Kemira B.V. operates a 1200 metric tpd (100%) high pressure nitric acid plant in Rozenburg, the Netherlands since 1968. Until the incident described here occurred, operation had always been uneventful. In August 1993, however, the ammonia/air mixer suddenly burst open, releasing large amounts of air and ammonia to atmosphere. Two persons working in the plant miraculously missed being hit by the gas jet and flying debris. This paper describes the incident, its cause and measures taken to prevent reoccurrence.