Subjective odour levels in an air - conditioned hospital ward.

Tests were carried out in an experimental air-conditioned hospital ward to determine what effect the mechanical ventilation and recirculation rates had on subjective odour levels in the ward. Odour conditions in the ward were not found to deteriorate with decreasing mechanical ventilation rate or increasing recirculation rate, but to fall into two distinct categories, which have been termed 'Acute' and 'Intermittent Background' conditions. 'Acute' conditions, where a particularly foul malodour prevailed in one or more rooms of the ward, were a rarity in the experimental general surgical ward; they occurred only twice during the testing period of approximately two years, and the mechanical ventilation rates tested were incapable of dealing with them. 'Intermittent Background' conditions, which are not attributable to a general prevailing odour level but rather to specific low level odour producing events, were satisfactory even under the most extreme test condition of three mechanical air changes per hour and 80% recirculation.