The most important criterion is the safety distance between your tank and the nearest building. This will depend on the type of construction involved, but can be up to ten metres (in the case of wooden structures). On this point underground tanks have a clear advantage, since the required safety distance for them is generally only one metre.
Another requirement is that, in the event of an unintentional loss of gas, the immediate environment is not endangered. There must be a minimum of three metres between places where gas may escape and any source of ignition or cavity into which escaping gas might seep, although larger minimum distances may be imposed depending on the nature of the surrounding terrain. Since gas can escape equally well from underground tanks, these minimum distances apply to both types of tank.
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