I don't think you have anything to worry about here unless the sand is very think (over 2+ inches). What you are describing is encapsulated gas from anaerobic bacteria, which contains a high level of methane. That is highly unlikely unless you have a lot of dead organic matter in your tank, trapped below the sand. Just be sure that you are using sterile sand formulated for aquarium use. If you plan to have a planted tank...you will have diatoms until your silicates are settled out.
D