These provide clear evidence of severe acute respiratory damage with intensity commensurate with the exposure level and duration.^4,5

Several investigators have attempted to follow subjects who have experienced acute symptomatic effects to determine whether these either persist or progress. To date, most of the reports of accidental overexposures suggest that individuals return to normal.^6,7 A few reports have documented persistent obstructive or restrictive effects in follow-up of 1, 3 and 12 years.^8,9,10 In one case report a previously healthy individual suffered onset of irreversible and debilitating asthma following a single overexposure.¹¹ In all instances there has been an absence of pre-accident health assessments so whatever residual effects are present at from 6 months to 13 years later cannot be attributed to the acute accidental exposure alone.

In contrast to these studies of single acute overexposure episodes, there are two populations of workers occupationally exposed to chlorine gas where the importance of accidental gassings has been evaluated. In a cross-sectional study of chlorine gas plant workers, 55 of 139 were reported to have experienced accidental overexposures against a background of less than 1 ppm.¹² Of those overexposed, only three showed significant impairment which might only represent statistical variability in the population. Overall there was, however, evidence of persistent minor airflow abnormalities.

In a more detailed study of pulpmill workers, evidence of an effect of gassings was presented.¹³ Although several irritant gases were present in the pulpmill, chlorine was the dominant irritant exposure. Overall the pulpmill workers had more symptoms but no pulmonary function differences compared to a control working population. However, those with gassings had all the excess of symptoms and had more airflow obstruction compared with the other pulpmill workers. Evidence of healthy worker selection was also noted as likely to have decreased the strength of the findings.

This population had been studied seven years previously by the same investigators. Those workers who had experienced chlorine gassings once or twice during the study interval were compared to the remainder. ¹⁴ For those whose gassing resulted in their seeking first-aid assistance at the time, there was evidence that respiratory symptoms and airflow obstruction had progressed when 1988 measures were compared to ones taken in 1981. These effects were present after controlling for cigarette smoking.

In summary, there is clear evidence of acute respiratory effects from chlorine exposures which include both acute bronchitis and airway obstruction as well as inflammatory bronchoconstriction (RADS). There is also evidence for a chronic effect from exposure to chlorine. The relationship of acute respiratory effects to chronic ones is also present,