<P> The project was renamed the Holland Tunnel in memory of its first chief engineer by the New York State Bridge and Tunnel Commission and the New Jersey Interstate Bridge and Tunnel Commission on November 12, 1924 . Holland was succeeded by Milton Harvey Freeman, who died of pneumonia in March 1925, after several months heading the job . After Freeman's death, the position was occupied by Ole Singstad, who oversaw the completion of the tunnel and designed its pioneering ventilation system . </P> <P> Tunnel construction required workers to spend large amounts of time in the caisson under high pressure of up to 47.5 pounds per square inch (328 kPa), which was thought to be necessary to prevent river water from entering prior to completion of the tubes . "Sandhogs", as they were termed, entered the tunnel through a series of airlocks, and could only remain inside of the tunnel for a designated time period . On exiting the tunnel, the workers had to undergo controlled decompression to avoid the bends, a condition in which nitrogen bubbles form in the blood from rapid decompression . Fortunately, no workers died as a result of decompression sickness: the work involved "756,000 decompressions of men coming out of the compressed air workings," which resulted in 528 cases of the bends, none fatal . Completion of the tunnel took nearly seven years and claimed the lives of 14 workers . </P> <P> The most significant design aspect of the Holland Tunnel is its ventilation system . At the time of its construction, underwater tunnels were a well - established part of civil engineering, but no long vehicular tunnel had been built . The technical hurdle was the ventilation required to evacuate the carbon monoxide emissions, which would otherwise asphyxiate the drivers . </P> <P> There are four ventilation towers serving the tunnel, designed by Norwegian architect Erling Owre . </P>

What does the holland tunnel look like underwater