Tanker · Center of Gravity, Surge, and Outage

A tank vehicle is never loaded right to the top. Why is that space at the top left empty, and does the same amount of it work for every cargo?

1.Because a liquid expands as its temperature rises, so room must be left for it to grow, and how much varies by product and must be known for the loadCorrect answer

2.Because a loading pump cannot meter the last few gallons accurately, and one fixed allowance covers that on every load regardless of product

3.Because the vehicle would otherwise exceed its gross weight limit, so the gap at the top is really a weight allowance, not a temperature one

4.No gap is ever needed at all if the product is loaded cool enough, since a liquid is assumed to never change volume once the tank has been closed

Explanation

The space is left because warming makes a liquid occupy more volume, and a tank filled to its brim has nowhere for that growth to go; the term for the deliberate gap is outage. How much is required is not one figure for everything, because products do not all swell by the same proportion for the same rise in temperature, so the driver's duty is to know what the particular bulk cargo calls for rather than to apply a habit carried over from the last load. 49 CFR 383.119(i) makes operating practices and procedures not otherwise specified a required knowledge area for the tank vehicle endorsement, and it states neither the reason for the gap nor any amount, so both come from the manual rather than from the regulation. The wrong options misread what the space is for: it is not a metering allowance, and it is not a weight allowance either, since legal weight is a separate limit on how much gets loaded rather than the reason for the gap at the top. The last option denies that temperature moves volume at all once the tank is shut, which is precisely the assumption the practice exists to defeat.

Source: 49 CFR 383.119(i)

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A tank vehicle is never loaded right to the top. Why is that space at the top left empty, and does the same amount of it work for every cargo?

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