Adm. W. J. Smith, 56, a native of Suttons Bay, Mich., has become the 13th Commandant of the U.S. Coast Guard at ceremonies held on board the Coast Guard Cutter Campbell on May 31, at Washington, D.C.

Admiral Smith relieved Adm. Edwin J. Roland, 61, who retires after 37 years of service and 4 years as Commandant.

The oath of office was administered by Assistant Secretary of the Treasury True Davis.

Admiral Smith is a 1933 graduate of the Coast Guard Academy. In 1939 he was assigned to flight training at Pensacola, Fla., and became a Coast Guard aviator in June 1940. Aviation

assignments took him to the Coast Guard Air Station at San Francisco during World War II and to Traverse City, Mich., in 1946 where he commanded the Coast Guard Air Station.

In 1951 he was graduated from the Armed Forces Staff College at Norfolk, Va. Later he commanded the Coast Guard's largest icebreaker, the Mackinaw, on the Great Lakes.

President Kennedy nominated him for flag rank effective July 1, 1962. He then became Superintendent of the Coast Guard Academy at New London, Conn.

His latest assignment was as Commander, 9th Coast Guard District, in

command of all Coast Guard forces on the Great Lakes.

Admiral Smith is married to the former Harriet A. Lary of Los Angeles, Calif. They have one son, Jeffrey, and a daughter, Lary Smith.

Admiral Roland, a native of Buffalo, N.Y., was graduated from the Coast Guard Academy in 1929.

Early in Admiral Roland's career he served on board Coast Guard destroyers detailed to suppress "rumrunners" during Prohibition. In 1936, while on board the cutter Cayuga he took part in the evacuation of (Continued on page 150)

COMBUSTIBLE GAS

INDICATORS

How does a combustible gas indicator work? What properties of the air-gas mixture can one determine by the use of this instrument? Richard O. Fleming, Chairman of the Marine Chemists Association, gave answers to these and other questions at the Marine Section of the National Safety Congress last fall. In the interest of marine safety we reprint his paper with pleasure.

FOR NEARLY 2 YEARS now it has been a Federal regulation to have a combustible gas indicator aboard all tankships and tank barges. This regulation came into being on June 5, 1964, in the Code of Federal Regulations, section 35.30-15. Since these regulations are enforced by the U.S. Coast Guard, I would believe all our vessels now have combustible gas indicators aboard.

This regulation was made for one prime reason, that being safety. It was believed that with a combustible gas indicator aboard, a man would not have to enter a compartment subject to gas accumulation without its first being tested and proved safe. Testing is usually done by a chief mate or captain at times when a marine chemist is not available or needed. This situation usually arises when the vessel is at sea or at a remote berth. Often a reach rod needs reconnecting, a leaky cargo line or coil needs banding, or a cement box installed to stop a leak.

Since we assume that all vessels have a combustible gas indicator aboard, we should be able to assume that someone aboard knows how to operate the instrument accurately; this is not the case. I have been on at least a dozen vessels this year where I was met by the officer on watch, have told him that I was sent by the shipyard or owner to check the vessel to see if it was gas free, and when I took out my combustible gas indicator he would say, "Say, I have one of those gadgets in my room; the company sent it a few months ago." Next, he often would ask if I would show him how

Courtesy Newport News Shipbuilding

it operates after I had completed my inspection. We usually would find a new meter without batteries or a book of instructions. Either the instruction book had not been sent with the meter or had not been referred to by the officer. This is not a criticism of anyone aboard a vessel who has a gas indicator and does not use it. More often than not they are not properly instructed in the use of the meter and thus apprehensive about using it.

The purpose of this paper is to better familiarize each one of us with the proper use, care, and limitations of combustible gas indicators.

Your life or the life of someone else may be dependent on the care with which you handle any combustible gas indicator. The sensing elements are only three one-thousandths of an inch in diameter, and the careless dropping of the instrument might very easily bend or distort the fine coils of these sensing elements, and thus, upset the calibration of the instrument. Then, too, the meter consists of a needle or pointer on a sensitive pivot. This pivot is mounted on a very small bearing. A severe jar may damage the pivot bearings.

A combustible gas indicator is an instrument for detecting gas-air or vapor-air mixtures in terms of their explosibility, to determine whether the mixture is safe against the possibility of fire or explosion.

Everyone who may have occasion to use a combustible gas indicator must become thoroughly familiar with the operation and limitations of the indicator, and should satisfy himself that the instrument is in proper operating condition.

Before going into details of operation and the interpretation of readings, it seems desirable to get certain definitions clearly in mind. While these definitions are probably well known, their repetition may help to clarify certain points which will be presented later on.

Lower Explosive Limit (L.E.L.) — This is the leanest mixture of gas or vapor in air, where once ignition occurs, the gas or vapor will continue to burn after the source of ignition has been removed.

Upper Explosive Limit (U.E.L.)This is the richest mixture in which a flame will continue to burn after the source of ignition has been removed.

Explosive Range (Flammability Limits)-The explosive range exists between the L.E.L. and U.E.L.

Flashpoint-The flashpoint of a flammable liquid is the lowest temperature at which it gives off enough vapors to form a flammable or ignitible mixture with air near the surface of the liquid or within the container used.

By Richard O. Fleming

Flashpoints vary with temperature, for example:

Kerosene, a high-flash product at room temperature, gives off almost no vapor, hence, an extremely low reading, if any, on a combustible gas indicator. Should you heat the kerosene, more vapors will be liberated, and you might expect a higher reading on the combustible gas indicator, providing the vapor does not condense back to a liquid before it reaches the analyzer cell. This vapor, which is being liberated due to the elevated temperature, may ignite when a source of ignition is present.

Gasoline, a low-flash product, at room temperature, will liberate an explosive mixture, which is extremely dangerous. A combustible gas indicator will indicate the concentration of the gasoline vapor present. Gasoline will continue to give off vapors and will not condense back into a liquid until an extremly low temperature is reached. If this were not the case, our automobiles would not run in cold weather.

Fire and Explosion Characteristics

Fire The combination of vapor, air, and heat results in a fire.

Flash Fire-The combination of an accumulation of vapor with air and heat in an open area will result in a flash fire.

Explosion-The combination of an accumulation of vapor, air, and heat in the correct proportions in a confined space results in an explosion.

Under all of the above, both the air and the heat remain constant, but the change in the fuel-vapor caused the fire or explosion.

Principle of Operation

Catalytic combustion is the burning of a combustible gas or vapor in air on a catalytic filament. A catalyst is a substance which accelerates a chemical reaction (the burning) without entering into the reaction. There are various catalysts. Most manufacturers of combustible gas indicators use a platinum wire filament, primarily because it is a good catalyst, and platinum wire has a high temperature coefficient of resistance. In other words, the resistance of the wire changes materially at different temperatures, thus, when such a filament is set up in a bridge circuit, it serves as the basic operating principle of a combustible gas indicator.

The name for the Wheatstone bridge circuit comes from its inventor. It was primarily designed for

measuring resistance and actually, when used in catalytic-type instruments, it is the change in resistance of the active filament, caused by the burning of the gas or vapor sample which causes a current to flow through the meter.

The manufacturers of combustible gas indicators make available several different models. Care should be taken in selecting the correct instrument for specific applications.

Many companies use these instruments for what we refer to as "GoNo Go," or to determine whether a flammable gas or vapor is present. They are not particularly interested in the actual percent of the gas or vapor present.

Testing steps often overlooked should be emphasized and practiced.

First Step: Test for tightness.-Any time a filament is replaced in the analyzing chamber, or any other work done on the sampling system, the indicator should be tested for tightness before being assembled and put into service.

With a finger held firmly over the inlet of the instrument, squeeze the aspirator bulb and hold a finger firmly over the outlet valve of the bulb. If all connections are tight, the bulb will remain deflated. If the bulb inflates, there is a leak in the system and it should be found and remedied.

Second Step: Sampling. The directions for sampling are on the nameplate in full view of the operator. These directions should be followed in proper order.

How to Check the Calibration

The assurance that a combustible gas indicator is in proper working condition, and, therefore, will give a reading of a gas and/or vapor air mixture which can be relied upon, is of prime importance in preventing property damage or loss of life.

An instrument which has been damaged or whose filament has been contaminated may give false readings and thereby lead to a false sense of security. Therefore, the matter of frequent testing of instruments assumes great importance.

One method of calibration consists of a known mixture of gas in the cylinder which is released into the evacuated bag. A sample of the bag is drawn into the combustible gas indicator. The reading is noted and compared with the correct reading shown on the label attached to the cylinder. Correct readings for all model instruments are shown on the label.

Accessories for Specific Problems

Probes are usually used when testing overhead, so that the hose may

same reading could have different meanings, depending upon the gas or vapor being sampled. This is the reason for the occasional need of calibration curves for field reference. When the needle shows explosive when you are at the lower explosive limit of hexane, other gases and vapors will read explosive when, actually, they are below the lower explosive limit. Thus, there is a safety factor built into the instruments. For example, if the meter reads full scale or explosive for hexane, actually there is only 68 percent of the lower explosive limit of hydrogen present. Most of the combustibles, commonly encountered in industry, have curves lying to the left of hexane curve, thus giving extra safe readings. Do's and Don'ts

(1) Keep your eye on the meter. Remember, you may sample a rich mixture which will cause the needle to go up scale and return to zero without you noticing it. Thus, an unsafe conclusion could be drawn.

(2) Select the correct sampling hose for your specific application.

(3) Follow the proper instructions for the care and maintenance of your indicator.

(4) Always use the shortest length of sampling hose. It will minimize the possibility of vapors condensing in the hose.

(5) Whenever a reading is obtained, it is always wise to clear the instrument, zero in fresh air, and take a second test to be certain of an accurate reading.

(6) It is always well to purge the meter by aspirating the bulb in fresh air, even if another sample is not to be taken right away, as this removes any possibility of corrosive gases in the combustion chamber.

(7) Check the calibration of your instrument to be sure that it is reading correctly.

(8) Check your battery voltage and/or zero adjustment periodically. (9) Check your instrument for tightness.

(10) Don't sample from elevated temperatures into a cold instrument. Condensation may occur and give a false reading. Whenever possible, the instrument should be at the same temperature of the vapor being tested.

(11) Don't remove the flashback arrester from the instrument. It prevents the explosion which occurs in the combustion chamber from passing back to the mixture being sampled.

(12) Don't use the indicator for sampling gasoline vapors containing Tetra Ethyl lead, unless the indicator has been approved for this application. (13) Don't let your sampling hose or probe reach into a liquid. (Continued on page 150)