Document n98okYj7RYYQvg1yDeVpd0y7m

46 INDUSTRIAL HYGIENE AND OCCUPATIONAL MEDICINE winter, as during the heating season the curve rises sharply. In 1938 this fact is most pronounced. By 1948 combustion was much improved, and in 1949 it was not greatly different in winter and summer. We attribute this result to the fine cooperation which the Bureau of Smoke Prevention has received from the citizens and the industries of Pittsburgh and also to the constant and careful work of months Chart 1.--The monthly average dustfall within the city limits of Pittsburgh in 1938, 1948 and 1949. The yearly averages are also represented. MONTHS Chart 2.--`The monthly average percentage of fixed carbon is shown for 1938, 1948 and 1949. The yearly averages are also represented. the bureau's inspectors. It is true that other factors have helped, such as the increased use of natural gas and the introduction of Diesels but not to such an extent as indicated by the combustion curves. The reason we do not include the volatile matter to obtain a measure of com bustion efficiency is because our analyses show that only, about one' fifth of the