A 30-year-old male had an occupational exposure while measuring selenomethionine. He left work due to onset of nausea, weakness and vomiting. He showered and changed clothes at home. Due to continued worsening of symptoms, four hours post-exposure he was brought to an urgent care center (UCC), where he was immediately transported via ambulance to an emergency department (ED). He was noted by UCC and ED staff to have a strong noxious chemical odor. The patient deteriorated rapidly requiring intubation, and PEEP with 100% O2. Naloxone, dextrose, bicarbonate, fluid resuscitation and dopamine infusion were administered. Twenty minutes after arrival, the patient experienced asystole. Resuscitation was not successful. Postmortem blood selenium concentration was 11,000 mg/L. A multi-agency hazmat investigation occurred. The UCC and the patient's home were locked down. Twenty-four personnel were quarantined on-site for 7 h. Eight employees of the UCC underwent decontamination and transport to an ED for evaluation. Family members and immediate responding officers were quarantined on-site. Volatile methylated forms of selenium excreted in breath and sweat and not residual selenomethionine powder likely caused the chemical odor reported by the ED staff. Secondary contamination of ED personnel is a risk from self-presentation by symptomatic patients after a chemical exposure. Secondary contamination of ED personnel is unlikely from a powdered substance after presentation of a patient who has showered and changed clothes but given the unknown nature at the time, Hazmat Incident Commanders may decide to exercise an abundance of precaution.