Drums should not be stored vertically for long periods, because the bungs are not airtight, even though they might stop fuel from leaking out (although it is good idea to stand them vertically for about half an hour before you use the fuel). When the contents contract as the air cools overnight, water inside the rim and collecting around the bung can be sucked in as well, so either store the drums on their sides, with openings at 3 or 9 o’clock, or stick something underneath at 12 o’clock that causes the drum to slant enough to stop rainwater collecting and covering the bungs. Other openings or connections should be protected with blanks or covers, or at least have their openings left facing downwards. Drain plugs, valves, filter bowls, sumps and filter meshes should be checked daily for sediment, slime or corrosion. Always have spare filters.
The reason why long-term storage is not good for fuel (up to two years for drums is the accepted maximum, but some companies reduce this to 1 year) is partly because of daily temperature changes. When it is warm, the fuel expands and some of the vapour-air mixture is driven out. When it gets cold again, the fuel contracts and fresh air is sucked in, to mix with more vapour. As the cycle repeats itself, the fuel inside gradually loses its effectiveness (it loses burn-units). Humidity will mean that water vapour will get in, too, and condense into liquid. Oxygen will also cause a gum to form, which is more apparent when fuel evaporates (the fuel filter is designed to remove it). Keeping the container full will minimise this, which also applies to fuel tanks on machines parked overnight. 100/130 will apparently last for decades, actually longer than the drum, which will deteriorate first, due to the chemicals inside - fuel in drums will interact with the Teflon coating on the inside, if it has fallen off.
Containers should be filled to 95%, and sealed tightly, in a place where the temperature is mostly below 80°F, out of direct sunlight. The 5% airspace allows room for expansion.
Fuel Checking
Each day before flying, and when the fuel is settled, carry out a water check in aircraft and containers (but see below, for drums). Collect samples in a transparent container and check for sediment, free water or cloudiness—if there is only one liquid, ensure it is not all water. The instructions for using water detectors are displayed on the containers. In the Arctic, unless there is a thaw in Summer, separated water will be frozen in the bottom of the drum, and you will only have to worry about that in suspension. Water-finding paste, however, will not detect suspended water, and is as an additional test, not a replacement for a proper inspection. Oxidised fuel will be darker than normal and have a rancid smell. A smell of rotten eggs indicates fungal activity.
Naturally, only competent and authorised personnel should operate fuelling equipment, who must also be fully briefed by their Company. In practice, of course, refuellers know very well what they're doing, but you should still be in full communication with them. In general, the following precautions should be taken: