Background: On May 4, 2013, a train transporting chemicals derailed in Wetteren, Belgium. Several tanks loaded with acrylonitrile (ACN) exploded, resulting in a fire and a leakage of ACN. Objectives: To determine exposure to ACN and to assess discriminating factors for ACN exposure in the emergency responders involved in the on-site management of the train accident. Methods: The study population consisted of 841 emergency responders. Between May 21 and June 28, they gave blood for the determination of N-2-cyanoethylvaline (CEV) hemoglobin adducts and urine for the measurement of cotinine. They also filled in a short questionnaire. Results: 163 (26%) non-smokers and 55 (27%) smokers showed CEV concentrations above the reference values of 10 and 200. pmol/g globin, respectively. The 95th percentile in the non-smokers was 73. pmol/g globin and the maximum was 452. pmol/g globin. ACN exposure among the non-smokers was predicted by (1) the distance to the accident, (2) the duration of exposure, and (3) the occupational function. Discussion and conclusion: Emergency responders involved in the on-site management of the train accident were clearly exposed to ACN from the accident. However, the extent of exposure remained relatively moderate with CEV concentrations staying within the ranges described in literature as background for a smoking population. Moreover, the exposure was less pronounced in the emergency responders as compared to that in the local population.