“…Generally speaking, the difference between indoor and outdoor concentrations depends on the frequency of the air changes (ventilation rate), i.e. on the typology of the building, on the wind speed and direction, on the difference between outside and inside temperatures, and on the number of doors and windows left open (Chen, 2009;Jetter & Whitfield, 2005;Lees, 2004;Montoya, Planas, & Casal, 2009). It is not possible to determine which houses had open windows the night of the accident.…”