602 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1930 



tinuous expansion chambers on either side of the roadway, thence 

 into the driveway. In the downward system, air was delivered to 

 the duct in the ceiling, thence through the ports into the upper ex- 

 pansion chambers from which it entered the roadway. 



A total of 17 tests were run with cars varying in number from 

 1 to 8, with concentrations of carbon monoxide in the driveway from 

 0.5 to 9.4 in 10,000 parts of air, at various temperatures and humid- 

 ities, and various methods of transverse ventilation. The tests veri- 

 fied the earlier conclusions, and demonstrated that with upward 

 ventilation the exhaust gases crossed the breathing plane of per- 

 sons in the tunnel but once, while with downward ventilation they 

 crossed this plane twice. There was also a lower concentration of 

 carbon monoxide with upward than with downward ventilation. 



Valuable and necessary as were the experiments required to de- 

 termine the various factors involved in the problem of adequate 

 ventilation for the Holland Tunnel, the data resulting from these 

 preliminary investigations had to be crystallized into tangible units 

 of ventilating equipment. 



These are the 84 giant Sturtevant Silentvane fans which are the 

 very lungs of the tunnel. Without such fans blowing in fresh air 

 and exhausting the vitiated air the tunnel could not be made to 

 function. 



The Sturtevant Silentvane fans are installed in the ventilation 

 buildings, of which there are two on each side of the river, one at 

 the pierhead line and the other inland. Each land shaft ventilates 

 four sections of tunnel, the adjoining portal sections of each tube, 

 the whole intermediate section to the pierhead shaft where traffic is 

 on a downgrade, and one-half of the parallel section where it is on 

 an upgrade. The buildings over these shafts contain four indepen- 

 dent sets of blower and exhaust fans. The pierhead shafts ventilate 

 three sections of tunnel, one-half of each of the 3,400-foot river sec- 

 tions and one-half of the intermediate section where traffic is on the 

 upgrade. In all there are 14 sets of blowers and 14 sets of exhaust 

 fans. Dividing the upgrade sections of the tunnels into three parts 

 gives added ventilation where the greatest amount of carbon monox- 

 ide is expected. 



There are 28 ducts — 14 blower and 14 exhaust, connecting the va- 

 rious sections of the tunnels with the ventilating buildings. Each 

 duct is equipped with three fans, two of which, when operated to- 

 gether, will supply the maximum quantity of air required. Their 

 capacities range from 81,000 to 227,000 cubic feet per minute and 

 they operate at static pressures varying from 0.6 to 3.75 inches of 

 water. This range in pressure and capacity is due to the great 

 difference in length of tunnel ventilated by different sets, those at 

 the outside of the pierhead shafts having 1,700 feet to serve while 



