Acute effects of nitrogen dioxide after accidental release

Objectives. Following an accidental release of nitrogen dioxide from a rail road tank car containing nitrous tetroxide, the authors undertook a study o f the health effects of the release, measuring the association between acut e low level exposure and pulmonary symptoms. Methods. The authors reviewed the records of three emergency department, su rveyed 80 emergency department patients, 552 community residents, 21 chemic al plant workers, and 29 emergency workers, and conducted a case-control st udy. Pulmonary case status was defined as having an objective pulmonary fin ding noted on the emergency department record, reporting that the onset of symptoms was subsequent to the release, and being within the city limits at the time of the release. Self-reported case status was defined as reportin g one or more symptoms consistent with exposure to nitrogen dioxide in the week after the release and having been within the city limits at the time o f the release. Control subjects were survey respondents who reported no sym ptoms in the week after the release and had been within the city limits at the time of the release. Chemical exposure was characterized by proximity t o, direction from, and being outdoors within one hour after the release. Du ration of potential exposure was not measured, Logistic regression was used to estimate odds ratios and 95% confidence intervals for symptoms by expos ure level, adjusted for age, sex, smoking, and preexisting pulmonary condit ions. Results. Local emergency department visits increased fivefold in the week a fter the release. The most common complaints recorded in a systematic sampl e of 528 visits in the first 30 hours after the release were headache (31%) , burning eyes (30%), and sore throat (24%). Objective pulmonary findings w ere recorded for 41 (5%) patients in the week before and 165 (4%) in the we ek after the release. The odds of being a pulmonary case increased by 40% f or each quarter-mile increment in proximity to the release (odds ratio [OR] 1.4; 95% confidence interval [CI] 1.1,1.7). while the odds of being a self -reported case increased by 20% for each quarter-mile increment in proximit y (OR 1.2, 95% CI 1.1,1.4), People who met the pulmonary case definition we re 2.5 times (CI 1.3,4.8) more likely than control subjects to have been ou tdoors and 6.4 times (CI 3.2,12.6) more likely to report a preexisting pulm onary condition. Self-reported cases were 2.6 times (95% CI 1.8,3.8) more l ikely than control subjects to have been outdoors and 1.9 times (95% CI 1.1 ,3.1) more likely to report a preexisting pulmonary condition. Conclusions. Emergency department visits increased fivefold, but serious ac ute health effects were uncommon, People who mel the pulmonary case definit ion were six timer more likely to report pulmonary symptoms than those with out preexisting conditions, This study was not designed to determine any po tential long-term effects of exposure.