Ventilation of Mechanical Refrigerator Cars to Prevent Carbon Dioxide Accumulation and Brown Stain in Lettuce Loads

Excerpts from the report: Increased concentrations of carbon dioxide (C02) have been shown in both laboratory and shipping tests to cause brown stain, a physiological disorder of lettuce. Accumulations of C02 in railcars of lettuce have been detected at east coast destinations since 1967, and concentrations as high as 6.6 percent have been observed. Three separate studies were conducted in 1970 and 1971 to develop practical methods of preventing the accumulation of dangerous levels of CO2 in conventional railcars of lettuce. The first two were preliminary and data for those are presented in the Appendix. The third study involved 28 commercial shipments of lettuce from California to the east coast, in which the water drains of 10 cars were propped open to partially ventilate the loads. Modified atmosphere cars also were studied in these tests