered at a local acute-care hospital emergency room for 3 hours. The employee completely recovered within 36 hours following exposure. The patient had no symptoms.

Following this incident, acidic cleaning products at hospital A were locked in the offices of housekeeping supervisors; access was available only to janitors and was denied to both nursing staff and patients. In addition, the hospital has prohibited the mixing of cleaning products. No further incidents have occurred. Hospital B

On December 7, 1988, a patient assisting in janitorial duties mixed bleach with phosphoric acid cleaner. Immediately a noxious gas with a strong odor was detected and prompted the evacuation of two wards for 1-1/2 hours. Fire department personnel using self-contained breathing equipment disposed of the chemicals and ventilated the area.

The patient experienced vomiting, cough, and inspiratory discomfort; elevated blood pressure and fever were noted when the patient was treated in the emergency room. Five employees who helped evacuate the ward complained of symptoms including eye irritation and shortness of breath. Employees and patients returned approximately 1-1/2 hours after the area was ventilated. After this incident, hospital B instituted warning labels on all chemical cleaning products and posted precautionary (i.e., "do not mix") signs on janitorial closets. Bleach and acidic cleaning products were restricted to use by staff. No further incidents involving phosphoric acid products have occurred at this hospital. Product Label Investigation and Modifications

The label of the phosphoric acid cleaner involved in all five incidents did not list the active ingredient nor warn of the potential for toxic reactions when phosphoric acid was mixed with other chemicals. The material safety data sheet (MSDS) did not describe potentially toxic chemical reactions or incompatibilities. The labels and MSDSs of two other products containing phosphoric acid in use at hospital A, including one with a 30% acid concentration, also lacked information on reactions and incompatibilities with hypochlorite.

After notification by hospital A in December 1987 about episodes 1-3, a new label was supplied by the chemical manufacturer in early 1988 for use by institutional customers wishing to transfer the product into smaller storage containers. The new label included the statement: "Do not mix with other chemicals (such as bleach or ammonia)." In 1989, the product's label was revised to add a similar statement. The MSDS was revised in May 1991; it now mentions incompatibility with ammonia or bleach but still does not state what will result from those mixtures.

The product is marketed directly by the manufacturer to institutions in Arizona, California, Montana, Oregon, and Washington. It is not sold in stores to the general public and therefore is not considered a consumer product by the U.S. Consumer Product Safety Commission (CPSC) and is exempt from labeling requirements of the federal Hazardous Substances Act. However, according to the California Department of Industrial Relations, Division of Occupational Safety and Health (Cal-OSHA), as a California workplace product it is subject to the state's hazard communication standards, which require the label to list the phosphoric acid and appropriate hazard warnings and the MSDS to include reactivity and incompatibilities; the wording to describe the chemical interactions is not specified by law (R.E. Erickson, Cal-OSHA, personal communication, 1991). Reported by: RP Hattis, MD, California Dept of Mental Health; JR Greer, MD, S Dietrich, DO, S Olafsson, MD, Dept of Preventive Medicine, Loma Linda Univ, Loma Linda; KR McAndrew, Long Beach Memorial Hospital, California. Health Studies Br, Div of Environmental Hazards and Health Effects, National Center for Environmental Health and Injury Control, CDC.

Editorial Note

Editorial Note: The chemicals involved in the first three incidents were a standard household bleach (5.25% sodium hypochlorite solution [NaOCl]) and a 4% phosphoric acid (H3PO4) cleaning agent. When sodium hypochlorite and an acid are mixed, chlorine gas and water are released (Figure 1a). Chlorine gas reacts with the water to form hydrochloric and hypochlorous acids (Figure 1b). Chlorine gas may cause a variety of symptoms as a function of the severity of exposure (1-3). Hydrochloric acid also causes inflammation that may, along with nascent oxygen release, be one of the mechanisms of tissue damage by chlorine (4).

Mild mucous membrane irritation may occur in some persons after several hours at levels as low as the threshold limit value (TLV) of 1 ppm (1,3); this TLV may warrant reassessment (1). A level of at least 3 ppm may cause extreme irritation of the eyes and respiratory tract, but a detectable odor is usually not present below 3.5 ppm (2). Symptoms following exposure to chlorine have included irritation of the eyes, nose, and throat; dizziness; cough; and chest pain or constriction. Severe exposure may cause pulmonary edema, bronchiolar and alveolar damage, and pneumomediastinum (1,2,4-6).

When bleach is mixed with ammonia-containing compounds, monochloramine (NH2Cl) (Figure 1c) and dichloramine (NHCl2) (Figure 1d) are formed, which may produce tearing, respiratory tract irritation, and nausea. These compounds decompose in water to hypochlorous acid and free ammonia gas (6-8); the former combines with moisture forming hydrochloric acid and toxic nascent oxygen (8); the latter is a respiratory and mucous membrane irritant and can cause pulmonary edema and pneumonia (6,7).

Only four case reports have been published of chlorine toxicity from mixing bleach with acid cleaning agents, including one describing near-fatal pulmonary edema, two of pneumomediastinum, and one of mild illness in which other family members also became symptomatic. None of these reports involved phosphoric acid; in three, inadequate ventilation probably contributed to the toxic effects (4-6). However, the American Association of Poison Control Centers data collection system listed 409 cases of chlorine exposure in 1990 from acid mixtures with hypochlorite that were reported from 72 participating centers serving 77% of the U.S. population. Of these cases, 395 (97%) were unintentional exposures and 356 (87%) occurred among persons aged >17 years; 128 required treatment in health-care facilities. Of 340 exposures for which outcome was known, 292 were considered to have caused minor and 30 moderate illness (9). Cases recorded by poison-control centers probably underrepresent substantially the episodes actually occurring; for example, no poison-control center was consulted about the five incidents in this report.

A directive for CPSC compliance staff for monitoring the chemical product industry requires labels on consumer products containing 5% or more hypochlorite to include warnings against mixing with acids and other household chemicals and for labels of products containing 3% or more ammonia to warn against mixing with chlorine-type bleaches or other household chemicals (10). There is no required warning for phosphoric acid, nor does the CPSC routinely inspect any chemical consumer products. Products sold only for institutional or other workplace use are not monitored by CPSC, and the responsible occupational health and safety agencies (the federal Occupational Safety and Health Administration or a state agency) rely on manufacturers/importers and employers to be informed of potential health hazards of workplace chemicals and to inform customers and employees by MSDSs (11,12). Agencies monitor workplace chemical labeling and MSDSs by periodic inspections, with feedback to companies with deficiencies (13). The probability that any given chemical product will be reviewed by this process is low. No complete compilation has been made of the millions of consumer and industrial chemical product formulations, labels, and MSDSs in the United States. There is no federal requirement that wording on labels and MSDSs be cleared by a regulatory agency as a precondition for sale or distribution of chemical products.

Three approaches can be implemented to prevent potential toxic exposures in institutional and other industrial settings from mixtures of bleach with other cleaning agents:

  1. Housekeeping policies should be established in institutions to educate new or untrained employees and patients or inmates who assist in cleaning about the potential danger of chemical mixtures and to provide constant supervision for persons whose judgement may be impaired. When this is not possible, use of such chemicals should be restricted to fully trained and experienced employees.

  2. When chlorine gas is unintentionally released, areas in which the gas could circulate should be evacuated until sufficient air exchanges have occurred to ensure that the gas has been eliminated. The absence of odor is not a reliable indicator of safety. Pending the complete evacuation of gas, employees involved in cleanup or onsite investigation of such incidents should wear protective respiratory equipment, and none should enter without a companion (14).

  3. OSHA and state agencies designated by federally approved state occupational safety and health plans should contact all known manufacturers and importers of cleaning products that contain hypochlorite, acids, or ammonia and are used in institutions and other workplaces to clarify and reinforce proper labeling and MSDS requirements and to encourage education of their customers about nonmixing.


  1. Arena JM. Poisoning--toxicology, symptoms, treatment. 5th ed. Springfield, Illinois: Charles C. Thomas, 1986:298-300,316- 8,692.

  2. Sax NI, Lewis RJ. Dangerous properties of industrial materials. 7th ed. Vol 2. New York: Van Nostrand Reinhold, 1989:768.

  3. Ellenhorn MJ, Barceloux DG. Medical toxicology: diagnosis and treatment of human poisonings. New York: Elseviere, 1988:878,891,903.

  4. Jones FL. Chlorine poisoning from mixing household cleaners [Letter]. JAMA 1972;222:1312.

  5. Gapany-Gapanavicius M, Yellin A, Almog S, Tirosh M. Pneumomediastinum--a complication of chlorine exposure from mixing household cleaning agents. JAMA 1982;248:349-50.

  6. Faigel HC. Hazards to health: mixtures of household cleaning agents. N Engl J Med 1964;271:618.

  7. Gosselin RE. Clinical toxicology of commercial products. 5th ed. Baltimore: Williams and Wilkins, 1984:111-204.

  8. Gapany-Gapanavicius M, Molho M, Tirosh M. Chloramine-induced pneumonitis from mixing household cleaning agents. Br Med J 1982;285:1086.

  9. Litovitz TL, Bailey KM, Mitz BF, et al. 1990 Annual report of the American Association of Poison Control Centers national data collection system. Am J Emerg Med 1991;9:461-509.

  10. Office of the Federal Register. Code of federal regulations: hazardous substances labeling guide. Washington, DC: Office of the Federal Register, National Archives and Records Administration, 1984. (16 CFR 1500.121).

  11. Occupational Safety and Health Administration. Preamble to final rule on hazard communication. Federal Register 1983:48:53337.

  12. Occupational Safety and Health Administration. Hazard communication. Federal Register 1987;52:31852-86.

  13. Occupational Safety and Health Administration, Office of Health Compliance Assistance. Inspection procedures for the hazard communication standard. Washington, DC: Occupational Safety and Health Administration, 1990. [Instruction CPL 2- 2.38C].

  14. NIOSH. Occupational exposure to chlorine: criteria for a recommended standard. Cincinnati, Ohio: US Department of Health, Education, and Welfare, Public Health Service, 1976.

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