If one of the cells has swelled then you should dispose of it. Discharge it to 3.0V/cell, tape up the terminals and recycle it through your local council tip. No need to put it in salt water.
Cell swelling and swelling is either due to (i) poor gas extraction during original formation at the time of manufacture, (ii) overcharge (iii) due to gas evolution caused by the breakdown /oxidisation of internal materials through cycling.
either way, discontinue use.
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