Civilian mass exposure to hydrazine after an F-16 crash: a retrospective descriptive study.

Background: Hydrazine is a volatile and highly toxic monopropellant used in the Emergency Power Unit (EPU) of F-16 aircraft. Although hydrazine is widely used in both military and industrial contexts, reports of its effects in non-occupational civilian populations are extremely limited. Acute civilian mass exposures are almost never systematically documented. On December 12, 2016, an F-16 crash in Diyarbakır, Türkiye, released hydrazine into an open-field setting, exposing unprotected civilians. This study aimed to characterize acute manifestations, evaluate associations with exposure duration and route, and identify operational implications.

Methods: We conducted a retrospective descriptive study of 30 previously healthy male civilians exposed at the crash site. Clinical data, laboratory findings, ECGs, and imaging were retrieved from standardized emergency department records. Exposure duration-triangulated from patient interviews and operational logs-was analyzed as a continuous surrogate for dose, in line with Haber's rule. Associations with symptom categories and exposure routes were assessed using nonparametric statistics, Fisher's exact tests, and exploratory receiver operating characteristic (ROC) analysis.

Results: Twenty patients (66.7%) developed symptoms, while ten remained asymptomatic. Symptom development correlated strongly with exposure duration (Spearman r = 0.61-0.68), with respiratory cases showing significantly longer exposures (median 45 vs. 14 min, p = 0.0017). Ophthalmologic findings (36.7%) were most frequent, while dermatologic (26.7%) and respiratory (13.3%) manifestations occurred exclusively in contact-exposed individuals (p < 0.001 and p = 0.012, respectively). Inhalation-only exposure primarily caused ocular irritation. No patient exposed ≤ 5 min developed symptoms, whereas all symptomatic individuals reported longer exposures; ROC analysis supported discriminatory potential (AUC > 0.80), though results remain exploratory. A 26-year-old first responder developed acute hypoxemic respiratory failure after 45-60 min, recovering with supportive care. No hepatic, renal, neurologic, or cardiovascular complications occurred, and all patients were discharged within 24 h.

Conclusions: This study provides one of the most extensive civilian datasets on acute hydrazine exposure. Findings highlight a strong dose-time relationship and route-specific patterns, with exposures > 5 min associated with clinically significant toxicity. While thresholds remain hypothesis-generating, all patients recovered rapidly with supportive care. Operational lessons include the need for rapid evacuation, immediate decontamination, and strict use of personal protective equipment, offering practical insights for toxicology practice and disaster preparedness.