Static pressure and ventilation rates in rooms

The British Standard Code of Practice, and other authoritative guides, recommend minimum rates of ventilation related to the size and use of rooms, and structural means for providing them. But the difficulty of measuring actual ventilation rates suggests that it is seldom done.
A standard way is to put into a room a known amount of some gas, measure the rate of decay of its concentration and hence infer the ventilation rate. (Renbourn, Angus & Ellison, 1949; Bedford, 1948; Lidwell & Lovelock, 1946). To estimate the ventilation rate by measuring the difference in static pressure between points inside and outside a room has been deemed impracticable (Carne, 1946). While investigating this conclusion, and, in the sequel, confirming it, observations on the relationship between air flow and static pressures, which may be of general interest, were made at the Ministry of Works Field Test Unit.