Through the Pipeline

Mr. Sample moved that enquiries be made concerning a badge of office for the Chairman. The motion was seconded and carried unanimously.

Afternoon Meeting

The afternoon session was devoted to a general discussion and an explanation of how various difficulties had been met.

Mr. Warren pointed out the difficulty of enforcing no smoking at unattended, coin-operated service stations.

Mr. Havercroft said that two note-accepter installations had experienced so much difficulty that the owners had ceased to operate them.

Mr. Gascoigne's authority would not accept latched nozzles on self-service stations.

Mr. Wood pointed out that when a licensed station closes it is doubtful whether the local authority can take any action in the period between the closing by the one licensee and the re-opening by his successor even though such a period extend over many months. Section 73 of the Public Health Act, 1961, makes the owner responsible but what could reasonably be required when the tanks still contained some petrol and the date of re-opening is unknown?

Mr. Gascoigne stated, in reply to a question, that his authority licensed car parks. In accordance with Home Office advice three gallons per car was taken as a basis and the licence was drawn up accordingly. It was essential to get agreement on requirements at planning stage.

He also mentioned the trouble caused by a tank which passed an ullage test but later failed a gas test. It was finally located by testing the slurry in a sewer into which it leaked. The sewer carried the smell for some distance so that several service stations and garages were suspect and all the tanks had passed an ullage test.

Mr. Sample mentioned the danger of plastic petrol tanks on vehicles. Mr. Gledhill pointed out that metal tanks are required by the regulations.

Mr. Gledhill cited two cases where cars had driven off and the latched nozzles, both of the same make, had failed to break. One type of nozzle became unusable very quickly if subjected to rough handling. There were six of each of two types of nozzle in use in his area on an experimental basis.

Mr. Wood stated that he had recently found an independent boiler for a domestic heating plant in a garage attached to a house.

by OTTO

WHAT'S THE CONTENT ?

Man an inquiring mind. When presented with a glass of cider and a straw he will not only suck and see how good the cider is. Occasionally he will blow for no other reason than to find out what happens.

Some experimenters will be satisfied with watching the bubbles of air detaching themselves from the bottom of the straw and admiring the patterns they form as they float to the surface. Others will note that a very gentle blow does _no more than depress the liquid in the straw below that m the glass outside the straw.

They will further by increasing the of the1r blow until they arrive at that stage of equ11Jb1rum where liquid is completely expelled from the yet no bubbles appear. They will note that if they increase the pressure beyond this point, surplus air again

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bubbles away from the bottom of the straw. They will reason that as a _of s_urplus air bubbling away, a constant pressure is mamtamed in the straw and that a harder blow than is necessary to push out the liquid does no more than increase the number and/or size of bubbles.

If James Watt invented the steam engine by watching a kettle boil then surely the man who invented the hydrostatic contents gauge must have enjoyed drinking cider through a straw.

Obviously one or two modifications had to be made before a reasonable contents gauge was achieved. No-one would fancy blowing a six foot head of petrol out of a tube extending down _into a tank_. So an air pump or a low pressure connect10n to an air supply had to be arranged for this purpose. In order to measure the pressure when liquid was fully excluded from the tube a manometer had to be provided.

The operation of a hydrostatic gauge is simple in the extreme. Either one gives a few pumps on an air pump until the pressure remains constant or one arranges a continuous flow of air at a rate of about a cubic foot per hour from some convenient source. Thereafter all one needs to do is to read the manometer.

The pressure recorded by the manometer is Wlz p.s.i.g. where W is equal to the pressure exerted by a one foot head of the liquid being measured and /z equals the head of liquid in feet. In a container of fixed size, there is no reason why h should not be recorded in gallons, as is done on a standard dipstick. Similarly, there is no reason why the manometer (recording Wh) should not be marked in gallons instead of pounds per square inch; this is what is usually done. ·

The manometer reading is not affected by changes in barometric pressure because this pressure acts also on the surface of the liquid in the tank ; hence any change is selfcancelling. However, the reading is affected by the additional pressure exerted on the liquid surface as a result of the difference in density between vapour laden air and fresh air. The same error is encountered when a dipstick reading is taken in a petrol tank which has a single vent and all other openings fitted with pipes carried down to near the bottom. The maximum possible error gives an enhanced reading of 0.1 inch for every 10 foot rise of vent pipe. To avoid the error in all cases it is necessary to draw sufficient petrol from the tank to ensure that only fresh air remains in the vent pipe immediately before a reading is taken.

There is one other variable to be considered. The value of Win the formula given above changes with the specific gravity of the liquid. For water W equals 0.434 per foot head; for petrol the correspondmg mates to 0.434 x 0. 72 or 0.317. In fact the specific gravity of petrol varies between O. 72 for regular petrol and 0. 77 for best grades. Thus on change of grade in a tank recalibration of the manometer dial for that tank may be necessary.

Hydrostatic gauges are particularly useful for satisfying Home Office Code requirements in respect. of tanks with off-set filling pipes. The gauges provide an efficient way of ascertaining the contents of a tank which must not be provided with a dipping opening.

It is wonderful what one can achieve by sipping cider through a straw !

WHAT'S THE RETAINER ?

Oil companies do not always agree _the regulations and licence conditions imposed by even tho_ugh they may usually suffer them gladly. There is one subJe?t, however, which is guaranteed to generate heated discussion and this is the question whether bunded enclosures around storage tanks should have hard or soft bottoms.

The oil companies favo1;1r soft bottoms .. And this is not surprising when one considers the appallmg co.st of viding concrete floors to the acres of land lymg ms1de bund walls. They urge that bund walls are really fire walls and that their purpose is to prevent spread of fire not escape of liquid. As a telling aside, they are wont to add that even if retaining walls and floors are made of concrete, it is virtually impossible to make the enclosures completely liquid tight.

The argument then develops with the question of why is it necessary to make the enclosures liquid tight anyway ? It is, after all, modern practice to fit high level alarms and/or high/high level cut-offs to storage tanks which are fed by barge, ship or pipeline and this makes overfilling virtually impossible. All valves are operated by experts so there can be no misuse or malfunction of them which will cause outflow. Tanks are regularly inspected for minor leaks. So what is left ? only catastrophic failure of a tank and whoever heard of that in this day and age !

That the authorities are not wholly convinced by these telling arguments must be due to their having seen too often spillages and leakages seeping away into the soft bottom of a bund to reappear in lakes, rivers or at some other inconvenient point and there frequently to create conditions of real danger. Even when there is no danger, the problem of pollution arises.

The authorities applaud the use of high level alarms and high/high level cut-offs and are prepared to agree that the catastrophic failure of a tank is indeed rara avis. But they have a healthy scepticism regarding the "experts" who operate valves and the ability of oil company personnel to spot leaks in the very base of a tank resting on the ground. Experience too often has shown that all is not for the best in this best of all possible worlds.

The authorities accept that it is most difficult to make a bunded enclosure completely liquid-tight but they recognise a difference between a seepage rate of a few gallons per hour and a soft floor which allows outflow at the same rate as input.

And there the battle lines rest. Authorities say that the floors of bunded enclosures should be paved with concrete whereas the oil companies say that this is far too expensive.

The question of expense is very valid and it is therefore surprising that more thought has not been given to making enclosures liquid-tight other than by use of concrete. It would for example be possible to coat the floor of the enclosure with a macadam in which the binding material is coal tar pitch. Pitch mastic complying with British Standard 1450, 1963, might also be acceptable for this purpose. Both these coverings should provide reasonably impermeable barriers to petroleum outflow during the period any spillage is likely to remain unmoved in bunded enclosures. If this solution is adopted, each tank should be supported on a suitably coated concrete raft which should be shaped to encourage any leakage from the base of the tank to flow towards its . sides where the leakage would become visible. The raft could well extend a few feet beyond the edges of the tank.

It will be necessary to provide drainage to any enclosure made liquid-tight in order to dispose of surface water. Preferably the drainage should be to a sump within the enclosure whence it could be pumped to a petroleum interceptor before passing to the public drains. However, it might be reasonable to allow direct connection from the sump to the petroleum interceptor provided drainage is controlled by a lockable valve which is opened only by or under the constant supervision of a competent and responsible person. Moreover a suitable high level alarm could be arranged in the second chamber of the petroleum interceptor to indicate the presence of a head of petroleum prior to the breaking of the water seal in the chamber.

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