In 2013 a fire broke out in the Nursing Home (NH) in the Henryszew village 5 km away from the district hospital in Żyrardów. At the time of the incident 52 residents and 16 staff members were present in the building. Due to a large number of casualties, the occurrence was classified as a potentially mass casualty incident (MCI). Troops of the State Fire Brigade, Paramedic Rescue Squads, choppers of the Helicopter Emergency Medical Service, the Police, and the NH staff took part in the rescue operation. The priority was given to the evacuation of the NH residents carried out by the NH staff and firefighters, extinguishing the fire, as well as to primary and secondary survey triage. Due to the pre-accident health state of the victims, the latter posed a considerable difficulty. A decisive role was played by the need to conduct non-invasive measurements of carboxyhemoglobin in all the casualties, which then made it possible to adequately diagnose the patients and implement proper procedures. The rescue operation was correctly followed although it proved to be a serious logistical and technical undertaking for the participating emergency services. The residents were not found to be suffering from carbon monoxide poisoning, therefore 46 of the residents safely returned to the building. The fact that all the Paramedic Rescue Squads were equipped with medical triage sets and were able to conduct non-invasive measurements of carboxyhemoglobin made it possible to introduce effective procedures in the cases of suspected carbon monoxide poisoning and abandon costly and complicated organisational procedures when they proved to be unnecessary. Med Pr 2014;65(2):289–295