Automobile Exhaust Gases in Vehicular Tunnels

Automobile Exhaust Gases in Vehicular Tunnels

THE rapidly increasing use of motor vehicles and trucks in the United States is creating an entirely new problem in the proper ventilation of tunnels, subways and other confined spaces through which such machines must pass. This problem has become of immediate importance because a tunnel 8,000 feet long is being designed to pass under the Hudson River between New York City and New Jersey. Another tunnel at Pittsburgh 5,700 feet long through the South Hills, is already under construction, and a third tunnel, 6,000 feet long, between Boston and East Boston is proposed. It is probably that other tunnels will he started in various parts of the United States in the near future.

The ventilation of such tunnels is a serious matter, on acount of the poisonous nature of automobile exhaust gases. It is not uncommon to read about finding a man dead in his garage. Generally this happens on a cold, winter morning, after he has been running the engine with the doors and windows closed.

The poisonous constituent of automobile exhaust gas is carbon monoxide. It is the same gas which has caused the death of so many miners after mine fires and explosions. It is also found in illuminating gas, and there, likewise, has caused the death of many persons.

Carbon monoxide has no color, taste, or smell. The smoke issuing from the exhaust of an automobile is not carbon monoxide, although where there is smoke, there is usually carbon monoxide present. The amount of it present in automobile exhaust gases varies under different conditions of running a machine. Probably the principal cause for variation is the adjustment of the carburetor. A rich mixture may give as high as 10% carbon monoxide in the exhaust gases. A very lean mixture will give an exhaust gas containing nothing, or perhaps not more than one or two per cent. All gradations between these percentages occur. For this reason, engineers who have to design the ventilation for tunnels have no accurate information on what the average percentage of carbon monoxide is likely to he.

Very few tests have ever been made on cars taken from the street and tested in the condition under which they were operated, and the only way to obtain this information is to run a great many tests on the road under exactly the same conditions as will prevail in tunnels, using cars and trucks of various sizes, so that average results may be obtained for each type of machine.


In order to obtain information as to the amount and composition of automobile exhaust gases, the Bureau of Mines has undertaken to make tests at its

Pittsburgh station, on a number of passenger cars and trucks, about 100 in all. The expense of carrying out the work is being borne by the New York and New Jersey State Bridge and Tunnel Commissions, who need the the information for designing the tunnels under the Hudson River. Pittsburgh is also contributing to the work by furnishing the necessary cars and trucks for making the tests, as the local need for the information is great, to insure adequate ventilation for the tunnel under the South Hills. The work on this problem was started last December. Up to the present time, 24 passenger cars and trucks have been tested.

In making the tests, an accurately graduated tube containing the gasoline to be used is attached to the carburetor. Another apparatus for collecting the gas sample is attached to the exhaust pipe by means of a rubber tube. The car is taken to the test course and run for exactly one mile at the required speed. Doing this period, the gasoline is accurately measured and a sample of gas is collected. The gas sample is sent to the Bureau of Mines laboratories and is carefully analyzed for all constituents; and from these results the number of cubic feet of monoxide given off by the car is calculated.

Tests are made on a level grade and up and down a 3% grade, at rates of speed of 6, 10, 15 and 20 miles per hour. Tests are also made with the engine racing, idling ,and accelerating, so as to reprouce conditions in a tunnel when it is crowded with cars which are starting up after a blockade in the traffic. Nothing is overlooked in obtaining information which will show the worst possible conditions that might arise in a tunnel.


The carbon monoxide in exhaust gases is an active poison, for the reason that it unites with the red coloring matter of the blood and prevents it from taking up oxygen from the air. The victim really suffocates in much the same way as if his air supply were shut off. Only very small percentages of carbon monoxide are needed to render a person unconscious. One per cent, in the atmosphere will produce death very quickly. I have been in 0.1% carbon monoxide for one hour, and suffered a distinct headache from this exposure.

In order to properly calculate the amount of air that is needed to sweep out exhaust gases from a tunnel, engineers must know what is the largest allowable percentage of carbon monoxide that a person may breathe for several hours without any ill effects whatsoever. This problem is also being investigated by the Bureau of Mines. The work is carried on by Dr. Yandell Henderson, of the Bureau, at the Physiological Laboratory of Yale Medical School, New Haven, Connecticut. He is determining just how many parts of carbon monoxide in 10,000 parts of air may be considered safe.

At the present time, authorities differ somewhat in this respect. Practically all of them agree that 1 to 3 parts in 10,000 are perfectly safe for at least an hour. A few authorities believe that even 5 or 6 parts may be safely tolerated. The work being done by the Bureau of Mines should determine which figures shall be used. These tests are made by subjecting a large number of people, who volunteer themselves for test, to air containing these small percentages of carbon monoxide.


The automobile exhaust gas tests when completed will also be of great value to owners of automobiles and trucks, and also to dealers, as it will furnish reliable unbiased information on the efficiency of a given machine under particular conditions. For examlpe, the tests thus far may have shown no difference in the efficiency of different makes of cars and trucks as regards gasoline economy, but cars of the same make showed large variations, due to the fact that the owners were running the machines with improper adjustment of carburetors. Most of them were using very rich mixtures. In fact, the average of 24 cars tested showed that 20 to 30% of the heat in the gasoline went out in the form of unburned gases in the exhaust. In other words, if the mixtures had been leaner, the owner would have gotten 25% greater mileage from a gallon of gasoline.

Drivers naturally adjust their cars to start easily in the winter time. This means that they will use rich mixtures, as a rich mixture starts more easily than a lean one.

It is expected to continue the automobile and truck tests throughout the summer, in order to find out whether less carbon monoxide is produced when the machine operates in warm weather, and the Bureau of Mines in very anxious that owners of automobiles and trucks continue their cooperation in furnishing cars for test.

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