HA-77-03-2 -- Design Criteria for Railway Tunnel Ventilation Systems

The construction of the 'New' Cascade Tunnel started on December 1925 was a part of an extensive improvement project which included the relocation of all but seven miles of the old 50 mile line between Peshastin and Scenic, Washington (1). The engineering judgement at that time stated that electrification was required in order to operate trains through the new 7.79 mile Cascade Tunnel. A thirty year power contract for the electrification was signed July 31, 1926 committing the electrification to July 31, 1956.

In 1944 diesel locomotives were used as supplementary power in the electrified zone. At this time the Bureau of Mines conducted tests in the tunnel to determine how the exhaust from a diesel locomotive affects the air quality. Berger and McGuire (2) state in their report that no significant contamination or hazardous concentrations of noxious fumes were observed in the tunnel air.

The report (4) considered several schemes for a ventilation system and two were judged to meet most nearly the requireme~ts of preventing excessive engine over-heating and clearing the tunnel at a reasonable cost. The first method was to direct air against an east bound train assuming a portal door at the east portal in the closed position and against the empty tunnel to remove the exhaust fumes. The fan and door installation would be at the east portal. The second method would direct air past the east bound train keeping the exhaust gases ahead of the train and against the empty tunnel to complete the removal of exhaust fumes. The fan and door installation would be at the west portal. The second method would reqqire 1,000,000 cfm of air at approximately 3,000 hp versus 200,000 cfm at approximately 400 hp (4). On the basis of first cost and operating costs, the first method was selected. The report also reveals the need for more data from extensive tests either in the field or the use of a model to further define tunnel resistance, train resistance and how best to achieve the cooling o(the trailing diesel locomotive units. The concept of adding air to supplement the air produ~edby the piston effect is sound in principle since this would produce high air velocity relative to the train while at the same time diluting the hot exhaust gases with a large volumepf cool air. The venture, i.e. the concept and Ultimate plan for the Cascade Tunnel ventilatic)Il system, required a reaffirmation on the part of the designer and client that basic scienti~i7,principlescan be logically applied. Subsequent field tests are testimony to the validity of, the concept and that the first design was very conservative.