Hazardous Chemical Information System (HCIS)

Chlorine

Exposure Standard first adopted in 1990

Review notice: Reason for review - review of peak value.

Peak limitation notice: For some rapidly acting substances and irritants, the averaging of airborne concentration over an eight hour period is inappropriate. These substances may induce acute effects after relatively brief exposure to high concentrations and so the exposure standard for these substances represents a maximum or peak concentration to which workers may be exposed. See Chapter 6: Guidance Note on the Interpretation of Exposure Standards for Atmospheric Contaminants in the Occupational Environment, published by Worksafe Australia.

No standard should be applied without reference to Guidance on the interpretation of Workplace exposure standards for airborne contaminants.

Documentation notice: National Occupational Health and Safety Commission documentation available for these values.

1. IDENTITY

2. CHEMICAL AND PHYSICAL PROPERTIES

Chlorine is a greenish-yellow, non-compbustible gas at atmospheric pressure, with a pungent odour. Its chemical and physical properties include:

3. MAJOR INDUSTRIAL USES

Chlorine has a wide range of industrial applications, mainly in the manufacture of chlorinated solvents, plastics, household bleach and pharmaceuticals, in purifying water, and as a bleaching agent in the pulp and paper industry.

4. TOXICOLOGICAL MECHANISMS

Chlorine is rapidly converted in the body to hypochlorous acid which can penetrate the cell and react with cell protein to form chloramines (compounds of chlorine and nitrogen), which in turn disrupt cellular integrity

². In microbiila test systems, chlorine is able to disrupt cell wall permeability and this property may explain the ability of chlorine to casue oedema and acute tissue injury

³.

5. ANIMAL STUDIES

Back et al reported a LC₅₀ of 293ppm for rats and 137ppm for mice, after a one-hour inhalation study

⁴.

In an animal inhalation study

⁵, groups of male Swiss-Webster mice were exposed for 10 minutes to chlorine at concentrations 0.7-38.4ppm and to hydrogen chloride (HCl) at 40-943ppm. The decrease in respiratory rate during exposure was used as the response indicator for sensory irritation. Dose-response information suggested that chlorine was 33 times (95% confidence level = 18.6-57.1) more irritating than HCl. The researchers further suggested that 1ppm should be the upper acceptable limit for exposure to chlorine.

Barrow et al

⁶ discovered that rats pre-treated with 1ppm chlorine developed a sensory irritation tolerance to subsequent chlorine exposure. The researchers believed that this phenomenon was relevant to human exposure.

Jiang et al

⁷ exposed groups of mice and rats to 9-11ppm, for 6 hours a day for 1, 3 or 5 days. Lesions were observed in nasal passages of the animals, with partial or complete degeneration of the olfactory sensory cells.

6. HUMAN STUDIES

Rupp and Henschler

⁸ found in a human volunteer study that coughing began at an airborne concentration of 0.5ppm. Sensory irritation was markedly felt when the concentration exceeded 1ppm.

In 1970, Patil et al

⁹ studied 332 workers in 25 chlorine-producing plants in the USA and Canada. Air sampling was carried out within each plant every two months throughout the study year. Eight-hour

TWA exposure data were calculated for each worker. Only six of the 332 workers had

TWA exposures above 1ppm and only 21 had

TWAs above 0.52ppm. The average duration of chlorine exposure was 10.9 years. The investigators found no dose-response relationship between prevalence of colds, dyspnoea, palpitation or chest pain. Evaluation of chest X-rays, ventilatory capacity, maximal ventilatory capacity and forced expiratory volume indicated no evidence of permanent lung damage attributable to chlorine at the reported levels. Of the 329 electrocardiograms (ECGs) from 332 workers, 9.4% were abnormal as compared to 8.5% in the controls. However, the number of ECGs taken in each group was not stated. Leukocytosis (p<<o.05) and low haemocrits (p<<0.017) showed some relation to chlorine exposure. No neoplasia or serious pulmonary disease was reported.

Capadoglio et al

¹⁰ reported a study of 52 electrolytic cell workers. The average length of service was 10 years; the average exposure was 0.298ppm (SD=0.181). No permanent or temporary clinically significant incapacity was found.

Anglen

¹¹ exposed up to 29 subjects to 0.0, 0.5, 1.0 and 2.0ppm of chlorine for four- and eight-hour periods. The subjects were asked to record their sensory irritation levels at regular intervals during the experiment. Lung function tests, including forced vital capacity (FVC) and one-second forced expiratory volume (FEV1), were also carried out before, during and after the experiment. The findings indicated that exposures to 1.0ppm chlorine for eight hours produced statistically significant changes in pulmonary function and increased subjective irritation. Medical examination of six of these 14 subjects showed increased mucus secretion from the nose and increased mucus in the hypopharynx. Exposures of up to 30 minutes to 2.0ppm produced no significant increase in subjective irritation over that seen during control exposures. Exposures of 2 hours at 2.0ppm chlorine produced no significant changes in pulmonary function.

Based upon the results of the investigation, the author recommended an eight-hour

TWA exposure standard of 0.5ppm and a 15-minute short-term limit of 2.0ppm.

7. OVERSEAS EXPOSURE STANDARDS

* Under review by HSE

8. CONCLUSION

Chlorine is a strong respiratory irritant. There is not sufficient information regarding the chronic effect on the respiratory passages of long-term exposure to low concentrations of the gas.

There is sufficient evidence to indicate that an eight-hour

TWA concentration of 1.0ppm for chlorine may result in irritation of the nose, throat, and conjunctiva of exposed workers. Similar eight-hour

TWA exposures at 0.5ppm will produce markedly less severe subjective irritation.

9. RECOMMENDATION FOR EXPOSURE STANDARD

To minimise respiratory irritation, the Exposure Standards Working Group recommends a peak exposure standard of 1ppm for chlorine. The Working Group also believes that this peak standard should also keep the

TWA exposure below 0.5ppm in most industrial situations.

1. National Institute for Occupational Safety and Health (NIOSH), Criteria for a recommended standard...Occupational exposure to chlorine, NIOSH, HEW Publication No.(NIOSH) 76-170, 1976

2. National Board of Occupational Safety and Health, (NBOSH), Scientific Basis for Swedish Occupational Standards II 1982: 9, p 6-14, Criteria Group for Occupational Standards, Solna, Sweden, 1982

3. World Health Organization (WHO), Chlorine and Hygrogen Chloride, Environmental Health Criteria No.21, Geneva, WHO, 1982.

4. Withers R M J and Lees F P, "The assessment of major hazards: the lethal toxicity of chlorine", J Hazardous Materials, 12, p.231-282, 1985

5. Barrow C S et al, "Comparison of the sensory irritation response in mice to chlorine and hydrogen chloride", Arch Env Health, March- April, p.68-76, 1977

6. Barrow C S & Steinhagen W H, "Sensory irritation tolerance development to chlorine in F-344 rats following repeated inhalation", Tox Appl Pharm, 65, 383-389, 1982

7. Jiang XZ, Buckaley & Morgan, "Pathology of Toxic Responses to the RD50 concentration of chlorine gas in the nasal passages of rats and mice", Toxicol Appl Pharmac, 71, 225-236, 1983

8. Rupp H & Henschler D (in German), In: National Institute for Occupational Safety and Health (NIOSH), Criteria for a recommended standard...Occupational exposure to chlorine, HEW Publication No. (NIOSH) 76-170, p.58-59, 1976

9. Patil LRS, Smith RG, Vorwald AJ & Mooney TF, "The health of diaphragm cell workers exposed to chlorine", Am. Ind. Hyg. Assoc. J., 31, 678- 86, 1970

10. Capodaglio E et al (in Italian), In: NIOSH Criteria for a recommended standard...Occupational Exposure to chlorine, HEW Publication (NIOSH) No.76-170, p.67-68, 1976

11. Anglen DM, In: American Conference of Governmental Industrial Hygienists (ACGIH), Documentation forTLVs and BEIs, 5th edition, Cincinnati, p.117, 1-3(87), 1986

Footnotes:

Review notice:
A review notice indicates that the substance requires further review by the Exposure Standards Expert Working Group. In most cases the ACGIH documentation should be consulted for these substances.

Peak limitation notice:
Peak - means a maximum or peak airborne concentration of a particular substance determined over the shortest analytically practicable period of time which does not exceed 15 minutes.

Documentation notice:
Entries carrying a notice for National Occupational Health and Safety Commission documentation indicate that these substances have been reviewed in detail by the Exposure Standards Expert Working Group and that documentation supporting the adopted national values is available in the National Commission's Documentation of the Exposure Standards [NOHSC:10003(1995)].